on Seer Sepeiersias ‘ se. ererered Stehsertehstesaectes een i eres onoan apegoorsher sy Beer oot Sie =o “ Sener ans ror ahatebecets peereer) tteels wists Ser esepetiaes re aesronnee Br Erinn erate ee Birra sees le mee ents ansreeern ee eters piaisiasaiaiabeeeiataieustelels Chios in ae Cosmet hess 5 Preheat Sines sinneet 4 ee tcp ashe bit eatcashaes Sentra peeeass Serene ere Si asepeantounsaet paste tt erpape senior rt per es ro penne pererene ets seretseset entitles “TA inf GS\ KUT \S0S Cornell Aniversity Library BOUGHT WITH THE INCOME , FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henry W. Saaqe 1891 Mme UIE cess 2 oa Me... ral Ti CONCRETE AND REINFORCED CONCRETE CONSTRUCTION cI SE EIN APRN TINE NET BOOK — This Book is supplied to the trade on terms which do not admit of discount. THE MYRON C. CLARK PUBLISHING CO, NEW YORK AND CHICAGO ings, THE MYRON C. CLARK PUBLISHING CO. 1908. CONCRETE AND REINFORCED CONCRETE CONSTRUCTION BY HOMER A. REID Assoc. M. Am. Soc. C. Ev. Assistant Engineer, Bureau of Buildings, New York City, NEW YORK AND CHICAGO THE MYRON C. CLARK PUBLISHING CO. 1908. CopyRIGHT, 1907, BY Tas Myron C. CLarg PusiisHine Co. PREFACE. The marvelous growth of the cement industry during the past few years has led to the present time being spoken of as the cement age. The use of cement concrete in many forms of con- struction for which heretofore other materials have been used has created a demand for concise and reliable information in regard to the use of concrete. It has been the author's aim in the prep- aration of this book to make it, as far as possible within reason- able limits, a complete treatise on the properties and uses of con- crete and reinforced concrete, as applied to construction. As far as is possible, a logical development of the subject has been fol- lowed. The book is not only intended as a reference work for engineers, architects and contractors, but, it is believed, the treat- ment is sufficiently simple for the engineering student and.general ‘reader. Clearness in the development, and, as far as possible, a continuity of treatment of the subject matter has been attempted, at the risk, perhaps, of some repetition. In the early chapters a discussion of the materials used for concrete has been given. While perhaps a knowledge of how cement is manufactured is not necessary to doing good work in concrete, it certainly can do no harm, and it is believed by the author that the more that a cement user knows about tlle material with which he is working the less danger there is of his abusing it. Following the discussion of cement, the aggregate is taken up for consideration; the different mixtures used are considered, together with the effect of size of sand, gravel and broken stone, and the effect of impurities. Proportioning concrete for differ- ent uses is next considered, and the methods of determining the voids briefly discussed. The methods used for both hand and machine mixing are described. The various types of machine mixers are discussed, and a machine of each type described. ‘A number of examples of mixing plants are given. In Chapter VI., on Placing Concrete, the use of grout and of rubble concrete is briefly discussed. The tools for mixing, conveying and ramming concrete are described, and the methods of laying and protect- 1v PREFACE. ing concrete in freezing weather are described. The various methods of depositing concrete under water are also considered. In Chapter VII., on Cost of Concrete, no attempt is made to give a large number of cost data, but rather it has been the author's purpose to analyze the factors entering into cost, so that the estimator may form a correct cost estimate from known con- ditions. Chapter VIII. describes the various methods of finishing and treating concrete surfaces, together with methods of making ornamental mouldings, etc. The methods of coloring concrete are also described. Chapter IX. discusses the effect of freezing on concrete, tells how to secure an impermeable concrete, and describes various methods of waterproofing. The effect of sea water on concrete and the effect of oil on cement and concrete are discussed. The preservation of metal in concrete, adhesive coefficient of expan- sion and fire resisting qualities of reinforced concrete and effect of flue gases are also discussed. Chapter X. treats of the strength and elastic properties of concrete. The various elements affecting these properties are also given, and the results of numerous tests are quoted. Chapter XT. treats of the reinforcing metal. In Chapters XII. to XVII. the principles and disposition of the reinforcement are discussed. The methods devised to secure mechanical bond, together with various styles of reinforcements used for slabs, beams, columns, walls, arches and pipes, are described and illus- trated. Chapter XVIII. treats of the general phenomena of flexure. The action of a beam under tests and when tested to failure are discussed, together with the various stresses developed. The results of the latest tests are freely quoted in this chapter. Chapter XIX. gives a clear and concise exposition of the theory of beams, while various beam theories used and proposed are set forth in Chapter XX. Chapter XXI. gives the theory of columns with both straight and hooped reinforcement. Working formulas are given, and results of latest available tests quoted. Chapter XXII. discusses the bearing power of soils, spread and pile foundations, and gives a large number of examples of foundations actually built. PREFACE, v Chapter XXIII. discusses the application of reinforced con- crete to building construction. Columns, floor slabs between beams, monolithic floors, arch floor construction, walls, partitions, roofs and stairways are taken up, described and illustrated, and examples from actual work given. In Chapter XXIV. the prac- tical construction of buildings is taken up. Sheathing and cen- tering are discussed. Illustrative examples of forms for columns, floor, girders, roofs and walls are given. Chapter XXV. is devoted to the discussion of retaining walls, also the expansion and contraction of concrete due to setting and thermal changes. Numerous examples of retaining walls of T-section and of the counterfort types are given. In Chapter XXVI. the application of reinforced concrete to the construction of dams is discussed, and illustrative examples of types to be used under varying conditions given. In Chapter XX VII. the application of concrete, both plain and reinforced, to the construction of sewers and conduits is taken up. European and American methods for the manufacture of cement pipe are given. Numerous examples are given of sewers and conduits, particular attention being paid to the methods employed by American engineers. Chapter XXVIII. is devoted to tank and reservoir construc- tion. The application of reinforced concrete to stand pipes and water towers is discussed. Its application to reservoir construc- tion is illustrated by a number of well-known American reser- voirs. Its use for grain elevators, sand storage bins, coal pockets and gas holder tanks is taken up. In Chapter XXIX. the application of reinforced concrete to chimney construction is illustrated by a number of examples. Its use in tunnel and subway construction and for railroad ties, fence posts, piers and wharfs is also considered. Chapter XXX. is devoted to bridge construction. Girder bridges of various types are considered, and examples of the different types given. Arch bridges of concrete, with and with- out reinforcement, are also considered, and numerous examples given. The subject of culvert construction is also amply illus- trated in this chapter. In Chapter XXXI. the subject of forms and arch bridge centers is discussed. Chapter XXNII. illustrates the application of reinforced con- TABLE OF CONTENTS INTRODUCTION? ciavuvjuavernedrasiew ccciass4 Saat aire cleus ee 7 1 Hydraulic cement; Its earliest use; Smeaton’s rediscovery. Early manufacture of natural cement.—Portland cement, in- vention; early manufacture in England, Germany and America. Cement concrete defined.—Reinforced concrete defined;, First use; Monier’s applications; Early use in America by Ward, Hyatt and Ransome; Later development in Europe and America. CHAPTER I—CLASSIFICATION AND MANUFACTURE OF CHUM BINUD ascichacs chatiaie'e stents Gunarsae a SO OE aT ee er eerie 7 Cement defined, classified.—Hydraulic limes.—Natural cement and its manufacture.—Portland cement and its manufacture. Composition.—Dry process of manufacture.—Cement, machinery. Wet process .with rotary kilns; with stationary kilns.—Port- land cement from blast furnace slag.—Slag cement and its manufacture. CHAPTER JI.—PROPERTIES OF CEMENT AND METHODS OR EES TIN Ge se. cosss send sci cha: anntne esate aug. calggnnesoveeandss Chsgasarowetlens dsivbtendvaudiovarexe 19 Distinguishing characteristics of Portland, natural and slag cements.—Field inspection.—Methods of shipping and _ storing. Sampling; Size of sample and method of taking.—Properties of cement.—Desirable characteristics; Definite strength, con- stant volume and _ durability.—Color.—Specific gravity, de- fined; Indication of thoroughness of burning; Adultera- tion; Value as a test.—Range of value.—Activity; Initial set; Hard set; Variation in time of setting; Conditions affecting time of setting.—Soundness defined; Causes of unsoundness; Im- purities, Age; Ordinary tests; Accelerated tests.—Fineness; Effect of fine grinding; Usual requirements.—Strength tests; Tensile tests; Relation between tensile and compressive strength; Mixtures used for samples.—Standard briquettes.—Normal con- sistency of mortar.—Method of mixing.—Storing briquettes.— Testing machines.—Strength of cement mortars.—Compressive strength of neat cement.—Chemical composition of cement. Literature on cement testing. ; CHAPTER III—SAND, BROKEN STONE AND GRAVEL........ 37 Aggregate defined.—_Best aggregate for given locality.—Defini- tion of mixtures.—Sand: Size and shape of grains.—Effect of loam in sand.—J. C. Hain’s tests.—Prof. Sherman’s tests.— Effect of clay and loam; U. S. Engineer’s tests.—Effect of coal in sand.—Sand washing; by hand, by machine, by concrete mixer. Cost of sand.—Stone dust vs. sand; Capt. Harry Taylor’s tests. Stone and gravel; kinds to be avoided.—Gravel vs. broken stone. Ashes, cinder and coke aggregates.—Crushing stone; Types of crushers; advantages of each type.—Crushing plants.—Cost of stone crushing.—Screening stone or gravel.—Cost of screening. x CONTENTS. Page CHAPTER IV.—PROPORTIONING CONCRETEH..... cc cseeeeeeenee . 50 Characteristics required for an ideal concrete.—Proportion- ing concrete for different uses.—European and American prac- tice.—Impervious mixtures.—Filling the voids.—Method of de- termining voids.—Thacher’s Tables.—Gillette’s Formulas.—Voids in sand.—Voids in broken stone and gravel.—Specific gravity of stone and common minerals.—Size of cement barrels.—Meas- uring the aggregate—Amount of water.—Sussex tests.—Rafter’s tests. CHAPTER Vi—MIRING CONCRETE ccc ctw on een nuwane dei ay Rem 69 Methods of mixing.—Essential points to be obServed to secure good concrete.—Long time mixing.—Machine vs. hand mixing. Hand mixing; Methods.—Machine mixers; types, continuous, batch and gravity mixers.—Cube mixer.—Smith mixer.—Ran- some mixer.—Gravity mixer.—Automatic measurers.—Mixing plants; U. S. Government plants; Standard Ransome plant; Ransome hoist; Ingalls building plant.—Cost of mixing. CHAPTER VI—PLACING CONCRETE........ 0... .cee cece cence ees se Ae Methods of conveying from mixer to work.—Joining up old work with new.—Grouting.—Rubble concrete, use; Poughkeepsie Bridge; Dry Dock, Charleston Navy Yard.—Quinebaug River Dam, Boonton Dam.—Tools for mixing, conveying and ram- ming.—Laying concrete during freezing weather; Precautions necessary; Heating the materials; Use of salt; Protecting ‘sur— face with coverings; Housing; Heating enclosed space.—Depos-— iting under water; Grouting loose stone fill for foundation; Con- crete depositing bag; Depositing concrete in buckets; the O'Rourke Bucket.—Depositing by chutes. CHAPTER VII.—COST OF CONCRETE....... shud ih Spe hasane debe iSedotea. de eina natin’ 110 Average costs New York City.—Costs for reinforced concrete work.—Cost items summarized.—Cost of sand.—Cost of gravel and stone.—Totai cost of materials.—Cost of transporting and dumping materials.—Cost of hand mixing.—Cost, of machine mixing.—Economy of machine mixing.—Cost of loading and transporting concrete.—Cost of dumping and _ spreading.—Cost of ramming.—Cost of forms.—Summary of cost. CHAPTER VIII.—FINISHING CONCRETE SURFACES.......... 117 Methods of finishing concrete surfaces.—Mortar coatings. Treating a pitted or mottled surface.—A rubbed finish.—Acid washes,—Pebble dash facing.—Tool-dressed ‘surfaces.—Colcrs for concrete finish.—Use of mineral pigments.—Colored sands. Painting concrete surfaces.—Masonry facing.—Mouldings, orna- mental shapes and veneering slabs.—Casting in sand moulds.— Wood moulds.—Concrete moulds.—Stamped metal and glue moulds. Concrete sidewalks.—Tools for finishing concrete sur- faces.—Variation of color in concrete.—Efflorescence.—Protect_- ing concrete surfaces. CHAPTER IX._GENERAL PHYSICAL PROPERTIBS............ 133 Retempering; Goddard and Evans’ tests.—Watertown Arse-— nal tests.—P. In Wormeley, Jr.’s, tests.—Effect of freezing on -concrete.—Impermeable concrete—Rich surface coatings — CONTENTS. xi Page Alum, lye and cement wash.—Sylvester process of waterproof- ing.—Cost of Sylvester process.—Other waterproof compounds.— Waterproof Portland cement.—Asphalt waterproofing.—Asphalt or felt waterproofing—Method of laying paper or felt.— Cost of waterproofing with tar felt and asphalt.—Effect of sea water upon Portland cement mortar and_ concrete.— Concrete structures in sea water.—Strength of cement mix- tures in sea water.—The effect of oil on cement and concrete, Preservation of metal in concrete.—Adhesion between concrete and steel.—Shrinkage and expansion of cement mortar and con- erete when setting.—Coefficient of expansion.—Fire resisting qualities of reinforced concrete.—Prof. Woolson’s tests.— Strength tests on concrete after application of heat.—Effect of flue gases and moisture on concrete. CHAPTER X.—THE GENERAL ELASTIC PROPERTIES 0O eek bars Sead a eicapemin ord’ — R&Balnd Mir AA Ohad ned Causes affecting strength of concrete.—Tensile strength.— Prof. Woolson’s tests on large specimens.—Working stresses.— Compressive, 'strength.—Effect of amount of cement on com- pressive strength.—Effect of variation in size of stone.—Effect of mixing.—Effect of amount of water.—Effect of azge.— Thacher’s formulas for compressive strength.—Rafter’s tests.— Elastic limit.—Working stresses.—Cinder concrete.—Transverse strength of concrete.—Shearing strength of concrete.- Massa- chusetts Institute of Technology tests.—Safe working value for shearing.—Modulus of elasticity.—Method of computing modulus of elasticity.Effect of density of concrete and the amount of water used in mixing on _ coefficient of elasticity.—Coefficient of elasticity of concrete under ten- sion.—Coefficient of elasticity in compression.—Water- town Arsenal tests.—Woolson’s tests on large specimens.— Thacher’s formulas.—Elastic properties of cinder concrete.— Limiting stresses to be used in choosing modulus for com- putations. CHAPTER XI.—PHYSICAL PROPERTIES OF REINFORCIN Wrought iron.—Steel; soft, medium and high steels.—Require- ments for good steel.—Medium vs. high steel.—Cost of reinforce- ment. PORCE MEE cnixtenner acaawtmire aaorsn mek idee ERR AEE Fundamental principles.—Classification of reinforced concrete members.—Straight pieces: Beams and slabs.—Flexural stresses._—Vertical shearing.—Lines of stress due to flexure.— Disposition of reinforcement. Longitudinal shearing stresses.—Use of mechanical bond. Composite bars.—Indented flat bars.—Twisted steel bars.—De Man Bars.—Corrugated Bars.—Thacher Steel Bars.—Special arrangement of bars.—Stirrups.—Light skeleton trusses.—The Kahn trussed bar.—The monolith steel bar.—Unit girder frame.— The Scofield spacing and reinforcing bars.—Cummings chair. F 1s5 G 212 CHAPTER XII.—PRINCIPLES AND DISPOSITION OF REIN- CHAPTER XIIL—MECHANICAL BOND........::eeeeee ee eee ee eens 225 xii CONTENTS. Page CHAPTER XIV.—STYLES OF SLAB REINFORCEMENT...... ... 236 Slab and I-beam reinforcement.—Independent bar reinforce- ment.—Monier reinforcement.—Hyatt ssystem.—Donath system.— Expanded metal.—Schltiter system.—Cottancin system.—Lock- woven wire fabric.—Tie-locked fabric.—Welded wire fabric.— Manner of using wire mesh.—Matrai system. CHAPTER XV.—STYLES OF BEAM REINFORCEMENT........ 245 Ribbed slab or T-beam construction.—Reinforcements used for beams.—Bousseron system.—Locher system.—Cummings sys- tem.—Kahn system.—Coignet system.—Pavin de Lafarge sys- tem.—Cottancin system.—Chaudy system.—Degon system.— Hennebique system.—Coularou system.—Maciachini system.— Lattice trusses.—Siegwort system.—De Valliere system.—Visin- tini system. CHAPTER XVI.—CURVED PIECES STRAINED IN FLEXURE... 256 Arches.—Stresses in arches.—Methods of failure of arches.— Methods of reinforcing arch ring.—Secondary ‘stresses.—Sys- tems of reinforcement.—Monier, expanded metal, Melan, Thacher and Hennebique systems.—Ribbed arches.—Golding arched floors.—Inverted arches. CHAPTER XVII.—COLUMNS, WALLS AND PIPESG....... Somes os 208 Straight pieces strained in compression.—Disposition of the reinforcement.—Walls.—Hennebique, Degon, Chaudy, Ransome and Monier trellis walls.—Columns.—Hooped columns.—Piles.— Curved pieces strained in compression.—Curved pieces strained in tension. CHAPTER XVIII.—GENERAL PHENOMENA OF FLEXURE.... 271 Action of beams under tests.—Prof. A. N. Talbot’s tests.— Method of failure of beams under tests.—Primary and ultimate failure.—Failure by tension in steel.—Failure by compression of concrete.—Bond or resistance to slipping of reinforcing bars.— Failure of bond between steel and concrete.—Types of bond failures.—Vertical and horizontal shearing stresses.—Diagonal tension in the concrete.—Failure by splitting of bars away from upper portion of beam.—Position of neutral axis.—Conservation of plane sections.—Distribution of stresses in a beam.—Stresses under varying modulus of elasticity.x—Elongation or stretch of concrete in a reinforced beam.—Tensile resistance of concrete in reinforced beams. CHAPTER XIX.—THEORY OF BEAMG............0...cccceee cence 299 Theory of beams.—Assumptions upon which theory is based.— Nomenclature used.—Development of beam formulas.—Formula for location of neutral axis.—Formula for bending moment.— Tables of values for K to be used in formula M = Kbd?.—Use of formulas.—Shearing stresses in reinforced concrete beams.— Method of treating, shearing stresses.—Empirical methods; by use of diagram of shears.—T-Beams.—Usual assumptions.—An empirical method of design.—Theoretical formulas.—Beams with double reinforcements.—Formulas for beams with double rein- forcements.—Effect of use of double reinforcement. CONTENTS. xiil Page CHAPTER XX.—VARIOUS BEAM THEORIEG........... ha See a we oo) Formula for beams, based on a_ rectilinear distribution of stress.—Formulas for beams, based on distribution of stress proposed by Capt. John S. Sewell.—T-beam formula.—Prof. A. N. Talbot’s beam formulas; Notation; Relation between stress and deformation for concrete in compression; Distribution of stress in beams; Relations in the stress diagram; Neutral axis; Resisting moment; Compressive stress at upper fiber.—Wa- son’s formula.—Ransome’s formula, for simple beams, for ribbed floors, for cantilever beams, for wall and pier footings.—Thach- er’s formulas, for simple beams, for beams with double rein- ‘forcements, for T-beams.—Thacher’s constants.—Hennebique’s form- ulas for beams, slabs .nd columns.—Hennebique’s formulas for stir- rups.—-Coignet’s formulas for pipes and slabs.—Bonna’s formula for beams.—Johnson’s theory for beams, slabs and T-beams; Shear in steel-concrete beams. CHAPTER XAL—THEORY OF COLUMNS y ss esas + yaya canes eo emu 879 Concrete columns with straight reinforcing rods.—Columns lightly reinforced.—Columns heavily reinforced.—Column for- mulas.—Application of Euler’s formula for flexure to reinforced concrete columns.—Use of column formulas.—Relative cost of columns with light and heavy reinforcement.—Shrinkage stresses.—Hooped concrete.—Woolson’s tests on concrete under heavy pressure.—Considére’s tests on elastic behavior of hooped concrete.—Elastic behavior of hooped concrete.—Compressive resistance.—Formula for hooped concrete.—Spacing of hoops.— Working formula for hooped concrete.—Concrete columns in the light of recent tests at Watertown Arsenal. CHAPTER XXII—FOUNDATIONS 2... see cece eee eee eee e teen eens 407 Bearing power of soils.—Bearing power allowed for important structures.—General considerations in regard to foundations.— Pile foundations.—Bearing power of piles.—Formula for bearing power of piles.—Reinforced concrete foundations.—Spread foundations.—The Chicago foundation.—Examples of Monier construction for foundations.—Footings for Atlanta Terminal Station.—Column footing, Bush Terminal Co. Factory.—Contin- uous and spread footings for Thompson & Norris factory build- ing; for garage, Decauville Automobile Co.; for New York City residence; for Shayne store building; for warehouse at New Castle, Eng.—Henhebique footing.—Pile foundations with rein- forced concrete caps.—Capped pile foundation for Yonkers power house, for Penrose Ferry Bridge.—Concrete piles.—Piles built in place.—The Raymond pile.—Collapsible core and pile drivers used for driving Raymond piles.—Raymond pile with collapsible shell for sandy soils.—Simplex pile.—Driving form.—Washington Bar- racks foundations.—Cast-iron and concrete pile points.—Alli- gator point.—Method of reinforcing simplex piles.—Safe sustain- ing power of simplex piles.—Chimney foundation.—Steel-concrete pile—Driving apparatus.—Reinforced concrete piles with en- larged footing.—Reinforced concrete piles moulded before driv- ing.—Hennebique piles.—Hollow pile.—Hennebique sheet piling.— Triangular pile.—Piles with I-beam reinforcement.—Gilbreth xiv CONTENTS. Page corrugated pile-—Moulding piles.—Plant and pile drivers for moulding and driving piles for Union Station, Hamburg, Ger- many.—Driving reinforced concrete piles.—Special caps used for driving reinforced concrete piles——Armored timber piles.—Ar- mored steel piles—Caisson foundations.—Monier cylinders for Cockle Creek Bridge.—Caissons for Union Street Wharf.—Pneu- matic caissons of reinforced concrete. CHAPTER XXIII.-GENERAL BUILDING CONSTRUCTION.... 465 Advantages of reinforced concrete as a building material.— Building construction.—Columns.—Hennebique column, exam- ples.—Column for Chicago store building.—Column with bracket supporting crane-run girder.—Columns for Ingalls Building.— Columns for Pacific Coast Borax factory building; Columns for 12-story loft building, New York City.—Hooped columns.—Ex- amples.—The Cummings column.—Expanded metal hooping.— Hooped cinder concrete shells for Bush Terminal Company’s building.—Monolith Steel Co.’s hooped column.—Use of metal columns in reinforced concrete structures.—Connections between metal columns and reinforced concrete beams, girders and col- umns.—Beam, girder and slab construction.—Classification of different forms of floor construction.—Filling slabs between beams.—Monier constructions, expanded metal floors.—Roebling floor.—Columbia floor.—American Concrete Steel Co.’s_ floor.— International Fence & Fireproofing Co.’s floor.—Corrugated bar floor construction.—Arched floor slabs.—Golding floor.—Expanded metal arch.—Roebling arch.—De Man arch floor.—Monier arch floor with single and double arch reinforceement.—Melan system.— Wunch system.—Monolithic floors.—Hennebique and Matrai sys- tems.—Mushroom system of construction.—Ribbed slabs.—Typical Hennebique construction.—Palais de Justice and Petit Palais des Beaux Arts floors.—Floor for Chicago store building.—Ran- some floor construction in Pacific Borax factory, Kelly and Jones factory and United Shoe Machinery Co.’s buildings.—Floor con- struction for Thompson and Norris factory.—Reinforced Ce- ment Construction Co.’s system of floor construction.—The Rob- bins garage floor.—The Hugh Bilgram building.—Overhauling shop, Philadelphia Rapid Transit Co.—Central Felt and Paper factory.—Sub-station Brooklyn Rapid Transit Co.—Long span girder, Lyric Theater, Cleveland, O.—Unit Concrete Steel Co.’s system.—Construction used for Bush Terminal Co.’s factory.— Ridgefield Electric Co.’s power house.—Cummings construction used in Taylor-Wilson Mfg. Co.’s shop.—Ingalls Office Build- ing.—Plain arch floors.—Hennebique arch construction, Wunch arch.—Ribbed arch floors.—Hennebique _constructions.—Tile- concrete construction.—Continuous beams and _ slabs.—For- mulas.—New York Building MRegulations—Walls and parti- tions.—Wall construction for bank building at Basel, Switzer- land.—Window and wall framing for main shop, United Shoe Machinery Co.’s building.—Wall construction, Central Felt and Paper Co.’s factory.—Wall construction for Ingalls Building.— Concrete wall construction without wooden forms.—Weiderholt system.—Plaster partitions—The Roebling partition.—Cast slabs CONTENTS. xv Page and cement block partitions.—Roofs. —Reinforced concrete roofs supported by steel framework.—Roof for “Chittenden Power Co.—Roundhouse roof construction, Canadian Pacific Ry.— Monolithic roof construction.—Roofs for Kelly and Jones fac- tory, Central Felt and Paper Co. building, United Shoe Ma- chinery Co. building and Medical Laboratory, Brooklyn Navy Yard.—Long span roof, Los Angeles, Cal.—Roof for Northwest- ern Ohio bottle factory.—Saw tooth roofs for Bilgram Machine Shop, Philadelphia, Pa., and factory building at Stamford, Conn.—Dome for U. S. Naval Academy chapel.—Reinforced con- crete roof trusses. —Roof trusses for Terminal Station, At- lanta, Ga.—Stairways.—New York Rapid Transit subway sta- tion stairways.—Stairway for Medical Laboratory, Brooklyn Navy Yard, for Pacific Borax Co.’s factory and Kelly and Jones factory.—Hennebique stairway for Mr. W. C. Sheldon’s resi- dence.—Overhanging stairway construction.—Shaft hangers.— Slab and beam hangers for United Shoe Machinery Co.'s build- ings.—Pipe sluts for hangers.—Cast-iron hanger for light loads.— Expansion joints.—Expansion joints for Pacific Borax Co.’s fac- tory and for United Shoe Machinery Co.'s buildings.—Buildings constructed of members moulded in advance.—Bush Terminal Co.’s buildings.—The Visintini system.—The Textile Machine Works building, Reading, Pa. CHAPTER XXIV.—PRACTICAL CONSTRUCTION..............055 513 Strong and rigid forms necessary.—Timber.—Sheathing with splayed and caulked joints, covering with canvas.—Sizes of sheathing and posts.—Falsework.—Adhesion of mortar to forms.—Methods of treating forms to prevent adhesion.—Design of forms.—Column forms, various types used.—Hennebique col- umn forms and clamp.—Column forms for Central Felt and Paper Co.'s factory, United Shoe Machinery Co.’s_ buildings, Ingalls building, Kelly and Jones factory, Parkville sub-station, Brooklyn Rapid Transit Co., Atlantic City hotel and Borden- town water tower.—Forms for fluted columns and other special surfaces.—Centering for floor slabs between beams; Form for flat slab resting on top flange of beam.—Form for flat slab resting on bottom flange of beams, special method of supporting forms from top and bottom flanges of beams.—Methods of laying con- crete to be used and those to be avoided.—Monolithic floor con- struction.—Two methods of form construction wsed.—Descrip- tion of Hennebique type of mould.—Hennebique clamp.—Girder form for Ingalls building.—Independent mould.—Modification of Hennebique ‘ould, clamps omitted.—Methods ‘of construction used in the United Shoe Machinery Co.’s factory.—Girder and beam forms for same.—Girder and column form for Minneapo- lis, Minn., warehouse.—Slab and girder mould, Central Felt and Paper Co.’s factory.—Beam mould and slab centering for Atlan- tic City hotel—Girder forms for Central Pennsylvania Traction Co.’s car barns.—Unit Concrete Steel Frame Co.’s slab ard girder ‘forms.—Slab and girder floor forms, Pacific Borax Co.’s fac- tory.—Slab and girder floor mould, Kelly and Jones factory.— Method of forming expansion joints.—Concreting, tamping, xvi CONTENTS. Page spading and rolling.—Methods of stopping off work.—Methods of supporting floors after removal of fozms and centering.—Finish of floors.—Construction of walls and partitions.—Potter wall form.—Ransome wall forms.—Form for wall moulding.—Wall forms for Central Felt and Paper Co.’s factory.—Forms for hol- low walls.—Concrete mixture to be used’in wall construction.— Wall mould ties.—Roof forms.—Forms for slab and girder roof for roundhouse Canadian Pacific Ry. CHAPTER XXV.—RETAINING WALLS.............. cece eee eee . 607 Retaining walls, general discussion.—Inverted T-section walls described.—Comparison of cost of plain and reinforced concrete walls at Lebanon, O.—Retaining wall, American Oak Leather Co.’s building, Cincinnati, O.—Walls with counterforts.—Henne- bique wall.—Retaining wall, Great Northern Ry., Seattle, Wash.—Relative costs of wall with counterforts and plain con- crete wall.—Retaining wall, Brooklyn Grade Crossing Commis- sion.—Walls for Atlanta Terminal Station.—Retaining wall for sunken street, Paris, France.—Braced walls.—Expansion and contraction.—Stresses in concrete due to setting.—Thermal and shrinkage stresses combined. CHAPTER XXAVIA-DAMS cisscvaseveeeee Lada len Seuss aes? weeetoa os 622 Adaptability of reinforced concrete to dam _ construction.— Saving in cost and increased stability.—Various types for differ- ent kinds of foundations.—Open front, half open front and cur- tain dams.—Theresa, N. Y., dam.—Fenelon Falls, Ont., dam.— Schuylerville, N. Y., dam.—Danville, Ky., dam.—Dam _ enclos- ing power house, Cannon Falls, Minn.—Intake and gatehouse for dam, Walton, N. H. CHAPTER XXVII.—CONDUITS AND SEWERG........-.....:00005 6 General discussion of use of concrete for sewer construction.— Comparative costs of brick and concrete sewers.—Formula for conduits under pressure.—Pipe cost in advance for conduits and sewers.—Monier pipes.—European method of 'manufacturing re- inforced concrete pipes.—Joint for Pavin de Lafarge pipe.—Bor- denave pipes.—Bonna pipe.—Steel lining and joints for Bonna pipe.—U. S. Reclamation pipe tests.—Precautions to be ob- served in manufacturing reinforced concrete pipe.—Jackson re- inforced concrete pipe.—Wilson & Baillie cement pipe; methods of manufacture; Standard sizes of pipe; Strength of pipe.— Reinforced concrete conduits built in place—Simplon Aque- duct.—Salt Lake City Aqueduct.—Aqueduct, Cedar Grove Res- ervoir, Newark, N. J.; Forms and methods of construction em- ployed.—Conduit for Jersey City Water Supply Co., sections used, forms and methods of construction.—Torresdale filter con- duits, sections used, forms and methods of construction.—Provi- dence sewer.—Harrisburg intercepting sewer.—Wilmington, Del., sewer.—Cleveland, O., sewer.—United Shoe Machinery Co.’s sewer.—Brooklyn, N. Y., sewers.—South Bend, Ind., sewer, forms and methods of construction.—Des Moines, Ia., sewers.—Special mould for small sewers.—Sewer form used at Medford, Mass.— Special steel forms; Blaw collapsible steel centering; Forms used at Washington, D. C.—Ransome pipe mould.—Cost of Ransome pipe as compared with vitrified clay pipe. CONTENTS. xvii Page CHAPTER XXVIII.—TANK AND RESERVOIR CONSTRUCTION. 688 General discussion of tank and reservoir construction.—Meth-. ods of reinforcing used.—Tank for Pittsburg Lamp, Brass & Gas Co.—Standpipe, Milford, O.—Water tower, Fort Revere, Mass.—East Orange Reservoir.—Fort Meade Reservoir; method of construction employed.—Bloomington, Ill., Reservoir.—Failure of Madrid Reservoir.—Grain elevator bins.—Canadian Pacific grain elevator, Port Arthur, Ont.—Failure of Duluth, Minn., grain elevator.—Sand storage bins.—Coal pocket for Pennsyl- vania Cement Co.—Atlantic City coal pocket.—Concrete gas holder tank, New York City.—Gas holder tank, Dubuque, Ia. CHAPTER XXIX.—CHIMNEYS, TUNNELS, SUBWAYS, RAIL- ROAD TiES, FENCE POSTS, PIERS AND WHARVES.. 720 Chimneys, general discussion.—Rectangular chimney for United Shoe Machinery Co.—Chimney for power house, Los Angeles, Cal., forms and methods of construction.—Weber chim- neys.—Advantages of reinforced concrete chimneys.—Weber chimneys for United Shoe Machinery Co., Beverly, Mass., and for Butte Reduction Works, Butte, Mont., forms used and methods of construction.—Tunnels and subways.—New York Rapid Transit subway, sections and forms used.—Philadelphia, Pa., subway.—Aspen Tunnel, Union Pacific R. R.—East Boston Tunnel.—Ossining Tunnel.—Railroad ties.—Tie for French Ry.— Ulster and Delaware R. R. tie——Kimball tie-—Buhrer tie, L. S. & M. S. Ry.—Reinforced concrete fence posts; forms used, methods of construction and cost.—Piers and wharves.—The Southampton piers. —Atlantic City pier. CHAPTER XXX.—CONCRETE IN BRIDGE CONSTRUCTION... 751 Bridge construction; Classification of bridges, general discus- sion; cost.—Girder bridges, general discussion.—Beam bridges.— Hennebique bridges.—Moller bridges.—Sutton Drain Bridge, Hull, Eng.—Milan Skew Bridge.—Albany, Ind., Bridge.—Elmwood Bridge, Memphis, Tenn.—Open web girder bridge, Purleet, Eng.— Viaducts.—_Cave Hollow Bridge, Cc. B. & Q. Ry.; Viaduct for Cc. C., Cc. & St. L. Ry.; Guadalquiver River viaduct, Seville, Spain; Richmond & Chespeake Bay Ry. Co.’s viaduct.—Arch bridges.—Arch design, general discussion.—Thacher’s formulas.— Austell Bridge.—Grand River Bridge, Grand Rapids, Mich.; cen- tering and methods of construction; details of railing and forms; loading and _ stresses used.—Luten arch, Yorktown, Ind.— Melan arch, Dayton, O.; Melan hinged arch, Laibach, Austria; General details, centering and methods of con- struction —Gruenwald Bridge, Munich, Germany; details and methods of construction.—Parabolic arch bridge, Wabash, Ind.; Centering for Wabash bridge.—Ribbed arches.—Grand Rapids, Mich., bridge; General detail and centering used.—Deer Park Gorge Bridge, La Salle, Il.; Details of centering and methods of construction.—Three-hinged arch bridge, Brookside Park, Cleveland, O.—Piney Creek Bridge, Washington, D. C.— Pennypack Creek Bridge, Philadelphia, Pa.; General dimen- sions and centering wsed.—Weak haunch reinforcement.—Expan- sion joints.—Waterproofing and drainage.—Culverts, general dis- xviii CONTENTS, % 4 Page cussion, standard culverts for C. B. & Q. Ry.—Box culvert for Great Northern Ry.—Culverts for C., C., C. & St. L. Ry.—Cul- verts for N., C. & St. L. Ry.—Culverts for Great Northern Ry.— Arch culvert, L., S. & M. S. Ry., at Elkhart, Ind. CHAPTER XXXI.—ARCH BRIDGE CENTERS AND METHODS OE AIS EI cat phish she PRN © Ree ee ieee ones 814 Requisites of good centering.—Classes of centering.—Discussion of centering.—Centering for 50 ft. arch.—Centering for 54 ft. arch at Plainwell, Mich.—-Centering for Austell Bridge.—Centering for Luten Bridge, methods of design used.—Centering for 140 ft. span Big Muddy River Bridge, I. C. Ry.—Centering for Con- necticut Ave. Bridge, Washington, D. C:—Centering for arch at Plano, Ill.—Centering for 50 ft. arch, B. & O. R. R.—Centering for Gruenwald ‘Bridge.—Centering for Raritan River Bridge, P. R. R.—Centering for Piney Creek Bridge, Washington, D. C.; Methods of erection used.—Methods of construction used for Belvidere, Ind., Bridge; Details of traveler used.—Placing the reinforcement.—Concreting.—Striking centers. CHAPTER XXXII.—BRIDGE FLOORS....... cece cee cee cece eee eee 834 Bridge floor for C., B. & Q. R. R.—Floor for Chicago & East- ern Illinois Ry.—Wabash Ry. Bridge fioors for deck and through bridges.—Chicago and Northwestern Ry. floor.—Floor for Phil- adelphia Rapid Transit Elevated Ry.—Highway bridge floor and cantilever sidewalk, South Bend, Ind. CHAPTER XXXIIL—BRIDGES, PIERS AND ABUTMENTS...... S41 Piers, general discussion.—Pier K. C., M. & O! Ry.—Illinois Central R. R. piers at Gilbertville, Ky.—Small draw-span pier and abutment.—Abutments, general discussion.—C., B. & Q. Ry. abutment.—K. C., M. & O. Ry. abutment.—Wabash Ry. abut- ment at Monticello, Ill—Western Maryland Ry. abutment.— Abutments for Cairo Bridge, I. C. R. R. CHAPTER XXXIV.—CONCRETE BUILDING BLOCKS........... 855 Concrete blocks, general discussion.—Materials for concrete blocks.—Cement.—Lime.—Proportioning.—Proportion of water.— Mixing and depositing.—Curing blocks.—Facing blocks.—Exam- ples of block construction.—Porch work.—Concrete block resi- dences at Albuquerque, N. Mex., and Newark, O.—Shape_ of blocks.—Two-piece block.—Processes of manufacture.—Block machines.—Building construction.—Cost of concrete building blocks. TIN Bee caer 2 ae aes ek eins eae BO vb siete, Tapani sib, oz: va aiiisdcdidintes @RRIARIERES SIE Concrete and Reinforced Concrete Construction INTRODUCTION, Use of Cement. by Egyptians and Romans.—The recent mar- velous growth of the cement industry, due to the wide use of concrete in construction, has led to its being spoken of as a new industry. Yet hydraulic cement has been used since the dawn of civilization. It is known that the Egyptians, 4,000 years ago, made-a natural cement which set under water. While Carthage was at the height of her glory, some 2,300 years ago, an aqueduct over 70 miles in length was built to furnish a water supply for that ancient city. Natural cement was used in its construction. To cross a valley, over 1,000 arches were built. Many of these were ever 100 feet high, and some are still standing. Cummings, in his “American Cements,” states that'at one pdint a piece of masonry ever 100 feet long has fallen from the top of the aqueduct to the rocks below and still lies there intact, unbroken, illustrating the toughness, tenacity and durability of the natural rock cement used by these early constructors. The Romans used hydraulic cements of such good quality for the construction of sewers, water mains, foundations, buildings and roads that relics possessing great strength and toughness are to be seen at the present day. The dome of the Pantheon, erected at the beginning of the Christian era, is perhaps the largest ex- ample of concrete construction coming down from the ancients. This magnificent structure, which is 142 feet in diameter, and contains a 30 foot opening at the top, has withstood the destruc- tive elements of time for Ig centuries, and to-day does not show 2 INTRODUCTION. a single crack. It is stated that in Mexico and Peru, natural rock cement was used so long ago in stone masonry, that the stone has worn away, leaving the projecting mortar joints. Smeaton’s Rediscovery of Hydraulic Cement.—The art of manu- facturing hydraulic cements seems to have been lost in the East- ern Hemisphere during the Middle Ages, while it also passed away with the decline of the early civilization in the Western Hemisphere. John Smeaton, in 1756, when building Eddystone lighthouse, discovered that argillaceous limestones produced limes that would set under water, and thus rediscovered hydraulic cement. His investigations were carried far enough to secure a good hydraulic lime or natural cement, which, through its durability in the Eddystone lighthouse, secured to Smeaton last- ing engineering fame. Early Manufacture of Natural Cement.—Joseph Parker in 1796 manufactured a species of natural cement, which he called Ro- man cement, by calcining and crushing septaria nodules found on the Isle of Sheppey, off the coast of Kent, England. Natural cement was also produced at Boulogne, France, in 1802, from septaria, called Boulogne Pebbles. M. Vicat, during the years 1813-18, produced hydraulic cement by mixing chalks and clays. In the United States, the first nat- ural cement was made in 1818 by Canvass White, from natural rock, near Fayetteville, New York, and was used in the con- struction of the Erie Canal. Since that time natural cement has been extensively manufactured throughout the United States. During the period from 1818 to 1830, 300,000 barrels were manu- tactured. The industry gradually increased until the high water mark was reached in the year 1899, when a grand total of 9,868,- 179 barrels were produced. The production of natural cement has fallen off during the past few years, owing to the reduction in cost of the manufacture of Portland cement, the total output for the year 1905 being only 4,473,049 barrels. Aspdin Patents Portland Cement—Portland cement was first Produced in 1824, by Joseph Aspdin, a brick mason of Leeds, England, who took out a patent for producing cement by calcining a mixture of lime and clay. He gave it the name * Portland ” on account of its resemblance, when hardened, to the famous odlitic lumestone used for building, from the quarries on the Island of Portland, in Dorsetshire, on the southern coast of England. The INTRODUCTION. 3 first plant for the manufacture of this cement was established at Wakefield by Aspdin in 1825, and the first important piece of engineering work in which it was used in any quantity was in the construction of the Thames tunnel in 1828. The quality of the cement was greatly improved during the years 1845-50, due largely to the exertion of John Grant, an eminent English en- gineer, who used it extensively on the London drainage works. For a time England led in the manufacture of Portland cement, but Germany took the lead in its production, and, until the past four or five years, has been the foremost country in the produc- tion and use of Portland cement. During the past few years, however, the United States has surpassed all other countries as a manufacturer and user of Portland cement. The first American Portland cement was manufactured by David O. Saylor, of Coplay, Pa., in 1875. The development of this new industry was so slow, however, that in 1890 only 335,500 bbls. were manufactured in the United States. Since that time the development of the industry has been rapid, reaching a grand total of 35,246,812 bbls. in 1905, over. one half of this being produced in the Lehigh district of Pennsylvania and New Jersey. Classification and Manufacture of Cement-Concrete Defined.— Concrete is a species of artificial stone formed by mixing cement mortar with broken stone or gravel. Sometimes the broken stone cr gravel is replaced by cinders,slag or coke,making a lighter but weaker concrete, especially adapted for fireproof floors. The cement is the active element of the concrete, and is sometimes called the matrir, while the sand and broken stone which form the body of the mixture are inert materials and are called the aggregate. Reinforced Concrete Defined.—Reinforced concrete, sometimes called concrete-steel, ferro-concrete, or armored concrete, is a heterogeneous material utilized in construction, and composed of a metal skeleton-work imbedded in a mass of concrete or cement mortar. Iron, in the form of rods and bars, has been used to tie to- gether and strengthen masonry structures for hundreds of years. Its use, however, was confined to cut stone masonry in the form of clamps and dowel-pins. Cut stone and rubble masonry do not adapt themselves to the use of iron rods, to take care of tensile 4 INTRODUCTION. strains, hence not until after the advent of modern concrete do we find masonry structures having a metal reinforcement. First Use of Reinforced Concrete——The first authentic record of the use of reinforced concrete was at the World’s Fair in Paris, in 1855. At that time a small row boat, Fig. 1, built by M. Lambot, having a sheet of cement mortar 114 inches thick, re- inforced by a wire netting, was on exhibition. This boat is still in use at Meraval, France. At a somewhat earlier date a trellis of iron bars was used by a number of builders in the construction of slender cement fire- proof partition walls. In 1865 Francois Coignet explained the principles of reinforced concrete, and proposed methods of application for the construc- tion of slabs, arches, large pipes, etc. Fig. 1—Lambot’s Boat of Reinforced Concrete, 1855. To F. Joseph Monier, sometimes called the father of reinforced concrete, who first took out a patent in 1865, is given the credit for the invention of this new form of construction. His patents related to the combination of iron and cement mortar, in the con- struction of basins and tubs for use in horticulture. Monier, who was, it is said, a gardener, while constructing some tanks and reservoirs, wished to reduce the thickness of the walls, and con- ceived the idea of increasing their strength by incorporating within them a metal trellis work. He persisted in his idea, and for a number of years constructed reinforced concrete troughs, pipes, reservoirs, etc., but it is not probable that he even sus- pected what a imarvelous growth his conception would have. Neither Monier nor any of his countrymen appreciated the scien- INTRODUCTION. 5 tific value of his idea, and it was the Germans who first developed this form of construction. Early Use in America.—While the French and German en- gineers were bringing about the development of the Monier sys- tem, American inventors seem to have worked out independently the general principle of reinforcing concrete with iron rods to supply the necessary tensile strength in beams and slabs. Probably the first man to use these materials scientifically, the metal being buried in the lower or tensile side of the concrete, was W. E. Ward, who mn 1875 constructed a building at Port Chester, N. Y. In this building, not only the exterior walls, cornices and towers, were formed of concrete, but all the beams, and the roof were made entirely of concrete reinforced with light Fig. 2.—_Reinforced Concrete Arch Bridge built in 1889, at Golden Gate Park, San Francisco. Cal. iron beams and rods. Ward built rods into the lower sides of his beams and joists, much as they are built to-day. Not having any formulae to guide him, he relied entirely upon his judgment in proportioning them, Fig. 2 shows what was probably the first reinforced concrete bridge built in the United States. It was constructed in 1889, by Ransome & Smith Co., at Golden Gate Park, San Francisco, Cal. Mr. Thaddeus P. Hyatt, a native of New Jersey, but at the time living in London, while studying the question of fireproof floor construction, conceived the idea of making beams of con- crete, strengthened by imbedding iron bars in their lower edges to care for the tensile stresses. He made many experimental beams, introducing the iron rods in a great variety of ways and 6 INTRODUCTION. employed Dr. David Kirkaldy, of London, to make a series of tests on reinforced concrete beams. The results of these tests were published by Mr. Hyatt in 1877. Unfortunately the edition was limited and the book has long been out of print. These re- searches were of great value in the development of the science. In 1877 Mr. H. P. Jackson, C. E., of San Francisco, applied Mr. Hyatt’s invention to building construction, and from that date forward used the new form of construction whenever possible. To Mr. Edwin Thacher is largely due credit for the successful introduction of reinforced concrete bridges in the United States. Later Developments in Europe and America.—The development cf the Monier system dates from 1880, when the patents of this inventor for Austria-Hungary were secured by a German com- pany. Under the management of G. A. Wyss, experiments were made, and principles to be followed in its application were es- tablished. Gradually this form of construction came into popular favor throughout the German Empire, and it may truthfully be said that to the Germans is largely due the successful develop- ment of reinforced concrete. During the years 1889 to 1894 a new impetus was given to this method of construction by the inventions of M. Bordenave, Cottancin, F. Hennebique, Edmund Coignet in France, Moller, Rabitz, Konen in Germany, Wiinsch in Hungary, Melan in Aus- tria, and Ransome in the United States. Some ten or twelve years ago I. Von Emperger introduced the Melan system in the United States, and constructed a number of Melan arch bridges. Since that time hundreds of arch bridges have been constructed after this system. CHAPTER I. CLASSIFICATION AND MANUFACTURE OF CEMENT. Cement may be defined as a pulverized material, composed prin- cipally of silica, alumina and lime, which, when mixed with water, undergoes a chemical change forming new compounds that de- velop the property of setting or crystallizing into a solid mass cven under water. Classification of Cements.—Cementing materials naturally fall into two groups—von-hydraulic cements and hydraulic cements. Non-hydraulic cements are made by burning either gypsum or pure limestone at comparatively low temperatures. The products obtained by burning gypsum are known as plaster of aris, Keene’s cement, cement plaster, etc. The product of burning limestone is common lime. While limes and plasters are exten- sively used for building purposes, they are not used in reinforced concrete construction. Hydraulic cements are those which set under water, and are included under the following four general classes: 1. Hydraulic Limes. 2. Natural Cements. 3. Portland Cements. 4. Puzztiolana Cements. Hydraulic Limes——Hydraulic limes have been defined as the products obtained by the burning of argillaceous or silicious lime- stones, which, when showered with water, slake completely or partially without sensibly increasing in volume. Argillaceous limestones used in the manufacture of hydraulic limes usually contain from 10 to 20 per cent. of clay homogeneously mixed with carbonate of lime as the principal ingredient. Silicious limestones ‘contain from 12 to 18 per cent. of silica, small percentages of oxide of iron, carbonate. of magnesia, etc. No hydraulic limes are manufactured in the United States, 8 CONCRETE AND REINFORCED CONCRETE. and, while they are manufactured extensively in certain localities in Europe, the subject is not of sufficient interest to warrant a Cescription in this place of the methods of manufacture. Natural Cement and Its Manufacture.—Natural cement is the product resulting from the burning and subsequent pulverization of a natural clayey limestone (containing 15 to 40 per cent. of silica, alumina and iron oxide), without preliminary mixing and grinding, the heat of burning being insufficient to cause vitrifica- tion. During the burning the carbon dioxide of the limestone is _almost entirely driven off, and the lime cgmbines with the silica, alumina, and iron oxide, forming a mass containing silicates, aJuminates and ferrites of lime; or, if magnesium carbonate is present in the original rock, magnesium compounds will result. It is necessary to grind this burned mass rather fine, for it will not slake as it comes from the kiln if water be poured on it. This finely ground powder when mixed with water, hardens or sets rapidly, cither in air or in water. American natural cement was formerly called Rosendale ce- ment, due to the fact that it was first manufactured at Rosendale, N.Y. The manufacture of natural cement from a mechanical stand- point is a comparatively simple process, consisting of burning the rock as it comes from the quarry, in plain upright kilns, and grinding the burnt friable pieces to a powder. The rock in its natural state contains the proper ingredients for natural cement. The limestone is usually stratified, the strata varying somewhat in ‘chemical composition. Several strata are usually mixed for any given brand of cement, the idea being that if one layer contains too much silica it may be corrected by another containing too much lime or magnesia. The rock is either quarried in open cut where the stripping is light, or is mined by means of tunnels and chambers. The rock, as‘it is quarried, is broken into sizes con- venient for handling, and then run through an ordinary rock crusher, which breaks it into pieces varying in size up to six inches; then it is conveyed, usually by an ordinary tramway, Cirectly to the loading platform at the top of the kiln. With but few exceptions, the kilns used in the American natural cement industry are of the vertical continuous mixed-feed type. They are commonly about 45 ft. high and 16 ft. in diameter, and are built of masonry, lined with firebrick, or have an iron CLASSIFICATION AND MANUFACTURE OF CEMENT. 9 shell, lined with fire brick. Fig. 3 shows a vertical section of such a kiln. The rock and fuel are spread in the kiln in alternate layers, the proportion of fuel being regulated by the man in charge of burning. Either anthracite or a good quality of bitu- minous coai is used, according to the locality. When anthracite coal is used it requires about 10 lbs. of coal to burn 100 Ibs. cf rock. The temperature of burning varies according to the character of the rock. It is somewhat greater than that used for burning lime, but is generally considerably below the point of incipient fusion reached in burning Portland cement. kK-------------- 20 4---------- wrote > YR Geni ceecs i ! ' i Sa 3! S. Ss NK ite y " i 1 ! nw { aie a, ! * | 1 al + & I * N Is NY ' : : i at te Nw. Fig. 3.—Kiln for Burning Natural Cement. It is impossible to burn the rock uniformly, hence it is necessary to sort out and throw away the under burnt and over burnt clinker. Bad weather, bad management, the character of kiln used, etc., determine the amount of loss, which varies from Io per cent. under the best conditions to 33 1-3 per cent. under bad con- ditions, with a probable average loss of about 25 per cent. The sorted calcined rock is conveyed to crushing machines, usually ef the rotary type, such as the “pot cracker,’ consisting of a ribbed, steel-faced, or chilled iron, cone revolving within a cor- rugated conical shell, as shown in Tig. 4. Io CONCRETE AND REINFORCED CONCRETE. The material is conveyed from this machine to screens, which teke out the cement that is fine enough to pack. The coarser particles go to fine grinding machines. These machines may be either edge runners, ball or tube mills,’or ordinary mills, or emery faced stones. The methods used during this part of the pro- cess are essentially similar to those employed in the manufacture cf Portland cement. The product passes from the reducing mills to the mixers by means of which a more thoroughly uniform Fig. 4.—Pot Cracker for Natural Cement Rock. product is obtained. It is then conveyed by chutes to the bags and barrels in which it is packed. The cost of manufacture varies with local conditions. The various items which go to make up the cost are: cost of quarry- ing, or mining the rock, cost of labor at the kilns and mill, cost of fuel for the kiln, cost of power, interest and depreciation of plant. These may vary from 15 to 50 cts. per barrel of cement manu- factured. Portland Cement and Its Manufacture——Portland cement is an artificial product obtained by finely pulverizing the clinker pro- duced by calcining to incipient fusion a natural or artificial mix- CLASSIFICATION AND MANUFACTURE OF CEMENT. 11 ture of finely ground argillaceous and calcareous materials, this mixture consisting approximately of three parts of carbonate of lime or lime oxide to one part of silica, alumina and iron oxide. The essential components of Portland cement are silica, alumina and lime; while the ingredients always occurring with these in appreciable quantities are iron, magnesia, alkalies, sulphuric and carbonic acids, and water. These ingredients should approximate the following limits given by Le Chatelier for commercial Port- land cement: Per cent. SUIGd ayy dowew ies Larrea ee eee Wee ea eid Bt se 21 to 24 PONT TS ad asters to er tees ess aaece sale sides Wao gods m anbseogmua eae aeniaodee 6 to 8 Won: Qhaderr O85 aes Bib hte and Wit God tea ade dot tek) 2to 4 LAME: pare 5s eeretek bie NE OREe see EEE EN mE ead 60 to 65 Magnesia. cce:vadaseisa serait eee wean resis wee Swe ca o5to 2 sala: ACI sce tevcsied Sani ena aunts shad aliaiase baba aac wa ake 0.5 to 1.5 Carbonic Acid and Water..........00 foe eee eee I to 3 The materials from which Portland cement is manufactured vary with the locality, and usually consist of either cement rock and limestone, limestone and clay, marl and clay, chalk and clay or slag and limestone. Cement rock and limestone are chiefly used in the Lehigh district, and constitute the raw materials used for two-thirds of the Portland cement manufactured in this country. Limestone and clay are the materials used in the New York State cement region, marl and clay are used in the cement mills of the middle west. Chalk and clay are the materials used in the states bordering the Mississippi River on the west and in Texas. Slag and limestone, although extensively used for the manufacture of cement in Europe, have as yet been little used in this country. For a more extended discussion on the raw material used for the manufacture of Portland. cement, see “Cements, Limes and Plasters,” by Edwin C. Eckel. In the early days of the industry, Portland cement was calcined in stationary kilns similar to those used in the manufacture of natural cements. This type of kiln is still occasionally used in this country, and is used to a larger extent in France and Ger- many. Although the coal consumption is smaller than with the rotary kiln, labor is a much larger item, and on this account the stationary kiln is not an economic method of manufacture unless 12 CONCRETE AND REINFORCED CONCRETE. the cost of labor is quite low. The only essential difference be- tween this method and that used for the manufacture of natural cement consists in the grinding and mixing of the raw material while wet, and moulding the mix into bricks, which are dried hefore being calcined. ‘i , The Dry Process of Manufacture.—Rotary kilns are used almost exclusively for the manufacture of cement in the United States. Two processes are employed, the dry process and the wet pro- cess. The dry process with rotary kilns may be considered as the Fig. >.—Ball Mill of the Krupp Type. typical American method for the manufacture of Portland cement. The wet process does not differ materially from the dry process. The dry process is adaptable to any class of materials, which ‘can he quarried and pulverized in a dry state, and is briefly as follows: The raw material is conveyed from the quarry to the mill and is first passed through crushers, which reduce it to a maximum diameter of 2 or 3 ins. It is then conveyed to storage bins, where it remains until the chemical composition has heen determined, so that the mix can be properly proportioned. A suitable mixture by weight is then made and conveyed to a dryer, which is kept at a temperature sufficiently high to drive CLASSIFICATION AND MANCE.ACTURE OF CEMENT. 13 eff the greater part of the moisture contained in the rock. The dryer usually consists of a rotary cylinder 4 or 5 ft. in diameter, 40 to 50 ft. long, with its axis slightly inclined to the horizontal. Fig. 6.—Tube Mill of tne Davidsen Type. The materials enter at the upper end and are discharged at the lower end. Heat is usually supplied by a small furnace. From the dryer, the material is conveyed to a preliminary grind- ing machine, usually of the ball mill type, which reduces it to Fig. 7.—Griffin Mill. Figure 5 shows the usual type of ball mill. The mixture then fasses to the fine grinder, where it is further reduced until from 69 to 95 per cent. will pass a No. 100 sieve. The tube mill (Fig. 6) or Griffin mill (Fig. 7) is usually emploved for fine grinding. 14 CONCRETE AND REINFORCED CONCRETE. Fig. 8.—Longitudinal Section of Rotary Kiln. From the grinding machines the mixture is conveyed to bins above the rotary kilns into which it is fed automatically. The rotary kiln (Figs. 8 and 9) is a steel cylinder, varying in length from 40 to 150 ft. and from 4% to g ft. in diameter, lined with from 6 to 12 ins. of fire brick, with its axis inclined 8 or 10 degrees to the horizontal, and arranged to rotate at a speed averaging about one turn per minute. The raw materials are introduced at the upper end in the form of powder, and in passing through are calcined to a clinker, which leaves the kiln at the / lower end in small balls, ranging from 1% to 11% ins. in diame- ter. Tinely pulverized gas slack coal is generally used for fuel, although both gas and oil have been employed, but with poorer results. The coal is blown into the lower end of the kiln, and instantly ignites, forming a flame reaching from 15 to 25 ft. into the kiln, and producing a temperature of from 2,600 to 3,000 degrees Fahrenheit. The coal is pulverized in the same manner, and to about the same degree of fineness as the raw materials. The temperature and time of burning vary with the nature of the raw materials. The clinker as it leaves the kiln is sprayed with a small stream of water, which cools and makes it more easy to pulverize. It then passes through coolers, which reduce it to a normal tem- perature. [rom the coolers the clinker passes to the pulverizing and grinding machines, which are similar to those used for re- Fig. ‘.—Rotary Kiln as Made by the Bonnot Co. CLASSIFICATION AND MANUFACTURE OF CEMENT. 15 ducing the raw material. The finished cement from the grind- ing machines is conveyed to the stock house, often being stored for a time to give it a chance to “season” somewhat. It is then packed in bags or barrels for shipment. The Wet Process—The wet process may be used either with rotary or stationary kilns. In the United States it is usually only employed by the mills in which the raw material used is marl, al- though it is adapted to chalk or other materials, which are easily reduced when in a wet condition. When water is used in re- cucing the material, less power is needed for operating the ma- chinery. The saving in this part of the process is, however, more than balanced by the cost of the additional coal needed to evapo- rate the water from the slurry after it is fed into the kin. The cost of handling wet material is less than dry material, as it may be pumped from one part of the plant to another. Wet Process With Rotary Kilns.—If we assume that marl and clay are used, the process is as follows: The marl, after excava- tion, is passed through a disintegrator and sometimes a stone and grass separator, and run into storage basins, while the clay is dried, pulverized, and then mixed with a proper amount of marl in pans of the edge runner type (Fig. 10) the slurry containing enough water to give it a thick creamy con- sistency. In some mills this process is varied."by mix- ing the clay with water before adding it to the marl. The mixture is then ground, while still in a wet condition, in either cdge runners, or tube mills, from which it is run into slurry tanks, where it is kept agitated by revolving paddles or by compressed air, and from which chemical analyses are made to check the ac- curacy of the proportions, corrections being made if necessary. Centrifugal pumps and compressed air are both used for handling the slurry. The wet slurry is then pumped directly into the upper ends of rotary kilns, which are usually somewhat longer than those em- ployed in the dry process, so that the waste heat may be utilized in driving off the excess water. About 150 to 160 Ibs. of coal per barrel of cement are necessary for the burning, which is from 30 to 50 per cent. more than required in the dry process, ‘but this disadvantage is largely compensated by the cheaper method of handling and preparing the raw material. The treat- ment of the clinker is similar to that of the other processes. 16 CONCRETE AND REINFORCED CONCRETE. Wet Process With Stationary Kilns.—In this process the clay and marl, or chalk, are first ground, if necessary, and then mixed together in a wash mill with a large excess of water, the lumps teing broken up by means of agitators. When the materials have thus been reduced to a very finely divided state, the mix- ture is run into settling basins, where the solid matter settles and Fig. 10.—Mixing Pan for Marl and Clay. Edge Runner Type. from which the excess of water is drawn off. The slurry, when still further hardened, is formed into bricks and burned in sta- tionary kilns. A modification of this method, known as the semi-wet process, consists in-mixing with a smaller amount of water, sufficient to give a creamy consistency, the operation being similar to the CLASSIFICATION AND MANUFACTURE OF CEMENT. 17 wet process with rotary kilns, except that the slurry is partly dried and formed into bricks instead of being fed directly into the kilns. The chief disadvantages of the process are the large space necessary for settling and drying the slurry and the greater amount of labor required. It/is used extensively in Europe, and in England a few years ago might have been considered the typical process. It is, however, not used in this country. Portland Cement. from Blast Furnace Slag.—This has been manufactured in Europe fcr several years, but its manufacture has only recently been undertaken in the United States. As the method involves the utilization of the waste products from the blast furnace, it is likely that it will become popular. The method of manufacture is briefly as follows: The slag, as it comes from the blast furnace, is sprayed with water, which granulates it and changes its chemical composition, the water combining with the calcium sulphide, which is injurious to cement, to form a lime and sulphuretted hydrogen. The gran- ulated slag is then dried, mixed with the correct proportion of dried limestone, and ground to extreme fineness. The mixture is then burned in a rotary kiln. The remainder of the process is essentially the same as that already described for the manu- facture of Portland cement from ordinary material. Slag Cement and Its Manufacture.—Slag or puzzuolana ce- ment is made by intimately mixing granulated blast furnace slag of proper composition with slaked lime, and reducing this mixture to a fine powder. This product differs materially from Portland cement, although it is sometimes called a Portland cement by the manufacturers. While it is an excellent material for many purposes, it possesses certain qualities which prevent its use as a substitute for Portland cement in many classes of work. The largest piece of work in the United States, known to the author, upon which slag cement has been used to any extent, was the drainage system for New Orleans. The method of manufacture is-briefly as follows: Slag of the froper composition is chilled as it comes from the furnaces by the action of a large stream of cold water under high pressure. The slag is, thereby, broken up; about one third of its sulphur is eliminated and it undergoes other chemical changes. A sample ef the slag thus granulated is mixed with a proportion of pre- pared lime, and ground in a small mill, thereby producing a small 18 CONCRETE AND REINFORCED CONCRETE. amount of actual slag cement. If the tests upon this trial cement are Satisfactory, the slag is dried and then ground, first in a Griffin mill and then in a tube mill. Then it is mixed with the proper amount of prepared lime, and the two materials are ground and intimately mixed together. The resulting product is said to be so fine that 95 per cent. will pass a No. 200 sieve. The lime is burned from a very pure limestone, and stored in bins, beneath which are two screens of different mesh, the coarser at the top. A quantity of lime being drawn on the upper screen, is slacked by the addition of water containing a small percentage cf caustic soda. The lime passes through the two screens as it slakes, and is then heated in a drier, the slaking being thus completed. The lime may then be incorporated with the slag. The purpose of the caustic soda used in the above process is tu render the cement quick setting. CHAPTER II. PROPERTIES OF CEMENT AND METHODS OF TESTING. Portland cement is used for reinforced concrete construction, almost to the exclusion of other cements. Its great strength, uniform composition and the regularity of its properties emi- nently fit it for this class of work. In manufacture, the distin- guishing characteristics of Portland cement are the use of an artificial mixture, the grinding of the raw materials before burn- ing, and the calcining to incipient fusion. In use, its distinguish- ing characteristics are its high specific gravity, dark color, slow- ness of setting and great strength. Natural, quick setting’ cements are used for reinforced con- crete only in special forms of construction, viz., in repair work, as when quick setting is necessary in order to enable the structure to sustain moderate loads or enable its use within a few hours; in hydraulic work, as in the construction of reservoirs and con- duits ; and in the construction of reinforced concrete pipe. They are, however, extensively used for plain concrete work. Some- times when quick setting with great strength is desired, a mixture of natural and Portland cement is employed. In manufacture, the distinguishing characteristics of natural ce- ment are its production from a single variety of material, un- ground and burned at a low temperature; and in use, its lighter weight and color, quick setting property, and small strength in the early stages of hardening. Slag cements, as yet, have not had extensive use in this coun- try. They are characterized, in manufacture, by their produc- tion from intimately mixed granulated blast furnace slag and slaked lime, without the usual process of calcining employed in the manufacture of other cements. In use, slag cements are commonly distinguished by their light color, inferior specific gravity, slow set and lower strength. The low strength, variable composition and uncertain properties, of both natural and slag 20 CONCRETE AND REINFORCED CONCRETE. cements, render them undesirable for reinforced concrete struc- tures. Field Inspection.—Cement is usually sold in barrels, or in cloth cr paper bags. When in danger of being subjected to dampness in shipping from the place of manufacture to the site of the work, barrels are employed; but in the majority of cases, cement is shipped in cloth bags. Cement is generally stored temporarily at the site of construction on raised platforms for about 10 days, in order that the necessary tests may be made. At the time of delivery the condition of the packages should be observed ; they should be plainly marked with the brand and name of the manufacturer. A field inspection often enables a correct judgment to be formed of the condition of the cement. Old or well-seasoned cement is generally lumpy, but the lumps are easily broken up. If, however, the cement has been subjected to excessive dampness, or has been wet, lumps will be formed which are hard and difficult to crush. This ce- ment is probably hydrated and of inferior quality. It should also be noted whether the cement runs uniformly in color, as a change in color may indicate a change in brand or quality, and should lead to careful testing. Sampling.—For the purposes of testing, samples should be taken from bags at random. There are several good methods cf sampling, but perhaps the most satisfactory is to take-a small sample from each of a number of bags, mix these lots together and separate the same into a convenient size for testing. When a sample from a single bag is taken, it is usually stipulated that a sample shall be taken from one bag in ten, the bag being picked cut at random. When small lots of cement are used, the samples should be taken more frequently, a sample from every five bags being about right. Care should be taken that the sample be representative of the material in the bag, part being taken from the surface and part from the interior. Usually a sample weigh- ing 8 to 10 lbs. will be enough for the ordinary purpose of testing. Samples should be placed in a tightly covered can and stored in a dry place until tested. Properties of Cement—lIn order that cement shall come up to the requirements necessary for a high class of work, it must possess certain desirable properties, and be free from others which may be injurious. The desirable elements are: (1) That CEMENT AND METHODS OF TESTING. 21 when treated in the proposed manner it shall at the end of a definite period develop a certain strength; (2) that it shall con- tain no compounds which may at any future time cause it to change its form or volume, or lose any of its strength; and (3) that it shall withstand the action of any outside agency which may tend to decrease its strength or destroy its durability. When a cement fulfills these requirements it will be a safe and satisfactory construction material. To determine whether it fulfills these requirements, certain properties must be considered and certain tests made to determine other properties. In de- termining the value of a given cement for structural purposes, the qualities usually considered are: (1) Its color; (2) specific gravity; (3) activity; (4) soundness; (5) fineness; (6) strength, and (7) chemical composition. In the examination of a given sample of cement its ‘failure to conform to the usual requirements in regard to any one of these qualities should not necessarily lead to its condemnation, hut rather classify it as suspicious, and it should be tested care- fully in every possible manner before accepting or rejecting. Color—While the color of cement has little bearing upon its quality, it may indicate an excess of some one ingredient; and for any given brand, variation in shade may indicate differences in the character of rock used, or in the degree of burning. Portland cement should be a dull gray. Bluish-gray probably indicates an excess of lime; dark green, a high percentage of iron; brown, an excess of clay; and a yellowish shade indicates ever burning. Natural cements vary greatly in color, ranging from a light yellow to dark gray, and even to a chocolate brown. Generally the color is no criterion of quality, but may be considered as giving some indication of the uniformity of a given grade or brand of cement. Slag cements are usually much lighter in color than Port- lands, and slightly different in tint, while they differ markedly in tint from most natural cements. They are commonly bluish- whité to lilac, the exact color of any specimen depending partly on the respective colors of the lime and slag which have been used in its manufacture, but more largely on the relative pro- portions in which these two ingredients have been mixed. Slag cement, after being kept under water, shows, when fractured, 22 CONCRETE AND REINFORCED CONCRETE. a bluish-green tint, which is supposed to be due to the presence cf sulphide of calcium. Slag cements do not stain masonry, hence they will have an extended use in architecture. Specific Gravity——The specific gravity of a substance is the ratio of its weight to the weight of an equal volume of water. As the specific gravity of a well-burned cement is known to have certain definite limits, the specific gravity of a cement may be said to give a true indication of the thoroughness of burning. The higher the temperature used in burning, the more thoroughly will the ingredients be combined; and it follows that their volume will contract, resulting in a greater density or higher specific gravity. Too high a specific gravity will therefore indicate over burning. Over burning tends to break up some of the com- pounds which should be present in a normal cement, and to form others that may not be injurious, but, nevertheless, possess such feeble hydraulic properties that they tend to weaken the material. A low specific gravity indicates under burning, adulteration and hydration. An under burnt cement contains a large pro- portion of uncombined, or insufficiently combined, elements, some of which are sources of great danger. If the cement is used, these elements may cause disintegration and the ultimate failure of the structure. Adulteration, which may be detected by thé specific gravity test (excepting adulteration with gypsum or plaster of Paris, of which there is a legitimate use), may consist of the incorpora- tion’ of raw-rock, cinder, slag and natural cement. All these ingredients have a lower specific gravity than Portland cement. If the Portland cement is of high grade, as high as 20 or 25 per cent. of adulterants may at times be added, and the cement will still possess sufficient strength to pass the usual physical tests. The incorporation of so high a percentage of impurities, which possess a much lower specific gravity. is at once apparent when the specific gravity test is applied to the mixture. The specific gravity test, however, should not be relied upon alone for the detection of adulterants, since many other causes may operate to produce an abnormably low value, as the age of the cement, fineness of grinding, composition of material, etc. It should be taken as indicative, and should be verified by other tests before rejecting a material which does not come up to standard. CEMENT AND METHODS OF TESTING. 23 The specific gravity of natural cement is generally no crite- rion of its quality, but, to some degree, may be regarded as a measure of the uniformity of a single grade. The specific gravity of Portland cement varies from 3.00 to 3.25, but for the higher grades of American cements it is usually found to be between 3.10 and 3.25. The specific gravity of natural cement varies from 2.75 to 3.05. Slag cements are lighter than Portland, and in some cases lighter than natural cements, their specific gravity usually ranging from 2.6 to 2.0. A slight variation in the specific gravity often denotes a con! siderable difference in the quality of a cement, hence great care is necessary in making this test. The use of Le Chatelier’s * apparatus is recognized as the standard method of determining the specific gravity in American practice, and is recommended by the committee on Uniform Tests of Cement, of the American Society. of Civil Engineers. Activity—When cement is mixed into a paste with water and allowed to stand, it gradually hardens. The rate of hard- ening is'termed the time of setting or activity. Two distinct stages in setting are recognized: (1) the initial set; and (2) the hard set. The first takes place when the mass begins to harden; and the second, when the hardening has reached a point where the mass can not be appreciably distorted without rupture. The determination of the first period is important, as the material must be deposited and remain undisturbed before ‘the point is reached, for otherwise a great loss of strength will result. The time of setting may vary within wide limits, and is no criterion of the quality of cement. However, a cement may set so quickly that it is worthless as a construction material, or it -may set so slowly that it will greatly delay the progress of the work. Again, after it has been placed in the structure it should set and harden as quickly as possible, so that it can offer resis- tance to any external forces. Hence certain definite limits must he fixed for the time of setting. The best cements should be slow in acquiring initial set; but, after having reached that point, should harden quickly. A natural cement is generally much quicker in setting than *For an exhaustive description of the apparatus and method used for this de- termination see ‘‘Practical Cement Testing,’’ by W. Purves Taylor, New York, 1°08, 24 CONCRETE AND REINFORCED CONCRETE. a Portland, although slow setting natural cements are occasion- ally met with. In natural cements the hard set frequently o¢curs within a few moments after the initial set, sometimes within a period of 15 minutes, and should develop hard set in from 30 minutes to 3 hours. Initial set should in no case develop in less than 10 minutes. Portland cement should develop initial set in not less than 30 minutes, and hard set in not less than one hour, nor in more than 10 hours. Normal slag cements are slower setting than Portland. At times burnt clay, or slags high in alumina, or certain active forms of silica, etc., are added to increase the activity, the attempt being made to obtain a cement with about the same activity as that possessed by Portlands. The composition, degree of burning,.age, fineness of grind- ing, amount of water used in mixing, and the temperature and humidity of the air, affect the activity of a cement. It is usual to add a small percentage of gypsum or plaster of Paris during manufacture, to retard the setting. Small percentages of these materials increase the strength of cement, but larger quantities may cause it to blow or expand. A greater quantity than 2 per cent. is dangerous. A lightly burned cement, or a freshly burned cement, sets more rapidly than a hard burned or an old cement. This is due to the presence of non-hydrated free lime. Hence care should be taken during manufacture to secure sufficient burning. A moderate amount of “seasoning” is also helpful to secure good results in use; for, if cement is allowed to stand exposed to the air and to dampness, it gradually absorbs water and car- bonic acid. These produce a chemical change in the materials, resulting gradually in slower setting, and eventually the cement loses all its hydraulic properties, although a well protected ce- ment may be stored for a long time without appreciable de- terioration. Aging, therefore, under usual conditions is not to be desired. The effect of age on setting is generally less notice- able with natural than with Portland cements. The activity of a cement varies somewhat with the amount of water used in gauging; the greater the amount of water used the slower the setting. The temperature of the water also affects the setting; high temperatures accelerate the setting, A CEMENT AND METHODS OF TESTING. 25 finely ground cement is almost invariably quick setting, unless artificially retarded. This is due to the fact that a finely ground material is more quickly attacked by a solvent than a coarser ene. The temperature and amount of moisture in the air also affect the activity of a cement, high temperatures and a dry at- mosphere increasing the activity, while low temperature and a humid atmosphere retard the setting. For the apparatus and method used to determine the time of set consult “Practical Cement Testing,” by W. Purves Taylor, New York, 1906. Soundness.—The soundness of a cement refers to the property of not expanding, contracting or checking in setting. It is absolutely necessary that the cement shall neither shrink nor swell after the process of setting has once begun. When the ingredients of Portland cement have been improperly mixed, or the process of manufacture has been improperly carried on, the cement will have a tendency to expand, crack and disin- tegrate after the setting has commenced. Unsoundness is gen- erally due to an excess of lime, either free or loosely combined, which has not had an opportunity to become sufficiently hydrated. The presence of this lime may be due to incorrect proportion- ing, to insufficient grinding of the raw material, to under burn- ing, to lack of seasoning or to insufficient grinding of the cal- cined rock. The presence of sulphides, an excess of magnesia cr of the alkalies, may also cause expansion and disintegration, and at times may be more harmful than uncombined lime. Con- traction is sometimes due to an excess of clay. The age of a cement greatly affects its soundness. Almost every cement, no matter how well proportioned and burned, contains a small amount of free or loosely combined lime, which may cause unsoundness if the cement is tested before attain- ing sufficient age. This lime, however, if exposed to the air, will hydrate in a short time, becoming inert. In many cases, when a fresh cement tests unsound, it will be found that if it is stored for two or three weeks this unsoundness will disappear. Fineness of grinding is essential to perfect hydration, and it will be found in most cases that a coarsely ground cement is an unsound one, the larger particles not being readily subjected to hydration. Tests for soundness are among the most important to be made 26 CONCRETE AND REINFORCED CONCRETE. upon cements, and should extend over considerable time to fully develop possible inherent defects. The usual manner of de- termining whether or not a cement is sound, is to immerse in water a small pat of neat cement mortar, 2 or 3 ins. in diameter, with thin edges. This pat is examined from day to day to see whether it cracks or in any way becomes distorted. Another pat is allowed to set in air, and is examined for blotches znd discoloration. Another test for soundness is by measuring the amount of change in volume. A rough method is to press some mortar firmly in a glass tube or lamp chimney. Ifa dangerous amount cf expansion takes place the glass will be broken. Shrinkage may also be determined by pouring some colored liquid. into the chimney after the cement has thoroughly set. An idea of the amount of shrinkage may be formed by the amount of liquid that runs down the inside. Several more accurate, but much more complicated methods for making this test, are used in larger testing laboratories. “Practical Cement Testing,” by W. Purves Taylor, should be consulted if an elaborate discussion on this subject is desired. - Accelerated tests are widely used and are designed so to hasten the action of the expansive ingredients that the same re- sults will be produced within a few hours, or at most a week, that under normal conditions will not appear for weeks, months, er even years. These tests consist of placing a pat made of neat cement of normal consistency, and usually moulded upon glass, either in warm, hot or boiling water, or in steam for sev- eral hours. These severe conditions tend to warp or disin- tegrate unsound cements. In the Faija test, warm water at a temperature of 115° F. is used. In what is known as the “Hot Water” test a temperature ranging from 130 to 200° I’. is main- tained. In the boiling test the specimens are subjected to the action of boiling water from one to six hours. Sometimes the pat is sibjected to an atmosphere of steam above boiling water for 3 hours, or, when 24 hours old, is subjected to a steam bath for 3 hours, and then is boiled for from 2 to 6 hours. These tests are all more or less satisfactory, depending upon the degree with which they corroborate other tests for CEMENT AND METHODS OF TESTING. 27 soundness. Taylor states “that of a large number of tests which failed in the boiling test, 86 per cent. gave evidence in less than a year of possessing some injurious quality, and that, of those cements that passed the boiling test, but one- half of one per cent. gave signs of failure in the normal test pats, and but 13 per cent. showed a falling off in strength in a year’s time.” On the other hand, while conceding the value of this test, it often happens that a cement may pass the boiling test well, yet check and disintegrate in the normal tests. ‘Again, cements have passed sound which would not pass the boiling test. Hence we should consider this test as a corroborative test only, and not as final. Lastly, it is safe to assume that if 2 cement passes the boiling test it may be considered safe until the results of the normal tests are known, and, if it does not -pass the boiling test, it should be regarded with suspicion until the results of other tests are available. For natural cements, tests made on pats of neat cement paste kept in air and water under normal conditions are considered to be the only conclusive ones. Excessive expansion, checking or disintegration on normal pats exhibit similar phenomena in both natural and Portland cements. Accelerated tests have not proved successful for natural cements. In slag cements, unsoundness is usually due either to un- slaked lime or an excess of sulphides or magnesia. If the lime is not thoroughly slaked, or is coarsely ground, it will tend to produce swelling and disintegration as with Portland cement. The effect of sulphur in the form of sulphides is noticeable chiefly ia air, where they oxidize to sulphates with a great change in volume, thus causing disintegration. In water this change does not take place, although the pats generally show blotches of bluish or greenish-gray, probably due to the formation of iron sulphides. Tests of slag cement are usually made on normal pats and on specimens submitted to boiling, and, for normal tests, should give no indication of unsoundness, other than blotch- ing at the end of 28 days, and should pass the boiling test. If failure takes place, either test should be sufficient cause for the rejection of the cement. Fineness.—The finer a cement is ground, the better its quality. Water acts only on the finer particles, while the coarser particles, are almost always inert. The finer a cement is ground the 28 CONCRETE AND REINFORCED CONCRETE. greater will be its covering capacity, therefore, the greater its ralue as a cementing material. To produce the greatest strength each particle of the aggregate should be covered with cement- ing material. The greatest economy, other things being equal, will result when the cement is as fine as possible. However, while fine cement is more valuable than coarse, fine grinding increases the cost of manufacture, hence there is a limit to the amount of grinding which can be done economically. Again, a finely ground cement is less apt to blow or disintegrate than a coarse one, since the free or loosely combined lime being in fine particles, is thoroughly broken up and readily rendered innocuous by the water when it is added. A Portland cement of good quality should be fine enough to fass at least 92 per cent. by weight through a No: 100 sieve, and 75 per cent. through a No. 200 sieve. A No. 100 sieve has from 96 to 100 meshes per lineal inch, and a No. 200 sieve from 188 to 200 meshes per inch. The degree of fineness to which a natural cement is ground depends both upon the composition of the material and the process of grinding used. At times the percentage which will pass a No. 200 sieve will approximate that for Portland cement. Fine grinding is, however, not as essential in the manufacture of natural as in Portland cement, as the amount of free lime present is much less. If the requirements are such that 85 per cent. or more must pass a No. 100 sieve, and 70 per cent. or more must pass a No. 200 sieve, a good quality of natural cement should result. Slag cements of necessity must be ground much finer than is necessary for Portland cement. It is common practice to require not less than 97 per cent. to pass a No. 100 sieve and from go to 92 per cent. to pass a No. 200 sieve. Strength Tests—The strength of a cement mortar may be de- termined by testing it. The object of the test is to obtain a measure of the strength of a material as used in actual work. As a rule tensile tests only are made, although cement mixtures are used almost entirely in compression, and may be subjected to every conceivable form of stress. The reason for this is that the tensile strength is more easily determined, and is more cr less a true measure of the compressive, transverse, adhesive and shearing values. Again, investigation appears to show that CEMENT AND METHODS OF TESTING. f 29 the strength of cement in tension is more susceptible to any good or bad influences affecting the material, and, therefore, furnishes a better criterion of its value than tests made in any other manner. There exists a certain definite relation between the tensile and all other strengths, hence the results of the tensile tests give a reliable basis for computing the values of the strength under cther forms of stress. Tests are usually made on both neat cement and sand mix- Fig. 11.—Standard Cement Briquette. tures. While there is no definite relation between the strength cf neat and sand briquettes, neat briquettes are more susceptible to both internal and external influences, and are, therefore, better criterions of the character of the material and may be -consid- ered as a measure of its quality, while the sand tests are a true measure of the strength under actual conditions. For sand test of Portland cements, the mixtures are composed cf I part by weight of cement to 3 parts of sand; while for natural and slag cements, richer mixtures are used on account of the greater weakness of these materials in the early stages of setting, 1 to 1 and 1 to 2 mixtures being employed. Both standard and normal sands are used for these tests. The periods 30 CONCRETE ANP REINFORCED CONCRETE. © at which the briquettes are broken are 24 hours, 7 days, and 28 days for neat tests; 7 days, and 28 days for sand tests, although for experimental purposes much longer periods are necessary to secure reliable data. Standard Briquettes.—Tests are usually made with briquettes of standard form, having a minimum cross-sectional area of cne square inch. The standard American form of briquettes is shown in Fig. 11. This is the form adopted by the Committee of the American Society of Civil Engineers. Moulds for briquettes should be made of brass. They are either single, or in gangs of three or four. A simple form is shown in Fig. 12, which is the mould adopted by the Committee of the American Society of Civil Engineers, Normal Consistency of Mortar—The amount of water necessary to make the strongest mortars varies with each cement, and is -Fig. 12.—Gang Mould for Standard Cement Briquettes. usually expressed in percentages by weight. No fixed per- centage can be adopted, hence it is customary to mix with vary- ing amounts of water until a certain normal consistency of mor-’‘ tar is secured. The amount of water necessary to hring differ- ent cements to the same consistency varies with the composition, age, fineness, etc., so that the amount of water must be de- termined experimentally in each case. A normal consistency Getermined by what is called the “ball method,” is secured in the following manner: Cement paste is mixed to such a degree of plasticity that when a ball of the paste, about 2 ins. in diameter, is dropped upon a hard surface from a height of 2 ft., it will not crack or flatten to more than half its original thick- ness. This determination is extremely simple, easy to make, may be readily distinguished, is suitable for moulding, and, in the hands of an experienced operator, is extremely accurate. Method of Mixing—The proportions of cement, sand and CEMENT AND METHODS OF TESTING. 31 water should be carefully determined by weight, the sand and cement mixed dry, and the water added all at once. The mix- ing must be rapid and thorough, and the mortar, which should be stiff and plastic, should be firmly pressed into moulds with a trowel, without ramming, and struck off level. It will be found that if the mixing be rapid, it need only continue for about one Fig. 15.—Improved Form of Fairbanks Testing Machine. and one half minutes. The mixing should be done upon a glass cr slate slab, and the hands should be protected by rubber gloves. Storing Briquettes——It is customary to store the briquettes immediately after making in a damp atmosphere for 24 hours. They are then immersed in water until tested. The reason for this is to secure uniformity of setting, and to prevent the dry- ing out too quickly of the cement, thereby preventing shrinkage, cracks and greatly reducing the strength. To keep the samples damp when a suitable closet is not available, the briquettes are sometimes covered with a wet cloth having its ends dipped in water. Testing Machines.——A large variety of testing machines is ca the market, all of which are quite expensive. Any one of them 32 CONCRETE AND REINFORCED CONCRETE. will, if properly used, give satisfactory results. Figure 13 shows a cut of the improved Fairbanks machine, which will prove very satisfactory for ordinary testing purposes. The method of operation of this machine is as follows: The briquette is placed in the clamps, and adjustment is made by the hand wheel P until the indicators are in line. By means of the hook lever Y, the worm is engaged with the gear; the shot valve is opened, allowing the shot to run into the bucket, the crank is turned with sufficient speed to hold the beam in equilibrium until the briquette is broken. After the specimen has broken, the cup with its shot is re- moved and hung on the hook under the large ball, and the weight of the shot as given on the graduated beam shows the number of pounds required to break the specimen. A home- w! Fig. 14.—Home-Made Cement Testing Machine. made testing machine of low cost, devised by F. ‘W. Bruce, is shown in Tig. 14. This machine consists of a counterpoised wooden lever, 10 ft. long, working on a horizontal pin between two broad uprights 20 ins. from one end. Along the top of the arm runs a grooved wheel carrying a weight. The distance from the ful- crum in feet and inches is marked on the surface of the lever. A clip for tensile tests.is suspended from the short arm, 18 ins. from the fulcrum. The lower clip is fastened to the bed plate. The rail on which the wheel runs is a piece of light T-iron, fastened on top of the lever. The pin is iron, and the pin holes are reinforced with iron washers. The clamps are wood, and are fastened by clevis joints to the lever arm and bed- plate respectively. With care, very uniform results may be ob- tained with this machine. Strength of Cement Mortars——In making tensile tests the pri- mary object is to ascertain the strength which will develop within CEMENT AND METHODS OF TESTING. 33 a certain time. By determining the gain in strength between different dates of testing, some idea may be obtained of the ulti- mate strength which the cement will attain. In no case should a cement decrease in strength. Again, it should be remembered that the strength shown by a single test may not necessarily give a true indication of the value. Too high values for the one-day and seven-day neat cement tests should be regarded with suspicion, as the great strength is probably due to high liming, and the cement will after a time lose much of its early strength. as Specifications for tensile strength of cement usually stipulate that the materials must pass a minimum strength requirement at 7 and 28 days. The limit set is often so low that all but the poorest cements easily fulfill the requirement. W. Purves Taylor states that “the proper grounds for the judgment of the tests of tensile strength are four in number: (1) That both neat and sand briquettes shall pass a minimum specification at 7 and 28 days; (2) that the neat value at 7 days shall not be exces- sively great; (3) that there shall be no retrogression in the neat strength between 7 and 28 days, and (4) that the strength of the sand briquettes between these periods shall increase at least 19 or 15 per cent.” It must be remembered that the sand test is the true criterion of strength, and no cement failing to pass this test should be accepted, even though the neat tests are satis- factory. If, however, the sand tests pass, and the neat fail, it may at times be justifiable to use the material if it passes the tests for soundness satisfactorily. Mr. Taylor also gives the following rules for accepting or rejecting material on the re- sults of tensile tests: “At 7 days:—Reject on decidedly low sand strength. Hold for 28 days on low or excessively high neat strength, or a sand strength barely failing to pass requirements.” “At 28 days:—Reject on failure in either neat or sand strengths. Reject on retrogression in sand strength, even if passing the 28 day requirements.” “Reject on retrogression ii: neat strength, if there is any other indication of poor quality, or if the 7-day test is low; otherwise accept.” “Accept if failing slightly in either neat or sand at 7 days and passing at 28 days.” 34 CONCRETE AND REINFORCED CONCRETE. A first-class cement when tested should give approximately the following values for tensile strength per square inch: PORTLAND CEMENT. Neat. Age. Strength. 24 Hours ‘Gn MOISE Bit) secac sac caatkewavia ates ieee 175 Ibs. 7 days (1 day in moist air, 6 days in water)..............-- 500 “ 28 days (1 day in moist air, 27 days in water)........-....06. 600 “ One Part Cement, Three Parts Sand. Age. \ Strength. 7 days (1 day in moist air, 6 days in water)................ 170 lbs. 28 days (1 day in moist air, 27 days in water)............+6-- 240 “ NATURAL CEMENT. Neat. Age. Strength. 24. hours: (in ‘mOist air) soi ceccnsarysexaareeus pee versa neenos 40 lbs. 7 days (1 day in moist air, 6 days in water).............4-- 125 “ 2&8 days (1 day in moist air, 27 days in water)................ 225 “ One Part Cement, Two Parts Sand. Age. Strength. 7 days (1 day in moist air, 6 days in water).............06- 75 lbs. 28 days (1 day in moist air, 27 days in water)................ 140 “ SLAG CEMENT. i Neat. Age. Strength. 7 days (1 day in moist air, 6 days in water)..............-. 350 Ibs. 28 days (1 day in moist air, 27 days in water)..,............. 500 “ One Part Cement, Three Parts Sand. Age. Strength. 7 days (1 day in moist air, 6 days in water)................ 140 lbs. 28 days (1 day in moist air, 27 days in water)..............4. 220 *‘ Myron S. Falk states* that cement and cement mixtures at- tain a strength not differing greatly from the ultimate strength within a period of three months from the time of setting, and practically within a month or so after this period no appreciable change of strength takes place. Compressive Strength of Neat Cement.—The compressive strength of Portland cement bears a varying ratio to its tensile strength. The compressive strength usually increases faster than the tensile strength, but this ratio does not vary much from a fixed quantity, which may be taken as 10. Table I., taken from the Watertown Arsenal Report of 1902, gives values of the ratio between tensile and compressive strengths of neat cement mortars. Ten specimens of each kind were tested with varying percentages of water and at different ages. *Cements, Mortars and Concrete, N. Y., 1905, CEMENT AND METHODS OF TESTING. 35 TABLE I, Gauged with 20 Gauged with 22 Gauged with 25 per cent. water. per cent. water. per cent. water. of ab. of Z of a Age i Beg oe Bag ota Bo5 84 Air. Water, a5 See Ratio. a8 225 Ratio. #28 SEA Ratio. Days. Days. Rae a2 kag aa Rae e3 ese “Es age "es gga “gs of E oe” g eS” 8 1 717, 196 3.7 595 189 3.1 430 190 2.3 7 Re 3,040 354 86 3,260 302 83 2,610 402 6.5 28 2... «693,990 «560 7.1 863,760 457 823,130 4507.0 I 6 4,250 78 5.5 4,720 666 58 3,880 329 11.8 I 27 7,370 906 8&1 6870 866 7.9 7,580 758 10.0 The shearing strength of cement is somewhat greater than the tensile strength. According to Bauschinger, in the Proceed- ings of the Munich Technical Institute, its value is from 1.03 to 1.57 that of the tensile strength. A value of 1.25 times the tensile strength may be taken as a safe average value for the shearing strength of cement mortar. Chemical Composition of Cement.—The chemical composition is one of the most important guides in determining the character cf a cement, and an analysis should always be carefully made when large quantities are to be used. The proportion of mag- nesia and anhydrous sulphuric acid, and of soluble silica and alumina, to the lime should be determined. It is customary for cement chemists to grind up as fine as possible a given sample ef cement, then determine the percentages of silica, alumina, lime, etc. A proper method of analysis would seem to be to determine the character of the cement as it is used without pulverizing or otherwise changing its physical character. The free silica should be separated from the mixture and the pro- portion of combined silica carefully determined, for it alone is an active agent, the free silica being inert and acting only as so much free sand. The following table shows both the chemical composition as it is usually given, and as shown by an analysis, in which the free and combined silicas are separated: I 2 3 4 5 SHC co caganinas SiO, 21.90 Soluble (SiO,). ...... 18 45 Alumina....... . Al,O, = 7.89 Alumina and Iron Oxides Iron Oxides...... Fe 0, ce 108 Al 203 + Fe: O5...., ty ge Lime sacies aes CaO. 62.04 Ca0.. dhepe tu cdbeeindeunte 61.89 Magnesia........ MgO. 2.33 IMFO) secsieceyess ieetaneais bis 1.78 Sulphuric Oxide... SO, 1.49 SOp sivieweces seeks 1.87 SiO, Insolvble in 10° HCl. 4.38 35 CONCRETE AND REINFORCED CONCRETE. Column 3 shows the average composition of 11 well-known American cements, and column 5 shows the average composition of 7 high-class American cements. Gypsum is sometimes added to a cement to increase its time of setting. When gypsum is used, an excess of lime is sometimes added to hide it. The addition of a solution of carbonate of soda to a cement adulterated with gypsum will again cause it to set quickly. : ‘Literature on Cement Testing.—Burr, William H. The Elas- ticity and Resistance of the Materials. of Engineering. John Wiley & Sons, New York, 1903. (Chiefly mathematical, little practical data.) Butler, David B. Portland Cement, Its Manufacture, Testing and Use. Spon & Chamberlain, London, 1906. (Gives English methods and practice in manufacture and testing.) Falk, Myron S. Cements, Mortars and Concrete, 1904. (Data on investigations of physical properties. ) Grant, John. Portland Cement, Its Nature, Tests and Uses. E. & F. N. Spon, London, 1875. (Data on strength of cement, chiefly historical.) Johnson, J. B. The Materials of Construction. John Wiley & Sons, New York, 1898. (Mathematical discussion, general description, and many valuable data.) Jameson, Chas. D. Portland Cement, Its Manufacture and Use. D. Van Nostrand Co., New York, 1898. (A concise treatise on the properties and methods of testing of Portland cement.) Meade, Richard K. The Examination of Portland Cement. The Chemical Publishing Co., Easton, Pa., 1906. (Methods of chemical analysis. ) Sabin, Louis C. Cement and Concrete. McGraw Publishing Co., New York, 1905. (Valuable data on the properties of ce- ment and their application to practical construction.) Spalding, Frederick P. Hydraulic Cement, Its Properties, Testing and Use. John Wiley & Sons, New York, 1906. (The nature and testing of cement—-no data.) Taylor, Frederick W. and Sanford E. Thompson. A Treatise on Concrete, Plain and Reinforced. John Wiley & Sons, New York, 1904. (Data on cement and concrete and practical appli- cation to construction work.) Taylor, W. Purves. Practical Cement Testing. The Myron C. Clark Publishing Co., New York, 1906. (A complete treatise on modern cement testing. ) CHAPTER III. SAND, BROKEN STONE AND GRAVEL. The sand and stone in concrete are called the aggregate. It is necessary that the aggregate for reinforced concrete be selected with great care, for no matter how much or how good the cement, if the aggregate be of weak or inferior material, the concrete will be of poor quality. The materials which may be easily obtained near the locality in which the structure is to be erected are often not of the best; but, if properly used, will firove satisfactory. Tests should be made to determine the strength of concrete made of the available materials; and if the strength thus de- termined is used in the design, a satisfactory structure may often he secured, the cost of which will be considerably less than when first-class materials brought from great distances are used. Sometimes cinder is used in place of the broken stone or gravel for light weight floors. Definition of Mixtures—When mixtures of cement, sand, gravel or broken stone are proportioned by volume, it is cus- tomary to designate them in multiples of the cement, which is taken as the unit of measure. Thus a 1:2:5 mixture consists cf I part by volume of cement, 2 parts of sand and 5 of broken stone or gravel. A I:3 mixture consists of I part of cement by volume to 3 parts of sand. When the sand and gravel are mixed together and not screened, as is often the practice in Europe, the mixture is spoken of as a I:3 or I:4 mixture, whichever it may be as in speaking of mortars. Sand: Size and Shape of Grains.—Sand is used to fill the voids in the stone or gravel aggregate, and reduce the amount of ce- ment required. The usual specifications for sand require that it shall be clean, sharp, coarse, and free from ioam, clay and all vegetable matters. However, it is not essential that the sand he sharp and angular. The highest tests with cement have been ebtained with sand having rounded grains with a dull surface. The rounded grains pack more closely than the angular grains, thus giving a smaller percentage of voids. 38 CONCRE1E AND REINFORCED CONCRETE. To secure a minimum of voids, 2 mixed size of grain from fine to coarse should be used. Such a sand is better than one having grains of uniform size, and gives as great or greater strength than a coarse sand. A fine sand does not give as great strength as coarse or mixed sized grains. Sand of uniform size and fine enough to pass a No. 40 sieve gives about 20 per cent. less strength than the larger sizes. There is no appreciable variation in strength when using different sized sands whose grains will not pass a No. 4o sieve. Hence it is not always essential that the sand be extremely coarse. Effect of Loam in Sand.—It has been recognized by engineers for a number of years that the presence of moderate quantities of clay or loam in sand or gravel has no injurious effect on mortars and concrete. Recent tests seem to confirm this opinion. A series of tests made by J. C. Hain, Assoc. M., Am. Soc. C. E., show that sand containing loam is equal, or superior to, clean sand. Tests were made on 1:2 and 1: 3 mortar, comparing clean sand with sands containing 2, 5, 10, and 20 per cent. of loam. A 1:2 mortar of clean sand gave slightly better and more uniform results. The 1:3 mortar, with sand containing up to 20 per cent of loam by weight, gave as high averages as clean sand, but the results were not as uniform as the latter. Tests were also made with sand from different pits, and containing from 2.5 to 7.7 per cent. of loam and clay. The sands centain- irg the highest percentages of impurities gave the best results. Prof. Sherman, Ohio State University (Eng. News, Nov. 19, 1903), reports tests on 1:3 cement mortars made with various percentages of clay and loam up to 15 per cent. of the sand, and states that of 72 tests, only 5 fell below the tensile strength of mortar containing no impurities. He concludes that clay or loam up to 15 per cent. is beneficial to cement mortars. Hence we may conclude that clay or loam in moderate quantities will not be injurious to mortar or concrete, if the concrete be thor- cughly mixed and wet. It will be well, therefore, to make tests of sands containing impurities and compare results with tests on washed and standard sands before deciding against the use of the former, when they may, on account of their proximity to the work, prove economic. Care should be taken in the selection of sands to exclude all those which have come in contact with acid or alkali solutions. SAND, BROKEN STONE AND GRAVEL. 39 TABLE II. SHOWING EFFECT OF LOAM AND CLAY ON TENSILE STRENGTH OF CEMENT MORTAR. Old Shipment. c I Days Th 28 Days Y No. 1. No. 2. No.3. No.1. Wo. 2. No. 3. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Sand and cement, 3 to 1.... 170 166 190 240 240 260 180 168 191 245 236 265 Sand with 5% loam.......... 187 eras Abate 250 ees _— 183 wee its 245 et Sand with 10% loam........... ... 165 ao) os 241 175 fay aus 250. ice Sand with 15% loam.......... ... webs 203 nian nc 275 210 eiee eon 275 New Shipment. Test completed................... Sept. 7th, Nov. 5th, Feb. 5th. 1904. 1904. 1905. Age of briquette when broken...... 7 days. 28 days. 3 mos. 6 mcs. | Siteigth = Lbs. Lbs. Lbs. Lbs. Sand and cement, 3 to I........... 210 316 350 339 207 337 328 246 Se MCT Ay ide ~ hy celitenrhes bate aoioslp tnd aatacnees 220 356 341 340 , 218 343, 336 334 5s IOattin hon wrmcewoengawemannotees 208 367 309 316 201 359 321 320 TO, CLAY acihane dc sad acho wawneees 210 321 329 227 213 330 336 334 TOO Meal naka OMnine dia Geniacneng Ahan 200 369 320 330 207 365 329 331 18% Clay cccseacaussaunsvere eae st 200 206 270 225 ; 208 301 260 220 HG Os. Ter Oia it 8 5 eencnstehan Sy dtc heirs gmrar septa 202 365 221 219 205 368 328 315 BO ‘Clay. son vector asks ueceieeinence bani ees 184 262 250 200 : 189 267 258 216 207 LOAM «aac cca ebadat ke eeeewes 220 370 250 230 216 372 241 225 BeOS C lati sestieas gral a itis nation iden tneiee 172 240 230 175 156 251 216 160 BOY NGA 2 asniicieaannser eee ean 221 373 230 222 ; 218 375 248 217 B07, Lio anl argos domuch wuerientyenleaieaoues 220 361 256 210 225 350 250 216 3674 TuOatth iain oacareer eee eee 205 300 239 220 198 306 248 BD 40% Loam) crise senaueottceateeiiina 198 290 240 198 189 279 232 213 40 CONCRETE AND REINFORCED CONCRETE. Effect of Clay and Loam.—The foregoing tests ( Table II) are from the report on Defences of Galveston, Texas, by Capt. Edgar Jadwin, Corps of Engineers. (See Report of Chief Engineers, U.S. A., for 1905.) The cement used was “Double Anchor” German brand; the sand, standard quality; the clay was taken from the cutter of a dredge working in Galveston Channel; the loam was heavy black soil from the main land. Both loam and ‘clay were thoroughly pulverized, free apparently from all vegetable matter and sand, and sifted to remove lumps. All briquettes were made from one sample on the same day under the same conditions. The clay acted so unsatisfactorily during the working of the 25 per cent. batch that no more briquettes were made for this particular test, hut the loam was continued to 40 per cent. Two shipments of cement were employed in the tests. As will be seen, the loam mixtures retained their strength up to 35 per cent. for 7 and 28 days and 3 months, but for 6 months tests, appear to lose their strength when more than from 10 to 15 per cent. of loam was used. The clay mixtures decreased in strength when more than 10 to 15 per cent. of clay was used. For lower percentages than these in almost all cases the mix- tures containing impurities were stronger than the clean 1:3 sand mixture. Effect of Coal in Sand.—In the construction of the Harrisburg sewer (see index under Sewers), the sand used for the concrete was dredged from the Susquehanna River near by, and contained from 12 to 18 per cent. of fine anthracite coal. A series of special tests was made on this sand to determine the effect of the presence of the coal on its tensile strength. The sand was first washed and screened to remove the coal, only that passing a No. 24 sieve, and retained on a No. 30, being used. The coal thus removed was likewise screened, and that passing a No. , to sieve, and retained on a No. 24, was used. All the cement used for these tests was taken from the same bag of Lehigh Port- land cement, which gave the following strength neat and mixed T to 3 with standard sand: Ti day; Meat. cacvunaueaande sary repeesemeenes be tess sacaeuws 354 Ibs. Pays: Meats sins ccicers sien nae ee eigen taut qatigid, agra nia aaeutspinabntuectnansn 686 “ 9 days, standard sand $23) 26 psecswaseviten oaucnsntucaeva vod s 183.5" 28 days; Standard: Sand “123° 522 e-e ye kei wis, bb espat sespendenernnonee Sees 272 “ SAND, BROKEN STONE AND GRAVEL. 41 The test briquettes were made up of one part Lehigh Port- land cement to three parts of sand, the sand containing varying rercentages of coal from 0 to 100,per cent. It was found that there was no apparent decrease in strength when from 0 to 28 per cent. of coal was mixed with the sand, but there was a grad- ual diminution in strength as more coal, up to 100 per cent., was added. The final strength for 100 per cent. of coal was about one- fifth of the strength of the clean sand mixture. Sand Washing.—When only dirty sand is available, and clean sand can only be obtained at a high cost, the dirty sand may be washed. When the quantity of sand to be used is not large, the washing may be done with a hose. A tank may be built about 8 ft. wide and 15 ft. long, with a bottom having a total slope of about 8 ins. in its length. The sides should be about 8 ins. high at the lower end, and increase gradually to a height of 3 ft. at the upper end. The lower end of the tank should be closed with a gate about 6 ins. high, sliding in guides, so that it can be removed. About 3 cu. yds. of the dirty sand are dumped on the upper end of the platform, and a stream of water from a 34-in. hose played upon it, the man standing at the outside of the tank near its lower end. The water and sand flow down the platform, and the dirt passes off with the over- flow of water over the gate. It will take about an hour to wash the 3 cu. yd. batch of sand. If two platforms are used the washing may be continuous. Halbert P. Gillette states,* that, when the operation is continuous, one man can wash 30 cubic yards a day at a cost of 5 cents per cubic yard for his labor. The cost of shoveling and extra hauling, due to the location of the washer, must be taken into account. When the water is pumped, about 10 cents more per cubic yard will be spent for coal and wages, making a total of about 25 cents per cubic yard. When large quantities of sand are to be washed, expensive machinery of special design is used, and greatly reduces the cost of washing. Mr. H. W. Roper states that the cost of washing sand for U. S. Lock No. 3, at Springdale, Pa., with a specially designed washer, was 7 cents per cubic yard. Concrete mixers are often used for washing sand, it being dumped into the machine in the usual manner. Water is then turned on, and when it overflows at the discharge end *Hand Book of Cost Data.’’ New York, 1905. 42 CONCRETE AND REINFORCED CONCRETE. the machine is started. The dirt is separated from the sand by this operation, and is carried off by the overflow of water. When the water runs clear, the washing is completed, and the sand is cumped in the usual manner. Cost of Sand.—The cost of sand varies with the locality. The prevailing price at which sand is sold in New York City averages $1.00 per cubic yard delivered at the. work. The items which go to make up the cost of sand are: (1) Cost of loading in the pit; (2) cost of hauling in wagons; (3) cost of freight; (4) cost of rehandling; (5) cost of screening and washing when necessary; and (6) cost of pit charges, or pit rental. The fol- lowing data are furnished by Gillette.* Cost of loading into wagons will average about 10 cents per cubic yard for either sand or broken stone, wages being 15 cents per hour. The cost of hauling in wagons may be taken at 28 cents per cubic yard, per mile, wages of team and driver being 35 cents per hour. Freight rate must be obtained for each individual case. The cost of rehandling will be as much (or more, depending upon conditions) as the original cost of loading. Screening necessitates an additional handling at a slightly greater cost, as the sand is thrown against an inclined screen. The cost of wash- ing, as stated above, may be taken at the outside at 25 cents per cubic yard. The above data, together with the cost of sand in the pit, will enable an estimate to be made of the cost of sand in each individual case. - Stone Dust vs. Sand.—It was formerly supposed that the pres- ence of stone dust in mortars and concretes was not only unde- sirable, but injurious. The dust was therefore screened out and replaced by sand. Numerous tests, made during the past few years, show that mortars containing stone dust are almost al- ways superior in strength to those made of sand. Harry Taylor, M. Am. Soc. C. E., Capt. Corps of Engineers, U. S. A., tested 1,650 briquettes of 1:3, 1:4, and 1:5 mortars at 1, 3, 6 and 12 months, using crusher dust, standard crushed quartz and Plum Island sand. The briquettes made with crusher dust had an average strength 72 per cent. greater ‘than crushed quartz bri- quettes, and 2.3 times greater than Plum Island sand briquettes. A 1:5 mixture with stone dust proved stronger than a 1: 3 mix- ‘*“Hand Book of Cost Data.” SAND, BROKEN STONE AND GRAVEL. 43 ture with crushed quartz. Many other tests might be cited which show results equal to or greater than those quoted above. Capt. John S. Sewell, Corps of Engineers, U. S. A., states that while using crushed gneiss the dust was found to contain minute flakes of mica, which when wet behaved like quick-sand, and when used in any quantity ‘killed’ the cement so that it hardly set at all. This is a rare case, however, and undoubtedly in the use of almost all kinds of stone the dust can be employed with economy and no loss of strength. Stone and Gravel.—Either broken stone or gravel may be used in making concrete. Whichever material is used, it should be hard and free from soft particles and all impurities. The strong- est concretes are made from the hardest stone, crushed flint, quartz and trap rock giving better results than sandstone or lime- stone. Limestone should not be used for concrete employed in the construction of fireproof buildings or structures liable to be subjected to fire, as there is danger of this material calcining when subjected to high temperatures. The writer has seen lime- stone concrete used for a fireproof floor which after being sub- jected to extreme heat was so thoroughly calcined that the mass remaining after the fire had the appearance and consistency of freshly burned lime. Mixed sizes of stone should be employed, as, by their use, a minimum of voids is obtained, and less mortar is needed to fill them. If the material be uniformly graded, screening is not nec- essary. In fact, many competent engineers use unscreened stone entirely, not even excluding the dust from the crusher. Thorough mixing, however, must be insisted upon, as it dis- tributes the fine particles of dust throughout the mass, fills the voids of the aggregate and increases the strength. Gravel vs. Broken Stone.—Many engineers consider broken stone superior to gravel for concrete. Spencer B. Newberry states that “good quartz gravel is harder than any broken stone, except trap or quartzite, and owing to its rounded form contains much less voids than stone.” There is no ground for believing that rounded stone or rounded sand gives less strength with cement than material composed of angular fragments. Certain ratural sands, with nearly spherical grains, show much higher tests with cement than angular crushed quartz. . ‘PUA S44 (ioe eatoaraen dees tetarteceea pe toadea ei eaeats sie 5: i be eang, Bx a uOh- IS “WOE 4 o oS fol =e ot gxaxa'7 yy a neuen ! t le! e000000006 Hy 1 pod ‘ Fe yi et S34 ior et 1 | pe ie) ios boot +} - ybs NOY Spun 4, ip ! vy eR wes ge uouipey ‘spun og Asjuden purs Py tea uoqapay eo Lt e065 16 Axp0d09 ‘el = | Vi ‘yun, 4afoM 1S ! et alt : NG PLACING CONCRETE. 95 heating the water as well as providing heating surface for the stone and gravel. These heaters weigh about 1,200 pounds, and are easily transported from one job to another. It is stated that they can be built at a cost not exceeding about fifty dollars. For heating concrete materials in cold weather Mr. Wm. H. Ward used the following method: A large watertight tank, cepen at the top, was constructed of such dimensions as would allow three ordinary dirt boxes to be lowered into it at the same time. This tank was filled with water, and a jet of steam kept the water hot in the coldest weather. The broken stone was loaded into boxes and lowered into the tank of hot water. A few minutes’ imimersion was sufficient to heat the stone to the desired tempera- eetsssse cette CG YQT ssses oy sone TD a LO Le 40-18" oe eerie ii ty on are ON cae gl ! AES Bl be bord gether sith fre Pda gael ace Als J 3 1 “6 Woh Ar Pipes: : Tubes wired together 0 1 db ee « r = = L___ sf Steam Pees" _g (Steam Pipe” FEY —titidd' Grosses | bx Te? foe kK soe a esssunnnnae meunanmnine «con fB GS Sone we se este of ase one sees of Bae" = Plank i - ‘ : i BY he PO GRe ke Biz honnr4 Wi L J'Steam Ppe__* ‘ : J Fr ta oe 3S iG Crosses.’ bigug Tee? a * RAG % i = i i i Bias ye. Fig. 45.—Arrangement for Heating Sand and Stone in Bins. ture, when it was hoisted out and dumped at the mixing machine. The stone was found to retain heat until setting had taken place. Extremely crude methods may be used successfully where the importance of the work does not warrant any considerable out- lay for apparatus. In the construction of the Foster-Armstrong Piano Company’s . shops, at Rochester, N. Y., storage bins were provided with ap- paratus to heat the sand and gravel. Platforms or gratings of tubes were set close together and supported, as shown in Fig. 43. Beneath these cavities V-shaped openings were formed in the sand and gravel. Pipes project through one end of the bin through these cavities from a hot-air furnace and a steam boiler. The hot-air pipes merely pass through the wall, but the steam Lipes continue nearly to the opposite side of the bin and are pro- vided with open crosses at intervals along their length. Where 96 CONCRETE AND REINFORCED CONCRETE. the pipes penetrate the wall and partition concrete slabs are in- serted. In addition to these there is a small pipe fur steam located below and near the bottom of the bin. The hot air pipes connect with a small furnace, and the air was forced through them by a No. 6 Sturtevant blower. The heating power furnished by this apparatus proved sufficient to keep the gravel and stone from freezing, although the top of the bin was open to the weather. Where only moderate quantities of concrete materials are ta be used a bottomless box containing a coil of steampipe may be used for heating the stone and gravel, the heated materials being drawn off from the bottom of the box to the mixing board or machine. Use of Salt.—Because of its cheapness and the ease with which it may be obtained, salt has been extensively used to lower the freezing point of water. Other materials, such as glycerine, alcohol and sugar, have been experimentally employed, but appear to have a tendency to lower the strength of the mortar. A common rule for the use of salt is to dissolve one pound of salt in eighteen gallons of water when the temperature is at 32 degrees Fahrenheit, and add one ounce for each degree of lower temperature. Professor Tetmajer’s rule, reduced to Fahrenheit units, requires I per cent. by weight of salt to the weight of the water for each degree of Fahrenheit below freezing. In the construction of the New York Subway 9 per cent. of salt to the weight of water was used. On the Wachusett dam, during the winter of 1902, four pounds of salt were used to each barrel of cement. For 1:3 mortar this corresponded to about 2 per cent. of the weight of the water. Experiments show that ordinary “quaking” concrete, in propor- tions of 1:214:5, requires about 120 pounds of water per barrel of Portland cement, and 10 per cent. of salt when used in such mixture is equivalent to 12 pounds per barrel of Portland cement. Ordinary 1: 2% mortar requires about 120 pounds of water per barrel of Portland cement. This would be equivalent to 12 rounds of salt per barrel of cement. The effect of salt seems to Le to increase the time of setting, although if not used in too lerge quantities no material decrease in strength of the mortar cr concrete results. Protecting Surface With Coverings.—After the concrete has Leen deposited the heat may be retained for several hours and PLACING CONCRETE. 97 until final set has taken place by covering the surface with sand, straw, burlap, sawdust or manure. A covering of sufficient thickness should be used. Sawdust when available will probably supply the best protection with little danger of injuring the concrete. Manure, perhaps, will retain heat best and keep the surfaces warmer than the other materials, as the decaying ma- terials, on account of the chemical change, give off considerable heat. Ammonia gases are generated and given off by the action of decomposition and may injure the concrete. Manure should be used with care for protecting concrete Tight Wood Floor y yG E " 1 | 1 I | ! \ Support for) Belt Course Forrn 2 < x a) 3 > Wall Column \ G | Fig. 44.—Sketch Showing Methods of Enclosing Building with Canvas Curtains. | | ' ! | | | | ! I t ' | iY, in freezing weather. When possible the concrete should first be covered with boards and the manure placed upon them. This will keep the manure from soiling the concrete and prevent any action of gases generated by the decaying materials. When there is liability of wet weather, followed by alternate thawing and freezing weather, manure should not be used. It is stated by Mr. Leon D. Conklin, City Engineer, Elmira, N. Y., that a concrete walk covered with manure for about a month crumbled and became badly broken up a short time after the manure was removed. It is probable, however, that only green concrete is injured by manure, as it has been used widely for stable floors, manure bins, etc., without any evidence of failure. 98 CONCRETE AND REINFORCED CONCRETE. The other materials may be used freely without any attendant dangers. Housing.—A suitable housing may be used at times for en- closing the concrete work. At Beverley, Mass., the three-story factory building described later, was enclosed in a house of canvas on a light wooden frame, so that the concrete was mixed and laid under cover, while the temperature was main- tained at the freezing point by means of stoves. In the construction of a dam at Chaudriere Falls, Province of Quebec, when the temperature was as much as 20 degrees be- [Ko ------------ -2/9" ----------4 >| a CS Ss ; 3 -}- Ca) ° B Ss ' PS & ' 14\Strip Double thickness as ' gs ’ & aN zt & 28 Sy PSs <8 & ty Sod is Pe 18 3 es 1s %) 0 Ha) ae 2 Qo 9 oo Ne Front. 10} lok --r6alv. Z"Rings 3 4 y ie “ Sewn same as Hooks t % | REQ lo SES iO} ~ hs lo} gy Os ) ask AS F 5S eI aks g ~ °| ..-/4" Double thickness ra” S SS "el os) SS eo z Ip 1 Ss ye WY lo} Bh lees oj 4.2 Rear. Fig. 45.—Canvas Curtain for Enclosing Buildings. fow zero, a house about one hundred feet long by twenty-four feet wide, was built over a portion of the dam, and heatéd by iron stoves burning coke. The concrete was mixed and laid in this house. When one portion of the dam was completed, the house was taken down and erected in another place anc the work continued. PLACING CONCRETE. 99 In the construction of the shops for the Foster-Armstrong Piano Company, at Rochester, N. Y., a special form of hous- ing was used. As the building was constructed a temporary structure of timber and canvas was erected to enclose the ex- terior walls. The open sides were composed of canvas cur- tains and the floor covered with timber shutters. The curtain (A), Figs 44 and 45, is held by tying-rings to a continuous string-piece (B), the upper portion, or flap D, being held down by a metal rod or other heavy object, so as to lap over the floor cover (E). At the bottom the curtain is attached the stringpiece (C). Figure 44 shows how the curtain adjusts itself to irregulat Fl 1 | | T | iy : ; Vxleo | es sal exs an-5----------/0 EZ If lee T T | | | TRO > eee | a ere f rr ! \ I ! | ! ec 1 Sectiorr A-B. Fig. 46.—Wooden Floor Panels. projections, such as the support for the belt course forms. To prevent the canvas from tearing on the timbers, these are cush- 1oned by rolls of bagging or other suitable materials. The con- struction of the wooden floor panels is shown by Fig. 46. They are.so designed that a hollow space is left between them and the floor. To provide for the circulation of air in this space, holes are formed through the concrete floor slab, as shown at H (Fig. 44). The drawing (Fig. 46) shows a 10 x 10 ft, panel, made of 12 x I-in. boards, nailed to the edges of 2 x 2 in. battens; to 100 CONCRETE AND REINFORCED CONCRETE. the opposite edges of the battens were attached 6 x 1 in. bars to stiffen the rods and give a good bearing on the green concrete. Heating the Enclosed Space.—The space enclosed by the housing was heated by means of coke fires in braziers and by a system of steam pipes from a central boiler. The open fires were scattered throughout the floor area and were simply fires of coke in home- made braziers of reinforcing metal. Each brazier held about five cubic feet of coke, and ten braziers were used for the enclosed floor, 50 x 200 ft. x 13 ft. high. The ten braziers and the steam piping kept the temperature at about 80 degrees Fahrenheit in the enclosed space below the floors, and at about 40 degrees in the space between the top of the floor and the outer covering. These temperatures were maintained when the temperature out- side ranged from zero to 10 degrees above. In the construction, the columns were concreted first, then the belt courses and the floor systems. As soon as the belt courses were completed, the canvas wall curtains were hung and likewise the floors were covered with wooden panels as fast as the concreting was finished. The concrete was deposited re- gardless of the temperature, it being the theory that when once laid, and whether freezing or not, it would be kept above the freezing temperature by the artificial heating arrangements until it was thoroughly set. The theory worked out perfectly and no damage resulted to the work because of the frost. In the construction of a number of one-story buildings for the Bush Terminal Co., at South Brooklyn, N. Y., the roof slabs were moulded in sections and allowed to set in a building heated by means of open coke fires, the coke being contained in a metal stove. Any means of artificial heating, such as stoves, hot air fur- naces or steam pipes, may be successfully used in a manner similar to that outlined above. Depositing Under Water.—In heavy construction concrete is often deposited under water. Reinforced concrete cannot, how- ever, be constructed under water; if this material is to be used for submerged structures it must either be constructed on shore _and sunk to place or else the space on the bed to be occupied by the structure must be laid dry by cofferdams, and the reinforced concrete construction be carried on as in the open air, and left until thoroughly hardened before the water is let in. PLACING CONCRETE. 101 In laying concrete under water, some means must be used by which it may be laid without the materials becoming sepa- rated as they pass through the water. This may be done in sev- eral ways, some of which are as follows: (1) The concrete is lowered in large buckets, which have a closed top and a hinged bottom that opens when the bucket reaches the bottom. (2) The concrete may be passed through tubes reaching the bottom, in which case the concrete should completely fill the tube and flow continuously until the depositing is completed; stone grouted in place has also been used for foundation work. (3) Concrete has also been successfully deposited in cloth sacks or paper bags. When cloth sacks are used an open woven cloth, like that used for gunny sacks, should be used. The sacks should be about two-thirds or three-fourths full of concrete, and, when practicable, placed in courses, header and stretcher system, ramming each course as laid. The bagging is close enough to keep the cement from washing out, and at the same time open enough to allow the whole mass to be united into one compact mass. This method has been successfully used. for bridge pier foundations. When paper bags are used they are filled with a fairly dry mixture and lowered into place, sometimes by means of achute. The water soon softens the paper, the pressure of the concrete breaks the bags, and the concrete becomes united into a solid mass. W. M. Patton recommends that concrete be allowed to take an initial set before placing it in water, as this will prevent the materials from separating and the cement being washed out. The author knows of no case in which this method has been used to any great extent. Concrete blocks are at times moulded on land and then placed in position by means of a stationary or floating derrick. This method has been extensively used by government engineers for building breakwaters, sea-wall foundations for light-houses, etc. The blocks are usually moulded in large sizes, weighing several tons, at a convenient yard. When it is desired to place them in position they are conveyed to the site of the work and lowered into place by means of a derrick. A diver is usually employed to see that the blocks are lowered into proper position. Grouting Loose Stone Fill for Foundation.—Concrete for sub- aqueous foundations may be placed by filling in the foundation 192 CONCRETE AND REINFORCED CONCRETE. area with loose stone or rubble, then sinking at intervals pipes per- forated at the bottom and grouting the stone work with a grout made of neat cement paste. This method has been extensively used by English engineers, both in England and India. The grout, on account of its heavy specific gravity, if given sufficient head, replaces the water in the interstices between the stones and firmly cements the stone into one mass of concrete. Neat ce- ment is preferable, as there is a tendency for sand and cement to separate when passed through water. Mr. H. F. White, M. Inst. C. E., states that a 1:1 grout was the leanest mortar that could be forced down a 2-in. pipe. In the construction of a breakwater at St. Helier on the coast of ‘Jersey, England, the entire foundation area was filled in with rubble stone and gravel, a diver then sunk the grouting pipes well down into the loose Line for _.» Lowering Leg Zoey 2 Wt lon Sar g Wa Trig. 47.—Bag for Depositing Concrete Under Water. stone fill at intervals of 10 to 12 ft. apart. These pipes were 3 ins. in diameter with the bottom end open, and were perforated with 34-in. holes for 12 ins. above the bottom. The grout was then poured into the pipes and kept flowing until the diver observed the cement coming to the top of the stone. Grouting was then stopped and the pipes placed in new positions. The water varied from 20 to 60 ft. in depth. for the St. Helier breakwater foundation. A Concrete Depositing Bag—Figure 47 shows a bag for de- positing concrete under water. The bag tapers 3 ins. on the side tc facilitate discharging. The mouth of the bag is closed by one turn of a line, which is provided with loops through which is a hard wood pin attached to a tripping line. The folds of the bag hold the pin in place while it is being lowered: when in position a sharp pull on the line releases the pin and the concrete is re- 103 PLACING CONCRETE. oO a he Stee /e 4 Kennet ans a 5 QE ann nnnnn-n nee Herrmann ee sree ee ene 30 End Elevation. Side Elevation Bottom Plan 48.—Bucket for Depositing Concrete Under Waier. a rig. 104 CONCRETE AND REINFORCED CONCRETE. leased. This bag may be made any desired size of canvas or cther suitable material and is adapted for use when expensive depositing machinery is undesirable. Depositing Concrete in Buckets—Figure 48 shows a concrete bucket used by Prof. W. D. Taylor for depositing concrete under water for foundation of bridge piers for the Coosa River bridge, Louisville and Nashville Railroad. Concrete was deposited as deep as 26 feet. When the water was pumped out of the coffer dams the concrete was found to be very hard, and required very little leveling up over an area of 15 x 38 ft. The bucket holds 1 cu. yd. of concrete and is handled with a derrick. The bucket is Fig. 49.—Cyclopean Bottom-Dumping Bucket. so designed that when its sides rest upon the bottom, the “scissors” unhook, releasing the dogs that hold the swinging bottom doors, allowing them to drop. It was found necessary to make the flanges on the bucket wider than shown, to keep them from cutting into the fresh concrete. In the construction of the foundation for a masonry dock at New Rochelle, N. Y., concrete was deposited at a depth of from 14 to 19 ft. below mean low tide. The concrete was lowered into place by means of a % cu. yd. bottom dump Cyclopean bucket. The bucket was lowered into the water by a derrick operated by a Lidgerwood hoisting engine on a scow, and dumped when near the bottom by means of a line operated by PLACING CONCRETE. 105 a man on the scow. Very little cernent was washed out of the concrete when the bucket was submerged. To provide for any possible waste, 25 per cent. excess of cement was used in mix- ing the concrete. Figure 49 shows the style of Cyclopean bucket most often used, while a style especially adapted for use in sub-aqueous work is shown open and closed in Figs. 50 and 51. In the construction of the foundation for the South Pier at Superior Entry, Duluth Harbor, Minn., a steel bucket, so de- signed that after it had been set upon the bottom, it was tripped by a special designed latch from which a rope led to the derrick man, was used. The bucket was covered with canvas covers or curtains quilted with sheet lead and fastened to opposite sides of Fig. 50.—Cyclopean Subagueous Fig. 51.—Cyclopean Subaqueous Bucket, Closed. Bucket, Open. the buckets. When in position the curtains overlap at the middie of the bucket, completely covering the exposed concrete. It is stated by U. S. Engineers in charge of this work that these covers proved entirely satisfactory. Covers of this kind could with little difficulty be attached to the Cyclopean and similar buckets, thereby further protecting concrete when placed under water. The O’Rourke Bucket—A similar bucket designed and pat- ented by John F. O’Rourke, M. Am. Soc. C. E., was used in the construction of the foundations for the City Island Bridge in New York City. Figure 52 shows the bucket closed to carry its load of concrete. It is rectangular in form, with flap doors 106 CONCRETE AND REINFORCED CONCRETE. at the top, while the bottom is left open. The timber irame at the bottom gives the bucket a wide bearing when it rests upon the soft deposited concrete, and prevents it from sinking into and cutting up the concrete. For holding the concrete in the bucket there are two interior flap doors, which, when closed, form a V-shaped interior hopper bottom, and when open swing back against the sides of the shell, and leave the bucket open its full bottom dimensions. The doors are held closed by chains attached to the bail, which is held by the key or pin shown just above the chain connections to the bail. When filled, the bucket is swung clear of the ground, and the pin or key is pulled out, Fig. 52.—O’Rourke Concrete Bucket, Closed. leaving the pull of the load on the bail to hold the doors cioseck In this condition the bucket is swung over the spot where it is desired to deposit its load, and then lowered until it reaches the bottom. As the bucket comes to rest, the load of concrete on the doors pulls on the chains, and this pull, added to the weight cf the bail, which is purposely made very heavy, causes the bail to slide down into the position shown by Fig. 53, and also causes the door to swing open as shown. As the- doors swing open they tend to force the water out of the shell, while the shutter attached to the door closes the slots, in which the pins PLACING CONCRETE. 107 at the ends of the doors slide back and forth. As soon as the doors have swung clear open the latches on the bail catch as shown in Fig. 53, and hold the bail from sliding up until the latches are released by hand. This bucket thoroughly protects the concrete until the mo- ment of dumping, discharges automatically with the largest possi- ble opening for the size of the bucket, and is extremely simple in construction. The discharge of the load is effected simply by raising the bucket free from it. Depositing by Chutes——A tube or chute, sometimes called a trémie, is ysed at times for depositing concrete under water. It Fig. 53.—O’Rourke Concrete Bucket, Open. consists of a tube open and usually flared at the top, to receive the concrete. The tube is built in detachable sections, so that its length may be adjusted to the depth of water. The tube is suspended from a crane upon a track so that it can be moved 2bout as the work progresses. The upper end is kept above water, while the lower end sets upon the bottom. The trémie is first filled by placing its lower end in a box with a movable bottom filling the tube, lowering it to the bottom, and then de- taching the bottom of the box. If it is not convenient to first fill the tube, it is lowered to the bottom and filled by dropping I08 CONCRETE AND REINFORCED CONCRETE. the concrete in the tube. When this method is used the first charge of concrete is lost.. Fig. o4.—Tremie or Tube for Depositing Concrete Under Water. Figure 54 shows a tube of this character used by Mr. Wm. H. Ward in the construc- - tion of the Harvard bridge foundations, for the foundations of the Brooklyn Heights Power House, and for a number of other structures the depths of water varying up to 18 ft. This system was also used in con- structing the foundations of the Boucicault Bridge over the Sadne River in France. A chute of this kind was used in the con- stuction of the foundations for the piers of the Charlestown Bridge, Boston, Mass. At this place the piers were enclosed with cof- ferdams and the concrete deposited on piles driven to such a depth as to secure a suit- able foundation. The chute was a tube 14 ins. diameter at the bottom, and 11 ins. at the neck, with a hopper at the top to receive the concrete. This tube was made in removable sections with outside flanges to. adapt it to different depths. It was suspended by a differential hoist from a truck that moved laterally on a frame, which traveled the length of the pier. (See Fig. 55.) In operation the foot of the chute rested on the bottom and concrete was dumped into the hopper. The chute was then raised and the concrete allowed to run out in a conical heap, the loss being made good by dumping in more concrete at the top. By’ moving the truck on the traveler, a ridge of con- crete was deposited across the pier, the chute always being kept full or nearly so. When a ridge was finished the traveler was moved and an- other ridge built, this operation being continued until the whole surface was covered. The thickness deposited depended upon the height to which the foot of the chute was lifted above the . PLACING CONCRETE. 109 bottom. Concrete was laid up to 6 ft. in thickness, but it was found that the best results were obtained when layers about 214 fi. in thickness were deposited. If the chute was raised too high or too quickly, a charge was lost. Fig. 55.—Mounting for Tremie, Charlestown Bridge Work. The chute seemed to work best when the concrete was mixed not quite moist enough to be plastic. If mixed too wet, the charge was liable to be lost; if too dry, there was a tendency to choke the chute. CHAPTER VII. COST OF CONCRETE. The cost of concrete varies widely, depending upon the char- acter of the construction, local conditions, and the cost of ma- terials and labor. For ordinary work, when concrete is laid in large masses, the cost per cubic yard will vary from $3 to $7. lor pavement foundations in Brooklyn, N. Y., when competition was sharp, bids as low as $3 a cu. yd. for a 1: 3:6 mixture, thick- ness about 6 ins., secured the work. Under usual conditions in New York and Brooklyn for this class of work, the bids average from $4.50 to $6.50 per cu. yd. For footings for wall founda- tions in building construction in New York City, a common price is 25 cts. a cu. ft., or $6.75 per cu. yd., for a 1:-3:5 mixture, where the yardage is small. When concrete is laid in thin sec- tions, as in sewers, small arch bridges, thin walls, etc., costs will range from $7.00 to $15.00 per cu. yd., including cost ot centering. For reinforced concrete work, as in buildings, when thin slabs, beams and columns are used, the cost, including forms, finish, etc., will vary from $10.00 to $22.00 per cu. yd. The cost will be found to be nearer the higher figure when first-class work is insisted upon. The items to be considered in figuring the cost of concrete are as follows: , (1). Cost of cement, sand and broken stone or gravel de- i:vered at the work. (2). Cost of loading the barrows, buckets, carts or cars used to convey the materials to the mixing board or machine. (3). Cost of transporting and dumping materials. (4). Cost of mixing by turning with shovels or by machine. (5). Cost of loading concrete into barrows, buckets, carts cr cars. (6). Cost of transporting the concrete to place. (7). Cost of dumping and-spreading. (8). Cost of ramming. COST OF CONCRETE. : III (9). Cost of forms. (10). Cost of runways, cement house, bins, platforms, etc. (11). Cost of finishing the surface. (12). Cost of superintendence and general expense. (13). Interest on capital invested and depreciation of plant. The cost of cement will vary with market prices, freight rates and cost of transportation to the work. The first two items must be determined for each piece of work. The cost of transportation will be 15 cents a ton-mile, assum- ing team wages at $3.75 a day, and length of haul ro miles, the wagon going one way empty. This gives a cost of 3 cents a barrel of 400 Ibs. per mile of haul. Cost of Sand.—The cost of sand, under exceptioral con- ditions, may be as low as 20 or 30 cents per cu. yd. delivered at the mixer, but under usual conditions will be found to range from 50 cents to $1.00 per cu. vd. When sand is very difficult to obtain, and must either be brought from a long distance or made by crushing rock, the cost may range from $1 to $3 per cu. yd. The cost of hauling sand will depend somewhat upon its unit weight. The weight will depend upon the character of rock from which it is made and upon its physical condition. Sabin* gives the following data in regard to the weight of sand: Natural sand, as it ordinarily occurs, will weigh about as follows, accord- ing to its condition: Lbs. per cu. ft. Moist and! loose: 2 unnecuiny sae cuns oaekn cana ner saaeaioe 70 to 90 Moist: and? shaken: ¢2necsuses tos ertemee ercanand ee koes 75 to 100 Dire dite TOOSEe..6.5.c sans tana ictacinmene gesbinerisne asietua ae ae eeuenanin 75 to 105 Dive and: Shaken a .s .09 a Total cost of labor .................04.. ‘ $0.50 Cost of materials, stone concrete, — a Total cost per cu. yd. ...... ee, $5.06 $4.70 CHAPTER VIII. FINISHING CONCRETE SURFACES. Methods of Finishing Concrete Surfaces.—Special precautions are necessary to secure a good finish to the exposed faces of con- crete work. In Europe it is customary to finish the surfaces with a thin coat of mortar, a 1: 2 or 1: 3 mixture being floated or trow- eled on the rough surface of the concrete as soon as the forms have been removed, and while the concrete is still green. In no case should a plaster finish be used, as sooner or later it will shell off, leaving the surface most unsightly. Where a mortar facing is desired, it is customary to make it from I to 1% in. in thickness, although it is sometimes made as thin as 4 in., or as thick as 3 ins. The mortar facing is usually composed of 1 part Portland cement to 2 or 3 parts of sand. When a special glossy finish is desired, a 1:1 mixture is used. However, the best results will be obtained when the ratio of sand te cement in the mortar is the same as that in the concrete. When a granolithic surface is desired, grit or crushed granite containing ro particles greater than 3 to I in. is used, in place of sand, and 114 to 2% parts stone to 1 of cement are used. The facing may be applied in several ways. A layer of mortar an inch or so in thickness may be troweled against the face of the form, and the concrete immediately deposited against it, holding it in place. By throwing the concrete against the face of the moulds with considerable force the larger stones will rebound and the mortar remain against the mould. Another, and more com- mon method, is to force a spade down the side of the moulds, pushing back the stones and allowing the mortar to flow in 2gainst the mould face. Sometimes a broad, flat shovel is used and mortar poured down between it and the mould. Another method by which a definite thickness of mortar facing is secured is to place a mould like that shown in Fig. 56 against the form and fill the space between it and the mould with mortar. This mould consists of a sheet-iron plate 6 or 8 ins. wide and 5 or 6 ft. long, having riveted across it on the side which faces the 118 CONCRETE AND REINFORCED CONCRETE. mould small angles the size of the thickness of facing desired, usually 114 x 1% ins., and spaced close enough together to sup- port the plate. The upper edge of the plate is flared, as shown, to assist in placing the mortar, and it has two handles to facilitate its removal. This form is placed with the projecting legs of the angles against the face of the mould and forms with the mould an open space about 1% in. wide. The space is filled with the facing mortar, which is lightly tamped; the concrete is then filled in behind the mould; the iron mould is then withdrawn, and the whole mass thoroughly tamped. The mortar is mixed in small hatches and deposited with shovels. Care should be taken not to mix the mortar too wet, or the larger stones in the concrete will be forced through the mortar face against the form when the Sane eae ee Fig. 56.—Mould for Applying Mortar Facing. mass is tamped. To secure a satisfactory bond, the mortar and concrete should be placed at the same time. Treating a Pitted or Mottled Surface — Whether or not a special mortar facing is used, the surface of the concrete will often con- tain pittings, bubble-holes, rough spots and grain marks from the wood of the mould. .\ mottled appearance due to variations in the color of the sand, etc., may also occur, and some special treat- ment is necessary to secure a uniform and pleasing finish. Immediately after the forms are removed, the surface should be cleaned of any grease or oil from the forms. Any small depres- sions or holes may then be filled with mortar well rubbed in; pro- jections or ridges due to holes or joints in the forms are rubbed down, and the entire face may then be washed with a grout of t part Portland cement and 2 parts fine sand. This should be applied with a brush. ; FINISHING CONCRETE SURFACES. 11g A pleasing finish may be obtained by using plaster of Paris in place of the sand. A mixture of equal parts of Portland cement and plaster of Paris gives a very light grey shade, and 3 parts of cement to 1 part of plaster of Paris gives a darker shade. ‘ A Rubbed Finish —This may be obtained by removing the forms hefore the concrete has set very hard, and rubbing the surface with a circular motion with a white fire-brick or a wooden float. The time the forms are allowed to stand before removing will vary from 12 to 48 hours, depending upon the cement, amount of water used in mixing and the state of the weather. Before rub- bing, any voids in the surface should be filled with mortar well rubbed in. If the concrete is quite green, an effect similar to rubbing is obtained by brushing the surface with brooms or stiff brushes. When the concrete is not green enough to dress easily, water way be used when dressing with the brush, and water and sand with the wooden float. A very satisfactory surface which has the appearance of cut stone may be obtained where a surface mortar of cement and crushed stone is employed. The color and texture of the crushed stone affects the appearance of the surface, special surfaces being obtained by the use of red or grey granite, sandstone, etc. It is customary to use for the facing a coat of 1: 2 or 1: 3 mortar. After the forms are removed the mortar covering the face of the par- ticles of crushed rock is removed by brushing or washing the sur- face with a weak solution of acid. The surface is then washed with clean water and finally with an alkali solution to neutralize the action of the acid. This treatment leaves the granular parts of the stone partly exposed and gives to the finished work a‘sur- face which is difficult to distinguish from natural stone. The size of crushed stone used in the facing will depend upon the character cf the finish desired. Usually it should pass through a sieve of 10 tu 30 meshes per inch. Pebble Dash Facing.—A unique surface finish which may some- times be used with good effect is secured by using rounded pebbles in olace of the usual stone for the surface layer of the concrete. After the forms are removed, and while the concrete is still soft, the cement and sand on the exposed face are removed until about half of the surface of the pebbles is uncovered. This finish was 120 CONCRETE AND REINFORCED CONCRETE. used in the construction of a reinforced concrete bridge in the National Park at Washington, D. C. It was found that the peb- bles were brushed loose 12 hours after the concrete was laid, and at 36 hours the mortar became so hard that it was removed with difficulty. The brushing was most successfully done when the concrete was about 24 hours old. The mixture employed con- sisted of 1 part Portland cement, 2 parts sand and 5 parts gravel between 144 and 2 ins. in the smallest diameter. The cost of brushing was about 60 cts. per sq. yd., or nearly 7 cts. per sq. ft. Tool-Dressed Surfaces—When the surface of the concrete has set so hard as to prevent its being treated by any of the methods already described, it may be tool-dressed by any of the methods employed for dressing stone. This is usually done either by hand or by the use of the pneumatic hammer. Hand work consists Fig. 57.—Ransome Ax for Dressing Concrete Surfaces. usually of bush hammering or pointing with a chisel. Bush ham- mering may be done by ordinary labor at a cost of about 14 cts. per sq. ft., as a man can bush hammer too sq. ft. in a 10-hour day. _ The Ransome concrete ax (Fig. 57) may be used to give a ham- mer dress finish to the surface of the concrete. It consists of a double-bit ax, having steel blades bolted to a casting in which the handle is inserted. The blades may be removed when dull and are sharpened with a file or an emery wheel. It is stated that a common laborer will average 100 sq. ft. of wall surface in ten hours with a Ransome ax, at a cost of 1% cts. per sq. ft. From 400 to 500 sq. ft. may be covered in a day with a pneumatic bammer, however, using a special pointed tool. Grooves are sometimes moulded in the face of the concrete, dividing it into imitation rectangular blocks resembling stone masonry. .This is done by nailing triangular strips on the face of the moulds. The same effect is obtained at a greater expense by FINISHING CONCRETE SURFACES. 121 chisel cutting. A chisel draft is at times cut an inch or two in width about these grooves. The concrete within these pitch lines may be roughly dressed in any manner desired. It is sometimes customary to remove the forms while the concrete is still green and pick over the whole surface rapidly with light picks. This gives an imitation of rough dressed stone. One man can pick over about 100 sq. ft. per day. By choosing the stone for the facing carefully, a very close imitation of natural stone may be secured. Granite crushed to the size of buckshot, or fine gravel, if carefully graded and selected for color, gives a very fine surface which will closely resemble natural stone. Colors for Concrete Finish—Coloring matter may be added to the cement to produce imitation stone of various colors. Lamp- black is employed to give various shades of grey, according to the amount used. Dry mineral colors, mixed in the proportion of 2 to 10 per cent. of the amount of cement, gives various shades of the colors used. The following colors have been used without any apparent injurious effect: Lampblack (boneblack), Prussian blue, ultramarine blue, yellow ochre, burnt umber and red iron ore. Red lead is injurious, even in so small quantities as I per cent., and greater amounts should never be used. Common lampblack and Venetian red should not be used, as they are apt to run and fade. It has been found that ultramarine blue does not affect the strength of the mortar if not used in ex- cessive quantities. Other coloring matter should be used in mod- erate quantities. Germantown lampblack is also a good material to use on account of the small quantity it is necessary to use to . secure good color. The color of a mortar or concrete will vary with the color of the cement, sand and stone used; the color of these ingredients will also affect the final color when coloring matter is used. To produce a colored mortar the coloring matter should be thoroughly mixed with the cement, the sand then added and the whole thoroughly mixed dry, and when stone or gravel is to be used it should be incorporated in the mixture dry, the whole mixed until of a uniform color and then water added gradually, the mixing being continued until the proper consistency is ob- tained. Table XVIII. gives the usual proportion by weight of, different coloring matters to be added to 1 sack of cement and 2 cu. ft. of sand (a 1:2 mixture) to secure different colored mortars. 122 CONCRETE AND REINFORCED CONCRETE. TABLE XVIII—COLORING MATTER FOR CEMENT MORTAR. Weight of coloring matter to 1 sack of cement for a1 : 2 mixture. For white stone: White Portland cement, 1 part; Pulverized lime, %4 part; Pulverized marble, % part; Light colored sand,.1 part. On account of the inferiority of white Portland cement the above is seldom used. For black stone: 3 Ibs. Excelsior carbon black, or 11 lbs. manganese dioxide. Grey stone: 1 lb. Excelsior carbon black, or % Ib. Germantown lamp black (bone black). Brown stone: 4 to 5 lbs. brown ochre, or 6 Ibs. roasted iron oxide, best quality. Buff stone: 4 Ibs. yellow ochre. Red stone: 5 lbs. violet iron oxide (raw). Bright red stone: From 5% to 7 lbs. English or Pompeiian red. Yellow stone: 5% Ibs. ochre. Green stone: 6 lbs. of greenish blue ultramarine blue. Blue stone: 2 lbs. ultramarine blue. Dark blue stone: 4 lbs. ultramarine blue. Purple stone: 5 lbs. Prince’s metallic. Violet stone: 5% lbs. violet oxide of iron. In the construction of six emplacements at Fort Wadsworth, New York, the exterior surface was coated with colored mortar mixed according to the following formulas: For green color: Cement, 1 bbl.; Sand, 2 bbls.; Ultramarine blue, 50 Ibs.; Yellow ochre, 73 lbs.; Soft soap, 7 lbs.; Alum, 7 Ibs. For slate color: Cement, 1 bbl.; Sand, 2 bbls.; Lampblack, 50 lbs.; Ultramarine blue, 35 lbs.; Soft soap, 7 lbs.; Alum, 7 Ibs. After completion of the batteries, the color became much lighter with age. It was found that spraying with linseed oil very materially deepened its shade, FINISHING CONCRETE SURFACES. 123 Table XIX. is given by Sabin* for various colored mortars. TABLE XIX.—TABLE SHOWING COLORS GIVEN TO PORTLAND CEMENT MORTARS CONTAINING TWO PARTS YELLOW RIVER SAND TO ONE CEMENT. Cost_ of eoloring Dry Weight of Dry Coloring Matter to 100 pounds of Cement. matter material ~ per lb. et. used, 42 pound, 1 pound, 2pounds. — 4 pounds. 15 Lamp Black Light Slate Light Grey Blue Grey Dark Blue Slate 50 Prussian Light Green Light Blue Blue Slate Bright Blue Blue Slate Slate Slate 20 Ultra Ma-—.......... Light Blue Blue Slate Bright Blue rine Blue Slate Slate 3 Yellow Eight :Greea ecceccsnae cunaen dunn Light Buff Ochre 10 Burnt Light Pink- Pinkish Dull Laven- Chocolate Umber ish Slate Slate der Pink 2% Venetian Slate, Pink Br'g’t Pink- Light Dull Dull Pink Red Tinge ish Slate Pink 2 Chattanooga Light Pink- Dull Pink Light Terra Light Brick Iron Ore ish Slate Cotta Red 2% Red Iron Pinkish Dull Pink Terra Cotta Light Brick Ore Slate Red When a wet mixture is used, the color should appear several shades darker than will be required, as wet mortar looks darker than it really is, owing to the gloss of the water. As a rule, light shades should be chosen for artificial stone work, as dark colors are contrary to nature, stone in its natural state being of light color and shade. Coloring matter, however, should be used conservatively, as there is more or less liability of the colors fading with time. Tt will be found that by varying the amount of water used for mixing ordinary mortars and concretes different shades of con- crete can be obtained. Again, by the use of colored sands, dif- ferent colored concretes will result. Concretes thus obtained are to be desired over artificially colored ones, as the shades approxi- mate more nearly those found in nature. Painting Concrete Surfaces.—In some cases concrete surfaces may be colored by painting. Ordinary paints are sometimes used, but will not, as a rule, prove satisfactory. When such paints are used it is customary to wash the surface of the wall with dilute sulphuric acid, 1 part of acid to 100 parts of water, before apply- ing the paint. A grey finish may be obtained by painting with a thin grout *“Cement and Concrete,’’ Louis Cartton Sabin. 124 CONCRETE AND REINFORCED CONCRETE of cement and plaster of Paris. The sheathing should be re- moved as soon as possible, the surface cleaned from any oil or grease, and the grout applied with a whitewash brush. A mixture cf equal parts of Portland cement and plaster of Paris gives a very light grey finish, and 1 part of plaster of Paris to 3 parts of cement gives a trifle darker shade. Similar methods may be used with dry mineral colors. One pound of red iron ore to to lbs. cement, mixed dry, and then made into a very thin grout and applied to a clean concrete surface gives a pleasing brick- red color. A rich-dark red may be obtained by using 1 lb. of red iron ore to 3 lbs. of cement. The greener the concrete is when any of these preparations are applied the more likely they are to be permanent. In any event, such treatment should be more permanent than ordinary paint. Masonry Facing has been frequently employed on reinforced concrete bridges, and gives a very satisfactory surface. Any kind of masonry used in stone arch bridges may be successfully used for the purpose. Ashlar, rubble and boulder masonry fac- ing have all been employed. Plenty of headers should be used, and especial care taken to bind the facing firmly to the concrete backing. Metal clamps are sometimes used to assist in binding the facing to the concrete. The same care should be taken in cutting and setting the arch ring stone as in a masonry arch bridge. The soffit of the arch is never stone faced. Brick facing is sometimes used in place of a stone facing. Mouldings, Ornamental Shapes and Veneering Slabs.—Mould- ings and ornamental shapes are used in various parts of build- ings, bridges, etc., for mouldings, corbels, medallions, keystones, - railings, posts, etc. These are sometimes cast in place, but where many duplicates are to be used it is most economical to mould them in advance, using the same sets of moulds over and over again. Sand moulds are often used, but the moulds may also be of wood, metal or plaster of Paris. Casting in Sand Moulds.—The method of casting in sand moulds is similar to that followed in making iron castings. A pattern in wood of the exact size and shape of the desired casting is made, no allowance for shrinkage being necessary. The die is then moulded in iron moulders’ sand in a manner entirely similar to ‘that used in preparing the moulds for cast iron, and poured with a concrete mixture of. the consistency of cream, composed of FINISHING CONCRETE SURFACES. 125 cement and finely crushed stone. The excess water soaks into the sand, keeping the concrete moist during setting. The moulds are removed at the end of three or four days and the project- ing fins cut off. The sand mould gives a satisfactory surface to the castings. Care should be taken not to use too rich a mortar in making concrete mouldings, as unsightly hair cracks will be likely to form on the surface of the concrete, thereby destroying their beauty and possibly eventually their durability. Where it is desired to use cement mouldings for various pur- poses they can be run in long lengths in a sand or metal mould and then cut to the length desired for use. This method is especially to be recommended when the pattern to be moulded repeats a given figure at intervals. Mouldings thus formed are especially adapted for cornices, belt courses and panel facings in buildings, hand rails on bridges, etc. Wood Moulds.—Wood moulds have been successfully used. There is danger, however, of wood warping and cracking, and care should be taken to keep the surface of the wood well shel- laced to prevent moisture from penetrating the wood and caus- ing it to swell and crack or warp. Cement Moulds.—Cement moulds may be used in many cases for making the plainer ornaments or mouldings. To make a cement mould a reverse impression of the original is obtained by first coating the pattern with linseed oil to keep the cement from sticking, then pouring cement over the original pattern. When the cement has hardened it can be removed and the reverse impression obtained used as a mould for casting the ornament. Before using the cement mould thus obtained it should be given a coat of liquid asphalt, cut with turpentine or benzine. This will give the mould a smooth surface, which, if coated with soap solution, will not stick to the casting. Stamped Metal and Glue Moulds.—Stamped metal may be used as moulds for ornamental work. The metal may be stamped in ene piece or consist of several pieces soldered together. This mould may be used direct, but finer detail will be secured if a glue coating is used to take the impressions. Glue moulds give much ‘finer lines than those obtained by other-methods. With a well made glue negative as many as twenty impressions may be ob- tained, as its elasticity permits the removal of work having con- siderable undercut. The most intricate designs can be made 126 CONCRETE AND REINFORCED CONCRETE. from glue moulds, and a little practice should enable tne work- man to turn out very satisfactory ornaments. The glue mixture for making moulds is prepared as follows: Take the required amount of the very best glue that can be ob- tained, place it in cold water over night; the next morning, when removed, it will be found to have swollen. The water absorbed will be sufficient to melt it when heated. Mix with this glue an equal amount of glycerine, place the vessel containing them in a Fig. 58.—Ornamental Work in Moulded Concrete. steam or hot water bath until the water is nearly all evaporated and until the combined weight of the glue and glycerine about equals the weight of dry glue and glycerine used. This compound of glue and glycerine will never dry, and a mould of it can be melted and used over again many times. Figure 58 shows two more or less intricate designs of cement or cast stone ornaments which give some idea of the possibilities of cast mouldings. Cast ornaments can be made at a cost far below that of hand-cut stone ornaments. FINISHING CONCRETE SURFACES. 127 Concrete Sidewalks.—Concrete, when carefully placed, proves very satisfactory for constructing sidewalks. After the ground has been excavated to the required sub-grade, a sub-foundation usually of broken stone, gravel or cinders is carefully tamped in place. Care should be taken to properly drain the foundation, as if water collects and freezes there is danger of cracking and displacing the surface of the walk. _The foundation consists of a layer of 1: 2:4 or 1:3: 6 concrete, 3 or 4 ins. in thickness. Port- land cement should be used with stone and gravel less than 1 in. in size, the concrete being mixed medium wet, so that moisture will show on the surface without excessive tamping. A top surface of cement mortar, usually a 1: 1 or 1:2 mixture, is then spread over the concrete and well worked in to form a wearing surface. Usually a coarse sand or fine gravel is used for the aggregate. When great wear is expected, crushed gran- ite chips or flinty pebbles may be used for the aggregate. Hard, clean sand, however, will usually answer. Special care is necessary to secure a uniform and evenly graded surface. After the sub-foundation is placed, side pieces to act as forms to retain the concrete are put in place and held from spreading by stakes driven’3 or 4 ft. apart to proper grade. These side pieces act as guides for the straight-edge used in level- ing off the concrete and wearing surface. The sub-foundation should be well sprinkled and the concrete well tamped in place in sections about the width of the walk. A board is placed across the trench to retain the concrete. The concrete may be lined up with a straight-edge, as shown in Fig. 59, leaving from-14 to I in. for wearing surface. Three-eighth- inch sand joints should be used to separate adjacent sections, and should not be placed more than 6 or 8 ft. apart. These joints will prevent expansion cracks, or in case of settlement will confine the cracks to these joints. The location of the joints should be marked on the side of the forms, and care taken to form the joints in the wearing surface on the same vertical plane. The top dressing should follow up closely the concrete work, as it is desirable that the two set together. This top dressing should be worked well over the concrete with a trowel, pressing it heavily onto the concrete surface. Care should be taken that no air spaces are left in the mortar. The leveling off of the sur- face may be done with a straight-edge. The success or failure 128 CONCRETE AND REINFORCED CONCRETE. cf the walk will depend upon the thoroughness with which this work is done, since a good bond between the wearing surface and concrete base is absolutely essential. The mortar will work best when somewhat stiff. As soon as the film of water begins to leave the surface a wooden float is used, followed up by a plaster- er’s trowel, the operation being similar to that of plastering a* wall. The floating should not be continued too long, as it will bring a layer of neat cement to the surface and probably cause the walk to crack. The floating should be done lightly, to com- pact the surface and give it an unmarked appearance. The sur- face is then divided into sections over the joints in the con- crete, This is done with a trowel, guided by a straight-edge, Fig. 59.—Sketch Showing Sidewalk Construction of Concrete. after which the edges are rounded off with a special tool called a jointer, having a thin, shallow tongue. A special tool called an edger is run around the outside of the walk next to the mould, giving it a neat, rounded edge. A toothed roller, having small projections on its face, is frequently used to produce slight in- dentations on the surface, adding somewhat to the appearance of the walk, The complete work must be protected from the sun and kept moist by sprinkling for several days. Figure 60 shows the tools usually employed for finishing side- walk surfaces and similar cement constructions. The above method of finishing sidewalk surfaces may be used with slight modifications in finishing almost any kind of surface where a smooth, uniform surface is desired. FINISHING CONCRETE SURFACES. 129 Variation in Color of Concrete——Variation in the color of con- crete surfaces may result from one of several causes. A varia- tion in the color of sand used, the presence of dirt or other impurities, may cause a difference in color in different parts of the same wall. A change in the brand or even different batches of ‘the same brand of cement may change the shade, as no two cements are the same in color. A variation in the wetness of the mixture may change the character of the concrete and also its <2 iD-< Rotary Jornter. Fiutep Roiier Rounp Corner 7 : gq Srp e Forusein places too For finishing walks, SMOOTHING Trowet. EWALK EDGER aie for ordinary ete. For finishing corners in gutters, etc. Date Stamp. ; : BEeh, Name Prate. For stamping names Date Sramp. of makers on walks, For marking walks, artificial stone, etc. [anon ess) artificial stone, etc. Square Corner Rapius Toot. SmooTHinc Trowets FP For finishing inside or outside edges of =e Brass JornTErR. : : circles. For finishing joints Tamp. in walks. For tamping con- crete foundations, etc. Jornrer, : Centre KniFe, For finishing joints | For cutting the sur- in cement walks, etc. face of cement walks into flags. Driveway Impres- Hanp Brass Jornter. INDENTING ROLLER. SION FRAME _ For finishing joints Rounp Corner For indenting the For marking cement in cement. Smooruine TroweL. surface of walks. driveways. Fig. 60.—Tools Used in Finishing Cement Surfaces. coloring. The remedy for any of these causes evidently consists of as careful a selection of materials as is possible, the use of only one brand of cement on a piece of work where a uniform ap- pearance is desirable, and the use of a mixture of uniform con- sistency throughout the structure. Care should be taken to keep the forms clean, and avoid allowing any dirt to get into the con- crete while mixing or depositing, as this will often permanently soil the concrete. (30 CONCRETE AND REINFORCED CONCRETE. Efflorescence.—Another cause of ugly blotches, consisting of white and yellow stains on the surface of concrete exposed to the action of the weather, is termed efflorescence. The real cause of the deposition of this incrustation is not positively known, but it may probably be explained in one of the following two ways: First, the failure of the most finely pulverized portion of the cement to be acted upon chemically by the water, the cement re- maining inert and afterwards being washed to the surface, where it is deposited and there forms an unsightly incrustation. The incrustation is at first white, and afterwards turns yellow. This action is not unlike that which takes place in concrete deposited under water. As concrete is placed in water a light colored, powdery substance is held in suspension by the water and is usually called “laitance.” When a concrete is mixed very wet the same action usually occurs. An analysis of this laitance shows a composition agreeing very closely with that of cement, and it must be inferred that the laitance represents an actual loss of cement. Second, it has been observed that efflorescence rarely occurs when certain brands of cement are used, and when others are employed it is much more apt to appear. It seems probable that in many cases the trouble is caused by the presence of certain ingredients in the cement, probably sulphates of calcium, magne- sium, etc. : These sulphates are soluble in water, and when the wall is soaked they are dissolved and carried to the surface, where they are deposited when the water evaporates. A careful chemical investigation of various cements which do and do not effloresce would doubtless prove of great value in this connection. Whether the efflorescence is due to onesor the other of these causes, the action and the results are the same. If the wall be kept continuously wet the water will finally dissolve out all dis- coloring matter, and will deposit it on the face of the wall. The rain beating continuously on the face of the wall will gradually dissolve and wash off the incrustation, and after a time the whole discoloration will disappear. However, this action is more or less uncertain. In fact, the efflorescence may appear soon after the wall is built, or it may be that a long period will pass before this action takes place. The bleaching process may be extremely FINISHING CONCRETE SURFACES. 131 slow, sometimes lasting for years before the discoloration finally disappears, and on this account any attempt to remove it by scraping or dressing the wall will prove futile. This discoloration is most frequently noticed at and below re- newal joints where the laying of the concrete has been stopped perhaps over night. Laitance appears at the surface where the concrete was stopped. A close examination of this surface shows its presence in the form of a very thin layer of a soapy consistency. Where new work is joined to old, there is an excess of cement at the joint which makes it much more waterproof than the body of the wall. Water percolating through the wall washes out the above-named soapy material at this joint, thus causing oe cence. Mr. C. H. Cartlidge, M. Am. Soc. C. E., Bridge Engineer, C., B. & Q. R. R., states that the removal of this material by scrubbing the joint with wire brushes and then flushing with water from a hose prevents entirely the appearance of efflores- cence at or below renewal joints. While this method may avail for the removal of efflorescence due to laitance at renewal joints, as has been stated, the efflores- cence may be due to the presence throughout the mass of the con- crete of uncombined cement or soluble salts, which will be dis- solved out and stain the wall; hence we see that other methods of treatment may be necessary. By the use of one of the methods used to make concrete im- “pervious by the addition of alum and soap to the mixture the efflorescence can be effectually prevented. Again, if the concrete be laid fairly dry and deposited in lavers slightly slanting downward toward the back of the wall, the drainage will be carried.away from the face, and all objection- able incrustation be deposited on the back. This may be rendered doubly effective by treating the face of the wall with a wash for ‘rendering it impervious, such as Sylvester Process, page 141. Again, this process may be applied to walls made of very wet concrete, the wash preventing the escape of the efflorescence to the face of the wall. Other similar methods for rendering the concrete waterproof, which need not be described here, may be used equally well. The efflorescence may be removed by the use of wire brushes, the sand blast, tool dressing the surface by hand or with a pneu- 132 CONCRETE AND REINFORCED CONCRETE. matic hammer, or by washing it with diluted acids. Washes of diluted hydrochloric, acetic, or oxalic acids may be used for this purpose. A wash consisting of a solution of 1 part of hydro- chloric acid and 5 parts of water was successfully used in re- moving the efflorescence from a reinforced concrete bridge at Washington, D. C. This wash was applied vigorously with scrubbing brushes and immediately washed off with water from a hose to prevent the penetration of the acid. The cost for plain walls was about 20 cents per sq. yd. But, as already explained, there is no assurance that further efflorescence will not take place, and that such mechanical re- moval may prove only temporary. Protecting Concrete Surfaces.—After the concrete has been de- posited it is necessary to keep it moist if its surface is exposed to the direct rays of the sun. If the weather is hot and dry, it is also desirable to keep the surface moist, as a certain amount of water is necessary to the process of setting. If this is not done, the concrete will crack and the surface become unsightly, the cracks varying from a hair line to those of considerable size. Whenever it is feasible the surface may be sprinkled with water two or three times a day to keep it in condition. Burlap may be spread over the surface and kept wet. This will retain moisture for some time, and thus prevent danger from cracks. Sand and sawdust may be used in the same manner, but are not as effect- ive, CHAPTER IX. GENERAL PHYSICAL PROPERTIES. Retempering.—It is customary in specifications to require that cement or concrete be put in place before a certain interval of time has elapsed, as there is danger of injuring the strength of the concrete if it is disturbed after the initial set has begun. Very few data are available in regard to the effect of disturbing cement or concrete after the period of initial set has begun. A series of tests was made by Messrs. Goddard and Evans, at- Ohio State University, in 1892, to determine the effect of retem- pering. A batch of mortar was mixed in the morning to about the consistency of mortar as used in practice and was left on a clean glass. At intervals during the day the batch was stirred up and enough water was added each time to make the batch plastic. After eight hours the mortars were placed in the moulds and left over night. Generally the briquettes were sufficiently hardened in the morning to be removed from the moulds. Com- parative tests were made on mortars of the same mixture without retempering. The briquettes were broken at 7, 28, 56 and 84 days. It was found that the Portland cement mortars lost 45 per cent. of their strength at the end of 7 days, 20 per cent. at the end of 28 and 56 days, and 28 per cent. at the end of 84 days, while the Rosendale cements lost 83, 65, 54 and 42 per cent. at the ages of 7, 28, 56 and 84 days, respectively. A series of tests was made at the Watertown Arsenal to ascer- tain the effect on the final strength of delaying the time of put- ting the gauged material into the moulds. Some samples were prepared, tamped into the moulds and allowed to set without be- ing disturbed. At later intervals, other materials were taken from the mixing bed and similarly treated. In one series material was kept in the mixing bed a period of 102 hours before the last sam- ple was drawn. It was found that cementitious properties still remained in the material, as shown by the possession of tensile strength when subsequently tested at the age of one month. 134 CONCRETE AND REINFORCED CONCRETE. Chief interest, however, is attached to the behavior of mate- rials which were kept in the mixing board for a few hours only, and were used during the day the material was first mixed. The results of some of these representative tests are shown on the diagram (Fig. 61) of cement held in the mixing beds at differ- ent periods before the final setting. A domestic Portland is shown by the lower curve. This was 28 days old at the time of testing; 28.6 per cent. of water was used in the initial gauging. More water was added from time to. time as samples were taken out at two-hour intervals. in order to keep the batch plastic. The largest increment of water needed for these periods was added at 10 hours after mixing. The total 4000 Ss 2000 gth. 3 3 ° e ressive Stren PS } 3 3 4000 Com 2000 I 24 82 48 64 Hours. Vig. 61. Diagram Showing the Effect of Retempering Cement Mortars. quantity of water eventually used was nearly double the original amount. Tests were made on 4-in. cubes that had reached the age of about one month. Those which were placed in the moulds imme- diately after gauging had a crushing strength of 7,000 Ibs. per sq. in. The strength was well maintained for a period of 8 hours, at which time the strength was still about 6,000 lbs. per sq. in. Cubes at a period of 24 hours had nearly 3,000 Ibs. strength, and those after a period of 2% days displayed a strength of about one-fifth of the original batch. A German Portland was also used, being kept in the mixing bed a total period of 25 hours. The original gauging strength was about 3,600 lbs. per sq. in. At the end of 8 hours it had .a strength of 2,400 lbs. per sq. in.; that is, two-thirds of the orig- GENERAL PHYSICAL PROPERTIES. 135 inal strength remained. At 25 hours, 44 per cent. of the original strength remained. In another case, not shown on the diagram, a domestic Port- land developed practically the same strength in each of the sev- eral samples up to the limit of 8 hours’ delay; and still another domestic brand showed a higher strength in the 6 and 8-hour samples than those taken out of the mixing bed at earlier hours. There were brands which did not display so favorable results as those described, but in general a considerable part of the strength was retained by samples at a period not over 8 hours. These results should tend to relieve undue anxiety concerning the necessity of the very early use of cement after gauging. It should, however, be remembered that the mortar must be re- mixed or broken up thoroughly before it is finally deposited. The above tests were made under the conditions usual to be met with in a testing laboratory, and should not be taken as giving a criterion of the conditions met with in practical work. The tendency to use concrete that has been mixed for some time is to place it, after it has stood quiescent on account of un- avoidable delays, without remixing and retempering. If the re- tempering or remixing with an additional amount of water is not done, the mix, if deposited, will be absolutely worthless. It is interesting to note in connection with the above experi- ments that the inquiry was extended to embrace material which had hardened for several days and was then broken up and re- ground to a mortar. A Portland which had become so hard that a pickaxe was needed to break it up was reground and regauged 6 days and 2 hours after the original gauging, and even after so long a time as this it was found that the material acquired strength, and at the age of 1 month had a compressive strength of 700 Ibs. per sq. in. The normal strength at this age was ap- proximately 6,000 Ibs. A natural cement was experimented upon which had set suf- ficiently in four or five months to become resonant. The ma- terial for test purposes was scraped off the main batch. That which was scraped off two days after the original gauging, and then made into cubes, had a strength at the end of the month about one-half the normal value. Grouts were made in the after- noon and set the following morning and then retempered. In some cases surplus water was removed. At the end of 30 days 136 CONCRETE AND REINFORCED CONCRETE. the compressive strength ranged from 2,000 to 3,000 lbs. per sq. in. The lesson to be drawn from these experiments seems to be that the ordinary properties of cement continue active for some time after what is known as the final set has taken place. The loss of strength, as shown by these experiments, due to breaking the materials up, represents the strength gained up to the time of dis- turbing the mix. The additional or remaining strength shown at the end of the testing period represents the gain in strength from the time of remixing up to the time of final testing. Table XX. shows the effect of retempering cement mortars in tests made by Philip L. Wormeley, Jr., Testing Engineer, Office of Public Roads (see Farmers’ Bulletin No. 235, Department of Agriculture). The mortar used consisted of Portland cement and crushed quartzite. In each case, after the initial or final set had taken place, sufficient water was added in retempering to restore the normal consistency. The briquettes were tested at the age of four months. TABLE XX. SHOWING THE EFFECT OF RETEMPERING ON CEMENT MORTARS. { Tensile strength in pounds per square inch._— lpartce- lpartce- 1 partce- Treatment of mortar. Neat ce- ment, 1 ment, 2 me 2 ment. (a) pa parts arts sand. (b) sand. (c) Sand: (d). Mortar made up into briquettes 651 624 527 417 immediately after mixing. 650 701 493 385 673 624 529 421 634 581 480 403 679 610 492 409 Average ...... apisitin ls atereps 657 628 504 407 Mortar allowed to take initial 671 692 589 326 set, then broken up and made 593 670 554 349 into briquettes. 644 654 559 330 633 676 534 358 724 700 532 267 AVERaG Gt awe wrnninieseera sess 653 678 554 326 Mortar allowed to take final set, 455 527 492 364 then broken up and made into 522 569 491 380 briquettes. 525 587 497 301 558 566 486 315 642 568 531 345 AVERAGE cra sick Backes 540 563 499 353 (a) Initial set, 1 hour 42 minutes: final set, 7 hours 15 minutes. (b) Initial set, 1 hour 30 minutes: final set, 7 hours 15 minutes. (c) Initial set, 2 hours; final set, 7 hours. f (d) Initial set, 2 hours 20 minutes; final set, 7 hours. GENERAL PHYSICAL PROPERTIES. 137 Effect of Freezing on Concrete.—There is considerable differ- ence of opinion among American engineers in regard to whether or not freezing, and even alternate freezing and thawing, will injure Portland cement concrete. Falk states in his “Cements, Mortars and Concretes,” “that the hardening properties of frozen cement are not impaired if the freezing has taken place before the initial setting of the cement has begun. Under those conditions the physical action of the changing of the water into globules of ice has prevented the chemical action of the crystal- lizing of the cement particles; crystallization can not take place until the ice globules return to the liquid form. No damage will then have been done if freezing does not again take place be- fore the cement has set, but if continued thawing and freezing take place, allowing an intermittent action of setting, it is. very likely, under those conditions, that the cement will be injured. It is only necessary to bear in mind that the physical action of freezing must so far precede the beginning of the chemical action as to preclude the latter’s taking place.” Prof. Spencer B. Newberry states that “freezing does no, harm to Portland cement after the mass has fully set. The hard- ening of the cement is interrupted by freezing, but proceeds again without hindrance after thawing takes place. Damage from frost is to be feared before the setting, especially if excess of water is used. When work in extreme cold cannot be avoided, the sand and water should be warmed and the proportion of water reduced to a minimum. After putting in place, the work should be covered with straw or other non-conductor to protect it from frost. Mortar for use in freezing weather is often made with the addition of salt (about one pound to one gallon of water) and appears to give good results.” Edwin Thacher states that the Melan Arch Bridge at Mish- awaka, Ind., having three spans of 110 ft., was built between Oct. 26, 1903, and Feb. 25, 1904, in a temperature ranging from © to 55° above. The concrete was heated by admitting hot water to the mixer, and was deposited at about blood heat, and retained enough heat to melt snow at the end of 48 hours. No injury to the concrete could be observed. In this case the mass of concrete was of considerable thickness, and retained heat much longer than it would under ordinary conditions. There are, however, innumerable examples of concrete which 138 CONCRETE AND REINFORCED CONCRETE. has been seriously injured by freezing. It would seem advis- able whenever possible to avoid laying concrete for reinforced structures during freezing weather. When it is necessary to lay concrete in low temperatures, every precaution should be taken to secure the safety of the work, and no loading should be placed upon it until a sufficiently long time has elapsed for it to set after thawing out. Calcium chloride is also used to lower the freezing point of mortar and concrete. It has a somewhat lower freezing point than salt brine, which is usually assumed to lower the freezing point about 114° for each per cent. added. Salt has the effect of slightly reducing the early strength of cement, but probably does not affect the ultimate strength when used in quantities not exceeding 10 per cent. Salt also delays the setting of cement. No tests are available which give the effect of calcium chloride on the strength and activity of cement. However, neither of these ingredients will give the necessary action under low tem- peratures for 10 per cent. only reduces the freezing point to ‘17° F. and 20 per cent. to 2° F. Ingredients used to lower the freezing point of concrete should be used with care; in fact, the author does not feel that when other methods can be used that they should be employed when great strength is required as in reinforced concrete. Impermeable Concrete.—At times an impermeable concrete is desired, as in reservoirs, concrete pipes or to keep dry inclosed spaces below the water level. Numerous experiments have been made to determine the most efficient means of accomplishing this result. From these experiments the following general state- ments have been deduced: (1) The richest mortar and concrete show the least permeability; (2) when water passes continuously through concrete its permeability decreases very rapidly, and it will generally, after a time, become practically impermeable; (3) the ingredients should be proportioned so as to secure the densest possible concrete with an excess of cement; (4) the mixing should be done with great care to secure a thoroughly homogeneous mass; (5) plenty of water should be used, as wet mixtures do not pass water as readily as dry ones; (6) mixtures from I cement and 3 of sand and broken stone to 1 cement and 6 of sand and stone will usually give satisfactury results for GENERAL PHYSICAL PROPERTIES. 139. moderate pressures. A mixture richer than 1: 3 is liable to crack or check. In general it may be stated that in monolithic construction a wet mixture, a rich concrete and an aggregate proportioned to secure great density will in the majority of cases give the desired results. During the construction of the arched concrete dam at Barossa, South Australia, a number of tests* were made to determine the permeability of concrete under high heads. The aggregate was broken sandstone, 1% to 2 in. size, with sizes mixed so as to have 35 per cent. voids. The sand was a.mixture of natural sand and stone dust (% in. and less in size) in about equal proportions. The sand used was thoroughly washed. The con- crete was mixed by machine in 14 cu. yd. batches. Six cubes, 2 x 2 x 2 ft., were made. In the center of each block a T-piece pipe was embedded and a pressure equal to 100 ft. cf water was applied through a % in. diameter pipe from the top of an adjacent cliff. To prevent the ends of the T-piece hecoming blocked with mortar, it was bound around with hemp and small rope to form a bulb about 5 ins. in diameter. Table XXI. summarizes the results of these percolation tests: TABLE XNI. GIVING RESULTS OF PERCOLATION TESTS ON CONCRETE BLOCKS SUBJECTED TO HYDROSTATIC PRESSURE. --—Proportions of Ingredients— ‘Head of Water = 100 ft. -_ ae a o or on® Lol . £ gp GUE shbgd of wygdd SEEGER EEE Ee ezee, Z 8 Eves SE>HS HE GSS29 FyheZEERE ger ZE Ss fg 4 Reels) Si eel (Rue I Tr 7.84 5.26 28 5 II Unreliable. Unreliable. 2 I 1.84 5.26 26 5 II 34 34 in 7 weeks. 3 I F.50 4.63 27 5 10 18 */s0 in 4 weeks. 4 I 2.00 4.50 27 15 10 14 14 in 2 weeks. 5 I 1.75 4.13 28 15 9 12 27 in 7 weeks, 6 I 1.50 4.12 27 10 8 35 /so in 2 weeks, 7 YT 1.50 3.90 2 12% 6 28 , % in 2 weeks. 8 I 1.50 3.70 23 15 5 30 */so in 2 weeks, At the end of 80 weeks the same blocks were subjected to a 200-ft. head, but the percolation was not measured, as in cach block the effect closely resembled the results obtained from the head of 100 ft. *Mr. Alex. B. Moncrieff, M. Am. Soc. C. E., M. Inst. C. E. Trans, Assoc. of C. E., Cornell University. Vol. XIII. : 140 CONCRETE AND REINFORCED CONCRETE. While the above results seem to vary through a great enough range for all practical purposes, even the greatest percolation here shown for 100 ft. head, is negligible. Rich Surface Coatings——On horizontal or inclined surfaces, a rich coating of 1 to I or I to 2 mortar may be used to secure an impervious surface. This should be laid while the concrete is still green and carefully troweled in place. This coating varies from 14 in. to 1 in. in thickness. There is danger, however, when such a surface coating is used of its cracking and peeling off if exposed to the direct rays of the sun. If it is covered with water, as in the bottom and sides of a reservoir, no danger of this kind should be apprehended. Alum, Lye and Cement Wash.—A waterproof mixture of alum, lye and cement from which good results have been obtained is made in the following proportions: Dissolve 1 Ib. of concen- trated lye and 5 lbs. of alum in 2 gallons of water, care being taken to have every particle dissolved. Heating to near the boil- ing point will quickly insure this without injury to the mixture. This constitutes the stock mixture and may be used in any quan- tity. To one pint of the stock add 10 lbs. of cement, thinning it with water until the mixture spreads easily and well on the surface to be treated with a calcimine or whitewash brush, filling all the pores. The mixture will be found to be satisfactory when it lathers freely under the brush. Usually one pint of the stock put into a 12-gallon pail and 1o lbs. of cement stirred in, with enough water added to well fill the bucket, makes the wash about right. Much depends upon the condition of the surfaces to be coated. If they are too dry, wet them down with a brush ahead of the water-proofing, the object being to apply the wash as thin as practicable without running, rubbing it well into the surface with the brush. The wash should be applied while the concrete is still green, or within three or four days from the time it has been laid. The wash is not found to be satisfactory on old work, and should be applied while the concrete is protected from the sun and while it is still moist; otherwise, too rapid evaporation of the water in the wash will leave the cement without the necessary moisture to set and leave it so that it can be brushed off. The wash should not be applied too thick, as it is liable to scrape GENERAL PHYSICAL PROPERTIES. I41 off, Where a 1:2 facing mixture is used on the concrete, a I part stock to about 30 parts water will give good results. This leaves the surface as it comes from the moulds, without show- ing the marks of the brush. Mr. U. G. Hayne states that he has seen this wash used successfully on fortification work and for water-proofing tanks, etc. In one case, two tanks made to hold 6 ft. of water are stated to have been in continuous use for over seven years without any loss of water, except by evaporation. ‘Two coats of wash were applied to the inside and bottom of the tanks and also to the outside walls. In this case the concrete was first plastered with -a coat of 1 part cement to 2 parts of stock mortar. It is also stated that this wash will prevent fungus growth or discoloration of surfaces covered with it. It may be successfully used for closing the pores of plaster and insure dry walls in building construction. Prof. Ira O. Baker gives the following forraula for making impervious mortar: I per cent. by weight of powdered alum is added to the dry cement and sand, and 1 per cent. of potash soap (ordinary soft soap is good) is dissolved in the water used in mixing. The chemical action set up makes an insoluble com- pound, which practically fills all pores, making an impervious concrete. Prof. W. K. Hatt, Assoc. M. Am. Soc. C. E., has successfully used a 5 per cent. solution of alum and water and a 7 per cent. solution of soap and water, these solutions being used in equal parts in mixing the concrete. European engineers have exten- sively used a coating of from 4 to I in. of rich cement mortar to secure impermeability. Sylvester Process of Waterproofing.—lIf it is desired to render a wall waterproof after construction, it may be treated with ‘waterproofing washes, as in the Sylvester process. This process consists in applying two washes or solutions to the surface ofa wall, one composed of castile soap and water, and the other af alum and water. The proportions are three-quarters of a pound of soap to one gallon of water, and half a pound of alum to four gallons of water, both substances to be perfectly dissolved in water before using. The walls should be perfectly clean and dry, and the temperature of the air not below 50° F. when the compositions are applied. The first, or soap water, should be applied when boiling hot, 142 CONCRETE AND REINFORCED CONCRETE. with a flat brush, taking care not to form a froth on the masonry. This wash should remain 24 hours, so as to become hard and dry before the second or alum wash is applied, which should be done in the same manner as the first. The temperature of the alum wash, when applied, may be 60° or 70° F., and this also should remain 24 hours before applying a second coat’ of the soap wash and so on. Several coats are necessary to secure an im- pervious coating, the soap and alum combined forming an inso- luble compound, filling the pores of the concrete and preventing the passage of water. Cost of Sylvester Process——According to Mr. W. C. Hawley, as given in Gillette’s “Cost Data,” the cost of Sylvester wash and mortar is as follows: The Apollo Water-Works Co.’s covered concrete water well leaked, and it was therefore plastered with a Sylvester mortar; 1% Ibs. of a light colored soft soap were dissolved in 15 gallons of water. Three pounds of powdered alum were mixed with each bag of cement. The mortar was 1:2. Two coats of this mixture were applied to the walls, giving a thickness of 14 in. This stopped the leaking completely. The cost was as follows: 2 lbs. soap (with 24 gals. water), at 7% cts. .......... a T2 lbsy elute At 34S: (Cts, axdnaseereres ange eevee eeneaeseah SEO aL Gases sssunig ade eouctesledarios ai dadedubutu sass aoe aches evelcbanieylicasnescivioe’ $0.57 or 57 cts. for soap and alum per bbl. of Portland cement. A Sylvester wash was used in repairing the bottom of a reser- voir lined with 4 to 6 ins. of concrete. The soap solution was composed of 34 Ib. of Olean soap to 1 gal. of water, both being well dissolved and the soap solution boiled. This boiling hot soap solution was applied to the clean dry concrete, 24 hours later the alum wash, 24 hours later the soap wash, and then 24 hours later the alum wash again. Two men applied the solu- tions, using whitewash brushes, while a third man carried pails of the solution. While making the soap solution, two men at- tended the 4 kettles, one man kept up the fires and two men carried the solutions to the men applying it. It required fewer men to make the alum solution as it was made cold in barrels. After the second soap wash had been applied to the concrete’ slope, it became so slippery that the men had to be held by ropes te prevent falling. A rope was placed around two men who GENERAL PHYSICAL PROPERTIES. 143 started work at the top of the slope, while a third man payed out the rope. The work was done in 8% days, and cost as follows: Labor: T,140;hrsy labor: at. agi (cts. cciese ss <4 caweeasawe resis $171.00 83 hrs. foremen, at 30 cts. ....... ccc ee eee e eee eee 24.90 83 hrs. waterboy, at 6 cts. 0.0.0... ec eee ee eee eee @ 498 Add: for Stpt.; 15%: 6 <)2.66csseacetaes goed day da deondenuencanare ee 30.13 MEG tal VAD OE 20c. sis deat heeatuareie Rover asia eacebelenais ex oan $231.01 Materials: goo Ibs. Olean soap, at 4¥ cts. 6.0... cece eee eee ee $39.00 ZrO bss abuts at 3 CES ince ied cone cd soe an endeuecenetnserciat a 6.30 6 whitewash brushes (10 in.), at $2.25............... 13.50 6 stable brushes, at $1.25 .............. scr hn ares 7.50 MBotaloanatenalsy ccacnauguansic’ yh vice siewstavohiatethe’s —— $66.30 Total labor and materials ................0000. $297.31 This covered 131,634 sq. ft., hence the cost of the two coats of soap and alum was $2.26 per 1,000 sq. ft., or about 0.23 cts. per sq. ft. All but one leak from a small crack were stopped. The concrete lining of a new reservoir near Wilmerding was waterproofed by using caustic potash and alum in the finishing mortar coat. The stock solution was 2 lbs. of caustic potash and 5 Ibs. alum to 10 quarts of water. This was made in barrel lots from which 3 quarts were taken for each batch of finishing mortar, which consisted of 2 bags of cement mixed with 4 bags of sand. A batch of mortar covered an area 6 ft. by 8 ft. by 1 ft. thick. The extra cost of this waterproofing was: 100 lbs. caustic potash, at 10 cts. ..... ce eee ee eee eee $10.00 70 Ibs. caustic potash, at 9 Cts. ....... cece eee eee eee 6.30 960 Ibs. alum, at 3%, 3% and 4 cts. ........ 20. eee eee 34.38 60 hours’ mixing, at I5 cts. ....... eee ee eee eee eee elcareite 9.00 Freight, express and hauling ................... 0. eae TI.50 Total {or 74,800:Sq; ft cicneceaaam access saedaeed $71.18 It will thus be seen that the cost was 95 cts. per 1,000 sq. ft. cr less than 0.1 ct. per sq. ft. The cost was less than by using the Sylvester wash, and the result was better, for with the latter the penetration is only 1/16 to 4 in. It was found that if less than 2 parts of sand to I part of cement was used the mortar cracked in setting. Clean sand is imperative, as any organic matter soon decomposes and leaves soft spots. Do not use an excess of potash; a slight excess of alum, however, does not decrease the strength of the mortar. 144 CONCRETE AND REINFORCED CONCRETE. Other Waterproof Compounds.—There are a number of com=- pounds on the market of a fatty or waxy nature, which, when mixed with cement to the amount of one or two per cent. of its weight, increase its water-resisting qualities to a marked de- gree. By a thorough mixing of one to two pounds of a suitable compound to each sack of cement a mortar which is practically waterproof may be obtained at a small additional cost. In purchasing these waterproof compounds, however, care should be taken to select such as have proved to be permanent in effect, as some materials used for this purpose lose their effect after a few days exposure to the weather and are entirely worthless. Data in regard to the permanency and waterproof qualities of these various compounds are not available, and it will be neces- sary to use much care and judgment in selecting them, otherwise their use will prove a disappointment and a needless outlay of money. One of the best known waterproofing compounds of this char- acter is manufactured by the Sandusky Portland Cement Co., and is known as the Medusa Waterproof Compound. It is stated by the manufacturers that the addition of this compound, to the amount of 1 to 14 per cent. of. the weight of cement used, is sufficient to render concrete building blocks, made from a I cement 5 aggregate sufficiently waterproof to allow plastering direct on the inside surface, and that walls so built are perfectly dry. The compound is prepared by mixing from one to two per cent. of the preparation with the dry cement before adding the sand and water. This preparation is sold in 40 lb. sacks at 12 cts. per pound f.o.b. cars at Sandusky, Ohio. An absorption test was made by the manufacturers as follows: Hollow blocks 8 x 9 x 16 inches made of I part cement and 4.8 parts limestone screenings by weight with and without the waterproofing com- pound were exposed to weather for 9 months, and then allowed to become air dry in the laboratory, then placed in water and weighed at 1, 2, 3, 4 and 24 hours. The results were as follows: Amount waterproof compound, per cent. Water absorbed, per cent. oftotal weight. of weight of cement. Weight dry. Lhr. 2hrs. 3hrs. 4hrs. 24 hrs. No. 1—Waterproof compound 0% 60.62 lbs. 4.38 4.84 4.04 4.99 5.16 No. 2—Waterproof compound 1% 62.34lbs. 44 .44 .48 .54 .70 No. 3—Waterproof compound 2% 62.06lbs. .09 .09 .14 .14 .30 Waterproof Portland Cement.—It is stated that the Star-Stettin Portland Cement Works have recently invented a process b: GENERAL PHYSICAL PROPERTIES. 145 which a waterproof cement is obtained. The process is secret and details cannot be obtained, but it is probable that the water- proofing qualities of this cement are obtained by mixing some substance with the cement during the process of manufacture. The chemical action taking place on the cement in setting affects the material in such a way that it closes the pores in the con- crete without injuring in any way the strength of the cement. [t is stated that this preparation will successfully resist the action of frost, heat, hot water, sea water and dilute acids. If this proves to be the case, the problem of securing a waterproof con- crete for engineering structures has been solved. Dr. Michaelis recommends the use. of barium chloride for this purpose when the concrete is subjected to the action of sea water. Pages 152- 154 should be read in this connection. ’ Asphalt Waterproofing.—Asphalt is extensively used as a waterproofing material. It may be used alone or with paper or felt. When applied to concrete surfaces it will generally be found most satisfactory to first coat the dry surfaces of the concrete with a coat of asphalt cut with naphtha. This is applied as a paint to the concrete when the latter is perfectly dry and then the surface is covered with an asphaltic mastic composed of one part of asphalt to four parts of sand. This is smoothed off with hot smoothing irons and thoroughly tamped and pressed into place. When this coating is applied to the surface of a struc- ture, which is later to be covered with earth or broken stone, it is-better to cover the surface of the asphalt with washed roofing gravel so that the broken stone will not cut or damage the asphalt surfaces. : Various methods are employed in waterproofing concrete sur- faces with asphalt, such as embedding burlap, felt, paper, or other fabric, in the asphalt coating. It is very difficult to make hot asphalt adhere to a concrete surface, however dry the same may be, unless it is heated by artificial means. Hot asphalt laid on ordinary dry concrete will not adhere and can be rolled up like a blanket after it is cool. By heating the surface of the concrete with hot sand before applying the asphalt, the latter may be caused to adhere to the same. It will, however, generally be found preferable to use the asphalt cut with naphtha, applying it as a painting or swab- bing coat. The cost of this work with the present prices of 146 CONCRETE AND REINFORCED CONCRETE. first-class asphalt will range from 10 to 20 cts. per sq. ft., de- pending upon open conditions. No special expert knowledge is needed for its application. Some judgment should be used in selecting the asphalt to be used for waterproofing purposes. The following specifications for asphalt and naphtha water- proofing are used by the Chicago & Northwestern Ry. :* “The asphalt used shall be of the best grade, free from coal tar or any of its products, and which will not volatilize more than ¥Y% per cent. under a temperature of 300° F. for ten hours. It must not be affected by a 20 per cent. solution of ammonia, a 35 per cent. solution of hydrochloric acid, a 25 per cent. solu- tion of sulphuric acid, nor by a saturated solution of sodium chloride. “For metallic structures exposed to the direct rays of the sun, the asphalt should not flow under 212” F., and it should not become brittle at 15° I. when spread thin on glass. For structures underground, such as masonry arches, abutments, re- taining walls, foundation walls and building subways, etc., a flow point of 185° F. and a brittle point of o° F. will be required. The asphalt covering must not perceptibly indent when at a tem- perature of 130° I. under a load at the rate of 15 lbs. per sq. in., and it must remain ductile at a temperature of 15° F. on metal structures, and at o° I’. on masonry structures underground. “Before applying asphalt to a metal surface, it is imperative that the metal be cleaned of all rust, loose scale and dirt, and if previously coated with oil, this must be burnt off with benzine or other suitable means. The metal surface must be warm to cause the asphalt to stick to it, and the warming is best ac- complished by covering it with heated sand, which should be swept back as the hot asphalt is applied. When waterproofing masonry structures, if the surface cannot be made dry and warm it should be first coated with an asphalt paint made of asphalt reduced with naphtha. This is particularly necessary for vertical structures, “The asphalt should be heated in a suitable kettle to a tempera- ture not exceeding 450° F. If this is exceeded, it may result in ‘pitching’ the asphalt. Before the ‘pitching’ point is reached, the vapor from the kettle is of a bluish tinge, which changes to a yellowish tinge after the danger point is past. If this occurs the *W. H. Finley, M. Am. Soc. C. E. Paper read before Cement Users’ Association. GENERAL PHYSICAL PROPERTIES. 147 material should be tempered by the addition ,of fresh asphalt. The asphalt has been cooked sufficiently when a piece of wood can be put in and withdrawn without the asphalt clinging to it. “The first coat should consist of a thin layer poured from buckets on the prepared surface and thoroughly mopped over. The second coat should consist of a mixture of clean sand or screenings, free from earthy admixtures, previously heated and dried, and asphalt, in the proportion of 1 of asphalt to 3 or 4 of sand or screenings by volume. This is to be thoroughly mixed in the kettle and then spread out on the surface with warm smoothing irons, such as are used in laying asphalt streets. The finishing coat should consist’ of pure hot asphalt spread thinly and evenly over the entire surface and then sprinkled with washed roofing gravel, torpedo sand or stone screenings to harden the top. The thickness of the coating will depend on the char- acter of the work, and may vary from 34 in. to 2 ins. “Where a quantity of asphaltic concrete is required, such as in trough floors on bridges, the concrete should be made in the proportion of 1 part asphalt, 2 parts sand and 3 parts lime- stone screenings, thoroughly mixed and rammed into place with tamping irons on the first coat of pure asphalt with which the metal was originally covered. At all drainage holes large size stones should be carefully placed by hand to secure perfect drainage.” ‘ Asphalt or Felt Waterproofing -—Layers of waterproofing paper er felt cemented together with asphalt, bitumen or tar are ex- tensively used for waterproofing purposes in concrete floors, roofs and walls of underground structures, as tunnels, subways, etc. The materials range from ordinary tar paper laid with coal tar pitch to asbestos or asphalted felt laid in asphalt. Coal tar products will not prove permanent, as they will deteriorate when exposed to moisture. Asphaltic mixtures when exposed to the action of illuminating gas will also deteriorate. In the con- struction of the New York subway, layers of felt laid on with hot asphalt were used for waterproofing purposes, but trouble was experienced in several stations as the roof was found, after a time, to leak. After a careful investigation it was found that the asphaltic compound had been seriously injured by gas escap- ing from the mains in the street. Care should be taken under 148 CONCRETE AND REINFORCED CONCRETE. similar conditions to prevent gas from coming in contact with waterproofing mixtures, Method of Laying Paper or Felt.—It is customary to first place a layer of concrete or some other material. upon which to piace the waterproofing compound, then mop over the pre- pared surface with hot asphalt, spread the felt or paper, lapping the latter from 4 to 6 ins. After the first layer of the felt is in place the whole is mopped over with the hot asphalt compound. Another layer of paper is placed and the operation continued until the desired thickness is secured. From two to six layers were used in the construction of New York’s rapid transit subway. After this coating is in place the remaining concrete, forming the floor or upper surface, is then laid upon the top layer of the asphalt. Cost of Waterproofing with Tar Felt and Asphalt.—The cost of waterproofing the New York subway with asphalt felt, and asphalt, as given in Engineering-Contracting, July 18, 1906, is as follows: Per sq. yd., single. 1.11 sq. yds. asphalt felt, at 4% cts. (including 15% for laps) 5 cts. OB7 Gal:, ASHlialts Ate TS: tS. secagessnevecicaniiocconassandea eave adeavagoronsi tes 4%“ eA OE = saci tei 4 cnceyiu acon detnatd Anesdyaicoudvaceccvave daneansgunstcp nvtseto pacar paca venir ayn 5% * AO tale secerssersscyttede cher ncswemrrsqe nel 4s scyacaios niobate atarrvemeatemetes a a 15 cts. This is for one thickness of felt, so that for three thicknesses the cost would be 45 cts. per sq. yd. for labor and materials. Both labor and materials are high in cost. Labor cost was high because of poor supervision. The material was high priced, be- cause asbestos felt dipped in asphalt was specified. The cost of lining a large asphalt reservoir, as given in Gillette’s “Handbook of Cost Data,” page 296, is as follows: Cost of first asphalt coat on concrete bottom (34,454 sq. ft.). Labor: Total Cost. Cost per sq. ft. Building sheds, 25 hrs. at 20¢. $5.00 $0.00015 Spreading, 38 “ 20¢. 7.60 0.00022 Boiling, Bye OE OES eee 5.55 0.00016 Helpers, 48 * “ Te. 6.45 0.00019 Sweeping, 44 “ © te. 6.60 0.00019 Materials: Asphalt, 18,490 Ibs. at $0.01225 226.50 0.00658 Fuel, ft Cofd sssactcscueesss 2.50 0.00012 | Hauling 9.25 tons, at $0.47.. 4.35 0.00007 TOtals\ autestine dire Sevens $264.55 $0.00768 This gives a cost of $0.06912 per sq. yd. GENERAL PHYSICAL PROPERTIES. 149 Cost of second asphalt coat on bottom (34.454 sq ft.). Labor: Total Cost. Cost per sq. ft. Building sheds .............. $5.00 $0.00015 Spreading, 35 hrs. 5.25 0.00015 Boiling, 30 “ “ 4.50 0.00013 Helpers, 52%" 7.88 0.00023 Sweeping, 44% * 6.68 0.00020 Foreman, 17%” 4.38 0.00013 Materials: Asphalt, 19,591 lbs., at $0.01225 239.99 0.00702 Fuel, 1 cord, at $2.50 ........ 2.50 0.00007 Hauling 9.8 tons, at $0.47.... 4.61 0.00013 Totals aicss yeuceateees $280.79 $0.00821 This gives a cost for the second coat of $0.07389, or a total cost for two coats of .14301 cts. The waterproofing used for the Adtantic Ave. subway of the Long Island Railroad consisted of a tar felt paper, mopped with a coating of pitch. Over this was spread a 1 in. coat of cement mortar. The roofing felt consisted of pine wood paper pulp, or asbestos pulp, which had been thoroughly treated and soaked in refined coal tar, and which weighs for single ply at least 15 lbs. per too sq. ft. What is known as “medium hard” coal tar pitch of somewhat softer grade than used for roofing purposes, was swabbed over the masonry after it was thoroughly set and dried out. This pitch was poured or mopped onto the concrete surface until it had a perfectly uniform thickness over every part of not less than 1-16 in. The roofing felt was then laid upon the coat of pitch, while it was still soft, the felt being lapped at least 4 ins. on all cross joints, and at least, 12 ins. on all longitudinal joints. This was mopped over with a coating cf pitch, and upon that a second thickness of roofing felt was placed, and there- upon a third coating of not less than 1-16 in. of coal tar pitch ‘was deposited. The 1 in. coating of 1 to 2 cement mortar was then laid in uniform squares, in every respect similar to the plaster on top of granolithic pavement. The average labor cost of placing the two layers of felt and three coats of tar pitch was.5¥% cts. per sq. yd. The average labor cost of mixing and placing the 1 in. layer of cement mortar was 1434 cts per sq. yd., making a total cost for labor of 20 cts. per sq. yd. : Assuming that the cost of paper felt was 3 cts. per sq. yd. and 150 CONCRETE AND REINFORCED CONCRETE. the coal tar pitch at 12 cts. a gallon, the total cost per square yard for this work was: Two layers per. sq. yd. 2.13 sq.yds: paper felt; at $e. .¢eiv cian sadacywress ous $0.064 0.75 gals: pitch, at 126) snhswaveryirues o4 pomeweeeee ss .09 Labor. laying: felt os ccc, Sees eee nee eect eee e .055 Labor laying cement mortar ............-...-.- cece 145 Total, cost: vascaeoewstcndewc eee enies aaron eas $0.354 The cost of laying the top finish 1 in. thick of a cement walk, as given by Mr. C. M. Saville, M. Am. Soc. C. E., in Gillette’s “Handbook of Cost Data,” page 179, is as follows: . Per cu. yd. Per sq. yd. 4 bbls. per cu. yd., at $1.53 ........ $6.12 $0.171 0.8 cu. yd. sand, at $1 ............. 80 018 Eampblack: 2225 .244 weannde ads .29 209 Labor (2 walk masons, 1 helper).. 6.36 144 $13.57 $0.342 Thus we see by the above data that the costs of various classes ef work vary considerably under different conditions. The Effect of Sea Water Upon Portland Cement Mortar and Concrete-—The action of sea water upon Portland cement mor- tars is a phenomenon which is little understood. While it is true that some concrete masonry has withstood the action of sea water for a long time, other structures have been rapidly destroyed when subjected to the same action. Why one struc- ture has resisted well, while another similarly located and per- haps constructed with the same kind of cement has been rapidly destroyed, is a question which has long puzzled chemists ‘and engineers. \lany theories in regard to the. action of sea water upon the cement have been advanced, and something learned in regard to the subject, but thus far it has not been possible to determine whether or not a structure will stand when sub- jected to the action of sea water. It has been learned, however, that if any considerable amount of certain ingredients are pres- ent, failure is almost certain to take place, while, if they are absent, or only present in small quantities, there is at least a possibility of the structure standing for a time. The German Portland Cement Manufacturers’ Association for a number of years has beeen conducting a study of the action of sea waters upon Portland cement mortars and concrete, and, GENERAL PHYSICAL PROPERTIES. I51 largely through their efforts, considerable knowledge is avail- able on this subject. Sea water contains small percentages of magnesium chloride ond magnesium sulphate. These two ingredients are supposed to attack the free lime present in the cement, forming calcium- aluminum sulphates. The magnesium chloride has but a feeble ection, but the magnesium sulphate attacks the lime with great energy. According to Dr. Michaelis and M. Vicat, the action is explained by the chemical equation: Ca (OH), + MgSO, == Mg (OH), + CaSQ,. The calcium sulphate, owing to its taking a crystalline form with an increase in volume, swells and destroys the mortar. Alumina and gypsum are also supposed to be injurious. It was discovered by Messrs. Michaelis and Candlot that aluminate of lime, Al, O;, 3 CaO, which is present in the cement, possesses the property of combining with sulphate of lime so as to give the double salt Al, O, 3 CaO, 3 (SO, CaO) combined with a large quantity of water with great increase in volume. This substance has no firm coherence, and is soluble in pure water, but not in lime water. Whether this action, or the one previously explained, or some other action takes place, we must conclude that cements, rich in lime or alumina, or which contain a high percentage of gypsum, are dangerous for use in sea water, as they all disintegrate rapidly. On the other hand it has been found that the presence of high percentages of silica and ferric oxide seem to be beneficial. Dr. Michaelis found that the chemical action can be greatly improved by adding some pozzolanic material like trass to the cement. This material combines with the lime, forming a stable compound, which hardens under water. The lime necessary for hardening the pozzolani will come from the cement. This sec- ondary hydraulic action greatly improves the resisting power of the cement. It seems probable that well burnt clay may be used to replace the trass. Tt has been found that a dense concrete withstands the action of sea water better than a porous concrete, as the water does not readily penetrate the mass, and chemical action is not so readily set up. Hence well balanced mixtures, as dense as possi- ble, should be used. It has also been found that mortars made with fine sands are much more readily decomposed than those 152 CONCRETE AND REINFORCED CONCRETE. made with coarse sands. Hence fine sands should be avoided for this class of work. Messrs. Candelot, Le Chatelier, Vicat, Rebuffet and Feret, as well as Dr. Michaelis, have extensively studied the action of sea water on cements. The recommendations of, Dr. Michaelis, the greatest living authority on this subject, are given below. The general conclusions to be drawn from the writings of these authorities may be summed up as follows: Sand with a large percentage of fine grains should not be used for mortar and con- crete intended for use in sea water. A moderate amount of fine grains, when mixed with coarse and graded sized grains, will, however, increase the density of the concrete and prove bene- ficial. It also follows that the aggregate should be proportioned to secure the greatest density. Gypsum, which is sometimes used to regulate the time of setting, is dangerous. Portland cement for sea water should be low in alumina (8 per cent. being the maximum amount allowable, and as low as possible in lime). Puzzolanic material is helpful when added to cements to be used iit Sea water. Concrete Structures in Sea Water.—On the subject of the permanency of cement concrete when exposed to the action of sea water, Dr. Wilhelm Michaelis says in a paper* on the sub- ject: “The main points to be considered in erecting permanent struc- tures in sea water with the aid of hydraulic cements, in other words, concrete, are: (1) From the physical point of view, completely impermeable mixtures should be made, composed of 1 part of cement with 2, or at the most 2% parts of sand, of mixed grain, of which at least one-third must be very fine sand. To this the requisite quantity of gravel and ballast should be added. This impermea- ble layer should surround the porous kernel on all sides in suffi- cient thickness, even underneath. It would, perhaps, be unneces- sary waste of material, in the case of thick walls, to use the imper- meable mixture throughout; but, so far as possible, the compact shell and the poorer kernel should be made in one operation. Where this is not possible, and the shell is added subsequently, numerous iron ties should be used. (2) From the chemical point of view, cements or hydraulic *Trans, Inst. Civ. Engrs., Vol. XVII., p. 375. GENERAL PHYSICAL PROPERTIES. 153 limes rich in silica, and as poor as possible in alumina and ferric oxide, should be used, for aluminate and ferrate of lime are not only decomposed and softened rapidly by sea water, but they also give rise to the formation of double compounds, which in their turn destroy the cohesion of the mass by producing cracks, fissures and bulges. The salts contained in sea water, especially the sulphates, are the most dangerous enemies of hydraulic cements. The lime is either dissolved and carried off by the salts, and the mortar thus loosened, or the sulphuric acid forms with it crystalline compounds as basic sulphate of lime, alumina sulphate and: ferro sulphate of lime, which are segregated forci- tly in the mortar, together with a large quantity of water of crystallization, and*a consequent increase in volume results. The separation of hydrate of magnesia is only the visible, but com- pletely innocuous sign of these processes. The magnesia does rot in any way enter into an injurious reaction with silica, alumina, or ferro oxide; it is only displaced by the lime from its solution in the shape of a flocculent, slimy hydrate which may be rather useful in stopping the pores, but can never cause any strain or expansion, even if it subsequently absorbed carbonic acid. The carbonic acid, whether derived from air or water, assists the hydraulic cement as a preservative wherever it comes into contact with the solid mortar. It could only loosen the latter if present in such an excess that bicarbonate of lime might be formed. (3) The use of substances which render the mortar, at any rate in its external layers, denser and more capable of resistance. Such substances are: (a) Sesquicarbonate of ammonia (from gas liquor) in all cases where long exposure to the air is impossible. Such a solu- tion, applied with a brush or as a spray, and then allowed to dry, converts the hydrate of lime into carbonate of lime. The latter is not acted upon by the neutral sulphates present in sea water. Tt must be repeated that it is a decidedly erroneous opinion that the texture of otherwise sound cements is injured by the action of carbonic acid; on the contrary, it renders them more capable of resistance, except in the above mentioned case, which is ex- tremely rare, when bicarbonate of lime is formed and goes into the solution. 154 CONCRETE AND REINFORCED CONCRETE. (b) Fluosilicates, among which magnesium fluosilicate is most to be recommended. The free lime is converted into calcium fluoide and silicate of lime, and, in conjunction with the liberated hydrate of magnesia, these new products close the pores of the mortar. Both salts are sufficiently cheap to be used on a large scale. (c) Last, not least, barium chloride. Two or three per cent. cf the weight of the cement is dissolved in the water with which the concrete is mixed. This forms perfectly insoluble barium sulphate with the sulphates of the sea water, while the magnesia remains in the solution as magnesium chloride. Although in this case there can be no further closing of the pores, yet the insoluble barium sulphate, which is formed, affords some pro- tection and does not give rise to any increase of volume (swell- ing). From two to three per cent. of barium chloride does not in any way diminish the strength, as has been proved by means of comparative tests of English and German cements. Fre- quently the strength of the mortar is increased by this addition. This substance is only to be used in the external, perfectly water tight skin of the concrete; in other words, in the 4 to 8 in. coat- ing, composed of 1 cement, 1 to 2 sand and 3 to 4 gravel, flint, broken stone, etc.” Strength of Cement Mixtures in Sea Water.—It has been found that the strength of a cement mixture does not increase as rapidly in salt water as in fresh. Tests made by the Boston Rapid Transit Commission show that, during the early stages of setting, fresh and salt water briquettes possess practically the same strength, but at g months sea water briquettes decreased con- siderably in strength. According to M. Feret,* tension specimens hardened in sea water are stronger than those hardened in fresh water, but with compression specimens the reverse is true. In conclusion, it may be stated that if the material does not fail by disintegration, its strength under sea water will approximate but never exceed that of materials setting in fresh water. The Effect of Oil on Cement and Concrete.—Until within the last two or three years there has been considerable difference of opinion in regard to the effect of oil on concrete. Even to-day many consider oil entirely harmless, and to prove their assertions *Proceedings of Institute of Civil Engineers, Vol. CVII., p. 163. GENERAL PHYSICAL PROPERTIES. 155 call attention to machinery foundations in use for many years, which, though exposed to waste oil, are perfectly sound. On the contrary there are many who believe that concrete is in- jured by oils and substantiate their beliefs by citing examples of concrete which disintegrated when oil appeared to be the sole cause, In 1903 it was accidentally discovered in the cement testing laboratory of the Chicago, Milwaukee & St. Paul Ry. that oil disintegrates Portland cement. A neat Portland cement bri- quette, two years old, which had been used in the laboratory as a paper weight, was laid aside, where it was exposed to occa- sional droppings of signal oil. In ten months the briquette began to disintegrate. This led to an extensive investigation as to the effects of oils on cement and concrete by the engineering de- partment. The following are the results of the tests, taken from an article* by James C. Hain, Assoc. M. Am. Soc. C. E., then Engineer of Masonry Construction C., M. & St. P. Ry. An examination was made of a great many concrete structures on which more or less oil was found. There were a limited num- ber of instances where the concrete was possibly affected by oil. In these cases, however, the concrete was very old, and the char- acter of the original material and the workmanship were ques- tionable. On the contrary no concrete which was built in late years, and known to be of good quality, was affected to any per- ceptible degree. One case which particularly attracted atten- tion was the concrete floor of an oil house in which lubricating and lighting oils had been stored for six years without any apparent effect. The penetration of the oil was slight, perhaps not to exceed 1-16 in. Moreover, the saturated portion seemed to be as sound as the rest. There were other cases where the oil had penetrated deeper. For example, in the pits of the round house the oil had gone in from %4 to % in. In other respects the concrete seemed perfectly natural. These pits, however, had been in use’ only about a vear when investigated. These obser- vations proved nothing definite and, while the investigation seemed favorable for the structures examined, it could not be taken as conclusive for all concrete structures. Laboratory experiments were then taken up on Portland ce- ‘ment briquettes made of neat cement, of 1:3 sand mortar and *Eng. News, March 16, 1905. 156 ‘CONCRETE AND REINFORCED CONCRETE. of I :3 mortar of limestone screenings, which were allowed to age four days in the laboratory air, and were then subjected to applications of signal oil. At first small-quantities of oil (enough to saturate) were applied daily. Later the applications were less frequent, depending upon the amount of oil absorbed. Cracks developed in the sand and limestone briquettes first at the age of 214 months, while the neat briquettes showed cracks at the end of five months. All the briquettes ultimately disin- tegrated. The cement used in these tests was what is known as a stone and clay cement; 18 briquettes each of neat cement of 1:3 sand and of 1:3 limestone screenings gave practically uniform results as to time of disintegration, as given above. After the results of these preliminary experiments were avail- able a more extensive series was started. Instead of confining the tests to a single kind of cement and to signal oil, as was done in the first series, three kinds of cement and characteristic oils er fats of five different groups were employed. The oils and fats used were as follows: Class.... Animal fat Animal oil ———Vegetable oil —, Mineral oil Semi-Drying Drying Crude Kind.... Ext. of lard Whale oil Castor oil _—_ Boiled Petroleum Linseed oil oil Cylinder oil, which is a mixture of animal fat and mineral cil, was also used for the purpose of comparison. Well known brands of cement were used, one being selected from cement made from stone and slag, another from marl and clay and the third from slag and limestone. Neat briquettes and 1:3 sand briquettes for all varieties of cement were treated with each of the six varieties of fats and oils. All briquettes were left in the laboratory air seven days before starting the oil treatment. The oil applications were continued for nine months after they were started. A summary of the results is given in Table XXIT. The greatest effect was caused by animal fat or extract of lard oil. It disintegrated most of the neat and sand briquettes in from 2 weeks to 2% months, although it failed to destroy some even at the end of nine months. As a rule the neat briquettes were destroyed first, which was contrary to what might be ex- pected. It was found that in general cement made from stone and clay were affected the least, while slag cements were affected the most; this, however, was not true in all cases, and the GENERAL PHYSICAL PROPERTIES. 157 peculiar characteristics of each cement and not the materials from which it is made affected it the most. Next in effect was signal oil, a mixture of animal fat and mineral oil. It acted only slightly different from extract of lard, Following this were the whale and castor oils, which caused much less disintegration than either of the two just mentioned, affecting but small percentage of the briquettes. Petroleum and boiled linseed oils did not disintegrate any of the briquettes up to nine months. Petroleum, however, penetrated and affected the strength somewhat, and possibly would have eventually de- stroyed it, while boiled linseed oil formed a coating without pene- trating. Of the five classes, boiled linseed oil was the only one that apparently did not affect the strength of the briquettes. This was probably due to the oxidation, which prevented it from soaking in. Further tests were made on older briquettes cured according to the regular laboratory practice. Some of these tests were as follows: A neat; a 1:1, a 1:2, and a 1:3 sand briquette, all of which were two years old, were dried at the stove for 20 days and then treated with signal oil. After two years, with one exception, they showed no signs of disintegration. The above briquettes were made of silica cement instead of regular Port- land, which consisted of equal portions of sand and Portland cement, ground together to a fineness that passed through a No. 200 sieve. This cement makes weaker briquettes than those made from standard Portland cement. The one that failed was the weakest of the four, being a 1 to 3 mixture. Again a neat and a 1: 3 sand briquette were taken from the vat at the age of one year and treated with signal oil. They appeared to be perfectly sound after being soaked about one year. A 28-day briquette, after being dried in the laboratory air for three months, was treated with oil and was not distintegrated until after eight months. Eight-year-old briquettes were also treated and were unaffected efter nine months. A piece of concrete from the oil house floor spoken of above was immersed in oil for ten months and was un- affected. While the tests on comparatively new briquettes showed with but one or two exceptions disintegration from the action of oil, the tests on old specimens showed up much better. Out of 15 old briquettes, seasoned according to the usual laboratory practice, 158 CONCRETE AND REINFORCED CONCRETE. only two failed under the action of oils, although treated from nine months to 2 years, the two that failed being the weakest. The briquettes which were unaffected were cured from one to two years in water. TABLE XXII. SHOWING THE EFFECT OF OIL ON CEMENT AND MORTAR BRIQUETTES. . . Bd $ 3 3 & ixt g ni an #8 = No. bri- Class of Portland ae Bo So ae & gS = quettes Portland Cement x a made, Cement. and Sand. Time applied betore disintegration +—~—7 18 Stone and Neat '3mos, * = * ss = clay 12 Stone and 1:3 sand * * is me * clay 18 Marl and Neat 23?mos. * * me * 6 mos, clay 12 Marl and 1:3 sand ie * . Se - clay 18 Slag and Neat Imo. 3mos. 4mos, * * 1} mos. stone y 12 Slag and 1:3sand 7 mos. 4}mos.6} mos, * * 4 mos. stone * Sound after applying oi] 9 months, at which tests were discontinued, All briquettes set 7 days in air before applying oil. It was observed (1) that most oils penetrate concrete mortar and may weaken them. (2) That concrete-is more liable to be disintegrated when saturated with oils and fats if not thoroughly set. (3) A good quality of concrete is less susceptible to the effects of oil than a poor quality, such as a porous, frosted, lean, poorly mixed or improperly seasoned concrete. Ordinary con- crete work is rarely subjected to continued large doses of oils, being usually only spotted. Under such conditions little danger may be apprehended, especially if the concrete is of good quality and well seasoned, and even if the conditions are more severe there will, generally speaking, be small danger of dangerous dis- integration. Experiments were also made for the purpose of determining a cheap manner of treating concrete to prevent the disintegrating action of oil, but with unsatisfactory results, no satisfactory wash being found. One of the briquettes treated with signal oil was sent to the laboratory of Toch Brothers, Long Island City, and a careful analysis was made of it. Mr. Maximilian Toch states that a de-' termination of the soluble substances in the briquette showed that the disintegration was due to the formation of oleate and stearate cf calcium. To reduce this to its simplest expression, the animal GENERAL PHYSICAL PROPERTIES. 159 cils contain acids which combine with the lime and crystals of stearate and oleate of lime are formed. It is very likely that these crystals in the process of formation have increased the bulk in the briquette and the bond- which has been formed by the lime in the set cement has been totally disintegrated and . ruptured. These crystals were isolated and verified under the microscope . Mr. Toch also states that machine oils are almost all paraffine ails, do not contain animal fats, and hence do not affect concrete. Silicate of magnesia, sold under the name of fluate, has often been used as a wash to protect concrete against the action of oil. When this wash is applied to concrete, silicia is liberated and fills up the pores. The magnesium fluate acts as a binder, and the cement becomes excessively hard after a few months. Limestone and building stone have been treated with this material in Europe with great success. This compound is, however, expensive. Preservation of ‘Metal in Concrete.—One of the most important questions asked in regard to reinforced concrete is: Will it be per- manent; will the imbedded metal be preserved from oxidation? If not, the construction will deteriorate. Much evidence has been published showing that iron and steel are perfectly preserved in concrete, but occasionally evidence to the contrary is made known. Prof. Spencer B. Newberry, Assoc. M. Am. Soc. C. E., states the theory of the protection of iron from rust when embedded in concrete as follows: “The rusting of iron consists in oxidation of the metal to the condition of hydrated oxide. It does not take place at ordinary temperatures in dry air or in moist air free from carbonic acid. ‘The combined action of moisture and carbonic acid is necessary. Ferrous carbonate is first formed; this is at once oxidized tc ferric oxide and the liberated carbon dioxide acts on a fresh por- tion of metal. Once started, the corrosion proceeds rapidly, per- haps on account of galvanic action between the oxide and the metal. Water holding carbonic acid in solution, even if free from oxygen, acts as an acid and rapidly attacks iron. In lime water or soda solution the metal remains bright. The action of cement in preventing rust is now apparent. Portland cement con- tains about 63 per cent. lime. By the action of water it is converted into a crystalline mass of hydrated calcium silicate and calcium hydrate. In hardening, it rapidly absorbs carbonic acid -and be- comes coated on the surface with a film of carbonate. Cement 160 CONCRETE AND REINFORCED CONCRETE. mortar thus acts as an efficient protector of iron, and captures and imprisons every carbonic acid molecule that threatens to at- tack the metal. The action is, therefore, not due to the exclusion of air, and even though the concrete be porous, and not in con- tact with the metal at all points, it will still filter out and neutral- ‘ize the acid and prevent its corrosive effect.” In regard to the action of cinder concrete, Prof. Newberry writes as follows: “The fear has sometimes been expressed that cinder concrete would prove injurious to iron on account of the sulphur contained in the cinders. The amount of this sulphur is, however, extremely small. Not finding any definite figures on this point, I deter- mined ‘the sulphur contained in an average sample of cinders from Pittsburg coal. The coal in its run state contains a rather high percentage of sulphur, about 15 per cent. The cinders proved to contain 0.61 per cent sulphur. This amount is quite insignificant, and even if all oxidized to sulphuric acid it would at once be~™ taken up and neutralized in the concrete by the cement present and would by no possibility attack the iron.” Prof. Newberry states that a reinforced concrete water main taken up after fifteen years’ use in damp ground at Grenoble, France, showed the metal absolutely free from rust and the adhesion perfect. Mr. E. L. Ransome states that embedded steel rods used in a sidewalk in Bowling Green Park, New York, were found to be in perfect condition after twenty years’ use. He also mentions, among other examples, sidewalk slabs in Chicago, which, after be- ing broken up, showed the rods in perfect condition. The slabs were of limestone concrete, and had been in use for eight or ten years. Numerous other examples might be cited. Mr. Jas. S. Mack, Supt. of the Standard Mines of the H. C. Frick Coke Co., states that a 24-in. cast-iron pipe was used as a discharge pipe to carry off sulphurous water from the mine. This pipe was lined with a coating of Portland cement to protect it from the action of acid in the water. The coat was put on with a brush on the perpendicular line and had a thickness of about 14 in. On the horizontal line it was put on with a trowel and had a thickness of about % in. With the exception of one or twa places where the cement had worn through, the pipe remained uninjured after eighteen years of constant service. . GENERAL PHYSICAL PROPERTIES. 161 Mr. Ernest McCullough states that he placed some badly rusted iron rods in blocks of concrete of a 1: 2:4 mixture. The blocks were broken after about a year and the rods were found to be comparatively clean and bright. The rust was gone, but was not adhering in scales or flakes to the concrete. It seemed to have entirely disappeared, leaving the enveloping concrete somewhat discolored. The adhesion of the rods was seemingly perfect. Mr. Edwin Thacher, after extensive study and observation, states that he considers concrete to be a perfect protection for embedded steel. Prof. Charles L. Norton, of the Massachusetts Institute of Technology, Boston, Mass., made a large number of experiments with bricks of concrete 3 x 3 x 8 in., in which steel rods, sheet steel and expanded metal were embedded. One portion of the specimens, together with unprotected steel, was enclosed in steel boxes and exposed for three weeks to the action of steam, air and carbon dioxide; another portion to air and carbon dioxide; a third to air and steam, and a fourth left on the table of the testing room. His conclusions were as follows: First—Neat cement is a perfect protection. Second—Concrete should be dense, without voids or cracks, and be mixed quite wet when applied to metal. Third—The corrosion found in cinder concrete is mainly due to iron oxide in the cinders and not to sulphur. Fourth—Cinder concrete, if free from voids and well rammed when wet, is about as effective as stone concrete in protecting steel. Fifth—It is important that the-steel be clean when embedded in the concrete. Sixth—It is essential that the steel be coated with cement before embedding in concrete, the unprotected pieces being found to consist of more rust than steel. Additional tests made by Prof. Norton were as follows: Spec- imens of steel, clean, and in all stages of corrosion, were embed- ded in stone and cinder concrete, both wet and dry mixtures being used, and exposed to moisture, carbon dioxide and sulphurous gases. Some of the samples were treated in tanks supplied inter- mittently with steam, hot water, moist air, dry air and continuously with carbon dioxide for from one to three months. Under these conditions, unprotected steel vanished into streaks of rust; but, 162 CONCRETE AND REINFORCED CONCRETE. when protected by an inch or more of sound concrete, the steel was absolutely unchanged. He concludes that steel embedded in concrete mixed wet, whether stone or cinder concrete, will be per- fectly protected for all time. M.. Breuillié is said to have found that a chemical union takes place between the metal and the cement, forming a silicate of iron which is soluble in water. If this is true, when this salt is dissolved the bond between the metal and the concrete will be destroyed. The many excellent examples of successful rein- forced concrete whose strength is dependent upon the adhesion between the two materials would seem*to refute this statement. Again, the successful use of cement paint for protection would indicate that this celebrated French engineer is in error in regard to his deductions, or, what is more probable, the cement used by him in his experiments may have contained some injurious agent. Adhesion Between Concrete and Steel.—It is important that there be a positive bond between the concrete and the steel of a re- inforced member. Usually the entire stress in the steel must be transmitted by this bond or adhesion. The bond may be due (1) to the adhesion of the concrete to the steel, (2) to surface fric~ tion, probably due to shrinkage strains set up by the concrete upon setting, causing it to grip the steel firmly and generate a high frictional value; or (3) to some mechanical arrangement consisting of a deformed, twisted or corrugated form of rod, giv- ing an effective mechanical bond between the steel and concrete. When the shear per foot run between the steel and concrete exceeds the safe working adhesion or surface friction between the two materials, some form of mechanical bond should be used. The values given by different experiments for the adhesion in pounds per square inch of contact surface vary quite widely. It is probable that the adhesive strength under normal conditions is great enough to care for the shearing stresses until the elastic limit of the metal is passed, when the bar stretches, decreases in cross-section and is torn from the concrete. A rough surface gives a higher adhesive value than a smooth surface, rusted bars considerably higher values than those not rusted, while oiling or painting greatly reduces the adhesion. Round bars show the greatest adhesion; flat bars the least. M. Bauschinger and M. de Joly, from a series of experiments, conclude that the adhesion of concrete to iron or steel rods is GENERAL PHYSICAL PROPERTIES. 163 from 570 to 710 lbs.-per sq. in. of surface. These values appear to be somewhat high after a careful examination of a large number of recent experiments, some of which are here given. Prof. W. K. Hatt, in the Journal of American Society for Test- ing Materials, 1902, gives the following values for the adhesion of round rods, each value being the average of three tests, the con- crete being a 1:2:4 mixture, and its age about 32 days: Depth of Rodin Con- Ultimate adhesion in Ibs. per Size of Rod. erete in ins. sq. in. of rod surface. */1 in. 6.0 636 5 in. 6.4 756 The following values, Table XXIII., of the holding power of different types of rods, are from a series of tests by Prof. Charles Spofford, Massachusetts Institute of Technology, and reported bv him in Beton und Eisen, Part III., 1903. The mixture used was a 1: 3:6 Portland cement concrete, the stone being trap rock. The rods were all thoroughly cleaned with the sand blast before con- crete specimens were made. The coricrete was sufficiently wet to flush water to ‘the surface when tamped into the moulds. The time of test was 28 days. In the following table each value given is an average of several tests. TABLE XXIII. Number of Rods Adhesion in Ibs. Cross-section of Rods used to obtain per sq. in. of Type of Rod. used in inches. average value. contact surface. Ransome .... $x4—$x$andij}x 1} 12 296 Thacher ..... 4 — fand 14 9 275 Johnson...... 4x4d.3xPandripx1 9 339 Platine, i csteioncs & in, round 3 245 Plains ccc cscnssis $x 3 279 Plain Flats... «}x 4, 14x jand2}x} 9 164 The cleaning of the rods by sand blast made them much smoother than they are ordinarily. Hence the values for plain rods given above are, when compared with the values for de- formed rods, proportionately less than they would be under or- dinary conditions. The comparative resisting power of twisted and corrugated bars to longitudinal slipping is shown in Table XXIV. The area of contact surface between the twisted bars and the cement was taken to be the periphery of the bars, multiplied by its length in the prism. In computing the contact surface of the corrugated bars, the periphery was assumed to be represented “ 164 CONCRETE AND REINFORCED CONCRETE. hy the square circumscribing the corrugations. A part of the prism thus enclosed would be subjected to shearing stresses. TABLE XXIV—ADHESIVE RESISTANCE OF CORRUGATED AND TWISTED STEEL BARS EMBEDDED IN CEMENT AND MORTAR PRISMS. (From Watertown Arsenal Tests, 1904.) Nominal dimensions of prisms inches.....................00000- twisted, Effective sizes of rods taken, inches .. ; (corrugated, .73 x .73 Atlas brand cement used. Ultimate resist- Composition of Prisms. Kind of Rod. ance per sq. in, Remarks. Cement, neat) cecics stecuiexg ese Twisted 1,278 Rod broke a Re Ages 508s Geto eGTS o ey I, 303 uy a FC oaaceeaia = toe Bitte SoMa Corrugated 968 as es AO lays aba a hana ne os 958 as "s iY gees RELA RS ie 960 as FE CeMient, Tsang sc. cs cuczecaseueissn ss Twisted 1,318 “ E us eS elie esiisianah aban Corrugated 977 Rod pulled out { aE BO FE epee bee ace Twisted 1,199 ‘© proke HS Be Ne Mikes une. Btu Corrugated 934 «* pulled out tea oe I) ee cece aupsaie aay sienelens Twisted 7O1 ae “ te # Br NE ieee oatenacese Corrugated 735 ss “ yo BOE cecettielee-scuagrerde aes Twisted 796 re “ g) BE OE apiece) nae eee Corrugated 564 ¥e « The following tests, Table XXV., were made at Columbia Uni- versity in 1903, and have not been published heretofore: TABLE XXV. Adhesion, Ibs. Type of Rod. Condition. Sizeininches. Ageof Test. persq.in.sur. Remarks. Blame esse 4 Rusted fxd I month 437 Pulled out. BES goons ts s gx 3 months 642 Block split. ae Clean gx I month 204 Pulled out. Ee peiistabspe a Exe 3 months 431 Block split. BES sete ses acattie a gx¢ Imo. in water 146 Pulled out. Ransome Clean ix G 25 days 500 Block split. BO a ieaudntitrn a $x ss 520 se St cence a gx I month 457 oe OE teint ue’ “cc 3 x i “a 560 “ Thacher .... ss a os 700 ag “ wate “6 q ‘ec 788 “ “ woud cc t 6“ 450 “cc ‘6 M ce Z oe 410 “ According to the above tests, rusted rods give about 50 per cent. higher adhesive values than clean rods. Prof. Arthur N. Talbot, in the Bulletin of University of Illinois, Sept.1, 1904, reports the following results (Table XX VI.) of tests cf bond between steel and concrete. Plain round and square bars and Johnson corrugated bars were used. It will be seen that the Johnson bars split the concrete, while the plain bars slipped. No slipping could be detected before the maximum load was reached. GENERAL PHYSICAL PROPERTIES. 105 The range of resistance per square inch of embedded bars was great, being from 298 to 639 lbs. for the Johnson bar, and from 174 to 360 lbs. for the plain rods. In no case did the tension in the plain rods exceed the elastic limit. In tests Nos. 21 and 22 the bars were placed within 114 ins. of the face of the concrete block. Nos. 16 and 17, which had 24 ins. of rod embedded, show a small resistance per square inch of surface. This is probably TABLE XXVI—BOND BET WEEN STEEL AND CONCRETE. et 5 Re ge.8 Boo§ ge Hos “AS a's est Maximum Area 2UA9 27 ay 2s 0. Type of Rod. Load. sq.in. Q9 * QF 2 A Remarks. 1 %-in. Johnson 14,990 .20 74,950 625 60,000 Concrete split. 2 WW-in. Johnson 14,210 .20 71,050 593 60,000 Concrete split. 3 %%-in. Johnson* 12,605 .20 63,000 525 60,000 Concrete split. 27. %-in. Johnson* 15,335.20 76,650 639 60,000 Cylinder broke. 4 %4-in. Johnson 17,175 .365 47,050 573 58,300 Concrete split. 30 %-in. Johnson 11,755. 365 32,200 392 58,300 Concrete split. 26 %-in. Johnson 13,975 .365 38,300 466 58,300 Concrete split. 5 %-in. Johnson* 16,360 .365 44,800 545 58,300 Concrete split. 31 %-in. Johnson* 9.515 .365 26,050 317 58,300 Concrete split. 32 %4-in. Johnson* 8,960 .365 24,500 298 58,300 Concrete split. 29 4%-in. Johnson* 10,435 .365 28,600 348 58,300 Concrete split. 33 «%-in. square 4,780 .16 29,900 250 45,000 Rod slipped. 34 %-in. square 6,850 .16 42,800 357 45,000 Rod slipped. 13 %-in. square 5,850 .16 36,550 305 45,000 Rod slipped. 35 %-in. square* 6,810 .16 42,600 357 45,000 Rod slipped. 36 %%-in. square* 6,910 .16 43,200 360 45,000 Rod slipped. 18 %-in. square* 4,100 .16 25,600 214 45,000 Rod slipped. 14 %-in. square* 5,560 .16, 34,700 290 45,000 Rod slipped. 8 %-in. square 11,600 .56 20,620 322 35,000 Rod slipped. 9 %-in. square 11,850 .56 2i,100 329 35,000 Rod slipped. 10 %%-in, square 7,910 .27 29,320 317 33,300 Rod slipped. 15 %%-in. square 6,400 .27 23,700 256 33,300 Rod slipped. 11 %-in. round 3,255 .I1 28,800 228 42,500 Rod slipped. 12 %&-in. round 3,800 .II1 34,200 270 42,500 Rod slipped. 16 %-in. squaret “ 6,905 .16 43,150 180 45,000 Rod slipped. 17 %-in. squareT 6,690 .16 41,800 174 45,000 Rod slipped. 21 %-in. square 4,785 .16 29,930 249 45,000 Rod slipped. 22 %-in. square 6,000 .16 37,500 312 45,000 Rod slipped. 23 %-in. square 4,580 .16 28,640 239 45,000 Rod slipped. 28 %-in. square 6,540 .16 40,800 340 45,000 Rod slipped. 7 %-in. round 7,000 .452 15,500 245 40,500 Rod slipped. 6 %-in. round 11,000 .452 27,500 380 40,500 Rod slipped. due to uneven distribution of the transmission of stress from the bar to the concrete throughout the length, due to the greater stretching of the bar within the concrete. Age of test was 60 days. Eliminating tests 16 and 17 and tests struck by sledge, and av- eraging the values of tests on round bars, we obtain a mean value *Struck 6 quarter-swing blows with a 10-Ib. sledge. +Embedded for a length of 24 ins. 166 CONCRETE AND REINFORCED CONCRETE. of 281 Ibs., and for square bars a value of 298 Ibs., while the average for the Johnson bars is 530 lbs. per superficial inch of contact. The average of 30-day tests at Columbia University on Ransome bars is 509 lbs., and of Thacher bars 587 lbs., while the average of plain bars for one and three months agrees sufficiently well with those given by Prof. Talbot. We may then conclude that the ultimate surface bonding for plain bars, round and square in cross-section, may be taken at from 250 to 400 lbs. for an age of 30 to 60 days, with an average value of about 300 lbs., and for deformed rods, such as Ran- some, Thacher and Johnson, from 300 to 800 lbs., with an aver- age value of about 500 lbs. The safe working value for adhesion or surface bonding may be taken at from 40 to 100 Ibs. per sq. in. for plain rods and from 50 to 150 lbs. for deformed rods. é Shrinkage and Expansion of Cement Mortar and Concrete When Setting —It has been found that cement mixtures hardening in air shrink somewhat during the early periods of setting, while those hardened in water expand in like manner but in a less degree. The contractions and expansions are greatest in neat cement mortars, while the variations in volume are less in mor- tars containing sand and in concrete. Prof. G. F. Swain, who made some elaborate experiments upon 5-in. cement mortar cubes in the Massachusetts Institute of Technology laboratories, reports in the Transactions of the American Society of Civil Engineers for July, 1887, that the contraction at the end of 12 weeks is: HOP Meat CEMEME® 025.26 muna idaancuedn we dane escaeseins nets 0.14% to 0.32% Fort ceiient: 162 Sand: sc iccseuniewse hehe 0.08% to 0.17% Hor mnéat- Cement. ais2uaneresy weeeacess cs gies 0.04% to 0.25% For 2 cément. to § Sand) o.ccccayeans wred a eae 0.00% to 0.08% Prof. Bauschinger, of Munich, reports results similar to those of Prof. Swain. His test specimens were cubes 4.72 ins. on a side. The following table shows his results: Mixture. Contraction in per cent. Expansion in per cent. Cement to Sand. Age. ; Hardening in air. Hardening under water. Neat 16 weeks 0.12% to 0.34% 0.01% to 0.15% 123 16 weeks 0.08% to 0.15% 0% to 0.02% Es 16 weeks 0.08% to 0.14% — 0.03% to 0.02% Mr. John Grant records in Vol. 62, Proc. Inst. Civ. Engr., the results of his experiments on prisms 4 ins. long, hardened only in GENERAL PHYSICAL PROPERTIES. 167 water. Neat cements at the end of one year expand 0.09 to 0.21 per cent., and a 1: 3 sdnd mortar 0.01 to 0.06 per cent. He states that the addition of gypsum increases the amount of the expan- sion. In his book on “Portland Cement,” Dr. C. Schumann* reports the following results of experiments on prisms 3.9 ins. long and with a cross section of .775 sq. in. These were immersed in water: 1 Cement, Age in Weeks. Neat Specimen. 3 Normal Sand. I 048% .O15% 4 082% 021% 13 104% .024% 26 125% 028% 39 139% 030% 52 146% 033% M. Considére made valuable experiments on the behavior of both plain and reinforced concrete pieces setting in both air and water. The measurements were made with extremely delicate instruments. The mortar used was approximately in the propor- tions of 1 part Portland cement to 3 parts silicious sand. The TABLE XXVII—CONSIDERE’S TESTS, SHOWING EXPANSION AND CONTRACTION OF CEMENT PRISMS. -——Contraction of Prisms——~ -——-Exvansion of Prisms——~ Setting in air. Setting in water. Neat Neat Neat Neat No. cement, cement, Mortar, Mortar _ cement, cement. Mortar, Mortar, days. plain. reinforced. plain. reinforced. plain, reinforced. plain. reinforced I 060% 006% 022% 004% .007% .002% .003% .002% 2 058 .009 021 .006 O15 003 O10 .002 3 057 O12 .020 007 021 004 013 .002 4 058 O14 021 .008 027 005. .O15 003 5 .060 O16 022 .0GQ 032 .006 O17 .003 6 .064 O17 026 .009 037 .008 018 .003 7 .070 .020 .029 .009 O41 .009 O19 .004 14 095 022 .038 009) 059 O13 .020 .004 21 .110 023 042 O10 .069 O16 022 .004 28 118 .024 044 .O10 .073 018 024 .004 35 123 025 045 O10 . 075 .020 .026 .005 42 128 025 O47 .O10 077 021 027 005 49 .130 "025 047 O10 .078 .022 027 .005 56 131 .025 .049 OTO 078 022 .027 .005 63 132 025 .050 O10 .079 .022 .028 .006 size of the prisms was 2.360 x 0.98 x 23.6 ins. in length. The re- inforcement consisted of an iron rod 0.4 in. in diameter. This gives 5.45 per cent. reinforcement. The results are shown in Table XX VIL. At the end of two or three vears it was found ‘that the maximum *“Portland Cement,’’? 1899. by Dr. C, Schumann. 168 CONCRETE AND REINFORCED CONCRETE. contraction for neat cement not reinforced varied from 0.15 per cent. to 0.2 per cent., and the expansion appeared to be about the same, while the expansion of the mortar appeared to be about one-third of that of the neat cement. A calculation to determine the stresses in the reinforcement of the neat cement prism setting in air gave a mean compressive stress of 7,110 lbs. per sq. in., and a mean tensile strength in the cement of 410 lbs. per sq. in. In the mortar prism the reinforcement had a mean compressive strength of 2,845 lbs. per sq. in., while the tensile stress-in the concrete was 155 lbs. per sq. in. For the prism setting in water the mean tensile strength de- veloped in the reinforcement was about 6,250 lbs. per sq. in., and the mean compressive stress in the cement was about 360 lbs. per sq. in. For the mortar prism, the tensile stress in the reinforce- ment due to the elongation was about 1,700 lbs. per sq. in., while the mean compressive stress in the concrete was about 100 lbs. per sq. in. These stresses in both cases were for 5.45 per cent. of re- inforcement. M. Considére concludes that the initial tensions developed in the concrete of a prism while setting in air. by the presence of reinforcement of sufficient sectional area very nearly approximates the ultimate resistance of similar pieces of plain concrete at the same age, and this is the reason for the regular contraction of reinforced prisms. A test was made by Mr. H. S. McCurdy for the Boston Tran- sit Commission* to determine the amount of shrinkage of con- crete in setting. The specifications for the Boston Transit work called for a 1: 214: 4 concrete, gravel heing used for the aggre- gate. Two beams, one in air and one in water, 8 ins. square, and having an effective length of 8.9 ft. were tested. One end of the beam was anchored to the masonry of the subway, the other end was so connected to the trunnions of a transit instrument that any change in length caused the line of collimation of the telescope to revolve about its axis. The instrument was directed toward a leveling rod 240 ft. away; thus any change of length of the beam was magnified 3,850 times. Some changes in tempera- ture took place during the period of observation and an allow- ance was ‘made for expansion of .0008 in. for each degree of Fahrenheit. Mr. McCurdy concludes from his observation that *Seventh Annual Report Boston Transit Commission, 1901. GENERAL PHYSICAL PROPERTIES. 169 a concrete beam 100 ft. long, setting in air, would in 12 weeks, if the temperature remained constant, shrink about .o28 ft. His other observations were made on a beam of the same size as the first, but which was kept under water twelve weeks. He found that the shrinkage in this, after making allowances for changes in temperature, was about two-thirds that of the beam that was kept in air. These results do not agree very well with results obtained by other experimenters, but it should be remembered that the experi- ments were made on concrete blocks, and not mortar specimens as used by others. On the other hand, too few tests were made to draw any definite conclusions. Coefficient of Expansion.—The coefficient of expansion of con- crete, due to temperature changes, does not differ materially from that of steel. In Les Annales des Ponts et Chaussées, 1863, Bonniceau gives the following values per degree Fahrenheit : Neat Portland cement.........0....0000ce cece ee ee ees .00000594 One cement to two silicious sand..................-. .00000655 Concrete (proportions not given).................05. .00000795 Christophe, in “Le Béton Armé,”’ quoting Bonniceau, Meies, Adie and Durand-Claye, states that the coefficient varies from .000006067 to .c0000805. To determine the coefficient of expansion of concrete Sir Alex- ender R. Binnie, M. Inst. C. E., gives the details of his investi- gation as follows*: A block of I cement, 4 crushed granite concrete, 1 ft. square and roo ft. long was constructed a few years ago. The block was built to rest on rollers so as to be free to expand in any direction. Proper verniers were attached to either. end, moving against pillars detached from the block itself. For three years, summer and winter, expansion and contraction of the block was measured. The expansion and contraction was found to be in- fluenced considerably by the condition of the atmosphere, as well as by the temperature. In wet weather the expansion, due to absorption of moisture, was often as much as that due to summer heat. The action of the sun shining on one side of the block also had a disturbing influence. Taking the average of all con- ditions in various states of the weather, the expansion was 0.005226 in. for a rise of 1° F. for a block too ft. in length “Institute of Civil Engineers, December, 1904. 170 CONCRETE AND REINFORCED CONCRETE. and 1 ft. square in cross section. This gives a coefficient of ex- pansion of .000004355. In this connection it should be remembered that the concrete was a rich mixture and the aggregate granite, which is seldom used for concrete. A series of tests to determine the coefficient of expansion of concrete was made by Prof. Wm. D. Pence of Purdue University. Two series of tests were made. In the first the bars were 6 x 6 x 24 ins., but owing to the great length of time required to heat the 36 sq. ins. of section, bars 4 ins. in diameter and 36 ins. long were used for the second test. The stone was hand broken Bedford Golitic limestone for the first series and Kankakee limestone, crusher broken, for the second tests. A local pit gravel was used in both tests. The coefficient was determined by comparing the expansion of the concrete bar with that of steel and copper bars, subjected to the same condi- tion as regards heat and cold. The reliability of tests thus made involving the comparison of metal and concrete is open to ques- tion. The results of these tests are given in Tables XXVIII. and XXIX. TABLE XXVIIIL—COEFFICIENT OF EXPANSION OF 1 : 2 : 4 BROKEN STONE (PORTLAND) CONCRETE. Brand of Standard Coefficient of Series. Tests, Kind of Stone. Cement. Bar. Expansion (F) Ist No. 5 Bedford Lehigh Steel 0.0009052 Ist No. 6 Bedford Lehigh Steel 0.000005 3 Ist No. 7 Bedford Lehigh Steel 0.0000053 Ist No. 10 Bedford Lehigh Steel 0.0000057 Average results of first series................ 0.0000054 ad No. 2 Kankakee Medusa Steel 0.0000056 2d No. 3 Kankakee Medusa Copper 0.0000054 2d No. 8 Kankakee Medusa Steel 0.0000057 Average results of second series............. 0.0000056 Average of entire series of results on broken SUOME - COMET ELE Ss. 5 o.caae. 65 & casas cpaueuseds oo Sae ube 0.0000055 Coefficient of expansion, Kankakee limestone WSBT ents gt cc3 BB haat Idee gees esac anetnerng ed 0.0000056 TABLE NNIX.—COEFFICIENT OF EXPANSION OF rt 2:4 AND 1: § GRAVEL CONCRETE. 7 Brand of Standard _ Coefficient of Series. Tests. Proportions. Cement. Bar. Expansion (F). Ist No. 4 122 i4 « Lehigh Steel 0.0000054 ad No. 4 1:5 Medusa Steel 0.000005 5 ad No. 7 1:5 Medusa Copper 0.0000053 2d No. 10 1:5 Medusa Steel 0.0000052 Average of results of second series.......... 0.0000053 Average of entire series on gravel concrete... 0.0003054 GENERAL PHYSICAL PROPERTIES. i7l Experiments made by Rae and Dougherty, under the diection of Prof. Hallock, Columbia University, resulted in obtaining the following values: I ceinent 2 sand 0.00000655 5 gravel An average of these is 0.00000608. Clark gives the value at 0.00000795. If an average of the mean values as given by the last three experimenters be taken, there will result the value 0.00000648. The rate of expansion per degree of Fahrenheit for wrought iron and steel, as given by Kent, is from 0.00000648 to .00000686 ; and, as given by U. S. Government Reports on Iron and Steel, it varies from .o0000617 to 0.00000676. The mean of these values is 0.00000654 or 0.6 per cent. greater than the mean value for the expansion of concrete given above; and, if the mean of the U. S. Government values be used, the difference is 0.2 pér cent. greater for the concrete. These values are so nearly equal that it is evident no special consideration need be taken in regard to the relative coefficients of expansion of steel and concrete in structures subjected to ordinary temperatures. It will be of interest in this connection to compare the co- efficient of expansion of concrete with that of various stones and other substances. Table XXN. is taken from Engineering News. Oct. 23, 1902, p. 341: The method of treating concrete constructions to prevent un- sightly cracks, due to expansion and contraction, is discussed under “Retaining Walls.” Fire Resisting Qualities of Reinforced Concrete.—Many claims, some often extravagant, have beerr made as to the fire’ resist- ing qualities of concrete, both plain and reinforced. The word “fireproof” is a relative term. A material that will resist fire at high temperature indefinitely is unknown. Material that will re- sist the flames and heat of an ordinary conflagration, in such a manner that the structure will be intact and safe after moderate repairs, may be called fireproof. Reinforced concrete certainly falls within this classification, as shown by numerous fire and water tests, and by a number of structures, which have passed through severe fires. A fire in a building filled with combustible materials will de- velop, for short periods, temperatures as high as 2,000° F., or I cement oe saath }o.00000361 172 CONCRETE AND REINFORCED CONCRETE. higher: The Building Code of the City of New York requires that a structure to be considered fireproof shall withstand, when fully loaded, a temperature averaging 1,700° F. for four hours, and then be subjected to a stream of water discharged from a 14 in. nozzle under 60 lbs. pressure for five minutes without failing. A number of systems of reinforced concrete have with- TABLE XXX.—COEFFICIENTS OF EXPANSION OF VARIOUS MATERIALS. C £ Ly Material Authority. Coefficient of Modulus of for 100° expansion. elasticity. F. Brick, Common........ Haswell .OOO0012 3,500,000 420 Bricks Fire. sccm oe ais Haswell 0000028 Sti... ss CEMENt cciacaceomeens Haswell o000080—t—t—«=‘(‘ Concrete, I :2 4— Lehigh, Portland and Pence .0000055 1,000,000 555 Limestone......... 2,000,000 1,100 Lehigh, Portland and Pence 0000054. iw ss ee eee BBA Gravel............ Granite— Aberdeen ........... Dana 10000044! a xiezxnere-s Cece New England....... Dana .0000048 5,500,000 2,640 13,000,000 6,240 Iron or steel, average. . Haswell .0000066 27,000,0C0 17,620 Limestone— : Sing Sing, N.Y..... Dana .0000057. iw ww ws see wes Bedford, Ill......... Pence .0000056 1,500,000 940 3,300,000 1,850 Marble sstevesieecete: Ganot and —_.o000048 2,500,000 1,200 Haswell Sicily Gaksdianireuand Dana 0000061 iw“... Pottery— Wedgwood.......... Enc. Brit. 0000049 ~—............ Bayeux tsyasaiadiecan Enc. Brit. .ooo0092 i... ee Quartz along axis.... Enc. Brit. .0000028 ~—....... .. Perp. to axis........ Enc. Brit. .0000043 sw... eee Sandstone ............ Haswell 0000068 tits Sandstone ............ - Haswell oooor0o8 St... Sandstone ............ Ganot 0000065 tix‘ ss ss ss Sandstone, red ....... Dana .0000095—i«“ts ses Sandstone, red ....... Thurston .0000033. iw sss sss Sandstone. red ....... Thurston 0000055 ws ees ee Slate svrscetasgna scans Spon’s Dic. .0000055 7,000,000 3,850 Wood, White Pine..... Spon’s Dic. 0000023 1,800,000 410 stood this test for beams, floor slabs and columns. Other sys- tems have failed, but the causes contributing to their failure have usually been traceable to concrete not sufficiently dried out, to in- sufficient thickness of concrete over the metal, and in one case to the use of broken stone containing a high percentage of lime. There is every reason to believe that reinforced concrete, when made of the proper materials should prove a satisfactory fire- GENERAL PHYSICAL PROPERTIES. 173 resisting material. The relative resisting qualities of concrete made from cinder, stone (trap rock) and slag are in the order named. Portland cement in hardening absorbs 10 to 20% of its weight cf water. This water is chemically combined and none of it is given off until a temperature of at least 500° F. is reached, the dehydration, probably not ceasing until a temperature of about 1,000° F. is reached. This water, as it is given off, vaporizes, and keeps the surrounding materials at a comparatively low tem-. perature. After the dehydration has taken place the concrete is much improved as a non-conductor of heat and greatly retards the dehydration of the adjacent concrete. Concrete itself is a poor conductor of heat, and the materials a fraction of an inch away may be practically insulated from the action of heat for a long time. Tests show that a thickness of from 34 to I in. of stone concrete is sufficient to protect the metal in a floor slab; and for cinder concrete % to 34 in. is suffi- cient, while for beams and columns the thickness should be from ly, to 2 ins. for a stone concrete, and from 1 to 1% ins. for cinder concrete, depending upon the size of the member. Care must be taken in selecting the cinders for cinder concrete, for if any un- kurnt coal is present the fire resisting quality is greatly reduced. Limestone should be avoided and granite may chip under the action of heat. The reinforced concrete factory of the Pacific Coast Borax Co., at Bayonne, N. J., passed through a severe fire in 1902. This structure was 4 stories in height, and, excepting the roof, was built entirely of reinforced concrete. The walls, posts, girders, floors and a number of partitions were of reinforced concrete. The floor slabs were 4 ins. thick, and were supported by beams 24 ins. deep, 4% ins. wide and 24 ft. long, spaced 3 ft. centers. The columns were square, and reinforced with 4 twisted steel rods tied together at intervals. The walls were 16 ins. thick with 9-in. hollow spaces in the center. The concrete was made from Atlas Portland cement and crushed trap rock, crusher run, all passing through a I-in. screen. No sand was used, the stone dust taking its place; 1:5 and 1:6% mixtures were used. The contents of the building were entirely destroyed. The walls and floors remained intact, and, except in one place, where an 18-ton tank fell from the roof to the floor, cracking some of 174 CONCRETE AND REINFORCED CONCRETE. the floor beams, and in another place on the outside of the wall, the concrete work was practically uninjured. It is stated that the fire was so hot that it melted brass and iron castings. This would require a temperature of upward of 2,000° F. The Baltimore fire is often cited as affording examples of re- inforced concrete structures, which withstood a conflagration. While much has been written about this fire, the fact remains that the number of reinforced concrete structures that went through it were so few that when the surrounding conditions are considered it does not appear. safe to draw any definite con- clusions from them. Very few experimental data are available as to the ability of concrete to withstand cracking or disintegration when subjected to great heat or as to its heat conductively. Prof. Ira H. Woolson of Columbia University (during the past two years) has made a series of tests on the fire resistance of concrete, that were fully reported in papers read before the American Society for Testing Materials at Atlantic City, N. J., in June, 1905, and June, 1906. An independent investigation was also made by a committee of the National Fire Protection As- sociation, and a report of the result of their tests was presented at the annual meeting, May 23-25, 1905. Prof. Woolson’s Tests——Fire resistance and crushing tests were made on 4-in. cubes, and tests for elastic deformation and crushing strength were made on 6 x 6 x 14-in. prisms of a 1:2:4 mixture of cement, sand and 34 in. broken stone. This is a mixture commonly used for reinforced concrete construction. The cement used was a mixture of different brands of the best grades cf American Portland cement. The sand was taken from a quantity used in the construction of a building on Columbia Uni- versity ground. It was medium size, fine quality and not es- pecially clean. Three varieties of stone, limestone, trap rock and ciean 14-in. quartz gravel, were used; cinder concrete specimens were also used in the final series. The concrete was mixed moderately wet and well tamped. The purpose of the investigation was threefold: To ascertain first, at what temperature the concrete began to lose crushing strength due to the action of heat; second, the rate of loss of strength resulting from the increase of heat, and third, the effect of varying temperatures upon the elastic properties of concrete, GENERAL PHYSICAL PROPERTIES. 175 the purpose being to determine if the elasticity began to diminish prior to the loss of strength or concurrently with it. The initial tests were made on specimens heated to 500° F., and the temperature was increased 250° F. for each succeeding set, up to 2,250° F. for the final set. In the final tests, made in 1906, it was decided that instead of raising the specimens very slowly up to a furnace temperature of 1,500° to 2,000° F., as done in the initial tests, it would be best to raise the temperature rapidly to some fixed point, then hold it there for a definite period; by these means duplication of tests could be more easily made and the conditions would more nearly approximate those of an actual fire. A temperature of 1,500° F. was adopted as a fair average and the furnace raised to this Degrees F. Minutes. Fig. 62.—Diagram Showing Rise of Temperature in Furnace-Hoated Concrete Blocks. temperature in 40 to 60 minutes and held there until the con- clusion of the tests. The heating was done in an oven type cf gas furnace. The temperature was measured continuously by a Le Chatelier pyrometer. In the 1906 tests a number of speci- meas had thermo couples cast in them, but unfortunately, with one exception, they were displaced by tamping the concrete, and the registered temperatures were confusing and of little value. The gravel specimens were the only ones which attained an interior temperature equal to the furnace temperature. It is rather surprising to note that the cinder concrete specimens came next to the gravel in the amount of interior heat recorded, for cinder concrete is well known to be an effective fire resistant. The thermal curves shown in Fig. 62 will serve to illustrate 176 CONCRETE AND REINFORCED CONCRETE. the rise of temperature in the interior of a specimen. The loca- tion of the thermo couples from 1 to 7 ins. from the hot face are shown in Fig. 63. In this particular specimen the position of the thermo couples was absolutely assured, and the resulting curves shown in Fig. 62 can be assumed to be reasonably correct. It will be observed that the curves all flatten out at or a little after the 212° point is reached, showing that after steam be- gins to generate there is little if any rise of temperature - until all the water in the concrete has been evaporated. While all the curves lag at the 212° point the lag is greater with increased thickness of the concrete. It should also be noted that up to 3 ins. thickness the recorded temperature at which it occurs is Hot Face af te te eS i} 8 a ay a | ‘ eae Bog | a Pe ee be RNoiouy eu oe #& of © ry how og ot | 2:2 ho a ‘ Hor NW ow a ag i Ce er ee | ‘ x oot eta Et wy Ho Plan es [Bg onneneeeenennennned ‘ a a) 0° 900000 rs Jt kept! : kip keg? x Elevation. Fig. 63.—Diagram Showing Location of Thermo-Couples in Test Cubes. above 212°, showing that the surface of the concrete heated rapidly and went above the boiling point of water. It is un- doubtedly these conditions which cause steam to generate rapidly enough to become explosive and burst off patches of concrete, which is a common occurrence in fire tests. The curves 6 and 7 are somewhat irregular. The reason for this is that the points 6 and 7 were 2% ins. from the ends of the blocks and received more or less heat through the ends of the block, throwing their temperature curves out of harmony with those of the other points, which were not thus affected. - In the initial tests made in 1905, a test was also made to de- termine the thermal conductivity of concrete. It was found that GENERAL PHYSICAL PROPERTIES. 177 by allowing 1 hour and 15 minutes to bring the furnace tempera- ture up to 750° F. and then holding the temperature constant, it required 2 hours and 40 minutes more for the interior of two different prisms to attain the same temperature. Then raising the furnace to 1,000° F. in 30 minutes it required 1 hour and 10 minutes more for the prisms to become uniformly heated through- out. These tests were also made by embedding thermo-couples in the middle of the prisms and connecting them by a switch to the same galvanometer on which the couple in the furnace was re- cording. The concrete when this test was made was 28 days old. In this instance it required 5 hours and 35 minutes to obtain a temperature of 1,060° F. through 3 ins. of concrete, when the specimens were surrounded by heat on all sides, with no radia- tion possible. These two experiments show conclusively the low thermal conductivity of concrete. They also show that two or three inches of concrete properly mixed, tamped and set will resist a fierce conflagration for hours without permitting a serious tem- perature rise upon the opposite side. It will be interesting to compare the results obtained by the committee of the National Fire Protection Association with the tests just given. Briefly the tests were as follows: Three round steel rods placed respectively 1 in., 2 ins. and 3 ins. from the hottom were embedded in 8 x 1134 ins. x 6 ft. concrete beams. Holes were cored in the beams reaching from the top down to the reinforcing rods; in these were placed thermometers. The several beams were laid close together side by side to form the top of a four walled gas furnace, the temperature - inside of which was gradually raised during three hours to between 1,900° and 2,000° F. The time required to heat up‘the rods in all samples, which had only 1 in. of concrete covering to a temperature of 770° F., was well within 1% hours or an average of 59 minutes for 11 samples. For 2 ins. covering it required 2 hours and 20 minutes and for 3 ins. of material it required an average of 2 hours and 30 minutes. At a temperature of 770° the strength of steel is reduced about 25 per cent. It is stated that the samples composed of the richest concrete mixtures proved to be the slowest conductors of heat, and that the rise of temperature in the cinder concrete samples was quite noticeably slower than in any of the other samples. 178 CONCRETE AND REINFOnCED CONCRETE. None of the samples showed any signs of breaking or chip- ping off of the concrete during the fire, but after being removed it was found that the material had lost practically all its strength to a depth of about 4 ins. from the sides and bottom and that it had softened perceptibly clear to the top. The effect was prac- tically similar in all specimens; those containing the most cement TABLE XXXI._SHOWING COMPRESSIVE STRENGTH OF 4-iN. TRAP-ROCK CONCRETE CUBES. (Woolson’s Tests.) -~ageins o a a ; s 2, 2. gee oe qe S62 388 .3 fee bg% $85 85 $5 52k =22 a a nag © q H eas 2 n a a ” Condition after heating. 1 32. .. Unh’t’d. 1,903 Bo 338° — hu ” 1,913 1,903 B32) tc x 1,892 4 36 2 500 1,808 5 36 2 500 2,100 1,920 6 36 2 500 1,853 7 36 2 750 1,880 : 8 36 2 750 1,690 1,840 Slight cracks. 9 36 2 750 1,950 10 36 2 1,000 1,547 Brittle and full minute cracks. Ir 36 > 1,000 1,273 1,413 Same. 12 36 2 1,000 1,418 Same. 13 36 2 1,250 I,1I0 Brittle. Had several small.cracks. 14 36 2 1,250 1,163 1,244 Same. 15 36 2 1,250 1,459 Same. 16 50 10 1,500 1,265 Few cracks. Appeared sound. 17. 50 Io 1,500 1,802 1,556 Sound. No cracks. 18 50 10 1,500 1,602 Same. 19 50 I0 1,750 644 Full of cracks. * 20 50 10 1,750 1,220 923 Same. One crack entirely around. 21 50 10 1,750 904 Full of cracks. 22 44 9 2,000 680 Full of cracks. One around three sides. 23 «44 9 2,000 1,072 847 Few cracks. Surface pitted. 24 44 9 2,000 790 Same. 26 «44 9 2,250 626 5or Very much fused on bottom. 25 44 9 2,250 458 Slightly fused on one edge. Few cracks. 27. 44 9 2,250 420 Full of cracks. Slightly fused on one side. appeared, however, to be the most sound. The samples tested were 1:2:3, 1:2144:5 and 1:3%4:7 mixtures, the stone being coarse screened gravel, limestone and red granite, not larger thar 114 ins., and cinders. The cinder mixtures were, however, 1: 2:5 and 1:2:6. The specimens were from 45 to 48 days old when tested. Strength Tests.—Tests were made upon specimens both before * GENERAL PHYSICAL PROPERTIES. 179 and after heating to detcrmine the effect of the application of heat upon the specimen. Table XX XI. gives the ultimate crushing strength of the 4-in. trap cubes which were heated to various temperatures and crushed after cooling. No appreciable effect vpon the strength can be noted until a temperature of 750° F. is reached; when slightly lower average strengths were obtained. TABLE XXXII—SHOWING COMPRESSIVE STRENGTH OF 4-IN. LIMESTONE CONCRETE CUBES. (Woolson’s Tests.) _ j~Agein« © g wad 2 eer ae gas gee a ow Gus Ff) q ees gh g f2 2 ah ai FA Zao gi, $5 628 Bez & ee g oi g < Fe Condition after heating. I 34 .. Unh’t’d. 1,968 2 34 2s * 1,843 1,817 B 34-4 “ 1,640 4 38 3 . 500 1,227 Somewhat brittle. 5 38 3. 500 1,290 1,234 Same. 6 38 3. «500 1,184 Same. 7 38 3 #750 I,122 Brittle. Gave metallic sound when struck. 8 38 3 750 1,440 1,244 Same. 9 38 3. «750 1,170 Same. 10 38 3 1,000 923 Stone slightly calcined. Ir 38 3 1,000 gor 1,052 Same. 12 38 3 4 1,000 1,241 Same. 13 38 3 1,250 988 Calcination throughout. 14 38 3 1,250 1,038 976 Same, but appeared sound. 15 38 3 1,250 903 Same; surface discolored. 16 44 3 1,500 680 Same; edges chipped. 17 44 3 1,500 778 765 Same. Full of small cracks. 18 44 3 1,500 838 Same. Crumbled easily. 19 44 3 1,750 832 Same and discolored. 20 44 3 1,750 684 813 Very fragile. 21 44 3 £#41,750 922 22 44 3 2000 .... Crumbled on cooling. 23 44 3 2,000 .... .... Same. 24 44 3 2,000 .... Same. 25 44 3 2,500 .... Same. 26 44 3 2,500 .... «... Same. 27. 44 «+3 2,500 .... Same. Beyond 750° F. the decrease was marked, with two or three ex- ceptions, notably at 1,500° F., where two of the specimens gave remarkably high results. The surface of all specimens heated over 750° F. were covered with minute cracks ; at 2,250° F. the cubes: were slightly fused, due to the fact that fire brick protection was displaced in removing previous specimens, exposing the re- mainder more or less to direct contact with the flames. 180 CONCRETE AND REINFORCED CONCRETE. er “bz ueyy JSIO MA, See eh we | aS Ree | Rizet eet, pews ooS‘t 6 9S pue padiem sapis fusuneds peq AJoA ‘cht Rees oor‘61 osz oos‘r 6 9s “sues 2 PEaG o00'Sz1 o00'fg SSor oSe1 €£ $s “SYOBIO [[PUIS YIM PatoAod soRJING t+'° ‘* o00'%zZI =: C00‘6g o16 ose1 € eS vameg oo0o0'zIzZ 000091 ool't ooofr & oS ‘yOnIjs UaYyM Burs oTe}UI pe_Y ‘aureg +t: “ oS'tZ1 ooo'gzr = SEL ooo'r = os ‘ajqiq nq ‘punos paivaddy ‘*''*** 9 d00'19h oo0%00b Seg o$Z e ov ‘yuoredde syovio aynumu AlaA coo'zZp = oo0’gzS_—s«0OOGF_=— ss OSz‘1 OSL £ 6b ‘aueS = go0‘ovo'r + 000086 = co0PEQe-s«OZG‘I~—s«080S 9 gr : “OURS 000'gg 000'206 = c00S14 Ss ORI = OOS. 9 gr ‘OWIeSG = 000‘019'I O00'0Z0'% OCOO‘OPE’E SZZ‘I ve “awe ooo'obh‘'z o00‘000'f ooo‘ogi‘€ ozg‘I ee ‘UOIIpuod poos ul uauisadsG ooofooZ‘'I ooo‘OhI‘e OOO‘OSH'E OOS‘T ee BUIVoy 10}JB UOLZIPUOD aes ake eee rea wed at ge By Fy2 Fyg RAE Ras g@86 BE "8 28 oe ee gh FRE e Usdep Ul es y~ (‘S}sa,], $,UOSsTOOM ) ‘SNSIYd ALAUYONOD MIOU-dVUL AO ALIOILSVTA HO SNTINGOW GNV HLONAULS AAISSHUMTNOD DNIMOHS—IIXXX ATAVL ase abe qilz qoz 41 O9r qe qzi Vil Vol SY SO oe ‘on wemlvedg 181 GENERAL PHYSICAL PROPERTIES. ‘Qa13ap Jassaq 0} Abe se awegG **'**** = ooo'€lI *paseqyeys _ pue pediem sapis {pourspes Ajaiua auoIG ttt ttt ‘IUIeS eee sense ooo‘Ol ‘SUI Z JO Ydap 0} pauoyed AjadUs aUdIG ttt OSOET =. ‘QUIeS Pensa eee 000‘Sgz “paursyeo ApWYSys oSp2 uo auojg otrrttee oo0‘o0z ‘UOIJIPUOD POO OOO‘Qgz OLO‘Pbz ‘sapIs UO YOoWS 30*- ooO'FFE ~ oOOOEEE ‘ames §000'zZ6 =—s Coo‘g ZI ‘UOTUIpUOD poos ut usWIIedS oO0‘Q4F ~— c00‘ZSE ooo0‘06E‘T =o00STZ'1 oco‘ogo’z §=o00‘0f £‘z 000'gzO'T 00'S 14‘I "BUIVVeY 10}JV WOIIpuoD ‘ur "bs aed ‘sqy OOOT 3% a ‘ar ‘bs aed "sql 009 # © ($3s9., S,UOSTOO MA ) ‘SWSTad YLHADNOD ANOLSANTT o000‘ZS1 o000‘tzz o00‘00S oo0‘of ‘1: oo0‘coZ 000‘00S ‘z ooo‘ore‘¢ o000‘000'f & “ul ‘bs a aod ‘sq[ 002 + 01g obZ og SPIT z£6 Fiz‘t OIL‘! Loz‘ gost gba'1 eSP‘T LeV't ‘ur ‘bs red "sqy ar yysuer4s eyeUy[(L 00S “Tye soolaap 07 peyeeH AO ALIOILSVTG JO SNTONGOW GNV HLONAULS AAISSHYdNOD DNIMOHS—AIXXX ATAVL 61 61 nn +t” t+ + nN WwW oot t WwW Rm KR OT TT FHM WWD L & 3uyvey oO g Meesyo 4 erojaqg = ™ = é V8 ‘on ueuosdg 7% OS 182 CONCRETE AND REiNFORCED CONCRETE. Table XXXII. gives similar data for limestone cubes. The strength of the limestone cubes approximated that of the trap mixtures. Heating to 500° F., however, gave a great loss oi strength. There were no evidences in the appearances of the cubes to indicate the deterioration. No further weakness resulted at a temperature of 750° F., but beyond this the loss of strength continued. After heating to 2,000° I*. and 2,250° F. the cubes appeared strong and in good condition while hot, but when cold they began to disintegrate, and at the end of a few days were so badly decomposed as to be unfit for testing. Table XX XIII. shows the results of the tests upon trap rock prisms. The values for the modulus of elasticity for the unheated specimens approximate closely results obtained by other investi- gators. As usual, the value of E diminishes with increase of pres- sure. With the heated specimens this is not so marked; in fact, it is often the reverse, particularly with the intermediate loadings. The value of E, however, decreases rapidly, due to the heating. This change is very apparent, even with a temperature of 500° F., and the value gradually decreases with the increase of heat. Table XXXIV. gives the data for limestone prisms. The value of E falls rapidly with the increase of heat applied, the same as for the trap rock mixture. The surfaces of the prisms of both mix- tures were covered with minute cracks after being subjected to ever 750° F. and then cooled. These cracks increased in number and size as the heat became higher, and at 1,500° the prisms be- gan to warp and disintegrate on cooling. This deterioration increased with time, and at the end of 9 days one prism of each mixture was so badly crumbled it was unfit for testing. This dis- integrating effect is probably due to the swelling of the cement as a result of recalcination. The great loss in strength arid elasticity of concrete when sub- jected to severe and continued application of heat would lead to the conclusion that reinforced concrete structures when sub- jected to a severe conflagration will be in danger of being so greatly damaged that it will be necessary to rebuild them as a whole or at the least in part. On the other hand, the high non- conductivity of concrete and its incombustibility make it an ex- cellent fireproofing material, which, under the action of an ordi- nary fire, will remain undamaged and add no fuel to the flames. Effect of Flue Gases and Moisture on Concrete.—Reinforced GENERAL PHYSICAL PROPERTIES. 183 concrete has been extensively used for the construction of chim- neys in the past few years, but very few data are available as to the action of flue gases upon concrete. Mr. Francis T. Haward, of Silberhiitte, Anhalt, Germany, gives the following information in regard to experience at the plant of the Anhaltische Bleiund- Silber-werke, in a paper presented at the Lake Superior meeting of the American Institute of Mining Engineers, in February, 1905: The flues and smaller stacks at the works were constructed of _ concrete consisting generally of 1 part of cement and 7 parts of sand and jigtailings (stone culled from the ore), but when rein- forcement was used a I to 4 mixture was employed. A continued temperature above 212° F. caused the concrete to crack and ultimately fail. Neutral furnace gases at 250° F. passing through an independent concrete flue and stack, caused so much damage by cracking that after two years of use the stack constructed of concrete pipe 4 ins. thick required thorough re- pairing and auxiliary ties for every foog of height. The side of the main flue, made of blocks of 6 in. hollow wall section, about 40 ins. by 20 ins. in area, were covered with 2-in. or I-in. slabs of reinforced concrete. In cases where the flue was protected by a wooden or tiled roof, and inside by an acid- proof paint, consisting of waterglass and asbestos, the concrete was not appreciably affected. In another case, where the protec- tive coat, both inside and outside, was of asphalt only, the con- crete was badly corroded and cracked at the end of three years. In a third case, in-which the concrete was unprotected from both atmospheric influences on the outside and furnace-gases on the inside, the flue was quite destroyed at the end of three years. That portion of the protected, concrete flue near the main stack which came in contact only with dry, cold gases was not affected at all. Gases alone, such as sulphur dioxide, sulphur trioxide and others, do not affect concrete; neither is the usual quantity of moisture in furnace gases sufficient to damage concrete; but should moisture penetrate from the outside of the flue. and, meet- ing gaseous SO, or SO;, form hydrous acids, then the concrete will be injured. Moisture alone does not injure concrete, but moisture mixed with flue gases will cause great damage. It is also stated that soluble salts, noticeably zinc sulphate, when let 184 CONCRETE AND REINFORCED CONCRETE. fall upon concrete, will penetrate it and, by crystallizing, cause the concrete to crack and shell of If a concrete chimney is lined to such a height that the flue gases acting directly upon the concrete do not exceed about 200° F., no danger need be apprehended. The many chimneys of re- inforced concrete now in use would lead one to infer that in a majority of cascs this material is satisfactory. CHAPTER X. THE GENERAL ELASTIC PROPERTIES OF CONCRETE. The strength of concrete varies greatly. This is due to a number of causes, among which the following are the most important: (1) the quality and amount of cement used; (2) the kind, size and strength of the aggregate; (3) the thoroughness with which the ingredients are balanced (the most dense con- crete giving the greatest strength); (4) the method of mixing and the thoroughness with which it is done, and (5) its age. To a certain extent the strength of concrete varies with the amount of water used in mixing, the amount of tamping done in deposit- ing, and the hygrometric state of the atmosphere during setting. The above five items will only be considered as regards thc compressive strength and elasticity of concrete, as concrete is seldom or never used in tension. Tensile Strength.—The ultimate strength of concrete in tension seems to vary in some manner with the richness of the mixture and the age of the specimen, but thus far experimenters have not been able to determine the relations which these quantities bear to each other, nor have they been able to determine any definite elastic limit at a point less than the ultimate strength. Prof. Tal- bot gives the values shown in Table XXXV. for the ultimate tensile strength of a 1: 3:6 concrete.* TABLE XXXV—SHOWING STRENGTH OF CONCRETE IN TENSION. Test Age. Maximum Load. No. Days. Mixture. , Lbs. per sq. in. Remarks. 7 50 1:3:6 178 Bending at start. 3 60 1:3:6 160 Bending throughout. 13 84 1:3:6 170 Bending throughout. 12 87 1:3:0 278 Little bending. The amount of deformation in these specimens varied from 0.00005 to 0.00006 of the length when the piece broke. Prof. Hatt states that his recent tests show the tensile strength of I : 2:4 concrete at 28 days to be about 300 lbs. per sq. in. He also gives the strength of 1 : 2 : 5 concretes, which are tabulated *Bulletin of the University of Minois for September, 1904. 186 CONCRETE AND REINFORCED CONCRETE, in Table XLIX., see page 204. Herr Saunders, in some of his tests, obtained tensile strength ranging from 310 to 450 lbs. per sq. in. for specimens one month old, and from 400 to 510 lbs. for concrete three months old, the proportions xf the material being 1: 2:2 gravel concrete. Tests were made by Prof. Ira H. Woolson, at Columbia Uni- versity, to determine the relative tensile strengths of large test pieces made with full sized stone, and small sized specimens made with sand and with crushed limestone. These tests gave the following results for small specimens of standard briquette size: 7 days. 28 days. Ibs. Ibs. 1 (Ceinent, 3: Sand eranene vv ens a cstals acrnguiie sea ease 6 a6bs 175 249 1 Cement, 3 Crushed Limestone..................20000 345 461 The sand used was a fair grade of moderately sharp sand, and contained less than 1 per cent. of loam. It all passed freely through a %-in. screen. More than 75 per cent. of it would pass a 20-mesh sieve. The limestone was a Hudson River bluestone and all passed a '%-in. screen. The large specimens were 6 x 6 ins. in cross-section and 3 ft. 6 in. long. During testing little or no bending took place, nearly all the specimens breaking within the middle third. The following re- sults were obtained from one series of tests on a I : 2 : 4 crushed limestone mixture. Strength. Days in Mould. Days in Water. Days in Air. Lbs. per sq. in, I 6 21 267 I 6 21 282 I 6 17 238 3 6 24 130 2 7 26 250 2 7 26 cor Average: stretigth) .cccnascemines dy scesa dedi 228 The broken stone for the large specimens all passed a 114-in. screen and remained ‘on a 3£-in. screen. The concrete was care- fully tamped into: the moulds in a moderately wet condition. These experiments would seem to indicate that the tensile strength of a 1:2:4 limestone concrete, made with full-sized stone, is slightly less than that of briquettes made from a 1:3 sand mixture, and about one-half the strength of briquettes made GENERAL ELASTIC PROPERTIES OF CONCRETE. 187 from a 1:3 crushed limestone mixture. Freshly broken stone on the fractured face would seem to indicate that the tensile strength of the concrete was approximately that of the stone. More data on this subject are greatly to be desired. In general, for a 1: 2:4 concrete the ultimate tensile strength for one month may be taken at about 300 lbs., and for three months from 400 to 500 lbs.; for mixtures ranging from I: 2:5 to 1: 3:6, for one month, 150 to 200 lbs., and for three months, from 200 to 350 Ibs. per sq. in. £ “4800 S = sat &.4000}-> Sis 8 ess a S RG <= 3200 N — NI wn 2 re, © 2400 ie x Fa Ne, 5 Pi IN w 1600 sate 2 No ° o as Pre, IN ~ g00 Lo, IN Q =| etek SA £ ~~18 \ 0 i ~n NS Oo 0 4 ES (2 3 45 67 8 9 0 ti 1 144 15 6 V7 Parts of other Materials to 1 of Cement. From Henbys Tests: Fig. 64.—Diagram Showing Effect of Amount of Cement on Compressive Strength. Working Stresses——When concrete is to be used in tension working stresses not greater than from one-fifth to one-sixth of the above values should be employed, giving a working stress of from 30 to 100 lbs. per sq. in., depending upon the age and rich- ness of the mixture. - Effect of Amount of Cement on Gompressive Strength.—The ultimate compressive strength of concrete decreases uniformly as the proportion of cement in the mixture decreases. Fig. 64 is a diagram in which the compressive resistances of Henby’s tests* have been plotted and the results averaged by means of a *Proceedings of Association of Engineering Societies, September, 1900. 188 CONCRETE AND REINFORCED CONCRETE. straight line. This diagram illustrates the relation between the strength and parts of materials to one part of cement, under cer- tain conditions. This is also shown by Rafter’s tests, described on page 193, and shown in Table XLV. The variations in strength of dry and plastic mixtures for different proportions are as follows: Proportions. Comp. Strength. Dry mixture .............. T:1:5 4,659 1:2:6 . 3,686 1:2:7 2,800 Plastic mixture ............ 1:1:4° 4,462 1:2:6 3,400 1227 3,132 Too much credence should not be given these tests in this connection, as different brands of cement were used. Kimball’s and the Watertown Arsenal tests of 1901 and 1904, shown in Tables XXXVI. to XL. and in Table XLIV., should also be consulted in this connection. Effect on cinder concrete is also shown in Table XL. Effect of Variation in Size of Stone.—The variation in ultimate compressive strength due to varying sizes of stone and gravel is shown in Table XXXVI., taken from the Watertown Arsenal Report for 1901. This table shows the ultimate crushing strength of 12-in. cubes. The cement used was Alpha Portland; the other ingredients are shown in the table. TABLE XXXVI—SHOWING CRUSHING STRENGTH OF 12-IN. CUBES. (From Watertown Arsenal Tests, 1901.) Composition. Age. Ult. Resist. in Cement. Sand. Broken Stone. Years. Months. Lbs. per sq. in. 1 2 4 %-in. Trap. I ih 3,187 I 3 Go o I 2,070 I 4 3 I 1,499 I 5 10 “ “ I 949 I 6 iz ~ I ac 791 I 2 4 1% and 2%-in. Trap 2 ais 2,789 I 2 41 and 2%-in. Trap 2 2,549 I 2 4 2%-in. Trap 2 ya 2,466 I 2 a + I 2 2,406 I 2 4 1% to 3-in. Pebbles. I 2 3,580 Table XXXVII., taken from the same report, shows the ulti- mate crushing strength of 6 x 6 x 36-in. prisms with an average age of 33 days: GENERAL ELASTIC PROPERTIES OF CONCRETE. 189 TABLE XXXVII—CRUSHING STRENGTH OF 6 x 6 x 36-IN. PRISMS. (From Watertown Arsenal Tests, 1901.) Number of Ult. Crushing Specimens Strength in Cement. Sand. Stone. Tested. Lbs. per. sq. in. I au 4 %-in. to 2-in. diam. Pebbles. 8 2,326 I 2% 4 %-in. to 2%4-in. diam. Gravel. 6 3,363 I 2% 4 I-in. to 2%4-in. diam. Hard 6 3,886 Trap Rock. Table XX XVIII. shows the effect of the variation in size of stone and gravel for a 1:1:3 mixture, the cement used being Alpha brand. Later tests, shown in Tables XXXIX. and XL., give the variations in strength from extremely rich to as lean mix- tures as are used in concrete work. These latter tables are taken from a table of tests made in the Watertown Arsenal in 1904. These tests show the effect of varying the sizes of the stone and gravel. TABLE XXXVIII—EFFECT OF SIZE OF STONE ON STRENGTH OF CONCRETE. (From Watertown Arsenal Tests, 1898.) 12-inch Cubes 1:1:3 Alpha Cement. Coefficient of Elasticity— -—Compressive Strength in— _ in lbs. per sq. inch. Be- Size and kind of Aggregate. lbs. per sq. in. at age in days. Swen loads of 100 and 8. per sq. in. 7-8 19-23 29-34 61-76 Aboutlmo. About2mos. ¥-in. trap rock bagi oe 1,391 2,220 2,800 5,021 3,571,000 4,167,000 %4-i cing “eee ees 1,900 2,769 3,200 .... 8,333,000 ........ I -in. “ wax bbb se s's 3,390 4,254 4,917 5,272* 6,250,000 8,333,000 r%-in. “ OD sean ephaais uc8 3180 4,006. 4,562 2,583 vareies «ex wainrs 2%-in. “ So attenencmeensas 2,400 4,143 4,140 4,523 5,000,000 12,500,000 1 oo ce “ al Pim e ea y 2800 3,786 4,340 4,544* 8,333,000 6,250,000 Yin, “ “1 part ) * 1 -in. “ “I part 2,800 4,156 4,800 5,542* 8,333,000 8,333,000 2\%e-in. “ or Mean strength trap rock.. 2,553 3,619 4,110 4,581 Gravel, ito. aaa eae 1,208 2,600 2,992 3,870 4,167,000 3,125,000 MS GUBANY scuaaives SER E% 2,276 3,186 3,817 4,018 4,167,000 2,778,000 “ ae bed J wu yagimy BRAT "Ty 11994 3,023 3.800 3,490 4,167,000 5,000,000 e Y%-in., I part “ 8-in., I part ~ .. 1,486 2,676 3,000 3,800 3,125,000 3,125,000 « yW-in., I part ) Mean strength gravel...... 1,764 2,871 3,402 3,704 *Not fractured. 190 CONCRETE AND REINFORCED CONCRETE. TABLE XXXIX—SHOWING EFFECT OF SIZE OF STONE ON STRENGTH OF CONCRETE. (From Watertown Arsenal Tests, 1904.) Average age, 173 days. -Mixture-——— Compressive Strength. Cement. Sand. Gravel. }-in. Trap. 2}-in. Trap. 4-in. Gravel. %-in. Gravel. i , I 6,400 hs eke I ae I sdgias 4,800 ae I ie I Rien er 4,360 I we I eae 4,200 seers I I 2 4,180 2,200 2,600 I 2 3 3,700 1,680 2,060 I 2 4 1,480 1,210 1,700 I 3 6 1,410 790 580 Table XXXIX. also shows comparative strength of stone and gravel conercte. TABLE XL.—SHOWING STRENGTH OF CINDER CONCRETE (From Watertown Arsenal Tests, 1904.) Mixture- Age Strength Percentage Cement. Sand. Cinders. in Days. in Lbs. of Water. I As I 174 2,930 35. I I 2 171 2,200 20.2 I 2 3 17I 1,400 43.8 I 2 4 171 800 57.1 I 3 6 I7I 740 80.0 It should be noted that a very high percentage of water is needed in mixing cinder concrete. Thus we see, if the ratio of cement to the aggregate remains constant, a variation in the size of stone used may give a different balancing of the mixture and directly affect the ultimate crushing strength. Effect of Mixing.—The effect on the strength of concrete due to the thoroughness in mixing may to some extent be understood by referring to page 70, where hand vs. machine mixing is discussed. Effect of Amount of Water.—In the past, considerable difference cf opinion has been held by engineers regarding tte amount of water that should be used in mixing mortars and concretes. Some years ago it was considered that concrete should be mixed dry and thoroughly tamped to secure the best results. At the present time, however, it is almost universally conceded that wet concretes possess practically as great if not greater strength than dry concretes. The saving in labor for tamping when wet mix- tures are used is a very important item in the cost of construction. This alone, even if considerable less strength results, would com- pel the use of wet concretes. The greater ease with which wet GENERAL ELASTIC PROPERTIES OF CONCRETE. ial suxtures are placed in reinforced concrete work, and the greater assurance that the metal will be thoroughly surrounded in ali cases, also make the use of wet mixtures almost imperative. Tests on mortars almost invariably show a reduction in strength with. the increase in the percentage of water used. T. S. Clark gives the following evidence in Table XLI.: TABLE XLI—EFFECT OF PERCENTAGE OF WATER ON STRENGTH OF MORTAR BRICUETTES. Average tensile Average tensile Age Percentage strength Age Percentage strength indays. ofwater. Ibs. per sq. in. indays. ofwater. lbs. per sq. in. 7 18 722. 23 18 684 7 20 680 23 20 762 7 22 638 28 23% 809 The effect of different percentages of water cn neat cement and mortar briquettes is also shown in Table XLII., taken from the report of Chief Engineer U.S. Army, 18098: TABLE XLII—EFFECT OF VARYING PROPORTIONS OF WATER. (From Report Chief Engr. U. S. Army, 1898.) Mortar, Water, -Streneth———_———" Proportions. Per cent. 7 Days. 28 Days. 6 Months. Neat 18.66 715 728 Neat 20.83 602 681 Tat 13.31 492 639 I: 15.00 384 624 122 12.00 330 525 a 1:2 12.37 288 470 1:3 11.00 229 385 1:3 12.50 182 312 se 1:3 7.36 250 308 371 1:33 8.25 271 321 437 133 12.50 168 242 343 The results of a series of tests made by J. W. Sussex, and pub- lished in the “Technograph” of the University of Illinois, 1903, are shown in Table XLII]. These tests were made on a concrete mixture composed of 1 part Portland cement, 3 parts sand, 6 parts crushed limestone. Forty-five (45) 6-in. cubes, mixed with three different percentages of water, were broken at the end of 7 days, 1 and 3 months. Two different degrees of tamping were also employed. Each result shown is an average of three tests. As will be seen, the wet concretes at the end of 3 months fur- nish the greatest ultimate resistance, although at the earlier periods the medium concretes gave higher results. The effect of tamping does not materially modify the relative strength as 92 CONCRETE AND REINFORCED CONCRETE. « affected by the degree of wetness. Rafter’s tests should also pe consulted in this connection. TABLE XLIIL—EFFECT OF VARYING PERCENTAGE OF WATER ON 1:3:6 CONCRETE CUBES. (Tests made by J. W. Sussex.) ; Crushing Strength in lbs. per sq. in-————> Dry, 6% water. Medium, 7.8% water. Wet, 9.4% water. Lightly Heavily Lightly Heavily Age. tamped. " tamped. tamped. tamped. 7 Gays vicciean 1,200 1,340 2,280 1,330 1,040 I month ...... 1,750 1,960 2,290 2,500 2,230 3 months ..... 2,500 2,600 2,150 2,590 3,040 Effect of Age-——The amount of increase in strength of concrete from 7 days to 6 months is shown in Table XLIV., which is taken from tests made by George A. Kimball on 12-in. cubes at Watertown Arsenal in 1899. TABLE XLIV.—SHOWING INCREASE OF STRENGTH WITH AGE. (From Kimball’s Tests.) Crushing Strength in lbs. per sq. in. Mixture. 7 Days. 1 Month. 3 Months. 6 Months. 1: ; 2 1,600 2,750 3,360 4,300 I: 1,525 2,460 2,944 3,900 I ai; 5 1,300 2,225 2,670 3,400 Ls 1,230 2,060 2,440 3,100 I 3, 7 1,100 1,875 2,210 2,800 1:4:8 1,000 1,700 1,980 2,500 1:25:10 800 1,350 1,520 1,900 1:6:12 600 1,000 1,060° 1,300 Table NLIII. should also be consulted in this connection. The average of Kimball’s tests, which were carefully made, would indicate a compressive strength for 1: 2: 4 concrete of 2,400 Ibs. at 1 month, 3,000 Ibs. at 3 months and nearly 4,000 lbs. at 6 months; and for 1: 3:6 concrete, 2,000 lbs. at 1 month, 2,400 Ibs. at 3 months and 3,000 lbs. at 6 months. From Kimball's tests Mr. Thacher has deduced formulas for the ultimate strength of concretes. These formulas give results which agree very well with the experiments, and may be used for obtaining the strength of concretes carefully made from good materials. Thacher’s Formulas—The ultimate strength in pounds per square inch of concrete: Volume of Sand 7 days old = 1,800 — 200 aes ee Volume of Cement 1 month old = 3,100 — 350 ) 3 months old = 3,820 — 460 ) 6 oe be 4,400 <5 600 : oe ) GENERAL ELASTIC PROPERTIES OF CONCRETE. 193 In addition to the tests already given, a series of tests made by Prof. Woolson, at Columbia University, deserves mention. A 1:2:4 concrete made from crushed limestone and tested at 30 days, gave an average of 2,450 Ibs. per sq. in. These tests agree quite well with those already given. Details of a number of these tests are given on page 207. It should be noticed that according to Mr. Thacher’s formulas the strength of concrete depends upon the ratio of the volume of sand to the volume of cement. A number of authorities hold that this ratio, rather than the ratio of aggregate to cement, correctly determines the variation in strength of concretes. If the aggre- gate be of good, clean material, so graded as to sizes that there will be a minimum of voids, the strength can be safely said to de- pend upon the richness of the mortar used, provided an excess of mortar over the remaining voids be used, always bearing in mind that it is practically impossible to fill all voids. The amount of mortar necessary to, fill the voids, and therefore the ratio of ce- ment to total aggregates, thus finally determines the strength. Finally, we must conclude that with a well balanced mixture, 1. e., where the voids are a minimum, the strength will depend upon the richness of the cementing material or the ratio of sand to cement, but under ordinary conditions it is safest to consider that the strength depends upon the ratio of aggregates to the cement. Rafter’s Tests—Probably the most exhaustive tests made on concrete in this country were conducted by George W. Rafter end recorded in the Report of the State Engineer of New York for 1897. Compressive tests were made on 544 12-in. cubes whose age at the time of testing averaged about 600 days. The concrete was prepared in three different ways: (1) in dry blocks in which the mortar was only a little more moist than damp earth, (2) in plastic blocks, the mortar of which was of the con- sistency of that used by masons, and (3) in blocks having-an excess, of water, so that the mortar quaked like liver when moder- ately rammed. Specimens of each batch were prepared and stored differently. ‘One block was placed in water for about 4 ’ months and then buried in sand until shipped to Watertown Arsenal for testing. The second stood in a cool cellar until shipment. The third block was exposed to the weather, and the fourth block was covered with burlap and wet with water several times a day for about three months, and then exposed to the 194 CONCRETE AND REINFORCED CONCRETE. weather until the day of shipment. Portland cement was used. The aggregate was a hard, broken sandstone. A careful examination of the results of the tests shows a great uniformity between the blocks of different groups, the method of storage not seeming to affect the strength of the concrete. The dry mixtures show a slight increase in strength over the wet, but it is not of much importance, and in practice the additional cost of tamping dry concrete would more than offset the gain of strength secured thereby. Another deduction from these tests is that the strength of the concrete increases with the richness of the mortar. Some of these tests are shown in Table XLV. TABLE XLV.—RAFTER’S TESTS OF 12-IN. CONCRETE CUBES. Ultimate ——— Modulus of Elasticity Brand of Approximate Consis- Strength 100-600 100-1,000 1,000-2,000 Cement. Proportions. tency. Ibs. per. sq. in. Ibs. ibs. Ibs. Genesee TSG Dry 4,059 3,571,000 2,812,000 1,667,000 Wayland 1:1:4 Plastic 4,462 4,167,000 2,500,000 1,219,000 Wayland = 1:2:6 Dry 3,686 2,083,000 1,875,000 I,II1,000 Ironclad 1:2:6 Dry 4,000 3,125,000 3,000,000 2,000,000 Champion 1:2:6 Dry 2,598 3,125,000 2,812,000 1,398,000 Champion 1:2:6 Plastic 2,400 2,500,000 2,143,000 1,163,000 Ironclad T2280 Plastic 3,000 3,571,000 3,000,000 2,000,000 Genesee 1 :2:6 Plastic 3,400 3,125,000 2,812,000 1,667,000 Empire 1:2:6 Excess 2,950 2,500,000 2,045,000 1,163,000 Ironclad £22:6 Excess 3,436 3,125,000 2,812,000 1,471,000 Champion 1:2:7 Dry 2,800 3,125,000 2,812,000 1,724,000 Tronclad 1227 Dry 3,283 2,500,000 2,368,000 1,282,000 Wayland = 1:2:7 Plastic 3,132 2,778,000 2,250,000 1,429,000 Empire 1257 Excess 3,400 3,571,000 2,647,000 1,250,000 Elastic Limit.—Concrete in compression has a fairly well de- fined point of elastic limit. This has been given as a little more than one-half of the ultimate strength. Henby, in the tests men- tioned above, places the elastic limit at two-thirds of the ultimate strength. The limit is probably somewhere between these points and the ultimate strength. Working Stresses—The proper working stress to be used in reinforced concrete work depends upon the character of the struc- ture; the nature of the stress, i. c., whether it is a direct or bend- ing stress; whether the load is a dead or a live load; whether it acts directly or through the médium of some inert material, and lastly upon the richness and age of the concrete. No fixed rule can be given for selecting the unit working stress, as each struc- ture is a problem requiring separate treatment by the engineer. The following values for factors of safety will give conservative working stresses and lead to safe designs: GENERAL ELASTIC PROPERTIES OF CONCRETE. 195 A factor of safety of 5 or 6 should usually be chosen for con- crete having an age of 3 months, although under exceptional con- ditions, with uniform loads, and when there is no vibration or impact, as low a factor as 4 is sometimes used. These factors are to be used’ with the proper ultimate strength for the given mixtures, as determined by Mr. Thacher’s formula, or chosen from some one of the tables cited. It is probable that the full load will be brought upon the given structure at the end of 3 months, and it is often desirable if not necessary that it shall be supported at the end of 1 month or 6 weeks. Any additional strength after 3 months may be neglected, as the critical period ot straining will then be past. If we assume a 1: 2:4 concrete having a strength of 3,000 Ibs. at 3 months, and 2,400 lbs. at 1 month, and use a factor of 6 at 3 months, we will have a working stress of 500 lbs. at 3 monthis and a factor of safety of 4.8 at the end of 1 month. In like man- ner, for a factor of 5 at 3 months, we have at that age a working stress of 600 lbs. and a factor of safety of 4 at 1 month. If the factor at 3 months be 4, the working stress will be 750 lbs., and the factor of safety at 1 month will be 3.2. In like manner, a 1: 3:6 concrete having an ultimate strength of, say, 2,400 lbs. and 2,000 lbs. at 3 months and 1 month, respectively, will give for a factor of safety of 6 a working stress of 400 lbs. at 3 months and a factor of 5 at 1 month. For a factor of safety of 5, a stress of 480 lbs. at 3 months and a factor of 4.2 at I month, and for a factor of 4, a stress of 600 lbs. at 3 months and 3.3 for a factor of safety at 1 month. Under normal conditions these factors will give ample strength. The manner in which the concrete is subjected to compression modifies somewhat the working values which should be used. The abave values may be employed for compression under bend- ing. For concrete used in direct compression, as in columns, values of about 80 per cent. of the above should be employed. Cinder Concrete.—For roof slabs and floors of buildings, and in other situations where light weight is desired, cinder concrete is sometimes used. The strength of cinder concrete is considerably less than that of stone concrete. Tables XL. and XLVI. give the results of a number of tests made at Watertown Arsenal for the Eastern Expanded Metal Co., of Boston, and show the average of a number of tests. Steam cinders were used, practi- 196 CONCRETE AND REINFORCED CONCRETE. cally as they came from the furnace, the large clinkers being broken up. Table XLVII. from Watertown Arsenal tests of 1903 and 1904 gives more recent tests on cinder concrete. Thece values appear to be somewhat high. Table LVI. shows the compressive strength of cinder con- cretes, age 30 and 60 days, of three different proportions, together with their coefficients of elasticity. These are taken from Henby’s tests, and each value represents the average of a number of tests. Table LV. also gives compression strengths for cinder concrete of different proportions. From the above tests we may infer that the strength of good cinder concrete is about 0.4 that of stone concrete. The strength of cinder con- crete is, however, much more variable than that of stone con- crete. “hus, for a I: 1:3 concrete, a-mixture frequently used for reinforced concrete floors, the strength, as shown by Tables TABLE XLVI—COMPRESSIVE STRENGTH OF 12-IN. CUBES OF CINDER CONCRETE. (Watertown Arsenal Tests.) Mixture. Average cur Bressivé Strength, Brand of cement. lbs. per sq. in. Agelmonth. Age 3 months. Germania Portland......... I:1:3 1,466 2,001 ES causa a nyo 1223 1,098 1,634 - oe 1:2:4 904 1,325 - Ce L285 769 1,084 7 SD Shadiiateat eee 1:3:6 529 788 Alpha Portland............ 1:1:3 2,329 2,834 7 A «ah gg haceeeacet 1:2:5 940 1,600 Atlas Portland............. Vsi33 1,601 2,414 = BE mieten aA punts T:2:5 696 1,223 TABLE XLVII—COMPRESSIVE TESTS ON CINDER CONCRETE CUBES. (Watertown Arsenal Reports of 1903 and 1904.) -—— Proportions c Age 7 Cement. Sand. Cinder. 38 days. 224 days. 1 year 3} months. U 2 4 1,950 Sahat 2,440 I 2 4 2,050 siege 2,490 I 2 4 seeds 2,600 2,610 I 2 4 Lays 2,500 2,410 I at 5 1,400 er 1,950 I 2y 5 1,400 esits's 1,630 I 2s 5 mes 1,980 1,480 I 2s 5 mee 2,020 1,740 34 days. 220 days. I 3 6 1,200 1,730 1,400 I 3 6 1,330 1,560 1,380 i 3 6 oma oe 1,290 T 3 6 1,380 GENERAL ELASTIC PROPERTIES OF CONCRETE. 197 XLVI. and LV., varies from 2,001 to 2,834 Ibs., while for a 1:2:5 concrete, also a common mixture, it varies from 1,200 to 1,715 Ibs. The uncertain strength of cinder concrete, and the slovenly manner in which it is usually pre- pared, make a high factor of safety imperative in determin- ing working values for this material. Factors as high as from 6 to 10 should be used. These will give working stresses of from 100 to 400 Ibs. per sq. in., depending upon the age, nature and richness of the mixture. Transverse Strength of Concrete.—The tensile strength of con- crete at the place of greatest strain, that is, at the fibre most re- mote from the neutral axis, limits the strength of unreinforced concrete beams. The value of this transverse strength is of little importance, because, on account of the brittleness of concrete in tension, its liability to crack from shrinkage or the shock of some ef the applied loads, it is unsafe to depend upon the tensile strength of concrete for the construction of slabs, beams or girders. For the same reason, it is now common practice to dis- regard in the design of reinforced concrete beams the tensile strength of the concrete. Under certain conditions, however, it may be necessary to take the strength of concrete in tension into consideration, as in the case of a foundation to be placed under water, when it is necessary to absolutely insure the protection of the metal from any possible contact with water. Under such con- ditions, stress in the steel and the resulting deformation should be kept so low that no perceptible cracks will result in the concrete, always retaining the proper ratio between the modulae of elas- ticity of the two materials. Sabin states that the ratio of the transverse to the tensile strength of concrete varies from 1.25 to 1.90 for Portland, and . from 0.95 to 2.19 for natural cement concrete. Shearing Strength of Concrete—The subject of shearing strength of concrete needs careful experimental study. The fol- lowing facts are gleaned from the little knowledge on the subject available: M. Mesager, Director of the School of Bridges and Roads, Paris, gives as a result of his experiments the shearing strength ef concrete at from 1.2 to 1.3 times its tensile strength. This agrees very well with the researches of Herr Bauschinger, whe states that the shearing strength of concrete 4 months old is 1.25, 198 CONCRETE AND REINFORCED CONCRETE. and at 2 years 1.5 times its tensile strength. M. Feret, Director of the Laboratory of Bridges and Roads at Boulogne, has stud- ied the shearing strength of concrete, and concludes that the ultimate shearing strength is proportional to the compressive strength, and gives its value at from 16 to 20 per cent. of its com- pressive strength. His results do not differ materially from those already given. All other results hitherto available agree well with those just stated. Details of the method of conducting the above.tests are not available. It is probable, however, that the specimens were subjected to more or less bending, hence the low values obtained are more nearly tension values, as what were taken as shearing failures were really diagonal tension failures. ‘Prof. Arthur N. Talbot states, in Bulletin No. 4 of the University of Illinois, that from tests made at the University of Illinois and elsewhere it is probable that the shearing strength of concrete is from 50 to 75 per cent. of its compressive strength. Massachusetts Institute of Technology Tests.—Series of tests have been conducted at the Massachusetts Institute of Tech- nology. The 1904 and 1905 tests were conducted by Prof. Charles M. Spofford, and the 1906 tests by Prof. F. P. McKib- ben, the tests being under the general direction of Prof. Swain, Frofessor of Civil Engineering. The author is indebted to Professors Swain and Spofford for details of these tests. The test specimens were 5 ins. in diameter by 15% ins. in length, and in testing were firmly held in cylindrical bearings 5% ins. apart. The load was applied from above through a half cylinder bearing 5‘/,, ins. in length, so as to eliminate bending as far as possible. Tests were made on specimens which had set in air and on others which had set in water. The latter specimens set in air for 24 hours before being placed in water, while the air set specimens were sprinkled for six days after being removed from the moulds. The specimens were made from a cement composed of a mixture of several standard brands of Portland cement, a sand composed of equal volumes of Plum Island and Ipswich sands, and of a stone com- posed of a mixture of one volume of '%4-in. and two volumes of 1%4-in. Waltham trap rock. Roxbury pudding stone instead of Waltham trap rock was used for the 1904 specimens. The mixing was done in small batches and with great care. Crush- GENERAL ELASTIC PROPERTIES OF CONCRETE. 199 ing tests were made on 6-in. cubes. The values obtained for the 1904 and 1905 tests are as follows: I 1904. tf 1905. — Compressive Compressive Age. strength, Age. strength, days. Ibs.persq.in. days. lbs. per sq. in. I 2.457 30 2,070 i: 1,225 30 1,355 Es 1,104 27 1,275 A summary of the results of the tests for shearing strength is shown in Table XLVIII., together with the ratio of air set to water set specimens. As will be noted, there is consider- able variation in the shearing strength of the weaker speci- mens. By comparing the shearing values here given with the compressive values given in the preceding table, it would appear that the shearing strengths are slightly greater than 50 per cent. of the compressive strength. TABLE XLVIJI—SHEARING STRENGTH OF CONCRETE. Air set Manr-r_ Results, Results, Results, —— = Mixture. of set. 1904. 1905. 1906. Av. Water set PPB deans s8 Water. 1,192 1,649 1,397 1,427 \ 684 12 AD cacaieine Air. 973 1,314 1,200 1,192 : To BY Giecneaes Water. afials soci 879 begs | 0.89 To BY 2 Sesceas ae Sean, dectsaa 780 io . T. 3 Ara ara s ater. 579 1,121 ieee 50 Ts : ; os sect Air. 541 1,236 eons 889 } aod : Poe BE Obs a cio.sess Water. 599 1,123 701 808 } 108 3. SO isesueis Air. 629 1,185 615 808 : Sate Working Values for Shearing.-—Christophe, in Béton Armé, gives as safe working values from 14 to 35 lbs. per sq. in. These are somewhat lower values than are used in this country, values of from 40 to 75 lbs. being usually allowed. Of course, the richness and age of the concrete must be taken into account in choosing the working strength for shear. When shearing stresses greater than the above assumed values are met with in reinforced concrete work, special provisions, as by the use of stirrups, must be had recourse to. Modulus of Elasticity —The coefficient or modulus of elasticity of a material for tension, compression or shear is the ratio of the unit stress to the unit deformation, provided the elastic limit of the material be not exceeded. This coefficient is usually denoted by 200 CONCRETE AND REINFORCED CONCRETE. in which expression f designates the unit stress and ¢ the unit deformation. The stress-strain relation throughout the entire range of stress may be clearly shown by means of a diagram in which the stresses in pounds per square inch are plotted as ordinates, and the deformation per inch as abscissas. This will be understood by referring to Fig. 65. Thus the curve B will be found to pass through the line representing a compressive stress of 1,200 lbs. per sq. in. near its intersection with the de- formation line marked 5, which represents a decrease in length per inch of specimen of 0.0005 ins. The coefficient of elasticity of concrete is not a practically con- per in Lbs § a 1200 1100 3 S S Cylindrical Specie 300 ‘ of Neat Cement 800 Height 384 Inches Diameter 9.8 /11thes 89 Days Od Freoorted by Lach. 3 S Compressive Stress > = 2 nn S = Decrease in Length per Inch,of Specimen in .000! Inches. Fig. 65.—Elastic Deformation Curve. stant quanuity, like that for iron or steel, but for a given concrete has a value which varies with the load. As in some other ma- terials, it has been found that concrete takes permanent sets un- der very light loads. This involves a slight modification in calcu- lating the true value for the coefficient of elasticity, as these sets must be deducted from the total deformation under gradually increasing loads to obtain the true elastic deformation. To ob- GENERAL ELASTIC PROPERTIES OF CONCRETE. 201 tain accurate results, the load must be applied and removed until no further permanent sef can be observed when a loading is applied and removed. The total permanent set noted is then de- ducted from the total deformation observed for the maximum loading used in the given experiment to obtain the true elastic shortening. Figure 65 shows this method of determining the elastic deformation. Three curves are shown, curve marked A showing the per- manent strains or deformation, curve B the total strains, and curve C the true curve of elastic strains. The latter curve is cbtained by subtracting the amount of permanent set shown in curve A from the total strains as shown in curve B. Many engineers do not take the permanent set into account in computing the coefficient of elasticity of concrete. Curve B will represent the coefficient when thus considered, and may be rep- resented’ analytically by the expression f E= — € Prof. Bach, of Stuttgart, who has made the most elaborate re- searches thus far undertaken to determine the coefficient of elasticity of concrete, thinks the true curve of elastic strain may be expressed by an algebraic equation having the form of n being a numerical coefficient usually considered as having a value of 1 up to the elastic limit, as the curve is represented by a straight line up to that point. One of the usual methods of calculating E is by determining what might be called the instantaneous value of the coefficient cf elasticity. This is done by finding the elastic strain occurring ‘hetween any two applied loads and assuming that the curve is a straight line between two such points of loading. There results no appreciable error if the points chosen are sufficiently near to- gether. The following computation shows a usual method of computing the modulus of elasticity: Let E = the modulus of elasticity. P = total load in nounds. 202 CONCRETE AND REINFORCED CONCRETE. A = area of cross-section of test piece. ; ’ 1 = length of specimen in inches throughout which the deiormation is uniform. : \ = deformation in inches in the length, 1. Xr e = unit deformation = —. P f = unit stress = —. A unit stress f P r Pl But E = = — = FS unit deformation € A 1 Aad Let us assume a given test from which we have the following data : Concrete 1:2:4, age 3 months. Sectional area of test piece = 150 square inches. Gage length of test piece = 5 inches. Initial load, 15,000 Ibs., gives 100 lbs. stress with o compression and 0 set. Applied load of 90,000 Ibs. gives 600 lbs. per square inch stress with a total compression of .00093 inches and a set of .00030 inches. Then we have 1 =5 and — = 600 — 100 = 500. A X = .00093 — .00030 = .00063. and P 1 500 X 5 ES Kk = 3,968,000 Ibs. per square inch. A AN .00063 In eliminating the inelastic deformations, Prof. Bach removed the loading at least five times, and sometimes more. Such a com- plete elimination of set is probably not obtained in actual. struc- tures. In the “Watertown Arsenal Tests’? the usual method is to determine the total deformation and permanent set from no load to the ultimate strength. The increments of load are 100 Ibs. per sq. in. up to 1.000 Ibs., and from that point 200 Ibs. per sq. in. For each recorded load the total compression was read, the load removed and set measured, the load repeated and in- creased to the next higher one, and so on. It is probable that results determined from these tests are more nearly equivalent te those existing in actual structures than those obtained by Prof. Bach. Numerous experiments differing greatly among themselves have been made to determine the coefficient of elasticity of con- crete, both in tension and compression. Falk’s “Cements, Mortars and Concretes” contains a review of many of the later experi- ments. Still later ones may be found described in recent numbers GENERAL ELASTIC PROPERTIES OF CONCRETE. 203 of the “Engineering News” and “Engineering Record.” We will give the results deduced from the later experiments. This will enable the student to obtain briefly some knowledge of the best known facts and principles in regard to concrete. Experi- mental data of the proper character are not available for a thorough understanding of all the properties of reinforced con- crete. The subject has been taken up for exhaustive study by a Special Committee of the American Society of Civil Engineers. Tests will be made along definite lines and conducted in a uni- fcrm manner, and undoubtedly when the results are available a much more thorough understanding of the subject will be pos- sible. Effect of the Density of Concrete and the Amount of Water Used in Mixing, on Coefficient of Elasticity.—Considére found that the amount of water used in mixing the concrete had con- siderable influence on the coefficient of elasticity, its value dimin- ishing when an excess of water is used. Insufficient tamping also causes a decrease in the value of the coefficient, and in gen- eral increasing the density of a concrete tends to increase the ° value of the coefficient of elasticity. Coefficient of Elasticity of Concrete Under Tension.—The elastic behavior of concrete under tensile stresses is more variable than that under compression. There seems much difference of opinion among different experimenters in regard to the form of the curve of elastic deformation under tensile stresses. Some hold that the variations of the coefficient of elasticity in tension may be neglected by reason of its comparative smallness, and that: there is no point which can be taken as the limiting stzvess. Others hold that for small stresses the coefficient is practically invariable, but for larger ones the increments of elongation are great, and the shape of the elastic curve becomes very flat. It is reasonable tc suppose that if the tensile strength varies greatly the deforma- tions will be variable also. In his earlier tests Prof. Hatt made deductions which caused him to believe that the coefficient of elasticity in tension varied somewhat from the coefficient of elasticity in compression, but from a careful study of more recent tests he concludes that the two coefficients are practically equal. This agrees very well with other late experiments, and for all practical purposes may be thus considered. Table XLIX. gives the average of 37 com- 204 CONCRETE AND REINFORCED CONCRETE. pression and 27 tension tests, made by Prof. Hatt.* The broken stone was limestone, being crusher run below 1 in., and ' the gravel was pit gravel, including sand and pebbles. TABLE XLIX.—MODULI OF ELASTICITY. (Prof. Hatt’s Tests.) ‘Kind of Concrete 7 Cement. Sand, Broken Gravel, Are, Cgmpression fension > Ultimate Strength I 2 5 Pe 90 4,610,000 5,460,000 2,413 359 I 2 5 if 28 3,350,000 3,800,000 2,290 237 T re oo 5 90. 4,800,000 4,510,000 2,804 290 I 5 28 4,130,000 4,320,000 2,400 253 Table L. gives the moduli of elasticity for a number of tests made on large concrete specimens in tension by Prof. Woolson, at Columbia University. The specimens were made froin full sized stone and were broken at about 30 days. For further particulars in regard to these tests see page 207. M. De Joly states as a result of experiments made by him that no definite’ point could be determined for the elastic limit, but that it seemed to be very near the point of rupture for neat ce- ment specimens, and that it never fell below three-fourths of the ultimate resistance for mortars or concretes. TABLE L—MODULI OF ELASTICITY (E) FOR TENSION: (Woolson’s Tests.) 1:2:4 concrete. Specimens 6 x 6 ins. (Elastic Curve = Deformation Curve Minus Set Curve.) Crushed Limestone and Broken Limestone. Test E at 28 lbs. per E at 83 lbs. per E at 135 lbs. per Breaking Load. No. sq. inch. sq. inch. sq. inch. lbs. per sq. in. 3012 5,700,000 4,670,000 5,140,000 186 3013 5,170,000 4,085,000 4,310,000 I5I 3014 6,410,000 5,130,000 4,670,000 - 150 3015 5,170,000 3,610,000 4,010,000 158 3064 4,660,000 4,050,000 4,011,000 204 Average. .5,422,000 4,309,000 4,428,200 170 Sand and Broken Limestone. Test E at 28 lbs. per E at 83 lbs. per E at 135 lbs. per Breaking Load, No. sq. inch. _sq. inch. sq. inch. Ibs. per sq. in. 3067 4,790,000 4,790,000 4,790,000 153 3068 4,420,000 3,975,000 3,680,000 176 3069 6,275,000 4,710,000 4,400,000 153 Average. .5,161,700 4,491,700 4,290,990 161 *The Journal of Western Society of Engineers, June, 1904, page 234, GENERAL ELASTIC PROPERTIES OF CONCRETE. 205 The coefficient appears to increase with the ultimate strength of the material, but no definite relation between them has thus far been determined. Coefficient of Elasticity in Compression.—The coefficient of elas- ticity increases with the age of the concrete up to about three months. Beyond this time any additional increase may be neg- lected. Table LI., from Kimball’s tests, made at Watertown Arsenal in 1899, will give an idea of this increase. TABLE LI. (Kimball's Tests on 12-inch Cubes.) — Composition— : 5 ie Modulus of eae Meepes loads, per~ Seoresie ne i 5 4 Be A ait An BB aterm I 2 4 = 7 days. 2,593,000 = 2,054,000 11,351,000 1,730. I 2 4 I mo. 2,662,000 2,445,000 1,462,000 2,567 I 2 4 3 mos. 3,671,000 3,170,000 2,158,000 2,075 I 2 4 6 mos. 3,646,000 3,567,000 . 2,582,000 3,989 I 3 6 7 days. 1,869,c00. ~—«*1,530,000Sti«. ... 1,511 I 3 6 I mo.. 2,438,000 2,135,000 I,219,000- = 2,260 I 3 6 3. mos. 2,976,000 2,656,000 1,805,000 2,741 I 3 6 6 mos. 3,608,000 3,503,000 1,868,000 3,008 I 6 12 I mo. TG70,000! (iaumaant’ Lseeneiedere 1,146 I 6 12 3 mos. 1,642,000 1,364,000. ........ 1,359 I 6 12 6 mos. 1,820,000 1,522,000... . ss 1,592, Portland cement, bank sand and broken conglomerate stone. The coefficient of elasticity decreases as the unit stress in- creases. All of the most reliable tests show this decrease, and it ‘should be taken into consideration when designing concrete structures. The nature and amount of this decrease will be understood from a study of Table XLV., page 194, from the Watertown Arsenal: Report of Rafter’s Tests, 1898-9. Table LI., from Kimball’s Tests, also shows the decrease in strength ‘between the limits of loading given. Table LII. gives more recent tests, made at Watertown Ar- senal in 1904. The decrease in the value of the coefficient of elasticity here shown corroborates that given in. other tests. Prof. Ira H. Woolson made a series of experiments at Colum- hia University for the Astoria Light, Heat & Power Co., to de- termine the strength of concrete made of full-sized stone under erdinary working conditions. While making these experiments an effort was made to determine the elastic properties of the con- crete, both in tension and compression. An electric contact extensometer was employed for determin- CONCRETE AND REINFORCED CONCRETE. 206 Pease pietaaes o00‘00z‘T ogs ool o0g ‘PARIZ “UI-8% 9 e I Lz ee 000‘got‘z ees ood‘t IZ1 ozP ‘PRARIZ “Ul-8% v z I gz oo0‘org‘I O00'LS8'S tt ogo‘. o£1 SLE “PPAeIS “UL-Bh ec z I sz ooo'e ez OooZzZ'~2 tt 009‘z oL1 fee "PPATIS “UL-Sh z I I bz WERE 000‘160‘I obZ O41 00g “saapuld 9 £ I fz Taine eatin : o000'Z IFT cog IZ1 uZS ‘sIapulo v z I zz o00‘6zF'1 epee ran oor't IZ1 ger *sapuls £ z I Iz 000‘oor‘z ee 002% ZI z6z ‘stapulo z a. I oz of eet oco'Feg’z 064. IZI oro “yoor dei} ‘ul-y%z 9 £ i 61 ooo'coF’s tt OlZ'‘I SLI oer ‘yoo deij “ul-y%z E z I gl 000‘6zS'¢ Rae ea 0g9‘I SLI SLE ‘yor dei} ‘ul-%z ¢ z I LI OCO'SIQ'H tt o02‘z IZI Z0z *‘yoor deiz ‘ul-yz z I I Ol 000‘Zg99'1 ESRI OI ggI oor ‘yoor dei} “ul-% 9 Si I SI agen 000‘o0s‘z ean ogh‘I SZI OzP *yooi deiy ‘ul-% v z I v1 000‘4z6'z O0O'feEE 000‘S19'F Sean ooZ‘¢ eZ1 ocr *“yoor devi} “ul-% £ z I e1 ooo'oZg'€ = _ ooo'Z1z'S o0o‘co0'S ye ogi‘ eL1 z6z *yOor dei} “ul-3% z I I ZI ooo fees ooo‘oS 4‘ 000625‘ pre 09S ‘P fLZ1 oor ‘yoo. devi} “ul-% z I I Il +4 ees 000'go£‘z ooo ZzZ‘z eee ewe O16‘z CLI oor SESS bet ee ee £ I ol ooo'zgi‘z 000‘ZS9‘z 000625‘ sean ogee eZ1 ggt SESE ri z I 6 SEN? 000‘162‘z 000'gS 1‘ sana of6' PLI ose “s1apuld I ce I 8 oo0'0SZ‘E o00'6zS‘€ . oo0o'eee'e etpaetian 2 ooz‘b g41 Liz ‘yoo dei} ‘ul-%z I oe I Z oco‘gt rv 000‘00g'h 000‘000‘S Sen oor‘g FLI Lez “yoor dei} “ul-% I = I 9 000‘ZSg‘z 000‘o00't 000‘gS 1°e spy oge'b £21 gta ‘PPAVIS “UI-8A I en I S coo‘Zsgz 0009S 1‘F oo0'gS 1‘ ser oog‘F €Z1 ~ ose ‘[PAVIZ “Ul-H I = I b coo‘os Zt 000‘0Zg' 000‘9gz‘F EEE oF6‘9 €Z1 oof Sena sets es nie I I £ 000'0Z9‘t o00'6zh‘e 000‘9gz‘b eee o6r‘9 141 ose ahi ° a ‘7 yRON z o000‘0Z9'f oo0‘0S Z‘E coo‘ooo0'S SNARE oF6‘9 IZr o'0z peeiese Peg erate re 77 -ytaN I 000' PUe 9000'S 000'7 PEL OOO'T OOO'T PUL OOS OOS PUOOT “Webs ted -skep —“quo0 red “LOPUI) 10 “Tepuly “purg “queue “oN ——}o "ur “bs aed SPLOT Teeazoq ‘AJLONSRLG JO SHEN pOTY—~— on anes 5 ‘ey *IOPE A eU0}S JO pUlyT IO eu0}g 7 CHOGT ‘S}saL [euesiy 1M0719}8M\) (‘Sur ZI JO Y}Sua] asnes we uO padsasqo salj1adoid ose[y WYSIom Aq JUS. JO "JUad Jod ul pozeys posn Jaye AA © ‘pasn juawiss Jo puesq apuesnA “Ile ul skep g 03.1 WIOIF JO aS [CIPI 19}Je 19}eM UI Jos SuUsIIg) ‘SINSTUd ALAADNOD CNV UVLUYON ‘LNAWNSO ‘NI-ve x ? x ? AO SAILYAdOUd OLLSVTA GNV HLONAYLS TAISSAYANOO—IIT AIVL GENERAL ELASTIC PROPERTIES OF CONCRETE. 207 ing the deformations. The deformations were read in ten-thou- sandths of an inch simultaneously cz each side of the specimen. The gaged length was 18 ins. in tension and 12 ins. in compres- sion. In the tension tests readings were made at each load increment of 250 lbs. on the specimen, which was equivalent to about 7 lbs. per sq. in. in cross-section. Details of the tension tests are given in Table L. In compression tests, readings were taken at intervals of 5,000 Ibs., equal to about 140 lbs. per sq. in. of section, except at the start, when readings were-made at 250 lb. loads. Prof. Bach’s method of finding the true elastic curve was fol- lowed, and three curves plotted for each test; first, the curve rep- resenting the total deformation; second, the curve of sets, and third, the true elastic curve obtained by subtracting the second curve from the first, as shown in Fig. 66. 75,000 79000 65000 60000 55000 eggseseseges Compression in Inches. Fig. 66.—Stress Strain Diagram. For each test the coefficient of elasticity, E, was calculated for three points on the elastic curve for each specimen. Table LIII. gives values of the moduli for a number of compression tests. A fair idea of the value of the coefficient of elasticity is ob- tained from this table, although the values appear to be some- what higher than sthese given in Tables XLV.. XLIX. and 208 CONCRETE AND REINFORCED CONCRETE. LI. The tendency of the value to decrease as the load increases should be noted. The values of E, as here shown, do not appear to be affected by the ultimate strength. An average value of E for the crushed limestone, with the broken limestone mixture, as shown by this set of experiments, would be about 5,000,000 lbs. per sq. in. for both tension and compression, and for the sand and broken limestone mixtures about 3,600,000 Ibs. per sq. in. in compression and 4,500,000 lbs. per sq. in. in tension. These values are based on too small a number of tests to be considered as more than indicating what the probable value of the coefficient is for large concrete speci- mens, made from full-sized stone. They are, however, of value when considered in connection with other tests here given. Many more tests are needed to determine more definitely the real value of the coefficient of elasticity. TABLE LIII—MODULI OF ELASTICITY (E) FOR COMPRESSION. (Woolson’s Tests.) 1:2:4 Concrete. Specimens 6 X 6 ins. (Elastic Curve = Total Deformation Curve Minus Set Curve.) Crushed Limestone and Broken Limestone. Test E at 135 lbs. E at 682 lbs. E at 1,227 lbs. Breaking Load. No. per sq. in. per sq. in. per sq. in. Ibs. per sq. in. 3018 5,600,000 5,600,000 5,600,000 3,400 3019 3,306,000 4,132,000 4,380,000 2,040 3020 5,540,000 5,890,000 4,676,000 2,120 3024 5,460,000 4,820,000 4,610,000 2,160 3025 5,560,000 5,208,000 4,287,000 2,190 3051 6,810,000 6,290,000 6,130,000 2,580 3062 5,515,000 4,140,000 2,980,000 1,455 Average. .5,398,900 5,154,300 4,666,200 2,278 Sand and Broken Limestone. Test E at 135 lbs. " E at 682 lbs. Eat 1,227 lbs. Breaking Load. No. per sq. in. per sq. in. per sq. in. lbs. per sq. in. 3021 2,755,000 2,505,000 —........ 1,500 3022 4,130,000 3,940,000 3,380,000 1,920 3023 2,800,000 3,650,000 3,360,000 2,000 3026 4,100,000 3,725,000 3,210,000 1,850 3027 2,755,000 2,666,000 2,520,000 1,760 3058 4,190,000 4,190,000 3,350,000 1,672 Average. . 3,687,000 3,446,000 3,164,000 1,784 Limiting Stresses to be Used in Choosing Modulus for Computa- tions.—Inasmuch as the value of the coefficient of elasticity de- GENERAL ELASTIC PROPERTIES OF CONCRETE. 209 creases as the unit stress increases, the question at once arises, what value of the coefficient should be used in the computations? Tt seems rational that a value of the modulus for the usual allow- able stress, say from 0 to 600 lbs. per sq. in., should be used, it heing understood that the unit stresses are to be kept within these limits. If a computation is desired for the ultimate strength, a value of the modulus at the ultimate strength of the concrete should be employed. The coefficient of elasticity increases as the richness, and hence the strength, of the concrete increases. A study of Rafter’s tests seems to indcate that the coefficient of elasticity is some function of the compressive strength. Falk, after a careful comparison of a large number of tests, states that there appears to be a direct re- lation between the coefficient of elasticity and the compressive strength, that concrete in compression seems to have a point that may be called the elastic limit, and its value is between one-half and two-thirds the ultimate strength. He concludes that up to this elastic limit the compressive coefficient of elasticity may be taken at 1,325 times the ultimate crushing strength. Or, ex- pressed algebraically, we have: Ec = 1,325 fc. This formula gives slightly higher values than Thacher’s for- mulas, which are derived from Kimball’s tests, but agree more closely than the latter with more recent tests, which seem to in- dicate a higher coefficient than earlier ones. Thacher’s formulas are as follows for concrete: THACHER’S FORMULAS FOR COEFFICIENT OF ELASTICITY. volume of sand 7 days old E = 2,600,000 — 700,000 | —————————— — 2 volume of cement 1 month old E = 2,900,000 — 300,000 ( do. — 1). 3 months old E = 3,600,000 — 500,000 ( do. —2).° 6 months old E = 3,600,000 — 600,000 ( do. — 3). volume of sand : —c is zero or becomes a nega- If the term — volume of cement tive quality, the entire term is to be considered zero. Table LIV. shows values of the modulus for different mix- tures derived from the above formulas, the values of compres- sive stress used in Falk’s formula being taken from Thacher’s formulas, given on page 192. The values given in the last two 210 CONCRETE AND REINFORCED CONCRETE. columns of the table are average values and may be safely used in computations if desired. Values given in the above tables are for loads taken from o to 600 Ibs. per sq. in. If a higher loading than 600 lbs be used the values of the coefficient will be materially, reduced. It has been found that for loads from 1.000 to 2.000 lbs. its values will be from ?/, to 1% that given above for loads not exceeding 600 Ibs. per sq. in. TABLE LIV—SHOWING MODULI OF ELASTICITY OF CONCRETE. Thacher’s Formulas. Falk’s Formulas. Average Value. Mixture. I month. 3months. «month. 3months. tImonth. 3 months. 11:3 2,900,000 += 3,600,000 += 3,740,000» 4,450,000 += 3,200,000 += 4,000,000 :2:4 2,600,000 3,600,000 3,180,000 3,980,000 += 2,800,000 ~—« 3,800,000 :2$:5 2,450,000 3,350,000 2,950,000 3,640,000 2,600,000 3,500,000 :3:6 2,300,000 = 3,100,000 ~—-. 2,720,000 = 3,540,000 += 2,400,000 ~— 3,200,000 34:7. 2,150,000 2,850,000 2,480,000 3,230,000 2,200,000 3,000,000 1:4:8 2,000,000 2,600,000 2,250,000 += 3,930,000 += 2,000,000 ~—_ 2,800,000 ae eee The coefficient of cinder concrete differs somewhat from that of stone concrete. Table LV. gives the average values of a series of tests and is taken from the Watertown Arsenal Report of Tests for Eastern Expanded Metal Co. for 1898. Tests were in I2-in. cubes 3 months old: TAB_E LV.—ELASTIC PROPERTIES OF CINDER CONCRETE. (From Watertown Arsenal Tests of 1898.) 12-inch Cubes. Age 3 Months. American --Modulus of elasticity per sq. in., between— goes Portland ———Proportion ——- ‘ oads 0: strength Cement. Cement. Sand. Cinder. 100-6001bs. 100-1,0001bs. 1,000-2,000]bs. per sq.in. Alpha I I 3 2,500,000 2,500,000 1,429,000 2,780 Alpha I 2 5 1,087,000 957,000 Sake bed 1,402 Alpha I 2 5 1,471,000 1,286,000... . . 1,715 Atlas I I 3 4,167,000 3,214,000 1,190,000 2,368 Atlas I I 3 2,083,000 1,875,000 1,351,000 2,580 Atlas I 2 5 1,190,000 849,000 ix... ss 1,200 Atlas I 2 5 1,087,000 865,000 Si... 1,263 Table LVI. gives Henby’s tests for the compressive strength and the coefficient of elasticity of cinder concrete: TABLE LVI. (Henby’s Tests for Cinder Concrete.) Mixture. Age, days. Compression stress. Modulus of elasticity. 1:2:4 30 g 1,006 1,461,000 1285 30 823 1,396,000 1:3:6 30 500 1,225,000 T:2:5 60 700 1,330,000 1:3:6 60 640 916,000 ELASTIC PROPERTIES OF CONCRETE. 211 Table LVII. gives additional tests made at Watertown Ar- senal in 1903: TABLE LVII—ELASTIC PROPERTIES OF CINDER CONCRETE. (From Watertown Arsenal Tests for Eastern Expanded Metal Co., 1903.) Lehigh Portland Cement. 12-inch Cubes set in air. Gage Length 5 inches. Modulus of elasticity ; per square inch between Compressive -———Proportions —-——. loads of At ultimate strength per Cement. and. Cinder. Age. 500 to 1,000 Ibs. strength. square inch. I 2 4 38 1,786,000 1,136,000 1,950 I 2 4 38 1,923,000 1,136,000 2,050 I 2 4 224 1,471,000 1,087,000 2,600 I 2 4 224. 1,563,000 463,000 2,500 I 2s 5 38 1,250,000 ~~... . 2s 1,400 I at 5 38 893,000 ti... 1,400 I 2h 5 224 1,136,000 893,000 1,980 I 2s 5 224 1,250,000 694,000 2,020 I 3 6 34 781,000 ude wanes 1,200 I 3 6 34 1,000,000 ~—S—i.. . 1,330 I 3 6 220 1,000,000 694,000 1,720 I 3 6 220 735,000 463,000 1,560 For mixtures of 1: 2:3 or richer, it will probably be safe to use a modulus of 1,500,000 and for mixtures not leaner than 1: 3:6, a value of from 800,000 to 1,000,000. Authorities differ considerably on this question. The proper value of the coefficient of elasticity to be used wil. depend upon the safe working stresses chosen, the mixture used, and the particular theoretical formulas employed in the computa- tions. The values given above for different conditions will enable the engineer to choose a proper value for his computations. CHAPTER XI. PHYSICAL PROPERTIES OF REINFORCING METALS. Metal is a most important factor in reinforced construction, as dependence is put upon it alone to care for all dangerous stresses. The manner in which it is used and the different forms employed will be explained in the succeeding chapters, but it is necessary be- fore discussing the methods of determining the sectional area of metal needed for a given reinforced concrete member to take up in detail its physical properties, as it is necessary to understand them in order to make a proper choice for the reinforcement. Until quite recently, in Europe, wrought iron was used ex- clusively for reinforcement, and is still in great favor, although steel is gradually replacing it. Wrought iron possesses many valuable characteristics, among which not the least is its property, of being easily and safely welded. Steel possesses greater strength than iron and will, on this account, give greater economy if a high grade of concrete be used. The cost of iron and steel in Europe is about the same; in the United States, however, steel is the cheaper, and is used exclusively for reinforcement. Wrought Iron.—When employed for reinforcement, iron is most frequently used in the form of round and square rods and flat bars; these, being of a recognized standard commercial quality, are easily obtained. The iron should be of good quality, with a breaking strength of about 50,000 Ibs. ner sq. in., and an elastic limit of at least one-half the ultimate strength, and should have an elongation of from 8 to 12 per cent. in a length of 8 ins. A bar should bend when cold 180° around a curve whose diameter is twice the diameter of the test piece without evidence of failure. The unit breaking strength of iron increases as the section of the rod decreases, but the cost of the metal increases as the size becomes smaller. ‘ ; Steel—As has been stated, steel is used exclusively for rein- forcement in America. This is undoubtedly because it is cheaper than wrought iron. Unfortunately authorities differ as to the PHYSICAL PROPERTIES OF REINFORCING METALS. 213 quality of steel to be used for reinforcement, soft, medium and high steel being used by different engineers. If a steel of good quality be employed, it is immaterial which be used, as first class structures have been built with each. How- ever, soft and medium steel are better fitted for some classes of structures than high steel, while in others the high steel will answer just as well, with greater economy. Open hearth steel is preferable to Bessemer steel, as it is more uniform in quality and does not possess the brittleness sometimes met with in Bessemer steel, and which makes the latter at times extremely dangerous for use as a reinforcing material. For- tunately it is possible to secure such an excellent quality of either soft or medium steel in the open markets, which is manufactured .and sold under standard conditions, that an engineer can feel sure of the safety of his structure without the expense of -ex- haustive tests. Open hearth steel, either acid or basic, should conform to the following requirements: The maximum limit of phosphorus in the finished material should not exceed .07% for acid and .05% for basic open hearth steel. Soft steel should have an ultimate strength of from 54,000 to 62,000 lbs., and an elastic limit of not less than one-half the ultimate strength; it should elongate 25% in 8 ins., and bend cold 180° flat on itself without fracture on outside of bend. If medium steel is used, it should have an ultimate tensile strength of from 60,000 to 68,000 Ibs. per sq. in., an elastic limit of not less than one-half the ultimate strength and should elongate not less than 22% in 8 ins., and bend cold 180° around a diameter equal to the thickness of the piece tested, without fracture on out- side of bend. In the above bending tests for soft and medium steel, the quality of the metal should be such that it shall stand the above » described tests upon a test piece at least *°/,,-in. in diameter, after being heated to a cherry red and cooled in water at a tem- perature of 70° F. High steel, that is, steel containing a high percentage of car- bon, is used for reinforcement by some engineers. Brittleness is to be feared in high steel, although this quality is not so danger- ous when the metal is used in reinforced concrete as when used in heavy beams or shapes, as the concrete to a large extent ab- 214 CONCRETE AND REINFORCED CONCRETE. sorbs the shocks and protects the steel. As a rule, a satisfactory product cannot be obtained on the open market and, unless the quantity of metal desired is large enough to warrant unusual pre- cautions and careful inspection during manufacture, it will be almost impossible to secure a satisfactory material. The ex- pense necessary to warrant a careful inspection will so increase the cost of the material that little or no economy will result from the use of the high steel, even though it possess 50 per cent. greater -strength than medium steel. When it is desired to use a high steel it should contain little or no impurities, not more than .o6 per cent. of phosphorus, not more than .o6 per cent. of sulphur, and not less than 0.4 per cent or more than 0.8 per cent. of manganese and should contain from 0.5 to 0.6 per cent. of carbon. It should possess an ultimate tensile strength of at least 100,000 Ibs. per sq. in. and an elastic limit of not less than cne-half the ultimate strength, and should elongate not less than 10 per cent. in 8 ins. for a test piece from 3@ to 34 in. in diameter. A test piece 4 in. in thickness should bend 110° without fracture around a diameter equal to its thickness. In the design of steel structures it has been the custom to base the allowable working stress upon the ultimate strength of the steel, but in reinforced concrete design it is more rational to base the working stress upon the elastic limit of the steel. This practice has been adopted by the majority of engineers. The allowable working stress should fall well within the elastic limit, for as soon as this limit is reached the metal stretches rapidly ond, decreasing in section, is loosened from the concrete, there- by destroying the monolithic action existing before this point is reached. As the metal stretches the concrete cracks badly and its uscfulness as a structural material becomes impaired and is ultimately destroyed. ° Other things being equal, the steel having the highest elastic limit will be the most satisfactory for reinforcement. Unfor- tunately steel having a high elastic limit has approximately the same coefficient of elasticity as low steel. The resistance of steel te deformation depends upon its coefficient of elasticity. The elongation suffered by the metal will not be proportional to its elastic limit, but to its coefficient of elasticity. Thus a steel with an elastic limit of. say 30,000 lbs. per sq. in., will at this limit stretch about 0.0010 of its length, while a steel with an elastic PHYSICAL PROPERTIES OF REINFORCING METALS. 215 limit of, say, 50,000 lbs., will stretch about 0.00167 times its length at its elastic limit. The first limit, 0.0010, is, as is ex- plained in Chapter XVIII., about the maximum stretch allow- able in reinforced concrete work, hence little will be gained by the use of the high steel. However, a higher factor of safety will result when the high steel is used, and the working stresses may more easily approximate those developed at the allowable ‘limit of stretch, and a real economy secured by the use of high steel. When high steel of a satisfactory quality can be secured at a price not greatly in excess of that of medium steel, con- siderable saving may result. Thus a saving of as much as 25 per cent. over mild steel may ensue if the high steel rods be secured, as is ‘often the case, at an advance of about Io per cent. in price over mild steel. The elastic limit or yield point of ordinary mild steel varies from 30,000 to 40,000 lbs. per sq. in.; 36,000 lbs. may be taken as a fair average. The elastic limit of high carbon steel varies from 50,000 to 60,000 lbs. per sq. in.; 54,000 lbs. may be taken as a safe working value. If the high steel be used and it is assumed that the additional stretch in the concrete is not injurious, a much smaller percentage of steel will be needed to secure.the same moment of resistance than when mild steel is used. The question in regard to whether or not the minute cracks in the bottom side of the beams will prove injurious and permit _ the corrosion of the steel, is one requiring careful investigation. When data on this subject become available, many vexing ques- tions concerning reinforced concrete will be solved. In the meantime it would seem to be conservative practice to limit the stress in the steel so that the cracks cannot prove dangerous in as far as the economy of reinforced construction permits. When the concrete is to be subjected to a moist atmosphere or to corrosive gases, steel with lower working stresses should be employed or a different form of construction adopted. In many classes of structures there is no doubt high steel may be used with economy and without in any way endangering the structure. Thus in walls and floors in buildings not subject to shocks or vibrations, retaining walls, reservoirs, etc., not sub- jected to severe conditions, the high steel will, in the majority of cases, prove satisfactory. For railway bridges, factory and 216 CONCRETE AND REINFORCED CONCRETE. warehouse floors, subjected to vibration, shocks, etc., a soft duc- tile steel should in all cases be used. Where soft steel is used its great ductility will enable it to stretch and give warning of failure long before final rupture takes place. Cost of Reinforcement.—A statement of the comparative cost of a number of the special reinforcing bars in general use would be of interest. The cost of steel, however, fluctuates from time tu time, and prices are based on an average price per pound of plain steel rods in 50-ton lots at the mills. The standard size of rod on which a base price is assumed is 34 in. or over. For sizes below 34 in. the price increases, according to the schedule of the Associated Steel Manufacturers. Table LVIII. gives the relative prices for different sizes of plain rods, assuming the price of 34-in. plain Bessemer rods at ‘$30 a ton, or 1.5 cts. per pound. The cost of deformed rods is from $8 to $12 a ton more than the cost of plain rods, depending upon the condition of the market. Thus, the market price for a 34-in. deformed bar of O. H. steel, at an increase of $8 per ton, will be 1.65 + 0.40 = 2.05 cts. per pound. For Ransome twisted bars about $4 a ton should be added to tke cost of plain bars for twisting. For the Kahn bar, owing to its peculiar form, more metal must be used for equal strength than when plain or ordinary deformed bars are used. Hence, for equal pound prices the cost of the Kahn reinforcement will be higher. It should, however, be remembered that a large portion of this extra metal is used for’ stirrups. The manufacturers do not supply a schedule of prices for different sized bars, but quote special prices for each job upon which they bid. TABLE LVIII—COST OF DIFFERENT SIZES OF PLAIN RODS (Price in cents per pound on basis of 50-ton lots at mill.) . Bessemer Open Size. rods, plain. hearth. % to 3. inch 1.65 % to “/w “ 1.76 % to */w ‘ 1.86 V1 2.07 ¥% 2.18 */16 . 2.28 M% to "/a “ 2.39 The cost of putting in steel for retaining walls, arches and PHYSICAL PROPERTIES OF REINFORCING METALS. 217 ordinary constructions varies from $5 to $8 per ton. In building work it may run up to $15 a ton. There are a number of firms furnishing reinforcements for beams and girders fabricated into units or trusses ready to put into place. Some of these make special provision for attaching the slab reinforcement. This method of reinforcement, from experience up to date, has been found to cost from 33 to 50 per cent. more than properly constructed single-bar systems. CHAPTER XII. PRINCIPLES AND DISPOSITION OF REINFORCE- MENT. The development of reinforced concrete as a distinct system of construction dates from the time that the function of the metallic reinforcement was understood. The highest success in the use of this form of construction is attained only when a maximum strength is secured at a minimum cost. This is possible only by using the proper proportions of the two elements—concrete and metal—these being placed in such a manner as to obtain the greatest strength. Certain fundamental principles are essential to this system of construction. When a solid body is acted upon by external forces, stresses are produced in its interior, which tend to change its shape. These stresses may in general be resolved into three kinds, viz.: tension, compression and shear. The materials of which reinforced concrete is composed behave differently, accord- ing to the nature of the stresses brought upon them. The metal, iron or steel, resists these three kinds of stresses equally well. Cement concrete, however, while acting well under compression, offers comparatively small resistance to tension and shear. These facts form the basis for construction in reinforced concrete; for by providing an ample section of concrete to resist the compressive stresses and strengthening that part of the given structure where dangerous tensile and shearing stresses are de- veloped by incorporating in the body a metal skeleton, a safe and economic structure is obtained. At times metal is also used to reinforce the part under compression, but it 1s evident that the greatest utility is obtained when the only function of the steel is to take care of the tension. ; Many engineers neglect the tensile strength of concrete and rely entirely on the reinforcement to care for tensile stresses. While this is cn the side of safety, it is not always wise to neglect the tensile strength of the concrete. In order that this heterogeneous mass of reinforced concrete may act ai a unit, it is necessary that the internal stresses shall PRINCIPLES AND DISPOSITION OF REINFORCEMENT. 219 be transmitted from the concrete to the metal. That stability may be assured, it is requisite that the shearing stress developed at the surface of contact between the two materials shall not be greater than the adhesion between them. When the adhesion is less than the shear it is necessary to use some form of mechan- ical bonding. Classification of Reinforced Concrete Members.—Reinforced concrete pieces may be classified according to the manner in which they are used. This is determined by the form of the piece and the method of application of the external forces. Straight pieces, viz., pieces having a rectangular longitudinal section, may be strained in compression and flexure. Pieces hav- ing a curved longitudinal section may be strained in flexure, compression and tension. Pieces strained in flexure are in gen- eral subjected to shearing stresses. This will, therefore, not modify the following classification. We will divide reinforced concrete pieces into the five following classes: First: Straight pieces strained in flexure, as beams. Second: Curved pieces strained in flexure, as arches. Third: Straight pieces strained in compression, as’ columns. Fourth: Curved pieces strained in compression, as pipes sub- jected to external pressure. Fifth: Curved pieces strained in tension, as pipes subjected to internal pressure. Reinforced concrete is not adapted to straight pieces strained in tension. Straight Pieces—Beams and Slabs.—Definition: If the external forces act normal to the axis of the rectangular piece, it will be strained in simple flexure; if obliquely, in composite flexure. All cases of composite flexure may be resolved into compression and simple bending. Only in special cases of composite flexure, which cecur very rarely, when the compression is excessive, will it be necessary to modify the character of the reinforcement. Under such circumstances the piece should be treated as a straight piece subject to compression. A large variety of structures may be grouped under this classification. Straight pieces are of two kinds, slabs and beams. Sometimes slabs and beams are used together, and we then have ribbed slabs or T-beams. Reinforced concrete beams may have any one of the forms which are ascribed 220 CONCRETE AND REINFORCED CONCRETE. to beams.* Slabs are usually of three forms. They may rest simply upon the supports, be fixed at the supports or be con- tinuous over them. In the analysis of stresses, sections of a slab may be treated as a shallow beam. Flexural Stresses.—In a beam supported at both ends and acted upon by a force normal to its axis, it is evident that at any vertical ‘section, by virtue of the bending stress, that part of the beam above the neutral axis is under compression and that part below under tension. Both of these stresses attain maximum values at the outermost fibres of the beam and decrease to zero at the neu- tral axis. The intensity of this stress at any point may be ob- tained from the well-known equation of flexure: Mc I when M represents the bending moment, c = the shortest dis- tance from the given point at the neutral axis; I = the moment of inertia of the given beam, and f — the intensity of the stress at the given point. The bending moment M, and with it the intensity of the hori- zontal stress f, increases from the end toward the middle of the -beam. Thus we see that the horizontal stress f varies, not only in a vertical direction on both sides of the neutral axis, but aiso in the direction of the length of the beam. If we consider the beam as composed of a series of horizontal layers, this increase of horizontal stress from one layer to the next develops a force tending to slide one longitudinal layer past the ene next above. This force is called longitudinal or horizontal shear. Vertical Shearing.—The vertical shear at any section of a beam is the reaction due to the load at one end minus that part of the load lying between the end and girder section. Owing to the low shearing stress of concrete, this should not be neglected in proportioning reinforced concrete pieces. In order that there be equilibrium in a beam, the summation of the internal stresses must be equal to zero. By well-known meth- ods of analysis the direction and intensity of the stresses in a beam may be obtained. Fig. 67 shows the lines of stresses in a beam under flexure as given by Rankine. "Seo Merrimans Mechanics of Materials, Chaps. V., VI. and VII., 10th edi- tian PRINCIPLES AND DISPOSITION OF REINFORCEMENT. 221 Tensile and shearing stresses tending to rupture always exist in a concrete piece strained in flexure. In placing the metal rein- Neutral_| uy Lines of Tensile Stress --~----~-~ fk & » = Compressive Stress 8 S Fig. 67.—Lines of Stress in a Beam Under Flexure. forcement in a concrete piece, both the tensile and shearing stress should be taken into consideration. Disposition of the Reinforcement.—It is evident that in order tc Fig. 68. utilize the maximum strength of the reinforcement, it should be placed as near as possible to the outer fibre of the piece under tension. Let us first consider a simple beam loaded from above and sup- pe . T Fig. 69. ported at two points. Tensile stresses will be developed in the lower part of the beam throughout its length. To care for these the reinforcement should be placed in the bottom of the piece, as oe ey Fig. 70. near as possible to the lower face, and extend over the entire por- tion between the supports. The reinforcement may be straight, as in Fig. 68. This is the simplest form of reinforcement. It may be given a curved form, as in Fig. 69, since the bending moment and 222 CONCRETE AND REINFORCED CONCRETE. the tensile stress increase from the supports to the middle of the beam. This curved form should be compared with the curve of tensile stresses shown in Fig. 67. When the curved form is used Fig. 71. the lower face of the beam sometimes follows the curve of the reinforcement, as shown jn Fig. 70. When this form is used, care Fig. 72. > \\ “ S SN must be taken not to reduce the section near the supports so that it will be unable to carry the end shear. When the beam is fixed at the ends, as shown in Fig. 71, the ee : Ui I Fig. 73. bending moment changes in character between the supports. In the middle portion the lower part of the beam is in tension—near the supports the upper part is in tension. A straight bar extend- PRINCIPLES AND DISPOSITION OF REINFORCEMENT. 223 ing over the entire length of the bottom and two short bars at the top, extending over the region of tension, and anchored at the supports, provide one form of reinforcement for this form of LL ee As the region of tensile stresses is somewhat indeterminate, the top reinforcement is sometimes made to extend throughout the ‘length of the entire piece, as shown in Fig. 72. eee This gives us the type of double reinforcement. A single curved reinforcement, as shown in Fig. 73, may be used, extend- ing along the lower part of the middle of the beam and rising to the upper part at the support, giving the desired resistance, both 7 Fig. 74. Fig. 75. 3 at the center and the ends. A modification of the form of the piece by thickening the beam at the ends (Fig. 74), gives addi- tional strength at the supports. By s+ + HH? Le = z yr Fig. 184.—Hennebique Slab Reinforcement. the ordinary type of Hennebique beam as applied to floor con- struction. The slabs may or may not be reinforced. Figure 134 shows a cross section of a floor having the slab reinforced. In important construction reinforcement is added to the top flanges. Stirrups are placed astride of these rods and extend downward into the concrete. Round bars are used exclusively STYLES OF BEAM REINFORCEMENT. 253 in this system. A special arrangement of the metal with trans- verse rods to tie the whole together and avoid longitudinal cracks is used for beams of long span. ; Coularou System.—The Coularou system (Fig. 135) resem- bles the Hennebique. The stirrups, however, are inclined at an Fig. 135.—Coubarou Beam Reinforcement. angle of 45°, and their spacing increases from the supports to- ward the middle of the span. Each stirrup consists of a plain round rod hooked around the upper and lower reinforcement. The upper reinforcement is of light section and is parallel to the \& J € i » —__¥ C ) @ = f : ~ Fig. 136. Fig. 137. Fig. 138. Fig. 139. Figs. 186-139.—Maciachini Reinforcement for Beams. lower bar, where the stirrups are necessary. Near the middle of the beam the upper reinforcement is bent downward at an angle of 45° and joins the lower bar and is parallel to it over the cen- tral portion of the beam. Maciachini System.—The object of this system is to obtain for 254 CONCRETE AND REINFORCED CONCRETE. beams the advantage gained in the construction of columns by hooping the same. The hooping of beams is an extremely diffi- cult operation. S. Maciachini undertakes to obtain the hoop- ing effect in the following manner: Hooping wires of a suit- able diameter and as long as possible are bent up and down be- fore being placed in position, the height being that of the width or depth of the beam less about 134 ins. to allow for a covering of about 7% in. of concrete on all sides. The bottom and side hoopings are placed together, as shown in Fig. 136, so that when all connected these reinforcements appear as shown in Fig. 137. After the 7% in. of concrete has been deposited, this meshing, together with the bottom rods at the angles, is put in place and Fig. 140.—Siegwart Hollow Beam. the filling is brought up and well rammed until it reaches the level of the top rods. These are then put in place and the top portion of the hooping is threaded through the top loops of the sides and bent backward and forward, as shown in Fig. 138. After this operation is completed the remainder of the concrete is added. Fig. 139 shows a cross section of a beam of this form. Lattice Trusses——Lattice trusses are also used for reinforc- it.g concrete girders. Matrai makes use of this form to sup- port his girders. He also sometimes uses rolled beams. He greatly reduces the bending moment in his beams and girders by Fig. 141—De Valliere Beam Reinforcement. attaching the ends of the wires and cables supporting the floors as near as possible to the end of the beam. See the arrangement of wires, as shown in Fig. 158. Siegwart System.—This system consists of a hollow beam re- inforeed by round iron rods, its top face forming’ the floor slab and its bottom face the ceiling. The beams are moulded in STYLES OF BEAM REINFORCEMENT. 355 sections about 10 ins. wide and are constructed in advance. The open spaces between the beams are filled with cement grout and the whole mass becomes a more or less perfect monolith. These floors cost between 15 and 20 cts. per sq. ft., according to the span and load. Iig. 140 shows the nature of this hollow rein- forced beam. De Valliere System.—In its simplest form, this system consists of a main reinforcing bar with a web reinforcement of heavy wire bent in the form shown in Fig. 141. This system resembles that of Pavin de Lafarge, but in this case the top rod with its loop is omitted. The Visintini System.—This‘ system is the invention of Mr. Franz Visintini, of Ziirich. The Concrete Steel Engineering Co., of New York, controls the patents for its use in America. This system is used in the construction of floors and roofs, and consists Section A-B. Fig. 142.—Visintini Beam. of shallow beams moulded in advance. Floors are made up of a series of these beams placed side by side. The beams are usually moulded in widths of from 6 to 12 ins., and are 6 or 8 ins. in depth. The beams are in reality shallow Warren trusses, and are reinforced as shown in Fig. 142. No reinforcement is used in the web members, which are strained in compression. For deep girders spanning between columns, a similar beam, usually trussed according to the Pratt system, is used. In this case the verticals are in compression and are not reinforced. Round rods are used for the main reinforcements, and sometimes flats are used for reinforcing the diagonals in the shallow floor beams. The advan-. tages claimed for this system are economy in material, careful inspection and first-class workmanship during construction, and a .detinite action of stresses, according to the system of trussing used. CHAPTER XVL CURVED PIECES STRAINED IN FLEXURE. If a curved piece, resting upon two supports, be acted upon by external forces, the resulting deformation produces either a thrust or pull at the supports, and the internal stresses developed by the action of these forces may be either compression or tension, but usually, on account of the form of the piece, or because of unequal distribution of the load, flexure also exists. If the piece is loaded on the convex side, it is in compression and flexure. Curved pieces loaded on the convex side are used in many forms of construction, and may all be included under the general classification of arches. If the loading is on the concave side, the piece is in tension and flexure. Arches.—These, like straight pieces, will be divided into two classes: Those of uniform thickness in the direction parallel to the axis, and ribbed arches. In the ribbed form, the ribs are some- times constructed independently in the form of arches of rectan- gular section. Stresses in Arches.—The arch acts under compression and flex- ure. On account of the flexure both tension and longitudinal shear exist. In this form of construction the object of the rein- forcement is to supply the resistance needed by the concrete when it is subject to tensile stresses and to supplement its compressive resistance whenever it is necessary to do so. These two kinds of stresses are the most important and may be called principal stresses. Secondary stresses also exist, the most important of which is shearing stress. Provision is often also made for this stress, Before showing the arrangement of the reinforcement, we will review briefly the usual manner of failure of arches and the location of the dangerous stresses producing such failure. Let us consider that the arch under discussion is of concrete and fixed at the ends. The arch may fail (1) by crushing the concrete, (2) by shearing, and (3) by rotation. (1). If the thrust at any point exceeds the compressive CURVED PIECES STRAINED IN FLEXURE. 257 strength of the concrete, the arch will fail. By introducing a proper amount of reinforcing metal the compressive stress in the concrete may be kept within safe working limits. Hence, by the use of reinforcements the thickness of the concrete may be greatly reduced. (2). As in beams, when the arch is heavily loaded, particu- larly if it be a flat arch, the shearing stresses at or near the ends may become dangerously high. The arch ring is generally y Tension ee ‘Tension Figs. 143-144.—Sketches Showing Methods of Failure of Arches. strengthened by increasing the thickness near the springing points. Reinforcement, when used, will give it additional strength. (3). Failure by rotation. The methods of failure by rota- tion are shown in Figs. 143 and 144. A flat arch fails by sinking at the crown and rising at the baunches, a deep arch by rising at the crown and sinking at the haunches. In Fig. 143, tension exists in the intrados at the crown and springing points: in the extrados at the haunches. Fig. 145. In Fig. 144 tension exists in the extrados at the crown and springing points, and in the intrados at the haunches. By exam- ining these figures the proper distribution of the reinforcement is easily understood. ; The simplest form of arch fixed at the supports is a curved ring included within two curved surfaces. As in the beam the simplest form of reinforcement is a bar placed near the intrados as shown in Fig. 145. This form of reinforcement will be in- 258 CONCRETE AND REINFORCED CONCRETE. sufficient if the stresses due to compound flexure are of any magnitude. In a full centered or elliptical arch, tensile stresses occur, as shown in Fig. 143, at the haunches. Hence it is customary to strengthen the extrados by a supplementary reinforcement. In an excessively elliptical arch the joint of rupture generally occurs at a point slightly above the springing line. Hence the supple- mentary reinforcement begins at the springing line and extends over the dangerous space, as shown in Fig. 146. As this danger space is sometimes difficult to determine, it is often customary to extend the reinforcement at the extrados over the whole arch (Fig. 147), thereby obtaining the double reinforcement. The Fig. 146. Fig. 147. 5 . 4 ; ; Fig. 148. Fig. 149. double reinforcement in addition to caring for any dangerous tensile stresses supplies additional resistance to compressive stresses. Figure 148 is a modification of Fig. 146, the reinforcement at the extrados being bent downward to meet the reinforcement of the intrados. This form may be used in connection with a double reinforcement and we then obtain the form shown in Fig. 149. The above five forms apply to arches of constant thickness, but it is customary to vary the thickness with the pressure and bend- ing moment. * This gives a greater thickness at the springing lines than at the crown. The thickness may be increased until the extrados becomes a horizontal plane. The above systers- of reinforcement also apply to this form and we obtain the dis tribution of reinforcements shown in Figs. 150 to 154. CURVED PIECES STRAINED IN FLEXURE. 259 Secondary Stresses.—In arches the principal stresses are gen- erally of much greater magnitude than the secondary stresses induced by simple flexure, hence it is not necessary to make any special provision for shearing stresses. There are, however, seme arch systems which use special bonding similar to that used in straight beams. Another kind of secondary stress should be considerad. When arch rings or straight pieces are subject to heavy compression stresses, a compression of the concrete takes place, and at the same time a lateral expansion. Some method of transverse bonding is necessary to take care of this secondary deformation. If the piece be reinforced against this a Fig. 150. Fig. 151. Fig. 153. Fig. 154. lateral expansion, its resistance to compression is greatly in- creased. Systems of Reinforcement.—The systems of reinforcement des- ‘cribed in connection with slabs may be applied to the construction of arches of uniform thickness. The first and simplest form of arch reinforcement (Fig. 145) was first used in connection with a Monier netting. This did not materially strengthen the arch, as no provision was made to care for the tensile stresses produced by the bending moments at the extrados. Other methods of strengthening the arch ring were devised and the reinforcement took the form shown in Figs. 146 and 148, and finally the double netting was used, as shown in Fig. 147. In the Monier type the resistance bars were bent to the curve of the directrix of the arch and the distributing bars were straight 260 CONCRETE AND REINFORCED CONCRETE. and parallel to the axis, the two systems being bound together at intersecting points. Expanded metal has been extensively used to reinforce arches of short span, particularly for floor systems. The Melan system has been widely used in the construction of bridges. While this system is essentially a double reinforce- ment type, the reinforcements occur in a variety of forms. Steel I-beams have been extensively used, also various forms of lattice girders. The vertical bonding is sometimes omitted, and inde- pendent bars of various forms are used. These are placed parallel to the curves of the extrados and intrados. Mr. Edwin Thacher used the reinforcement shown in Fig. 78 for a large number of his earlier bridges. The reinforcing bars are spaced ct convenient intervals, and may or may not be con- FANE =" pope aess 93° x ~ \ ‘2 ae 2 DNF a fi | u u u_| Fig. 155.—Hennebique Arch Reinforcement. nected transversely. The latticed type of Melan arches has been used with hinges at the crown and springing points. : Hennebique adapts his system to the reinforcement of arches. Fig. 155 shows the arrangement which he gives to the rods. The bent bar, shown dotted in the figure, may or may not be used. The bent bar is sometimes used, and the upper horizontal bar omitted. As in straight girders these sets of bars are placed in the same vertical plane and are included between the same stirrups. Distribution bars may be used. These are placed parallel to the axis of the arch and above the intradosal bars and below the bent bars. Ribbed Arches.—From a theoretical standpoint if the arch acts under compression alone, it ought to be of uniform thickness, as CURVED PIECES STRAINED IN FLEXURE. 261 the thrust should be the same throughout its cross section. How- ever, on account of flexure and the concentration of loads at certain definite points through the medium of spandrels, a greater depth and a corresponding greater moment of resistance is at times desirable. Hence, as in slabs the ribbed type gives the desired strength without an excess of concrete. Ribbed arches are often more economical than arches of con- WIT TTL LLL LLL ! ; | a | . Fig. 156.—Hennebique Arch Rib and Flat Slab Construction. stant thickness. By using a thin arch at the extrados strength- ened by ribs, the amount of spandrel filling and dead load may be reduced. In this case either a curved or flat extrados may be used. The latter case gives arch ribs with a flat covering slab, as shown in Fig. 156. The Hennebique system uses the form of flat extrados. The reinforcement for the ribs is made up in the same way as in arches of uniform thickness, but in this Fig. 157.—Golding Arched Floors. case all three rods are used in the same vertical plane, viz., in- tradosal, bent and extradosal reinforcing bars. The slab is rein- forced in the same manner as ordinary floor slabs. In arches of large span the floor is itself sometimes arched giving an arch system, which is analogous to a ribbed floor slab with a certain amount of curvature over the whole span. The flat slab reinforced with arch ribs of moderate span has been ex- 262 CONCRETE AND REINFORCED CONCRETE. tensively used in floor construction. The Golding floor is the most common type met with, and is shown in Fig. 157. _ Inverted Arches.—A curved system of construction may be used, in which the arch is loaded on the concave side, in which == 1 Fig. 158.—Matrai Inverted Arches. the usual thrust at the supports becomes a pull and the piece acts under tension and flexure. M. Matrai (Fig. 158) adopts this form of construction for his system. The intrados may be either flat or curved. Fig. 154 shows the form with a flat intrados used by M. Matrai in the construction of floors. CHAPTER XVII. COLUMNS, WALLS AND PIPES. Straight Pieces Strained in Compression —In this classification belong all those structures in which compression acting in the direction of the axis of the piece is the principal stress. Secon- dary stresses produced by bending usually also exist. These latter stresses are due to external forces, acting normal and obliquely to the axis of the piece, or to an eccentric application of the forces producing the principal stress. Sometimes an uneven settlement of the foundation will also develop secondary stresses. Walls, col- umns, posts, piers, foundation piles, etc., acting in a vertical direc- tion, come under this classification. Disposition of the Reinforcement.—The reinforcement should be so arranged as to care for all dangerous stresses. In this class Fig. 159.—Typical Wall Reinforcement. of structure the function of the reinforcement is twofold, viz., to take care of any tensile stresses due to bending and to supple- ment the compressive strength of the concrete. When used prin- cipally in the latter capacity it is often possible to reduce ma- terially the section of the concrete. In general the reinforcement consists of straight rods placed parallel to the axis of the piece and is so arranged that the piece will resist equally well in all directions the action of the direct compression and the secondary flexural stresses. Walls.—The reinforcements in walls, to take care of trans- verse bending stresses and assist in carrying the vertical loads, consist of vertical rods placed alternately near each face, as shown in Fig. 159. Reinforced walls in reality are slabs, with double reinforcements, placed on edge. Some form of trans- yerse bonding is desirable, for when a piece is under compres- 204 CONCRETE AND REINFORCED CONCRETE. sion, transverse distortion accompanies the longitudinal contrac- tion due to compression. As in slabs, longitudinal rods spaced from 2 to 3 ft. apart should be placed horizontally throughout the height of the wall to prevent shrinkage cracks. Again it is ot daa tema a 4 | | j Ne oe a i | asa eats | L ! 1 T 1 : ar fo | | | [_ Tia eAawyaAahAY AL ry nrueréeeégrmreiaivTmy Fig. 16U0.—Hennebique Wall Reinforcement. often desirable to reinforce the wall in a horizontal direction in erder that it may act as a girder to distribute the loading over the foundation or to span openings; to this end, rods are placed horizontally throughout the height of the wall. VS) Fig. 161.—Degon Wall Reinforcement. M. Hennebique uses vertical round rods placed alternately near each face and ties them to the opposite face by means of stirrups, as shown in Fig. 160. Horizontal rods are placed along the axis of the wall to take care of vertical flexure. Fig. 162.—Chaudy Wall Reinforcement. Ransome employs a similar arrangement, but uses cold twisted bars without stirrups. The Degon (Fig. 161) and Chaudy (Fig. 162) systems for walls use an arrangement of the reinforcements similar to that employed in the construction uf these floor systems. COLUMNS, WALLS AND PIPES. 265 The Monier trellis, used as in a double reinforced slab, is em- ployed for wall reinforcement. A single trellis is often used for thin partitions. Any one of the latticed systems described under slabs may be used in a similar manner. Partitions are often made in panels moulded in advance, and put in place during the pro- cess of construction. . Columns.—Concrete and metal are used together in a number of ways in the construction of columns. Concrete was long ago used as a protecting coat against fire for all-metal columns. The column proper is usually built up of steel shapes, and surrounded with some form of metal lath or lattice, which is embedded in the surrounding concrete, as shown in Fig. 163. When used in this manner the concrete adds very little to the strength of aA fat pre: .°. 2 eed-- Expanded AM Conerove| ee] Metal Lath T. Core 2: “. Fireproofing Concrete Fig. 103.—Concrete Covered Steel Column. the column. If the interior of a hollow steel column be filled with concrete, additional stiffness is secured. Capt. John S, Sewell, Corps of Engineers, U. S. A., has used columns of this kind in building construction and states that by the use of a concrete core the saving of steel was great enough to pay for the filling. While the stiffening effect of the concrete core is some- - what uncertain, it is probably safe if large cross-sections be chosen to design the steel column in simple compression, without any allowance for flexure, dependence being placed on the con- crete to furnish the necessary stiffness. The usual method of reinforcing concrete columns is to place vertical reinforcing rods symmetrically spaced about the axis of the piece and as near as possible to the exterior faces. The columns may be square, round or of polygonal form. Usually from 4 to 20 rods, varying in diameter from 34 to 214 ins., and upwards are employed. These rods are tied together at inter- 266: CONCRETE AND REINFORCED CONCRETE. vals of about the thickness of the column. For these ties Henne- bique formerly used flat bars having holes punched in them (Fig. 164) through which the vertical rods are passed. In later con- struction he has used wire ties. Hoop iron straps are used in the Bousseron system (Fig. 165), while the Degon system (Fig. 166) employs wire ties bent in the form of a cross. A variety of other methods of wrapping are often employed. The Kahn system omits the cross ties, but, owing to the peculiar form of the bar used, it is tied firmly to the mass of the concrete. Fig. 164.—Hennebique Column Rod Ties. Hooped Columns.—It is a well known fact that when a concrete piece is subjected to high compressive stresses, a deformation and shortening of the column occurs accompanied by a distor- tion of the molecular structure and swelling of the concrete in a transverse plane. M. Considére conceived the idea of increas- ing the compressive stress of the concrete and preventing the horizontal distortions by means of hoops or helicoidal spirals placed at or near the face of the column (Fig. 167). By this means the compressive strength of the column may be increased from 2 to 2.7 times that obtained by the usual type of reinforce- ment. M. Considére found that the spirals should be spaced COLUMNS, WALLS AND PIPES. 267 from 1-7 to I-10 of the diameter of the column. Rods should vary in size from %4 to 34 in., according to the size of the column and the load to be carried. Vertical rods are used in connection with this hooping to care for flexural stresses. The Fig. 165.—Bousseron Column Rod Ties. confined concrete. carries all the direct compression. Expanded metal has been used in place of the spiral hooping. Piles—Concrete piles may be reinforced by placing a single rod or shape on the axis of the piece, or they may have a number of reinforcing rods arranged as in columns. Fig. 166.—Degon Column Rod Ties. Curved Pieces Strained in Compression—Vaults, reservoirs, sewers, pipes,etc., under pressure, acting upon their curved sides, are included in this classification when their form and the distri- bution of the loading is such that the principal stress developed is compression. A parabolic arch acted upon by a vertical loading 268 CONCRETE AND REINFORCED CONCRETE. uniformly distributed over its horizontal projection will be strained in simple compression. A circular pipe submitted to a uniform normal pressure acting from without will also be in sim- ple compression and may be considered as typical of this class of structure. Some form of lattice reinforcement is usually employed. The resistance bars are bent cr wound into circles or hoops and the distribution bars are straight and parallel to the axis of the pipe or cylinder. They are placed outside the directrix, or resistance ie SSS SS UT , ; : U SSS | SMM NON i TSS ff SHON INS : Fig. 167.—Typical Hooped Column Rcinforcement. bars. The two systems are bound together at their points of in- tersection by soft wire ties. The resistance bars may be in the form of hoops or manufactured of long rods spirally coiled. The rods may be reduced in size and woven into some form of wire meshing such as is used in slabs. When light wire fabric is used it is often strengthened and retained in the desired form by large rods woven spirally about it. Sometimes two or more meshes are used. Round and square rods and T, cross and I shapes are used for reinforcement. M. Bonna uses special steel sections having the form of a Latin cross; these vary in size from 4 in. to % x COLUMNS, WALLS AND PIPES. 269 15 ins. M. Bordenave, another specialist on hydraulic work, uses small I-sections. These vary in depth from 5-16 in., with an area of 0.023 sq. in., to I in., with an area of 0.161 sq. in. This engineer uses round rods for distribution bars. These small sized shapes necessitate an extra amount of rolling during manufac- “ture, which gives a higher elastic limit and ultimate strength than is obtained in round or square rods. The peculiar form of the rods gives a large area of contact for adhesion. The cost of manufacture is considerably higher than that of ordinary round or square bars. The reinforcement may be placed near the mid- dle of the cement ring, but is sometimes placed near the inner Fig. 168.—Bonna Reinforcement for Pipe. face, as in the simplest form of Monier arch reinforcement. When a double network is used, one should be placed near the inner and the other near the outer face. Curved Pieces Strained in Tension.—In this classification are to be found pipes and reservoirs subjected to internal pressure. The reinforcement is designed to take all the tension and is embedded within the concrete shell usually near the outer face. In this case, however, the distribution bars are placed within the resistance bars, the latter being plain hoops or spirals, as in pipes under com- pression. The concrete acts as a distributing and protecting me- dium to this skeleton work and should be able to care for all sec- ondary stresses. All the svstems which were mentioned in con- nection with pipes under compression may be used for pipes un- 270 CONCRETE AND REINFORCED CONCRETE. der internal pressure. Many of these systems have been developed in the construction of water mains and sewers. Figure 168 shows the manner of arrangement of the reinforcing skeleton work of the Bonna system. In this system, when the pipes are small the hooping is always used in the spiral form. The longitudinal rods are notched to receive the hoop-bars at intersec-. tion points, and the joints wrapped with soft wire. When the pipes are to be used under a head of 50 ft. or more, M. Bonna ‘places a sheet steel tube in the concrete to insure impermeability. CHAPTER XVIIL GENERAL PHENOMENA OF FLEXURE. Action of Beams Under Tests.—According to the experiments of Profs. Hatt, Talbot and Turneaure, reinforced beams under test exhibited four stages of flexure. In the first stage the combination acts as a true composite mem- ber. This period extends from the application of the load until the tensile strength at the extreme fiber of the beam, due to both d Load in Four » Appl:. | Deformation per Unit of Length Fig. 169.—Typical Load Deformation Diagram. its weight and the applied load, becomes equivalent to about 350 Ibs. per sq. in. Under the conditions of Prof. Talbot’s tests this was approximately at the ultimate strength of the concrete in tension. At the limit of this stage the deformation of the steel throughout the middle third of the beam is about 0.0001 of its length, indicating, if we disregard shrinkage stresses and use the value of the coefficient of elasticity of naked steel, that the reinforcement is stressed about 3,000 lbs. per sq. in. Up to the end of this stage the deformation curve is quite regular and the ratio between the load and the deformation is very nearly con- stant. Figure 169 from Prof. Talbot’s discussion of reinforced concrete tests, University of Illinois Bulletin No. 1, for Sept., 1904, shows the form of deformation curve during the various stages of flexure. Throughout this stage the neutral axis is be- 272 CONCRETE AND REINFORCED CONCRETE. low the middle of the beam. The point on the deformation curve which shows the limit of the first stage is designated by Prof. Hatt as “Point A.” The second or readjustment stage begins when the loading exceeds the limits stated for the first stage. The steel elongates more rapidly as the loading increases, the compression of the concrete increases and the neutral axis rises. No cracks are visible to the naked eye during this period, but Prof. Turneaure found evidences of cracks when wet beams were tested by the appearance of water marks or bands. The cracks develop dur- ing the next stage. The concrete, as shown by the fine cracks not visible to the naked eye, begins to give up its tensile stress to the steel during the early part of this stage. There is a marked change in the form of the deformation curve, and its reversal of curvature near the end of this stage seem to indicate that the concrete is broken in tension through a part of the depth of the beam and that portion of the load carried by the concrete in tension has now been transferred to make additional tension in the steel. This stage lasts until the deformation at the level of the steel averages about 0.00035. The condition for the usual working load of beams is included within the limits of this stage. During the early part of the third stage the entire tensile value of the concrete is lost and all tension is transferred to the steel. line vertical cracks well distributed along the middle third of the beam become visible to the naked eye and gradually grow more distinct. According to Prof. Hatt, the first crack becomes plainly visible to the naked eye under a load three and one-third times the load at “Point A,” and after a deflection, which is nearly six times that at “Point .\." The first crack in Prof. Turneaure’s tests on 1:2:.4 concrete appeared at an extension in the concrete of about 3 times that at ‘‘Point A,” and in Prof. Talbot’s tests on 1:3:6 concrete, at an extension of about 5.7 times that at “Point A,” indicating in the former case a stress in the steel of from 12,000 to 16,000 lbs. per sq. in., and in the latter case a stress in the steel of 23,000 Ibs per sq. in. These fine cracks close up when the load is removed and can not enlarge to a serious extent until the steel reaches its elastic limit. The appearance of the cracks is, however, not accompanied by any apparent change in the character of the load deformation curves, which are quite regular for both tension and compression through- GENERAL PHENOMENA OF FLEXURE. 273 ‘out this entire period. The increments of the deformation of the steel are very nearly proportional to the increments of the load as is shown by the approximately straight line in the diagram. The compression deformation also closely approximates a straight line as shown in the diagram. The position of the neutral axis is practically constant throughout this stage. On account of the straight load deformation lines for both tension and com- _ Pression, and the nearly constant position of the neutral axis, there results a definite proportion between the increment of the load and the increment of the resisting moment of the beam, if the latter be based upon observed deformation and the coefficiént of naked steel. While the observed deformation may differ somewhat from the deformation necessary to give the true resist- ing moment of the beam during the early parts of this period, due probably to initial stresses or other causes effecting the measured deformation, it will be found tha: at or near the limit of this stage these deformations are almost directly proportional to the increments of the load and at the maximum load the resisting moment, calculated from the observed deformation of the steel. will, in general, be nearly equal to the bending moment of the load. Unless there be an excess of reinforcement, this stage con- tinues until a point is reached at or near the maximum strength of the beam. The fourth stage, or stage of failure, begins at or near the maximum load. The deflection increases if a normal amount of reinforcement is used, or, when not enough metal is used to develop the crushing strength of the concrete, i. e., not more than 1% per cent. of metal for steel having an elastic limit of 33,000 Ibs., and 1 per cent. for steel with an elastic limit of 55,000 Ibs. per sq. in. The steel stretches rapidly, the cracks grow in width, the neutral axis rises, and there is a rapid increase of compression in the upper fiber of the concrete, due to the decreased compression area, until finally the concrete crushes at the top of the beam at a - load less than the maximum, and after the steel has stretched con- siderably beyond its yield point. According to Prof. Hatt, failure of the beam begins at a load about four times the load at point A, and at a deflection which is about nine times the deflection at point A. The steel has passed the yield point and the cracks are wide open and will not close upon the removal of the load. In Prof. Talbot’s tests, the values 274 CONCRETE AND REINFORCED CONCRETE. were 4.3 and 16, and in Prof. Turneaure’s tests 3.5 and 9, respect- ively, for ratio of load and deflection to that at point A. In Prof. Talbot’s tests, soft steel with an elastic limit of about 33,000 lbs., up to 1% per cent., was not sufficient to develop the crushing strength of the concrete. Prof. Hatt was not able to develop the compressive strength of the concrete with 214 per cent. of steel by the application of a central load. With a high percentage of steel ‘ Per Cent of “al” a Applied Load in Pounds. 13,000 12,000 goo 5 10,000 9,000 E 8000 7000 6000 5,000 & 4000 < 3,000 2,000 1,000 Deflection i Inches. in Po plied Load .0006 0020} 50 o Ss O22 -0026 3 S 0008 0012 0014 0016 0018 0020 2 2 2 5 GS Deformation per Unit of Length. . Fig. 170.—Diagram Showing Change in Neutral Axis and Deformation of Test Beam.. it is probable that the bars will slip, if not anchored, or the con- crete will shear along the plane of the reinforcement before 1: 2:4 concrete will fail in compression. It is evident that the range be- tween point A and the first crack will depend largely upon the age and quality of the concrete. The poorer and dryer the con- crete, the nearer will be the first crack to the point A. The deformation curves for this, as well as for the first three stages, will be understood by an examination of Fig. 170. It was found from the average of a number of tests that de- formation at the end of the straight line for mild steel bars is about .00115, and for high steel bars .oo20, which approximates GENERAL PHENOMENA OF FLEXURE. 275 closely the computed deformation for naked steel bars at the yield point, and we may conclude that the maximum load is reached at the yield point, and that the yield point may be properly taken as the ultimate strength of the beam. It seems also true that loads which will stress the steel to its elastic limit may be calculated by using the elastic limit of naked steel for the tensile stress in the beam and neglecting the tensile stress in the concrete. Where more than a normal amount of metal is used, the con- crete at the top of the beam will fail by crushing before the elastic limit of the steel is reached. In this case the deformation curve will be somewhat different. When a deformation in the upper fibre of about .0014 js reached the deformation line for the upper fiber curves off to the right and the compression de- formation increases more rapidly, the neutral axis lowers slowly and the steel deformation line continues straight. The final failure, due to crushing of the concrete at the upper surface, oc- curs before the deformation of the steel has reached that of the yield point of the steel and the final load is the maximum load. Fig. 171, shows the deformation in this case. These experiments should not be considered to indicate that the steel should be stressed below point A, but rather that the tensile resistance of the concrete should not be included when figuring the resisting moment ot the beam. As regards the allowable working stress on the steel reinforce- ment in the light of the experiments of Profs. Hatt, Talbot and Turneaure, it appears that on the average the point A corre- sponds to a stress in the steel of from 3,000 to 5,000 lbs. per sq. in. and that the first visible crack will not appear until a stress has been reached of from 12,000 lbs. in Prof. Turneaure’s, 23,300 Ibs. in Prof. Talbot’s and 27,000 lbs. in Prof. Hatt’s tests. It is therefore not necessary to confine the stress in the steel under the worst possible condition to less than 5,000 Ibs. per sq. in. and the usual practice of allowing working stresses as high as 16,000 lbs. per sq. in. will not, under normal conditions, give dangerous cracks in the bottom of the beam. Methods of Failure of Beains Under Tests——The discussion of various methods of failure of beams under test by Prof. A. N. Talbot, in Bulletin No. 4 of the University of Mlinois (April 15, 1906), sets forth so clearly the results of study of carefully con- 276 CONCRETE AND REINFORCED CONCRETE. se 0 PF 2 ‘6 40 = 60 S 90 100 wu Pounds, o eo s 8 a & in oo se Applied Load i 35,000 34,000 33,000 32,000 31,000 30,000 29,000 28,000 27,000 26,000 25,000 24,000 23,000 2 22,000 221,000 20,000 ¢ 19000 18,000 “5 17,000 © 16,000 — 15,000 ee 2 13,000 $ 12,000 11,000 10,000 9,000 8,000 7000 6,000 5,000 4,000 3000 2,000 1,000 2 Deflection in & a eg ea 0 o o 9 Ss Ss Ss o © S Ss Ss 0002 0004 0008 0010 0012 .0014 0016 0018 0026 0028 -0030 Deformation per Unit of Length. Fig. 171.—Diagram Showing Change in Neutral Axis and Deformation of Test Beam. GENERAL PHENOMENA OF FLEXURE. 277 ducted beam tests that it seems desirable to insert a portion of this discussion in this place. The author is indebted to Prof. Talbot for permission to use this material. Prof. Talbot states that in general a reinforced concrete beam may fail by one or more of the following methods: “1. Tension of steel; 2. Compression of concrete. 3. Shearing of concrete; 4. Bond or slip of bars; 5. Diagonal tension of concrete; 6. Mis- cellaneous methods, like the splitting of bars away from the con- crete, the effect of the bearings, etc. What one of these methods of failure will govern the strength of a beam is dependent upon percentage of reinforcement, kind of steel, quality of concrete, relation of depth of beam to length of span, disposition of re- inforcement, and other conditions. “The stress which reaches the limit of the resisting property of the material is the one which will control the strength of the beam. It is not likely that two or more of these stresses will reach their point of failure at the same time. It is not even generally feasible so to proportion a beam that its strength shall be the same in tension, compression, tond and diagonal tension. For other reasons the amount of reinforcement or depth of beam may be made the same in spans of different length, or carrying different loads, and such a variation will change the relative value of tension compression, bond, etc. While it may be well to calculate the various stresses, in many cases the relative dimen- sions and amount of reinforcement are such that the method of failure may be told without much calculation. “Primary and Ultimate Failure —In judging the results of tests a distinction must be made between primary failure and ultimate failure. Some change or failure may take place in the beam dur- ing the test which will greatly modify the conditions, and we may not properly judge of the conditions existing at this time by what happens later. This early or critical failure may be named the primary failure, and its cause should be called the cause of failure of the beam. Thus slipping of the bars may come after diagonal failure has occurred. It is not always possible to know positively the cause of failure, but generally a careful study of the test will give a trustworthy conclusion. “Failure by Tension in Steel—Beams having shallow depth as compared with their length and having a moderate amount of reinforcement may. when tested with the usual way of loading, 278 CONCRETE AND REINFORCED CONCRETE. be expected not to fail before the steel has been stretched to its yield point, and the maximum load carried will generally be but little higher than that carried when the yield point is reached. Fig. 172 illustrates the typical form of failure by tension in steel. It should be noted that the tension cracks shown in the figure will appear considerably before the steel reaches its yield ! eee Fig. 172.—Beam Failure by Tension in Steel. point. With other forms of failure these cracks may appear, but they do not grow to the extent they do in tension failures. “Failure by Compression of Concrete.—Beams having a large amount of reinforcement may fail by the crushing of the concrete at the top of the beam before the steel has been stressed to its elastic limit. As has been stated, the amount of reinforcement Fig. 173.—Beam Failure by Compression in Concrete. necessary to develop the full compressive strength of the con- crete depends upon the quality of the concrete and the elastic limit of the steel, and will vary from 1 to 1% per cent. Figure 173 illustrates this form of failure. If stress-deformation diagrams are made, the line showing the shortenings of the upper fibre of the concrete will curve away rapidly from the usual GENERAL PHENOMENA OF FLEXURE. 279 ' straight-line position, but the steel deformation line will not be modified materially until near the line of failure. This condition of the stress deformation curves is the best evidence that the crushing strength of the concrete has been reached without de- veloping the strength of the steel at the yield point. “Bond or Resistance to Slipping of Reinforcing Bars.—In order to have beam action there must be a proper web connection be- tween the tension and the compression portion of the beam. Where there is no metallic web reinforcement the concrete of the beam acts as this web. Of course, the amount of stress in the reinforcing bars and also in the compression area of the concrete varies at different cross sections along the length of the beam. The increment between consecutive sections of increase in the tensile stresses of the reinforcing bars is transferred to or con- nected with the increments of the compression stresses of the concrete by means of this web. In transmitting the increment of tension from the reinforcing rods to the surrounding concrete there is developed a tendency of the rods to slip in the concrete, and the amount of resistance to slip thus developed is called bond, and will be measured in terms of the area of surface in contact with the concrete. It will be seen that the total bond developed on the surface of the bars in one inch of length is equal to the total change in total tensile stress in the bar for the same inch of length. Bond may be compared to the action of the rivets joining flange to web in a riveted steel plate girder, except that in the reinforced concrete beam the contact is continuous. “For horizontal reinforcement the formula for bond may be de- rived as follows: For any vertical section of the beam the equa- tion M — A, f, d’ gives the resisting moment. (M = moment, A, = area of steel, f, == stress in steel, d’ == distance from center of steel to center of pressure in concrete.) Differentiating this equation, aiM dts dx dx d’ By the principles of mechanics of beams aM dx ? where V is the total vertical shear at the given section (reaction 280 CONCRETE AND REINFORCED CONCRETE. at support minus load between the support and the section con- sidered). Substituting and transposing, As d fs V dx d’ ; . A Asd fs Now the derivative dx expresses the rate of change of the total tensile stress in the reinforcing bars at the section under consideration; it is given in terms of a unit of length of beam (lb. per inch of length), and measures what is transmitted to the concrete by bond. Using m as the number of bars, o as the efficient circumference or peri- phery of one bar, the total surface of bar for one inch of length of beam is mo, and the bond stress developed is mou, where u rep- resents the bond developed per unit of area of surface of bar. Equating this to the value of the derivative given in the above equation, and solving Vv u= mo d’ This equation is not applicable in just this form when the bars are bent up or inclined from the horizontal, since in this case d’ is a variable, and this fact will modify the differentiation. “Failure of Bond Between Steel and Concrete.—Failure by the breaking of the bond between the steel and concrete is unusual for a beam having the proportions of ordinary test beams. The calcu- lated bond stress develofed in the beams tested at University of Illinois in 1905 ranges from 70 to 193 lbs. per sq. in., and the bond tests on plain mild steel rods give values from 200 to 500 lbs. per sq. in., and on some forms of deformed bars from 300 to 1,000 Ibs. per sq. in. Size of beams tested was 8 ins. wide, 11 ins. deep and 13 ft. long, with test spans of 12 ft. The center of steel rein- forcement was 10 ins. below top surface. The concrete used was a 1:3:6 mixture. It is true that conditions under which the bond tests are made differ from those in the beam, and also that bond stresses may not be distributed in the beam exactly as assumed, and considerable allowance should be made for these. Besides, the effect of time and of repetition of stress upon bond resistance is not known. For bars bent up out of the horizontal a much higher stress is brought into action near the end of the GENERAL PHENOMENA OF FLEXURE. 281 bar than with the bars laid horizontally throughout the length of the beam. The value of the bond resistance will depend upon the smoothness of the surface of the bar, the uniformity of its diameter, the adhesive strength of the concrete, and the shrink- age grip developed in setting. In most of the failures reported to be caused by slipping of the bars, it seems certain that this slip- ping occurred subsequent to diagonal tension failures or other changes which were the primary causes of failure. For mild steel reinforcement placed horizontally in beams of ordinary dimensions, the diagonal tensile strength of the beam will be a much weaker element than the bond stress between steel and con- crete. “Failure of the bond between the reinforcing rods and the con- crete is difficult to detect. The fact that a rod has been found after failure of the beam to have slipped is not evidence that slipping occurred before failure began and hence was the prim- ary cause of failure. In some instances reported as failure by slipping, the slipping evidently occurred as a consequence of the new conditions brought into play by whatever was the primary cause of failure, and slipping may not be considered the primary failure. “A number of beams reinforced with tool steel rods having a smooth, almost polished surface were tested. All these beams failed by slipping of the bars. Their appearance after failure is shown in Fig. 174. TABLE LXII. VALUES OF VERTICAL SHEARING STRESS AND BOND DE- VELOPED IN BEAMS REINFORCED WITH TOOL STEEL. Vertical Bond Shearing Stress 1b. per sq. in. Beam Ib. per sq. in. of surface of bar No. Vv Vv Remarks. bd’ : mod’ . 49 95 161 1.10% reinforcement. 53 72 123 1.10% reinforcement. 57 66 112 1.10% reinforcement. 60 107 181 - 1.10% reinforcement. 62 73 124 1.10% reinforcement. 61 73 124 1.10% reinforcement. SI Iol 114 1.66% reinforcement. 52 126 143 1.66% reinforcement. 55 107 120 1.66% reinforcement. Av. gl 133 61 61 69 1.66% reinforcement. 56 ane ie 1.10% reinforcement. 282 CONCRETE AND REINFORCED CONCRETE. “Table LXII. gives the bond developed in Ibs. per sq. in. at the time of failure, as calculated by the equation Vv u= ¥ mo d’ and also the vertical shearing stress developed with the same load. The weight of the beam and loading apparatus is included in these calculations. Beam No. 49 failed suddenly. The failure L iGenter_ line _ Center | Line Beam No. 55 Fig. 174.—Failures of Beams Reinforced with Tool Steel. shows a nearly vertical crack with a horizontal crack extending along the plane of the reinforcement toward the support. It * seems likely that slipping occurred from the end of the rods to the vertical crack, and also that the horizontal crack developed at the time of slipping and in connection with the vertical tension coming on the rod. The bond stress developed, 161 lbs. per sq. in. of surface of bar, is the largest except one developed in GENERAL PHENOMENA OF FLEXURE. 283 this series. The vertical crack was closer to the support than was the case with the other beams. “Eight beams may be described as slipping and failing gradu- ally. Ata load of 75 per cent. to 95 per cent. of the maximum, a crack, vertical or nearly vertical in position, appeared between the load point and the support and not very far from the former, and gradually increased in height until the maximum load was reached. The load then fell off, and this crack grew until sud- denly failure occurred at a load from 1,000 to 4,000 lbs. less ‘than the maximum. In beam No. 52 the critical crack appeared at 13,000 lbs., 87 per cent. of the maximum load. The direction and position of the critical crack are indications that slipping of the rods was the primary cause of failure. The cracks, as shown in Fig. 174, are as they appeared near the time of final failure. At first appearance only the vertical portion showed. It seems likely that this slipping occurred from the crack to a point under the load, there being no shear and hence no bond stress on the portion of the beam between the two loads at the third points of the beam. The calculated bond stress at maximum loads for these beams ranged from 114 to 143 lbs. per sq. in. Bond tests with this tool steel, the rods being embedded 6 ins. in the con- crete, gave values of 153, 147, 154 and 141 lbs. per sq. in. of surface, averaging 149 lbs. per sq. in. The critical crack in these eight beams first appeared when the bond stress developed ranged from 90 to 125 lbs. per sq. in. The position of the critical crack and the manner of failure of this group of beams are materially different from the conditions accompanying diagonal tension failures. It must not be overlooked, however, that the presence of this initial crack does weaken the resistance of the beam to diagonal tension, and thus increases the web stresses above the crack and also the vertical tension transmitted from the rod just beyond the crack, which together cause the final failure to be of the form shown. “There are two types of bond failures: (1) Slip from the direc- tion of the middle of the span, with a slowly developing crack slightly inclined from the vertical, which extends upward as the load is increased to the maximum load, growing still more as the test is continued at a dropping load, and finally breaking by splitting below and cracking diagonally above. (2) Slip from the end of the beam and a sudden failure at maximum load by 284 CONCRETE AND REINFORCED CONCRETE. the formation of a crack slightly inclined from the vertical and near to the support, together with accompanying splitting and diagonal cracking at the top of the beam. The characteristic of the first is slow failure along a crack which is nearly vertical, and which gradually grows with increasing load, and of the latter a sudden failure through a crack in a nearly vertical posi- tion not visible until time of failure is reached. It is likely that both are variations of a single form of failure, the former appear- ing when the vertical tensile strength of the concrete is exceeded. In failure by diagonal tension, the cracks formed are inclined more from the vertical than are these cracks. In none of the tests made with mild steel bars placed horizontally was there any evidence of slip of bar, although in one beam a bond stress of 193 lbs. per sq. in. was developed. “Vertical and Horizontal Shearing Stresses.—It is shown in the mechanics of beams that there exists throughout a beam vertical and horizontal shearing stresses which vary in intensity, and that at any point in a beam the vertical shearing unit-stress is equal to the horizontal shearing unit-stress there developed. As noted under bond, the total tension in the reinforcing bars varies along the length of the beam, as does also the total compressive stress. The horizontal shearing stress may be considered to transmit the increments or increase of the total tensile stresses in the rein- forcing bars (which is transmitted to the surrounding concrete by the bond stresses) to the corresponding increments of com- pression in the compression area of the concrete, the concrete thus forming the stiffening web of the beam. The amount of this horizontal tensile stress so transmitted from the reinforcing bars per unit of length of beam is by the equation Vv Mou == =: bd’ “Consider this distributed over a horizontal section just above the plane of the bars for a unit length of beam, and call the hori- zontal unit stress v. The shearing resistance per unit of length of beam thus developed is then b v, and equating this to mo u, Vv Vi roe: bd’ “This equation gives the horizontal shearing unit-stress, and therefore also the vertical shearing unit-stress, at a point just GENERAL PHENOMENA OF FLEXURE. 285 above the level of the reinforcing bars. As no tension is here considered as acting in the concrete, there will be no change in the intensity of the horizontal and vertical shearing stresses be- tween this line and the neutral axis. For the part of the beam where tensile stresses extend well down to the reinforcement some modification of this treatment may be made. Above the neutral axis the intensity of the shearing stresses will decrease by the law of change of horizontal shearing stresses for homo- geneous rectangular beams modified to suit the parabolic stress deformation relation. The distribution of the intensity of the Deformation Tension and Horizontal Compression Shearing Stress Fig. 175.—Distribution of Horizontal and Vertical Shear. horizontal shearing stress over a vertical section is represented in Fig. 175. “As d’ generally will not vary far from .85d, the shearing stress by equation Vv y= — bd’ will be, say, 18 per cent. more than if considered to be uniformly distributed over a vertical section extending down to the center of the reinforcing rods. Even if tension is considered to exist in the concrete for a short distance below the neutral axis, the shearing stress will not be greatly modified thereby. If the bars are inclined or bent up from the horizontal, the above equation must be changed to allow for a variable d’. The horizontal and vertical shearing unit-stresses obtained by Vv a are low, the highest value developed for the beams tested by Prof. Talbot being 151 Ibs. per sq. in. Even if we consider a point in a beam at which the concrete is carrying stress in tension up to its ultimate strength, the value of the diagonal shearing the use of the above equation y = 286 CONCRETE AND REINFORCED CONCRETE. will scarcely reach twice the vertical shearing stress. The shear- ing strength of concrete is much higher than this, probably from 50 to 75 per cent. of the compression strength. As a rule, rein- forced concrete beams do not fail by shear. What has been called shearing failures are really diagonal tension failures. “Diagonal Tension in the Concrete—In the flexure of a beam stresses are set up in the web which are sometimes called web stresses and sometimes secondary stresses. Besides the hori- zontal and vertical shearing stresses already discussed, tensile or compressive and shearing stresses exist in every diagonal direc- tion. In determining the bending moment only the horizontal components of these are taken. When there is no metallic web reinforcement all the diagonal stresses are taken by the concrete. By the analysis of combined shear and tension the value of the maximum diagonal tensile unit stress (see Merriman’s Mechanics of Materials, p. 265, 1905 edition) is found to be t=%stvVustv, “When t is the diagonal tensile unit-stress, s is the horizontal tensile unit-stress existing in the concrete,-and v is the horizontal or vertical shearing unit-stress. The direction of this maximum diagonal tension makes an angle with the horizontal equal to one-half the angle whose cotangent is 14 = v “Tf there is no tension in the concrete, this reduces to t—v, and the maximum diagonal tension makes an angle of 45° with the horizontal, and is equal in intensity to the vertical shearing stress, “When the diagonal tensile stresses developed become as great as the tensile strength of the concrete, the beam will fail by diagonal tension, provided there is no metallic web reinforce- ment. Fig. 176 gives the typical form which this failure takes. As the value of the maximum diagonal tensile stress developed in a beam is by equation c= G s4va ree dependent upon the horizontal tensile stress developed at the same point, it is difficult to compute its actual amount. The best method seems to be to compute the horizontal and vertical shear- ing unit-stress, and make all comparisons on the basis of this GENERAL PHENOMENA OF FLEXURE, 287 value. Beams which fail by diagonal tension and which are without metallic web reinforcement give a value of 100 to 1 50 Ibs. per sq. in. for the vertical shearing unit-stress when calculated by the equation Vv (=e bd’ (and lower values for poorer concretes), the limit depending upon the strength of the concrete. When these values are com- bined in the equation t=%stv% $4 vi with the probable horizontal tensile stress developed in the concrete below the neutral axis, the resulting diagonal tensile Fig. 176.—Beam Failure by Diagonal Tension. stress is evidently the full tensile strength of the concrete. Diagonal tension failures are frequently characterized by sudden breaks, without warning, as is the case in the failure of plain concrete beams. A variation from this gives a slower failure, “part of the shear being carried through the reinforcing bars and the ultimate failure involving the splitting and stripping of the bars from the beam above. It is evident, since the vertical or external shear is independent of the resisting moment, that the relation between the depth and length of a beam will determine whether the beam will fail by diagonal tension or by tension of steel or compression of concrete. In relatively short and deep beams the diagonal tensile strength will fix the strength of the beam, while in long, shallow beams this element may be disregarded. Since the diagonal tension may be resolved into horizontal and vertical or other components, the concrete may be relieved of a 288 CONCRETE AND REINFORCED CONCRETE, part of the diagonal tensile stress by one or both of two means: (1) By bending the reinforcing rods or strips sheared from them into a diagonal position, and (2) by making use of stirrups to take the vertical component of the diagonal tension.” (The va- rious methods of providing for these shearing stresses are dis- cussed in another chapter). “Failure by Splitting of Bars Away from Upper Portion of Beam.—Failures sometimes occur, either after a diagonal crack has appeared or at the same time that such a crack is observed, in which the reinforcing bars and the concrete below the level of the bars are split away from the remainder of the beam, the crack running horizontal for some distance. This stripping is caused by vertical tension in the concrete transmitted to it by the stiffness of the reinforcing bars after the concrete fails to carry its assignment of diagonal tension. In Fig. 177 consider that Fig. 177.—Failures When Bars Split Away from Upper Portion of Beam. a diagonal crack, C D, has been formed. Take 2 vertical section through AD. Qn account of the diagonal crack normal beam action does not exist, and part of the vertical shear from the main portion of the beam is transmitted by the projecting portion of the beam DCB acting as a cantilever, and the flexural stiff- ness of the bars to the point C, ard there applied to the left por- tion of the beam as a downward force. Figure 177 (a) shows the part at the left of A D acting as a free body. The part of the ver- tical shear applied at C tends to split the bars from the beam, starting at C and running toward E. This action is resisted by the tensile strength of the concrete in a vertical direction, and when this is exceeded the bars will split from the concrete above. This may happen without any horizontal movement or slip of the bars. Splitting of bars from the beam presupposes a failure in diagonal tension, for as long as true beam action exists vertical —” GENERAL PHENOMENA OF FLEXURE. 289 tension is not developed. ‘After the diagonal crack is formed this part of the beam takes on the nature of a truss. This form of failure is then a secondary failure, though under some con- ditions the load carried before splitting occurs may be consider- ably more than that at which the diagonal crack appeared. This explanation shows why the concrete at the bottom of the bars continues to adhere to the bars. There is no evidence of shearing failure in these cases.” Attention should also be called to the danger from spacing bars too closely or with not sufficient concrete below the bars. Tests were made to determine the effect of various kinds of loadings, repeated application of load, the effect of rest after release of load and effect of retention of load. Details of these tests can not be given in this place, but the conclusions drawn by Prof. Talbot are as follows: “Center loading may be expected to give results which are higher than those found by the ordinary beam formula. Moments of resistance derived from results of center loading tests may not properly be used as a basis of calculation for other forms of loading. The results with loading at the one-third points com- pare favorably with multiple-point loading, and are comparable with uniform and other distributed loading. “Repeated applications of a load which sets up high com- pressive stresses in the concrete give increasing deformations. The deflections after ten to fifteen applications were found to be 12% to 30% in excess of the deflection at the first application. “Beams which were loaded to give a stress of 15,000 lbs. per sq. in. in the steel and 800 lbs. per sq. in. in the concrete, or more, failed to’ return to their original position upon the removal of the load, the amount of the retained deflection being 20% to 35% of the deflection. No appreciable recovery of the set was apparent after periods of 15 to 40 hours. “Beams loaded so as to develop stresses of 18,000 to 32,000 lbs. per sq. in. in the steel and compressive stresses of 800 to 1,400 Ibs. per sq. in. in the concrete gave little perceptible change in appear- ance or growth of cracks after the load had been retained 20 to 38 hours, and upon the application of greater loads the load- deformation curves and deflection curves rose upward and took the general shape for such curves for progressively applied loads. During the retention of load, the deflection increased 12% 290 CONCRETE AND REINFORCED CONCRETE. to 35%, the principal cause of this’increase evidently being the increased compression of the concrete.” Position of Neutral Axis.—Observations were taken to deter- mine the position of the neutral axis throughout the different stages of flexure. During the first stage it remained below the middle of the beam, during the second stage the axis usually rises and then remains in one position during the third stage until the maximum load is nearly reached. Beyond the maxi- mum load for a normal amount of reinforcement the axis rises somewhat higher during the fourth stage, but with the excess of reinforcement it lowers during the rapid deformation of the upper fibre. During the third stage the position of the neutral axis did not differ materially for different forms of reinforcement. In gen- eral the neutral axis was found to be apparently lower than is given in several theories. Prof. Talbot states that the following formula locates fairly accurately the position of the neutral axis for Es = TOs c X = 0.23 + 0.16 p, x being the proportional depth of the neutral surface, and p the percentage of steel or the ratio of area of steel to the area of concrete, the depth from the top of the beam to the center of the steel being used in both cases. Conservation of Plane Sections—To determine if the usual hypothesis that plane sections before bending remain plane sec- tions after bending held true, Prof. Talbot made extensometer measurements on two similar beams, 1314 ins. deep, with the rein- forcement 12 ins. below the top face. On one of the beams the contact points were I1 ins. and 8% ins. apart vertically, the upper point of the extensometer in each case being 11% ins. below the top of the beams. In the second beam the points were 11 and 6 ins. apart vertically, with the upper extensometer point as be- fore. On each beam the readings of the extensometers were taken simultaneously as the loadings of the beams progressed. From these observations two sets of values of the elongation of the steel and compression of the concrete were determined and also the resulting positions of the neutral surface. Prof, Talbot states that the results agree closely, perhaps as closely GENERAL PHENOMENA OF FLEXURE. 291 as the variations in the transmission of the interior deformations, to the contact point, could be expected to agree. Distribution of Stresses in a Beam.—There is considerable difference of opinion in regard to the elastic behavior of the con- crete in a beam subject to flexure. As has been explained, the coefficient of elasticity, that is, the ratio of the stress to the de- formation, is not a constant quantity, but decreases as the load brought upon the concrete increases. The ordinary theory of flexure is based upon Hooke’s law, which is that the ratio be- tween the stress and the strain or deformation for a given ma- terial is constant within its elastic limit. It has, however, been found that this law holds true for concrete only when the stresses are quite low. The variations in the resistance of the successive fibres of the concrete above and below the neutral axis depend upon the con- servation of — sections. As has been stated Profs. Talbot eB Abels Ak—-fe_-->lB es x ——— i eee es ty Nau Se LK L « cla — ) = 7x thet + a. b, c. dl. Fig. 178.—Distribution of Stresses in a Beam. and Turneaure have demonstrated that for all practical purposes plane sections before bending remain plane after bending, and for the purpose of this discussion they will be so considered. Upon this supposition it follows that the distortion of any fibre will be proportional to its distance from the neutral axis and the law of variation of compression stress will be represented by some curve which closely approximates a parabola with its vertex at the fibre of greatest compression. It is upon the form of this curve that authorities do not agree. When its exact form is known the laws governing the relation between the elastic de- formation, the stress and the modulus of elasticity, will become known. ; Let Fig. 178(a) represent the cross section of a beam under flexure. Then Fig. 178(b) will represent the elastic deformations following the theory of conservation of sectional planes. Fig. 178(c) will show the conditions when the stresses are so small 292 CONCRETE AND REINFORCED CONCRETE. that the modulus of elasticity of the concrete may be considered as constant. In this stress diagram the triangie A O B represents the total compressive stress on the concrete for width of beam b, and as {,.’ represents the maximum intensity of the stress, the total stress acting will be represented by fe’xd b 2 . , and, as its center of gravity is —xd above the neutral axis, its Awe 3 moment about this axis is fe’xd b 2 fe'b x 2d? ——— x — xd; or, M = —__.. 2 FS 3 The conditions, which are considered to govern the action of the compressive stresses when the modulus of elasticity is as- sumed to be constant throughout the whole range of stress, are indentical with those given above. Such a distribution of stress is usually termed the rectilinear relation between stress and strain. Stress Under a Varying Modulus of Elasticity.—It is almost universally admitted that the coefficient of elasticity varies with the loading. This is undoubtedly true, as it has been demon- strated by a large number of tests. In spite of this the author has seen stated by a recent writer that, as a result of recent experi- ments made by him, the modulus seems to be constant. A study of his tests brings to light the fact that his experiments were made on a carefully balanced, extremely dense concrete and only represent the values of the modulus under exceptional condi- tions. Under normal conditions concrete will be far from as well proportioned or dense, and the curve of compression wili be more truly represented by a parabola or some other curve. In Fig. 178(d) the extreme fibre is supposed to be subjected to a stress f,, the fibres nearer the neutral axis, have a smaller stress per square inch, and the modulus of elasticity for each smaller stress is greater than of that for the fibre next above it and nearer the top of the beam, but as has been stated, in order that a section, which is plane before bending, shall remain plane after bending, the strain must be proportional to the distance from the neutral axis. It follows that the stresses on the inner GENERAL PHENOMENA OF FLEXURE. 293 fibres do not decrease according to a rectilinear law as repre- sented by the triangle of stresses, but are greater than are indi- cated by the ordinates of a triangle. If the curve O B is as- sumed to be a parabola, the total stress on the concrete above the neutral axis will be represented by the area within the parabola. This is 2/3 £, xd, and the total compression on the section of the beam, whose width is b, will be 2/3f,xdb. The center of gravity of the parabola is 54 xd above the neutral axis, and the moment of the total compressive stress on the beam will be 2/3 f, xd b x 5% xd, or M = */,, f, b x?d?. 'M. Considére considers that this parabolic distribution of stress represents closely the action of the internal stresses in the cross- section of a beam under flexure. The studies of Profs. Hatt, Howe, Talbot, Turneaure and others upon compression tests of 12-in. cubes made at Watertown Arsenal confirm M. Considére’s assumption, showing that the curve of compressive stresses close- ly approximates a parabola with its origin at the extreme outer fibre of the concrete, and its axis perpendicular to the direction of the applied forces. Capt. John S. Sewell has made a special study of the Water- town Arsenal tests, plotting the curves of a large number of tests, and states in a paper to the International Engineering Congress at St. Louis, in 1904, that while curves of individual tests were often quite irregular in form, by grouping and combining curves according to the strengths of the concretes, they became more regular, and that for the leaner mixtures they became quite regular. He suggests that the great variation in the specimens of rich concrete is probably due to shrinkage strains in setting. Details of Capt. Sewell’s studies can not be given here, but the results are as follows: The curve of stress was found to lie between the straight line of the triangle representing the recti- linear distribution of stress and the curve representing the parabolic distribution. He found that the areas included between the axis of coordinates and curves plotted from actual tests were about 20 per cent. in excess of the area representing the triangular distribution, while a parabolic representation is 33'/, per cent. in excess of the triangular areas, and the height of its center of gravity is between the heights 14 xd and 2/3 xd of the triangular and parabolic areas respectively. He, therefore, as- sumes its area to be 54 f.xd, and the height of its center of 204 CONCRETE AND REINFORCED CONCRETE. gravity to be 3/5 xd. The compressive stress upon the cross- section of the beam will, therefore, be 54 f, xd b, and its moment about the neutral axis 3¢f,bx*d2, This assumption probably gives a value of the stress nearer its true value than either of the other two methods outlined above, and would appear to give conservative results when used in the design of beams. Elongation or Stretch of Concrete in a Reinforced Beam.—In general the concrete in a reinforced beam stretches similarly to the concrete in a plain beam. In the latter case, however, the beam ruptures when the limit of stretch, sometimes called the elastic limit, is reached. Rupture does not occur, however, in a reinforced beam when the limit of the tensile strength of the concrete in the lower part of the beam is reached. In fact the stress often passes considerably beyond the rupture point of a plain concrete beam before visible cracks appear. This is proba- bly due to the action of the reinforcement in distributing the stress over the entire length of the piece, while in non-reinforced beams the stretch is localized and rupture takes place. Considére advanced the theory that the concrete in tension in a reinforced concrete beam can be strained far beyond its elastic limit, or far beyond the breaking point of non-reinforced con- crete. He bases this theory on experiments made by him, in which he found that reinforced beams took a deflection under transverse loading far beyond the point at which a beam not reinforced would break without any apparent injury to the con- crete on the tensile side of the beam. The usual amount of stretch of elongation, which plain concrete will. undergo before rupture, is about 0.0001 part of its length. Considére was not able to discover cracks or evidences of failure in some of his specimens when the stretch was 0.001 part of their length, and is said to have cut sections of concrete out of the beam below the reinforcement after having subjected it to such a stretch, and upon testing them in tension, found them to have the same tensile strength possessed by plain concrete specimens which had not been subjected to stretching. While recognizing the value of tests made by this eminent authority, the acceptance of the above _ theory without evidence from similar tests made by other experi- menters would seem unadvisable. Such a theory would indicate that the combination of the two materials possesses physical GENERAL PHENOMENA OF FLEXURE, 295 properties different from those shown by concrete, when con- sidered by itself. It is improbable that such is the case. In fact, Considére’s theory is not borne out by later experiments conducted by Profs. Talbot, Turneaure and others. Prof. Turneaure -made tests upon reinforced beams which had been kept under water until they were tested. By placing the beams in water, as soon as they were hard enough to do so, prevented the formation of hair cracks, due to contraction in setting. The beams, while wet, were tested with the tensile side up by applying the load from below. This enabled more careful observations to be taken. It was found by repeated tests that when the flexure was such that the unit elongation of the concrete was between 0.0001 and 0.0002 narrow bands of mois- ture, perhaps ¥4-in. wide or water marks, appeared on the sur- face at some places on the tensile side, the moisture apparently coming through cracks. That they were actual cracks at these water marks was proved by sawiny out a strip of concrete con- taining such a mark. In all cases the strips fell apart at the water mark. Strips cut between water marks on the contrary were uninjured. As the flexure was increased the marks developed into visible . dark hair-like cracks, and at a unit elongation at or above 0.00035 were plainly visible to the naked eye. We may infer from these tests that M. Considére did not happen to include a crack in the test pieces cut from the tension side of his beam. While it is possible his beam did not crack, Prof. Turneaure’s tests show that cracks at times do occur, and it is probable that they always occur when the stress in the tension side of the beam exceeds the tensile strength of the concrete. (Prof. Talbot showed by his tests that the concrete and metal act together as a homogeneous material until a unit fibre elongation of from 0,0001 to 0.000133 is reached; when the concrete seems to lose its ten- sile strength and its load is thrown upon the steel. The steel then begins to elongate more rapidly and fine hair cracks begin to appear when the tensile stress in the steel becomes about 15,000 lbs. per sq. in. . In plain concrete no water marks or cracks were observed before rupture. (A comparison of the observed and calculated elongations of the reinforced concrete with those for plain con- crete at rupture, shows that the initial cracking in the former 290 CONCRETE AND REINFORCED CONCRETE. occurs at an elongation practically the same as in the latter. Prof. Turneaure writes-as follows in regards to this phenom- enon:* “The significance of these minute cracks is an open question. It has been supposed that concrete reinforced by steel will elongate about 10 times as much before rupture as plain concrete. These experiments show very clearly that rupture begins at an elongation about the same in both cases. In the plain concrete total failure ensues‘at once; in the reinforced con- crete, rupture occurs gradually, and many small cracks may de- velop, so that the total elongation at final rupture will be greater than in plain concrete. In other words, the steel develops-the full extensibility of a non-homogeneous material, that otherwise would have an extension corresponding to the weakest section. “The presence of these cracks, of course, seriously affects the tensile strength of the concrete, and as they appear at an elonga- tion corresponding to a stress in the steel of 5,000 lbs. per sq. in. or less, it would seem that’ no allowance should be made for the tensile resistance of the concrete. Furthermore, if such cracks are present the calculation of the tensile resistance of reinforced concrete by the method used by Considére leads to no useful result. In his tests Considére determines the stress in the steel from measurements of its elongation and then assumes the concrete to carry the remainder. Assuming the value of E to be uninfluenced by the concrete, this would be correct, so long | as the stress in the steel and in the concrete is uniform between points of measurement. As stated by Considére himself, such results are only average values. But concrete may be cracked entirely through and yet possess a very considerable average tensile strength over a length of several inches. Obviously in that case an average is of no value; the strength of the concrete is usually taken at zero.” In practical design the most important question which arises is how far a concrete may be cracked without exposing the steel to corrosive influences. In this respect it seems to the writer that the minute cracks, which appear in the early stages of the tests, can have very little influence. However, the entire question of the effect of the cracks and pores in the concrete on the cor- rosion of the steel needs careful investigation. The question may well be asked if the presence of these minute *Proceedings of Am. Soc. for Testing Materials, 1904. GENERAL PHENOMENA OF FLEXURE. 297 cracks will prove dangerous to the steel. While reliable data on this subject are much needed to answer this important question, it is reasonable to assume that under ordinary conditions of load- ing the cracks are so small that no dangerous action will take place. Again, if the structure be occasionally strained up to or slightly above the assumed working stress of the steel, its elas- ticity is such that when this extreme loading is removed the cracks will close up again, expelling any moisture which may have collected. s ~~ The moisture and acid gases in the atmosphere are the active elements producing corrosion; that they will act in cracks so minute that they can not be detected by the unaided eye is im- probable, especially when we consider that their action must take place in close proximity to an alkali like cement, which is present in the concrete, and in all probability covers the metal with a protecting film, even if the concrete be ruptured clear to the metal. Care should be taken in the design of works to be subjected to extreme exposure in severe climates, to keep the unit stresses in the steel low, thereby avoiding entirely or reducing to a mini- mum possible cracking in the tension flange of the concrete. If an approximate computation be desired for the elongation in the bottom or tensile side of a beam it may be obtained by the use of the formula Pl Pl = —; transposing we obtain \ = —_, rv AE in which a is the deformation required , 1 = the length of steel in tension, A — area of steel and P = stress in steel, which may be computed in the usual manner. E may be taken at 30,000,000. Inserting these numerical values in the formula and solving the required elongation A will be obtained. Thus if P = 30,000 1 = 8 ft. 4 in. = 100 ins., A = 2 sq. ins., we have 30,000 X 100 . A = ————— = 0.05 inches. 2 X 30,000,000 Tensile Resistance of Concrete in Reinforced Beams.—From the facts as above set forth in regard to the experiments of Profs. Talbot and Turneaure, we may safely conclude that the tensile strength of the concrete should be neglected in all computations for the strength of beams, with the exception of computa- 298 CONCRETE AND REINFORCED CONCRETE. tions for the deflection of beams, when the stresses are quite low. This agrees very well with the practice Of most of the leading engineers in this country as well as in Europe. The regulations of the Building Department of the Borough of Man- hattan, New York City, the Prussian regulations for concrete buildings, issued by the Minister of Public Works of Prussia, and the regulations adopted by a commission of experts for the French Government to establish a building code for reinforced concrete structures, provide that the steel shall be considered as taking the entire tensile stress in beams. Hence, we conclude that all tensile stress in the concrete should be neglected and in the design of beams will assume that all tensile stress is carried. by the steel. CHAPTER XIX. THEORY OF BEAMS. Theory of Beams.—The theory of reinforced concrete has been the subject of much study by engineers and mathematicians for: a number of years. Theoretical investigations in conjunction with practical tests have been made and much valuable data ob- tained, but, unfortunately, very little uniformity is shown in tests by different experimenters and discrepancies in results necessarily appear ; nevertheless, much knowledge of the proper- ‘ties of this material of construction has been obtained. Within the past year or two a series of experiments has been undertaken by Profs. Talbot,.Turneaure, Howe, Hatt and others, in which great care has been taken to secure uniformity of conditions. Some of the results of the tests, already available, have been given in the preceding pages and have done much to clear up doubtful points. The continuation of these experiments will un- doubtedly do much to advance scientific knowledge on this subject. As the main object of reinforced concrete is to secure a ma- terial which will withstand strains due to transverse loading, it is of prime importance to secure a theoretical formula or formulas for use in the design of the section of beams, girders and slabs at the point where the bending moment is a maximum. It is de- sirable, if possible, to secure a rational formula, but it is not absolutely essential to successful design that the formulas be rational, as empirical formulas, if properly applied, may, and do agree closely enough, for all practical purposes, with the results obtained from actual tests upon reinforced concrete pieces. Many such formulas are used in the design of reinforced con- crete structures, yet, other things being equal, it is desirable to use the formula or formulas which embody most fully all condi- tions entering into the problem. The theory developed by Prof. Hatt, with certain modifications, seems to the writer the most rational of the numerous theories which have been advanced, and will be employed in this work for the design of beams, slabs and girders. The development of this theory is given in the suc- ceeding pages. In another chapter a number of the theories 300 CONCRETE AND REINFORCED CONCRETE. most widely used in this country at the present time will be given, not because any one of them is more essential to the suc- cessful design of reinforced concrete than any other, but to show the best known present practice. The present trend of thought on this subject seems to be to develop a rational formula and, after securing such a one, to determine as closely as possible the value of certain factors con- tained therein, inserting these values, neglecting other un- important factors and then reducing and simplifying these ration- al formulas until they take the form of straight line formulas. Prof. Hatt’s formulas, thus reduced, become very simple in appli- cation and are coming into great favor. The theory of reinforced concrete pieces, strained in flexure, is usually based upon the following assumptions: First. There is so perfect a union between the concrete and metal and the latter is so distributed that the two will act to- gether as a practically homogeneous material. Second. Sectional planes before bending remain plane sur- faces after bending within the elastic limit of the steel. Third. There are no initial stresses in either the concrete or the metal due to the shrinkage of the concrete in setting. Fourth. The applied forces are parallel to each other and perpendicular to the neutral surface of the beam before bending. Fifth. The values of the coefficients of elasticity obtained in direct tension and compression apply to the material under stress in beams. ‘ Sixth. The entire tensile stress is carried by the steel. First. As has been already stated, the utility and safety of reinforced concrete for structural purposes depends largely upon a close union between the two materials. When the adhesion is not great enough mechanical bonding should be used. In order that the stresses may be more easily transmitted from the con- crete to the steel, it is desirable that a number of small bars uniformly spaced be used in preference to one or more large bars. This arrangement will cause the combination to approxi- mate more nearly a homogeneous material. Second. The hypothesis of conservation of plane sections is universally accepted, and, as has been explained, is probably ap- proximately correct. Third. As a matter of fact, there are always initial stresses THEORY OF BEAMS. 301 due to expansion or contraction of the, cement in setting, to change of temperature, amount of moisture present during set- ting, etc. M. Considére demonstrated, by means of ‘tests on plain concrete, that when setting in water the specimens increased in length and when setting in air, contraction took place. The amount of change at the end of two or three years was probably from 0.0015 to 0.0020 of the length. The internal stresses are so uncertain and of so small importance that their effect is usually neglected in developing a formula for the strength of beams. Again an attempt to take them into. account would introduce great complications without in the least diminishing the possible error. Fourth. It is essential for the purpose of analysis that the applied forces shall be parallel to each other and perpendicular to the neutral axis; otherwise it will be necessary to resolve the torces parallel and perpendicular to the neutral axis. This will introduce another unknown quantity and greatly complicate the problem. ~ Fifth. It is assumed that the coefficient of elasticity of con- crete is variable within the limits of stress and an assumption is always made as to the form of the stress-strain curve of con- crete in compression. The form which the stress-strain diagram takes for a variable coefficient of elasticity has been explained in a preceding chapter. In this discussion we will first assume that the curve is a parabola and then give in a subsequent chapter the modifications necessary in the formulas when a rectilinear relation and the relation expressed by Capt. Sewell’s curve are used. ; Sixth. The results of all recent tests seem to indicate that the tensile strength of the concrete should be neglected, with the reservation that it shall be taken into consideration when calcu- lating the flexure of a beam under moderate stresses. Again, as was explained in the preceding chapter, it seems advisable that the tension in the lower part of the beam shall not be so great that the elongation of the concrete shall exceed 0.001 of its length. Let Es = modulus of elasticity of steel. Let Ee = modulus of elasticity of concrete in compression. fs = tensile stress in steel, lbs. per sq. in. fe = compressive stress in concrete, lbs. per sq. in. As = area of steel in tension. A = area of cross-section of concrzte from the top face to center of reinforcement, A = bd. 302 CONCRETE AND REINFORCED CONCRETE. s = unit elongation of steel in tension. : Xe = unit compression of extreme fibres of concrete in compression. b = breadth of beam in inches. d =depth of reinforcement below compression face of beam = effective depth of beam. : xd = distance of outside compression face of beam to neutral axis where d is depth of reinforcement. As Pp = = ratio of cross-section of steel in tension to cross-section of beam above center of gravity of steel. 3 e = = ratio of modulus of elasticity of steel to concrete. Ea We will assume a rectangular beam under flexure. Fig. 179 I i eS i foo b 3} prek pote a =o SS) hN-d eRe) 4 Neutral Anis N io dix) : 1 es 2 L— - ——_}- — - vse 1 4- (a) Aske Cd) ean (ce) sx Cross Section, Diagram of Strains or Deformation. ee of Stresses. Fig. 179.—Beam Deformation and Stress Diagram. a, b and c, shows a cross-section of the beam, and gives a graphi- cal representation of the deformation and stresses. A, in Fig. 179(b) represents the deformation of the extreme fibre of the concrete in the compressive side of the beam, and a, the unit elongation of the steel. Since sectional planes before bending remain plane after bending. da xd SS cy teens anenas es oer 1) Aes (1—x)d ‘ But fe fs Ee = and Es = ; e As or fe fs Ac = , and As = , Le Es Therefore Ae xd fe Es a SS OG SSS rrhioiene eae 2). As (1 = x) a Ec fs ( ) Transposing and reducing f Ec xfs ee et vn cn capensis (@): Es (1 — x) A The total stress on the concrete above the neutral axis is repre- THEORY OF BEAMS. 303 sented by the area within the parabola, when a parabolic dis- tribution of stress is assumed; this equals 2/3 f, xd, for a unit width, and the total compression I, on the section of a beam having a width b, is Be 2G PUD sae desc ay ees Sa ees (4). The total tension F, in the steel is Pas AG Ye) none ibid cate awnee < ota (5). For equilibrium these two forces, which act parallel to each other and in opposite directions, must be equal. They may be considered as the two forces of a couple and Asfs = % fexdb ee rc (6). Dividing both sides of this equation by bd and remembering that 3 A. bd == A, and — =p, we obtain A pfs SS SGP ORS ais ear eee ater to suai (7). Substituting for f, its value from equation (3) we obtain 2Ec fs x” pfs PT regs eae ee ay 3Es a — x) reducing Es 4% = CP S83) VD) Saseeea tesa (8). from which Es Es Es x=—% pel */o p(i1+ % Dr Wl sean esha (9). Ee Ec Ee Es or replacing by e. ec 3 3 xe hens a] Sep (1+ 6 ) Geass Kare g aie leeneeenates (io). 2 8 When the values of e and p are assumed, the position of the neutral axis may be found by solving this quadratic equation. Finally, when the position of the neutral axis is known, the moment of resistance of the beam may be found. Taking the center of moments about the neutral axis the total resisting moment of the beam is equal to the sum of the moments of com- pression in the concrete and tension in the steel, and if M, repre- sents the resisting moment of the beam, Mr = 5/2 febx*d?+ Asfsd (1 — x) ...... (11). But in order that the beam shall not fail, the resisting moment 304 CONCRETE AND REINFORCED CONCRETE. must be equal to or greater than the bending moment. Then placing M, = M, and reducing eq. 11 becomes M = [5/2 fex? + pfs (1 —x)] bd’ .............. (12). The coefficient in this equation contains both f, and f,, and, therefore, the equation is not in a convenient form for use in the solution of beams, as it is usual, when a definite value of p has been determined for use under the given conditions, to as- sume a safe working value for either f, or f,, compute the sec- tion of the beam and then determine if the working value of f, of f. for this section, as the case may be, comes within safe limits. By substituting successively in eq. (12) the values’ of f, and f, from equation (7) and reducing equation (12) takes the form: ; M = % fex (1 — % x) bd? ....... 22 (13). when the allowable stress of the concrete is assumed and M = pfs (1 — % X) bE occ cece cece (14). when the allowable stress in the steel is assumed. The coefficient p f, (1 — 34x) will be found to be the determin- ing factor when a low percentage of steel is used, or when a moderately low percentage of steel with a concrete of high strength is used. The coefficient 2/3 f, x (I—34x) will be the determining factor when a high percentage of steel is used, when a steel of high elastic limit is used or when a concrete of low crushing strength is used. These two coefficients become equal to constant quan- tities when definite values have been assumed for p, e, f. and f,. These coefficients may be represented by a constant K. Then K may have either of the values K = 2/3 f, x (I — 3x), or = pfs (1 — 36x.) Then our equations for the solution of beams are as follows: % fox = pfs aaa, ee ete aceasta et ik ac (7). =— %Aept V *%/2ep (1 + % ep) ..ceecceccvceceveeuee (10). MG ROP aes secocnce ace wonctenctrnccsorins avcsens (15). When definite values are assumed for e, p, fg and f, and inserted in the two coefficients 2/3 f, x (1 — 3x) and p f, (1 — 34x) two values will be found for K. The smaller of these values should be used for computing the resisting moment of the beam. Values of K for different values of f,, f,, p and e may be worked out and tabulated. When this has been done, by select- ing the proper value of K from the table and substituting it in equation (15) the solution of this equation for a given beam THEORY OF BEAMS. becomes very simple. f, and f, are given in Tables LXIII, LXIV, LXV and LXVI. TABLE LNXIII. VALUES OF K, FOR VARIOUS RATIOS, p, OF STEEL. DB .OO1 002 003 004 .005 .006 007 .008 ,009 010 O12 O14 O16 018 (20 025 .030 035 .040 045 0.0 p. .OOI .002 .003 .004 .005 .006 .007 .008 .009 ,O10 O12 .O14 016 018 .020 .025 .030 -035 .040 045 s0s0 d=1. fs = 12,000. fe = 400. e=6. e€=7.5. e=10. e=12, e=15. e=— 20. K K K K K K 12 12 12 II oie II 23 23 23 22 22 22 34 34 33 33 33 33 43 45 44 44 43 43 47 52 55 54 54 53 51 56 62 64 63 63 54 59 66 70 74 73 57 62 69 74 80 82 60 65 72 77 83 91 62 68 75 80 86 94 67 72 80 84 88 99 70 76 84 89 93 104 74 80 87 93 99 107 76 83 QI 96 102 TIO 80 86 04 99 106 113 86 92 IOI 105 112 120 QI 97 105 FLL 116 124 95 102 110 114 121 128 99 105 113 118 124 131 102 109 117 122 127 134 106 112 119 124 130 130 TABLE LXIV. VALUES OF K, FOR VARIOUS RATIOS, p, OF STEEL. == fs = 12,000. fe = 500. e=6. e=7.5. e=10. C= 12. C=15. C= 20. 12 12 12 II II VI 23 23 23 22 22 22 34 34 33 33 33 33 45 45 44 44 43 43 56 55 55 54 54 53 64 66 65 64 64 63 68 74 75 75 74 72 72 78 86 85 84 82 75 81 91 95 93 92 78 85 93 100 103 101 83 90 Too 105 1I0 120 gr 95 105 II 116 124 93 100 109 116 124 130 95 104 114 120 128 133 100 107 118 123 132 138 107 115 123 131 140 142 114 12I 131 138 145 149 119 127 137 143 I51 155 124 131 142 148 155 160 128 136 145 152 159 164 » 132 139 149 155 162 176 305 Values of K for various values of p, e, p .0OI .002 .003 .004 .005, .006 .007 .008 .009 O10 .O14 O14 O16 018 020 .025 .030 035 .040 045 .050 p. .OOI .002 .003 .004 .005 .006 007 .008 .009 O10 O12 O14 O16 018 .020 025, .030 035 .040 045 .050 306 CONCRETE AND REINFORCED CONCRETE. TABLE LXV. VALUES OF K, FOR VARIOUS RATIOS, p, OF STEEL. d=1. fs = 16,000. fe = 500. p. e=6. e=7.5. e=10. e=12. e=I15. €=20. p. .OOL 16 15 15 15 15 15 O01 .002 31 30 30 30 30 29 002 .003 45 45 44 44 44 43 .003 .004 54 60 59 58 58 57 .004 .005 59 65 73 72 72. 70 -005 .006 64 69 78 83 85 84 .006 .007 68 74 82 * 88 95 97 007 .008 72 78 86 92 100 109 008 .009 75 81 90 96 104 114 .009 O10 78 84 904 100 107 118 O10 O12 83 90 100 106 110° 124 O12 O14 88 96 105 112 116 130 O14 O16 93 100 110 116 124 133 016 .o18 96 104 II4 120 128 138 018 .020 100 107 118 124 133 142 .020 025 107 114 125 132 140 149 .025 .030 114 122 132 138 146 155 030 035 119 127 138 142 151 160 035 .040 124 132 142 148 155 164 .040 045 128 136 146 152 160 170 045 050 131 139 150 156 162 176 .050 TABLE LXVI. VALUES OF K, FOR VARIOUS RATIOS, p, OF STEEL. d=t. fs = 20,000. fe = 600. e=6. e=7.5. e=I10. e=12, C= 15. e=20. p K K K K K K p .OOI 19 19 19 19 19 19 OO1 -002 38 38 38 37 37 37 002 .003 57 56 56 55 55 54 .003 .004 65 71 74 73 72 71 .004 .005 71 78 8&7 90 8&9 88 .005 .006 76 83 04 100 106 105 .006 .007 81 89 99 106 114 121 .0O7 .008 86 93 104 III 120 132 008. .009 go 97 109 117 125 136 .009 O10 93 101 112 120 129 I4I .O10 O12 100 108 120 127 132 149 IZ O14 106 II4 126 134 139 155 O14 016 IIT 120 131 130 149 160 O16 018 114 125 137 144 153 165 018 .020 120 129 141 149 159 170 .020 025 129 137 151 154 168 179 025 030 137 146 158 166 175 186 .030 035 143 152. 164 172 181 192 035 .040 149 158 170 177 186 197 040 045 154 163 175 182 IgI 200 045 .050 158 167 179 186 195 204 .050 THEORY OF BEAMS. 307 The method of determining K and the manner of using it for determining the section of a beam will be shown by the solution of a problem. Example.—Design a beam of 12.5 ft. span to carry at the age of two months a load of 1,000 Ibs. per lin. ft., using a 1: 2: 4 Port- land cement concrete, with a factor of safety of 5, and steel hav- ing an elastic limit of 40,000 Ibs. per sq. in., with a factor of safety of 2% reckoned from the elastic limit. From page 192 we find that the crushing strength of a 1:2:4 concrete at I month is 2,400 lbs. per ‘sq. in. This gives us a working value of 480 lbs.; we will use 500 Ibs. From Thacher’s formula, page 209, we find the coefficient of elasticity of the concrete is about 3,000,000 lbs. per sq. in. The working value of the steel using a factor of safety of 2% at the elastic limit, .is 16,000 lbs., and its coefficient of elasticity may be taken at 30,- 000,000. Es Then e= Ec Inserting the values e = I0 and p = .o1 in equation (10), it becomes = I0. 3 X 10 X .O1 J 3 X 10 X .OF + xe (1 + % X 10 X .o1) 4 2 solving = — .075 + 0.3045, or, X = 0.3195 = 0.32, approximately. Now inserting the values x = 0.32 and fe = 500 in formula (13), K = % fex (1 — % x), 2 X 500 X .32 = ——___—__ (1 — % x .32), 3 and K = 94. This value of K should be employed for, substituting the values x = 0.32, p = .01, and fs = 16,000 in equation (14). K = pfs (1 — % x), we find Therefore K = 141. M M = 94 bd’, and bd? =—. M=% WI, 94 12,500 X 150 = ——____- = 234,375 in. lbs. 8 308 CONCRETE AND REINFORCED CONCRETE. ga 288875 94 bd’? = 2,494. Assuming a width of beam, ; b = 12 ins. 2,494 ; d= = 208, approximately. 12 d = V 208 = 14.4 ins. Using 14% ins. and adding 114 ins. of concrete to cover rein- forcement, we have a total depth of beam of 16 ins. Ac = bd = 14.5 X 12 = 174 sq. ins. But the percentage of reinforcement equals 1 or .o1, and A, = o1 A,. As = 1.74 sq. ins. Three rods 7% in. diameter give 1.804 sq. ins. area. Therefore, three 7g in. diameter rods will be chosen for the reinforcement, and we have a 12 x I6-in. section reinforced with three rods 7% in. in diameter. Shearing Stresses in Reinforced Concrete Beams.—There is some diversity of opinion as to the action of the internal stresses in a reinforced concrete beam under flexure and the best manner to care for them. The nature of these stresses and the different systems devised to care for them, have already been explained, and we will now discuss the manner of determining whether rein- forcement in the vertical plane of the beam is needed, the proper amount to be used and the most desirable location of the stirrups. As we have seen, the shearing strength of concrete is some- what in excess of its tensile strength. This strength will be found sufficient to care for all dangerous stresses due to verti- cal and horizontal shear in a majority of cases, with a normal amount of reinforcement for moderate and long spans. In com- paratively short spans or deep girders heavily loaded, failure may be caused by shearing or by diagonal tension. Failure usually takes place at or near the quarter points or between these points and the ends by means of diagonal cracks slanting upward toward the center of the beam. These failures are said to be due partly to shear and partly to tension, or, more strictly speaking, they may be considered as due to tensile stresses induced by shear. The diagonal cracking is supposed to be due either to the slipping of the rod or to the rupture of the concrete by diagonal tension. With plain rods this may be due to a reduction of the section of THEORY OF BEAMS. 369 the rod on account of the stretching of the metal. If the concret- ing is properly done, the adhesion should not fail in a beam of normal dimensions. Failure, due to stretching, can only take, place when the stresses in the rods are at or near their elastic limit, and in that event the beams would soon fail from other causes, Another and more common form of failure is by horizontal shearing at or slightly above the plane of the bottom or tension reinforcement. (If the stresses in the concrete along this plane be kept below a certain safe limit, longitudinal shearing will not take place. This may be accomplished by avoiding the use of too large rods, and where several rods are used, if a sufficient amount of concrete is kept between the rods, failure from this cause will be avoided.) The usual rule is to space the rods so that the distance between them is equal to or greater than 1%4 times the diameter of the rod. Another method of failure, sometimes called a shearing faiiure, is by diagonal tension in the concrete. This method of faiiure has already been explained. The tendency toward shearing may be prevented by anchoring the rods at their ends. Provision is also made to care for both kinds of shearing and diagonal tension by bending up alternate rods at about the third points of the beams and running them on a slant such that they reach the upper portion of the beam near its end. The Hennebique system employs these bent shearing rods, to- gether with stirrups. Stirrups are used to prevent horizontal shearing, both with and without the bent rods. The action of the internal stresses may be best understood by comparing the concrete beam with a metal plate girder. In the case of a single reinforcement the concrete replaces the web and compression flange, while the steel carries the entire tensile stress. The web of the beam cannot fail by buckling as in the plate girder, but may by shearing as above explained. The horizontal shear at the plane of the reinforcement at any point may be determined by well known methods of analysis used in determining the flange stress in plate girders. Thus, if two points in the beam A and B be chosen at # distance apart, the moment and flange stress at these two points computed, the differ- ence in stress between them will be the increment of stress or 310 CONCRETE AND REINFORCED CONCRETE. horizontal shearing between them. This stress must be cared for by the shearing strength of the concrete supplemented, if need be by some of the well known forms of stirrups. If the increment of stress over the distance +, divided by the horizontal section of the concrete through which it is distributed, does not exceed the allowable shearing stress, no web reinforcing will be needed. If it is exceeded, a proper allowance may be made for the strength of the concrete, and metal of sufficient section provided to care for the remaining transverse shear. Treating this shear from another standpoint, we have from well known principles of mechanics the following axiom, “that at every point in the beam the intensities of the vertical and hori- zontal shears are equal.”* The resolution of these two shearing stresses at the neutral axis gives two equal and opposite stresses at right angles to each other—one compression and the other tension—making an angle of 45° with the neutral axis. At some distance from the axis these stresses, which are called secondary ‘stresses, combine with the principal stresses in the top and bot- tom of the beam, giving the resuiting lines of stresses as shown in Fig. 67. Theoretically, these stresses are best cared for by a tension reinforcement inclined upwards toward the ends at an angle of 45° to the axis of the beam. This is the principle fol- lowed in systems heretofore described having inclined stirrups. For the successful transmission of the increment of stress from the tension reinforcement to the concrete, which acts as the web and compression flange, it is necessary that the stirrups be firmly anchored to the longitudinal reinforcement. This is only ob- tained by the use of two or three patent systems, one of which, the Kahn system, has the stirrups sheared from the sides of the Lar and forming an integral part of it. Nearly as good results may be secured with a V-stirrup hooked over the corrugated bar and in a less degree with other deformed bars. When thus used it is assumed that the combination causes a truss action analogous to the Pratt truss, the concrete being strained alone in compres- sion, while the steel cares for all tensile strains. However, in the one case the use of patent bars is expensive, and the placing of concrete with stirrups inclined at an angle of 45° is difficult, and makes the proper tamping of the layers of concrete almost im- possible. This is even more difficult when the stirrups are de- tached. *Hiroi’s Plate Girder Construction, p. 16 THEORY OF BEAMS. 311 A more rational arrangement would seem to be to use vertical stirrups to care for the vertical shear, securing thereby a truss action analogous to that of the Howe truss. This arrange- ment gives a more economical distribution of the metal, is just as efficient as ‘either attached stirrups or stir- rups used with deformed bars, without the additional cost of patented bars, and, lastly, concrete may be placed and tamped with much greater facility and at a lower cost. The author knows of no concrete girders thus reinforced with a proper amount of metal that have failed by shearing. Some designers space the stirrups by empirical rule. Mr. E. L. Ransome’s rule is to place the first stirrup a distance from the end of the beam corresponding to one-quarter of its depth, the second a distance of one-half its depth beyond the first, the third a distance of three-quarters the depth beyond the second, and the fourth a distance of the depth of the beam beyond the third. Other empirical rules are used by other designers, while several more or less theoretical formulas have been devised which need not be repeated in this place. The size and location of the stirrups may be calculated as in a plate girder, treating the stress as actual shear. This is best done by drawing the shear diagrams for concentrated and dis- tributed loads, it being assumed, as outlined above, that the beam acts as a Howe truss with diagonal compression members in- clined at an angle of 45°. The resultants of these diagonal stresses are equal vertical and horizontal forces. It is assumed that a part of the horizontal forces is provided for by adhesion of the concrete to half of the surface of the tension members and the remainder resisted by the transverse shearing strength of the vertical rods. It has been found that several small rods give better results'than one large one, as there is a more uniform distribution of stress. The rods are usually made of the same size and spaced closer together toward the ends, where the shear- ing stresses are higher. To determine the spacing an area equal to the adhesion is subtracted from the shear diagram and the remaining area is divided into panels such that each has an area equal to the maximum shear allowed for one rod or series of rods. As the height of the panels decreases their length increases giving a series of spaces representing graphically the spacing of each rod or series of rods. This will be understood by referring 312 CONCRETE AND REINFORCED CONCRETE. to Fig. 180, which represents the shear diagram of a beam with a uniform and concentrated loading. The area above the loading AB represents the shear due to a concentrated load P, and that below the line the shear, due to uniformly distributed load, con- sidering only the portion of the shear diagram to the right of Fig. 180.—Shear Diagram of Beam with Uniform and Concentrated Loading. the center line of the beam. Then if the area above the dotted line k-/ represents the allowable stress cared for by the adhesion of the rods, the portion of shear in the diagram below this line must be provided for by stirrups. If this be divided into equal areas a, such that the amount of shear represented by area a will be cared for by each stirrup, the resulting linear dimensions of the trapezoids a give graphically the desired stirrup spacing. T-Beams.—T-beams are extensively used in floor construc- tion, and with considerable economy of materials. A portion of the floor slab connecting the ribs or girders is considered as act- ing as flange area. This may be safely done when the girder. or rib is built as a monolith with the floor slab. In many cases this is not done; under such conditions the girder should be designed with a sufficient area of concrete to develop the full strength of the reinforcing metal in the tension flange. There is consider- able difference of opinion among engineers as to what portion of the width of the floor slab may be considered as furnishing flange area for the T-beam. It is usual to assume that a width equal to a certain number of times the width of the stem of the T, usually from 3 to Io times, should be used. It is evident that, under normal conditions, ten times the width of the stem “b” of the rib is far too liberal an assumption, while a value of three is much too small; a value of from four to six is probably about right to fit all cases without straining the concrete too high. It will be readily understood that if the construction is mono- lithic, the slab will be fixed at the beam, and when loaded the concrete will be strained in compression in the under side of the THEORY OF BEAMS. 313 slab out to the point of contraflexure at about the quarter points of the slab span. If the concrete is strained at right angles to the direction of the floor span due to the slab acting as flange to a T-beam, we see that the concrete will be strained in two directions, or will have a stress double that usually assumed for the unit-working stress. If both primary and secondary rib systems are used, a portion of the concrete will be strained to nearly three times the assumed unit-working stress. On account of the fixing of the slab over the beam, some engineers assume that the concrete may be considered as fur- nishing flange area out to the point of contraflexure, giving a width of one-half the distance center to center of beams. Others only allow one-third the distance center to center of beam. A more rational method would be to take the width B of the fSersvesthecesas= Bh eensteseac sss > : a ce = | a | a-gt Meso higy geo = Kb Fig. 181.—T-Beam Diagram. slab used for flange area as a certain number of times the thick- ness t of the slab. For: Let S, represent the total shear between rib and flange along their plane of union. Let S, represent the total shear in the flange along vertical planes that are a continuation of the planes forming the sides of the rib, and which cut off the wings of the flange. Then for equal strength in shear t should equal 4% b. When b is the width of the rib, b should never be less than 2 t, although t may be less than 14 b. Then the flange width B may be taken as 10 t, which, if 2 t = b, will be equal to 5 b. Referring to Fig. 181, the lever arm between the compression and tension forces is d — 4% t. If B is taken equal to ro t, the compression area will be 10 t?» The stresses in the slab, however, will vary from a maximum at the rib to o at the outer edges of the flange B. These compression flange stresses may be assumed 314 CONCRETE AND REINFORCED CONCRETE. to vary as the ordinates of a parabolic segment, and the area available for compression will be ?/, x 10 t?, and the total com- pressive stress will be 2°/, f, t?. This will be on the side of safety, as a portion of the stem of the T is generally available for flange area. Again, the center of gravity of the parabola is either 5% t or °/, t, above the lower face of the slab, depending upon whether the origin of the parabola is taken at the top or bottom of the slab. Thus the assumption that the center of gravity is at % t above the bottom face of the slab is on the side of safety. Formulas 7, 10 and 15, given above for rectangular beams, may be used without difficulty for designing T-beams. They will hold true if the neutral axis coincides with or is above the under side of the slab; if it falls below the under side of the slab the formula will err on the side of safety. The position of the neutral axis will, of course, depend upon the values of B, b, t, d, and the amount of metal used. An empirical method of design which, with slight modifica- tions, has been extensively used, is as follows: Assume that the floor slab furnishes the necessary compression flange area, and assume its center of gravity at the center of the flange thick- ness. In order that sufficient area of concrete shall be available to develop the full strength of the steel, the area = t? should 3 fs not be less than — ey ec: 20 t? Thus if fs = 16,000, and fe = 500, should not be less than 32 As. 3 If the bending moment M and width B are known, and thick- ness t and amount p of steel assumed, d may be approximated from the formula M = K bd?, taking bd = ?°/, t?, and taking the value of K from Table XLIV. Then M 20 —Kt 3 When the depth d is fixed, and it is desired to obtain A,, the area of the steel M = (d — ¥% t) f, Ag, or THEORY OF BEAMS, 315 M ip (d — 41) It should be remembered, however, that As should not be 3 less than 32 A,, and b should not be less than 2 t. It is desir- able that stirrups be used to connect the floor slab to the stem of the T. A number of theoretical formulas have been developed by different engineers for the solution of T-beams. No one of them, however, is entirely satisfactory, as they are all based upon more or less doubtful assumptions. Again, the mathe- matical work necessary to their solution is quite complicated, especially as it is usually necessary to determine the position of the neutral axis, at best a tedious solution. When it is desired to use such a formula, either for designing new work or for checking work designed by some such empirical formula as that given above the formula developed by Capt. John S. Sewell, given on page 325 should be used. It should, however, be noted that the origin of the parabola is taken at the neutral axis instead of at the extreme fibre, as is usually done. This changes slightly the position of the center of gravity of the compression area, it being °/, d instead of 5% d above the neutral axis. This is on the side of safety. It is to be regretted that few tests have been made on T- beams, and these tests were made to déstruction, giving no data of value for the development of formulas for the solution of T-beams. It is to be hoped that tests will be undertaken and suitable data obtained in the near future for the development of rational T-beam formulas. Beams with Double Reinforcements.—When excessive loads are to be carried and it is unadvisable to increase the depth of the beam the compression flange is sometimes strengthened by the addition of reinforcing. metal. In order that the concrete and the steel in the compression flange act together as a homo- geneous material, it is necessary that the stresses carried by the concrete and the metal shall be proportional to their respective coefficients of elasticity, 1. e., f° es fe Be 316 CONCRETE AND REINFORCED CONCRETE. On account of this law, quite low unit stresses will result in the steel in compression, and the large amount of metal needed for the compression flange will not give an economic form of construction. In fact, some authorities hold that double rein- forcements are never an economic form of construction, although they have been extensively used by some European engineers. To determine the effect of double reinforcement, let us first assume a beam of rectangular cross-section, with sufficient area of reinforcement A, in its tension flange to develop the proper working stresses in the concrete of the compression flange. Let d, in Fig. 182, be the effective depth of the beam, and xd the distance of the neutral axis below the top of the beam. If a compression reinforcement having an area A®, be added to the compression flange at a distance z above the neutral axis, the ds. Spee xd eS — din ea eee et Fig. 182.—Stress Strain Diagram of Beam with Double Reinforcement. position of the neutral axis will be changed if the beam is loaded as before. If, however, when the compression reinforcement A‘, is placed in the compression flange, additional steel having an area A’, is added in the tension flange to develop the strength of the compression reinforcement A‘,, the position of the -neutral axis will remain unchanged. In order that this may obtain we must have the relation As’ Zz Ass d(1 — x) But in order that the steel shall undergo the same deformation as the concrete, we must have the relation fs d (1— x) SSS Se Oe Se (17), 5° ‘zZ Multiplying by equation (16), we obtain THEORY OF BEAMS. 317 fs As’ fs° As® that is, equal forces have been added to each side of the beam. The resisting moment M! added to the beam will be equal to M’ = fs As’ [z + d (1 — x)] in inch pounds. ==", Or fe Ac! == fet Awe cosaceneeicies4 (18), But fs° Es = = 6) smye Perea. cs eeuwuae (19), fe Ee or, (fs° =e fe i and ) fs As’ = e fe As‘, or, e fe As® fs The resisting moment of a beam with a single reinforcement is from equation (11). M = °/2 febx2d?+As fed (1 — x), and for the resisting moment of a beam with double reinforce- ment, we will add the quantity obtained in equation (18), and we obtain M = /a febx*d?+ Asfed (1 — x) + fs As’ [2 + d (1 —x)] ....(20), Pein —— remembering that e fe As® fs To determine the effect of double reinforcement, we will take the beam designed on page 307 and note the effect of doubling the reinforcement, and then add enough steel to the compres- sion flange to balance the increase of steel in the tension flange and note the increase in strength obtained thereby. From page 307 we have the following data: Span = 12.5 ft., resisting moment = 234,375 in. lbs., b = 12 ins., d = 14.5 ins., p. = .O1, x = .32 d = 4.65 ins., d (1 — x) = 9.85 ins., A, = 1.74 sq. ins., net, or using three rods 7% ins. in diameter = 1.804 sq. ins. Doubling the reinforcement A, = 3.60 sq. ins. of metal. It is not necessary in this case to determine the value of x as K may be taken directly from Table LXV., K = 118. From equation (15) M = K bd?, hence M = 297,714 in. lbs., which is the re- sisting moment obtained by the doubling the area of reinforce- ment. or a total gain of 63,329 in. Ibs. As’ = 318 CONCRETE AND REINFORCED CONCRETE. Now let us place enough steel in the compression flange to care for the added 1 per cent. 1.8 sq. ins. of steel, A’, =1.8. Now from equation (19), € fe As° As’ = ———_.. fs fe = 500, fs = 16,000, e = 10, and 1.8 X 16,000 Ass = ————_—. = -5.76 sq. ins. 10 X 500 Six rods 1% ins. diameter = 5.94 sq. ins., will be used, plac- ing them 1.5 ins. below the top face of the beam and the distance between the steel in tension and compression, i. e., the lever arm of forces added is 13 ins., which equals z + d (1 — x) in equa- tion 18. The resisting moment obtained by the use of the steel in compression is 16,000 X 1.8 X 13 = 374,400 in. Ibs. it being remembered that 1.8 sq. in. of steel in tension is bal- anced by 5.76 sq. ins. of steel,in compression. The total resist- ance of our beam now is. 234,375 + 374,400 = 608,775 in. Ibs. The resisting moment obtained by the use of 2 per cent. of re- inforcement was 297,714 in. lbs., and we see that by the addition of enough steel to balance 1 per cent. of steel in tension, the re- sisting moment is more than doubled, and is 2.6 that when only I per cent. of steel was used, or considering it from another standpoint, the addition of 4.34 per cent. of steel increases the strength of the beam 2.6 times. The excessive amount of steel necessary for the compression flange, 1.67 times that used in tension, should be noted. This is due, as has been stated, to the necessity of having the same deformation in the steel and concrete. When a lower percent- age is used than that necessary to fulfill this requirement, the internal stresses will not be in accordance with the usual accepted and safe assumptions. CHAPTER XX. VARIOUS BEAM THEORIES. Formula for Beams, Based on a Rectilinear Distribution of Stress—We will assume a rectangular beam under flexure. Using tl. same nomenclature as. heretofore and neglecting the tensile stress of the concrete, the elastic deformations of the con- crete above the neutral axis will be represented graphically by the triangle aob in Fig. 183 (b), following the theory of con- servation of sectional planes. The triangle Ao B, Fig. 183 (c), will represent the total compressive stress on a unit width of con- crete, f, being the maximum intensity of stress, assuming that cb = Sai ee RT bi rune *K > B; de : fli |e ane beso ee d : Lat Neutral Axis o. ~ thle eel. fe a oe = Z : i Ct (a) wigs (b) Rene fgennal (3 Cross Secfion. Deformation Diagram Stress Diagram, Fig. 188.—Stress Strain Diagram of Beam Assuming Rectilinear Distribution of Stress. 3 the modulus of elasticity of the concrete is constant throughout the whole range of stress. This assumption gives a rectilinear re- lation between the stress and strain in the concrete. The total stress on the concrete for a unit width of beam then equals % fe xd, and the total compression on the section of a beam having a width b is Fe = % fe xd b. The total tension on the steel is Pe SAG fe: care suinnnes cate Seems (21), These two forces are equal, and ia Asis = 4% fexd Devcecseeeccue ees atiateneataul (22), As Reducing, remembering that a = p, and Ac = bd, pis=—=% LEX. scdrenncoaese es armed (23), But the relations between Ac, As, fe, fs, Ec and Es are the same as those explained on page 302, and are expressed by eq. (3). Ec x fs f. = ———-—_____. Es (1 — x) 320 CONCRETE AND REINFORCED CONCRETE. Substituting this value in eq. (23), we obtain E- x? fs pis = % —— —__, Es (1 — x) reducing Es %Bxy= CTs) Se cst oh add en dnc aushancadaovatecs (24), From which Es Es Es x= — p = 2 pir+% fy: |hawcause sacs (25), Ee Ec Ec Es or replacing by ¢, x=—ep+ V2ep (1+ Mep) ............005- (26), The resisting moment of the beam may now be determined as equation (26) gives the position of the neutral axis. Taking the center of moments about the neutral axis the total resisting moment will be equal to the sum of the moments of compression in the concrete and the moment of tension in the steel, and we have M = % fexdb x % xd + Acfsd (1 —X)......0000e. (27), = tebx*d?+Asfed (1 — x), reducing as before. M = [% fex? + pfe (1 —x)] bd@ .............. (28), Equation (28) contains both f, and f., and to reduce it tq a convenient form for use, we will substitute successively the values of f, and f, from equation (23). Substituting and reducing, equation (28) takes the form M=% fex (1 — % x) bd?................. (29) when the allowable stress for the concrete is assumed, and the form Mp fe Gh ho) it os geese oad (30), when the allowable stress in the steel is assumed. As before the coefficient p fs (1 — 1/3 x) will be found to be the determining factor when a low percentage of steel is used or when a moderately low percentage of steel with a concrete of high strength is used. The coefficient 12 f.x (1 —1/, x) will be the determining fac-: tor when a high percentage of steel is used, when a steel of high elastic limit is used and when concrete of low crushing strength is used. Definite values of these coefficients are obtained as explained VARIOUS BEAM THEORIES. 424 in Chapter XIX., in connection with the discussion of beams under a parabolic distribution of stress, which may be repre- sented by a constant K and, as before, we have for the solution of beams the equations Shs Us CIS ecco tan cee geneween a Ada event (23), X=—epzV2ep (1+ Weep) .....ccsscceeeee (26), and MeSH Ke bd? ses. psa eadeasenekieustanen (31); in which the coefficient K of equation (31) is obtained from the coefficients K=pf (7 — % x), = %fex (1 —%x). The smaller value obtained from these coefficients should be used. If desired a: number of values of K may be obtained by using various values of p, e, f, and f. and tabulated, then by selecting the proper value for use under the given conditions, the solution of the given problem will be greatly simplified. Example.—Design a beam using Formulas (23), (26), (31), having given the same data as was used for the example on page 307. From page 307 we have the following data: M = 234,375 lbs., e== 10, p= ot, f, = 500 and f, = 16,000. From equation (26) we have x=—10X of +V2xX 10x o1 (1+ % x 10X01), from which or x = 0.358. To cetera value of K, we insrrt value of fs = 16,000 lbs. in coefficient K = pfs (1 — % x), and .358 K = .o1 X 16,000 (1 — ——), from which K = 121. Again inserting value fe = 500 in oe K = % fex (1 — x). K = % x 500 x = (1 — ¥% X .358), or : K = 79. Hence the proper value of K to be used is 79; and we have M = 79 bd’. but M = 234,375, and we will assume b = 12. We then have 234,375 = 79 x 12 from which ; d° = 247.2, and , is d = 15.72 ins. depth of beam required. 322 CONCRETE AND REINFORCED CONCRETE. We will use 16 ins. and the area of beam == 12 x 16 = 192 sq. ins.; I per cent. of this is 1.92 sq. ins., which is amount of rein- forcement required. Three rods 1%/,, x 18/,, ins. = 1.98 sq. ins. Adding 1.5 ins. of concrete below the reinforcement we ob- tain a beam 12 x 17% ins., reinforced with three #°/,, x **/,,-in. rods. Formulas for Beams, Based on Distribution of Stress, Proposed hy Capt. John S. Sewell We will assume as before a rectangu- lar beam under flexure. As explained on page 293, the elastic deformations above the neutral axis, as found by Capt. Sewell’s study of Watertown Arsenal Tests on Concrete Cubes, under compression, are represented by a line lying between the curve representing a parabolic distribution and the straight line repre- senting a rectilinear distribution of stress. This may be shown graphically by the curve oxt in Fig. 184, in which the curve Fig. 184.—Stress-Strain Diagram of Beam Based on Distribution of Stress Assumed by Capt. J. S. Sewell. oyt is the curve limiting the parabolic distribution and the line ot the rectilinear distribution of stress. The height of the center of gravitv of the area oxtz above the neutral axis, as was stated on page 294, may be taken at ’/, xd and the area of stress is taken at 4 f,xd. The total compressive stress on the section of a beam having a width b is: Be 196 fe RO -B> eis 4s dessoresscsgaases s vena os eaves (32), fe being the maximum intensity of stress on the concrete. As before, neglecting the tensile strength of the concrete, the total tensile stress carried by the steel is Bie Aig ts: ace Sancn veh mnomen vecew sags (5). But these two forces are equal, and Bratt Oe te xd bec tcca saw vio ce hg dees (33), Reducing, remembering ne = p, and Ac = bd, Ae Ponta: SOB. Peat nas euunataa yea y eembtcntunnl dg (34), VARIOUS BEAM THEORIES. 323 But the same relations exist between Ae, As, fe, fs, Ec and Es as was ex- plained on page 302, and there exists the relation f Ec x fs a Gera atitacendatsseienraedieateeiele (3). Es (1 — x) Substituting this value in equation (34), we obtain 4 Es 3x = PGES) cede tid inepavagieinc euclessieide (35), From this Es 1 8 Es 2 Es : x=— 4, pf gies p(+= °) seipbaisnndts (36), Ee 5 Ee 5 Ee \ Es or replacing by e. 8 7, 2 x=—theptal—ep (1+ ep) abe esata tele ech (37), 5 5 The resisting moment of the beam may now be determined as eq. (37) gives the position of the neutral axis. Taking the cen- | ter of moments about the neutral axis, the total resisting mo- ment will be equal to the sum of the moments of compression in the concrete and tension in the steel, and we have: M = & fe xdbx%xd+Asfsd (1 — x), M = [% fex* + pfs (1 — x)] bd? .............. (38), But equation (38) may be reduced to a convenient working form, as was explained on page 304. By substituting successively the values of f, and f, from equation (34), we obtain reducing 2 M = % fex (1 — — x) bd?, 5 when the allowable stress for the concrete is assumed, and M = pfs (1 — */s x) bd’, when the allowable stress in the steel is assumed. As was explained before, the coefficient p f, (1 — ?/, x) will be the determining factor when a low percentage of steel is used, or when a moderately low percentage of steel with a concrete of high strength is used. The coefficient 54 fx (1 — ?/,x) will be the determining factor when a high percentage of steel is used. when a steel of high elastic limit is used and when concrete of low crushing strength is used. 324 CONCRETE AND REINFORCED CONCRETE. Definite values of these coefficients may be obtained and tab- ulaied, as before explained. — ‘Then, for the solution of a beam, using Capt. Sewell’s distri- bution of stress, we have the equations: pitas 96) fe Se 2 suis aly watsinseew es ea (34), 8 2 x=—‘*/,ep+ Ve (1+) Ssdieae iach etic (37), 5 5 MoS bd? saya cerns Reaemas (38), of the relations, ; K = % fe x (1 — */s X), or =pfex (i —%s x ). The solution of a beam is given in the following example: Example.—Design a beam, using Formulas (34), (37) and (38), having given the same data as was used for the example on page 307. From page 307 we have the following data: M = 234,375, € = 10, p= .01, f, = 500 and f, = 16,000. From eq. 37 we have 8 2 = — */5 X 10 X .O1 # y/= «10% 01 (1 + — X 10 X wor) 5 5 from which x = .328. To determine the value of K we insert the values of x and fs = 16,000 in the formula for the coefficient, which is K = pfs (1 — 7/5 x), and K = ..o1 X 16,000 (1 — 7/5 X .328), K = 139.- Again inserting value of fe = 500 in the coefficient, K = % fex (1 — 7/5 x). K = % X 500 X 328 (1 — */, X .328). K = 89. Hence, using the smaller value of K = 8, eq. 38 becomes M = 8 bd’, But M = 234,375, and assuming b = 12 ins., we have 234,375 = 89 x 12 d’, from which d? = 2109.4, and 7 d = 148 ins. depth of beam required. We will use 15 ins. Area of beam = 12 x 15 = 180 sq. ins., 1 per cent. of rein- forcement is used, 180 x .or = 1.8 sq. ins. = area of steel re- VARIOUS BEAM THEORIES. 308 quired. Three rods 7-in. diameter give an area of 1.804 sq. ins., which will be ample. Adding 1.5 ins. of concrete below the re- inforcement we obtain a 12 x 164-in. beam, reinforced with three 7-in. diameter rods. T-Beam Formula.—The following T-Beam formula* was de- veloped by John S. Sewell, Capt. Corps of Engrs., U.S. A. The assumptions are: Plane sections, unity of action of con- crete and steel, no initial stresses due to setting strains, loads ver- tical, beam horizontal, steel takes all tensile stress. The stress- strain curve is a parabola, with vertex on neutral axis, as A, Fig. 185. Let the dimensions of the sections be denoted by the letters in the figure, all being expressed in inches. Assume that the center of gravity of the area, BC GH, is at the center of the , : ‘ ‘ t flange thickness, so that its lever arm with respect to A is ys t —. Saniseane cen eceaees safe Al 2 k ie sy gee td eb es > a Je Le x eS tis --\y esac et | as | Tee Ne ay LS , ‘ a= * - + G hs ji Ps 1 > s -—}—e- bt —— — ~-tC ++ = [ Neutral Axis fe Neutral Axis at : se ‘ H ' tH 4 eocee te 2 4---b--4 Fig. 185.—Diagram Illustrating T-Beam Theory of Capt. J. S. Sewell. This is slightly in error, on the safe side. Assume that in any horizontal plane, the compression flange stresses vary as the ordinates of a parabolic segment, having its vertex where its plane cuts the curve A B, and its axis coincident with the line of inter- section of its plane, and a longitudinal vertical plane through the middle of the rib; the maximum ordinate of the segment being at the vertex, and equal to the F ordinate of the curve A B at the same point; its ordinates at the edges of the flange reducing to o Let Es Ee T ts F fe bi represent the represent the represent the represent the represent the represent the of area. represent the b represent the a represent the modulus of elasticity of steel. modulus of elasticity of concrete. unit tensile stress in the steel. elastic limit of steel. unit compressive stress in the concrete. ultimate compressive strength of concrete per unit width of flange of T. width of the beam, in inches. sectional area of steel per inch of width. “Theory developed from that of Mr. Johnson, (see page 272). 326 CONCRETE AND REINFORCED CONCRETE. ab represent the total sectional area of steel in the beam. yi represent the distance of the neutral axis from extreme element in compression. yz represent the distance of the neutral axis from center of gravity of steel reinforcement. \ represent the compression in the extreme element of concrete, per unit of length. X 2 represent the elongation in the steel, per unit of length. Pe represent the total compressive stress in the concrete. P’. represent the total compressive stress in the stem of the T. P’”. represent the total compressive stress in the flange of the T. Ps represent the total tensile stress in the steel. L represent the length of the span, in feet. s represent the shearing strength of concrete. Sn represent the total shear between rib and flange, along their plane of union. Sv represent the total shear in the flange along vertical planes cutting off the wings of the flange. ° ° Then, Vick yo Lori eteanaemares (1). re ye F T —=—,i = and A, = NX yi Ec Es Therefore, y2 T Ee i T Ec —-= , and y2 = Vir arrioueccecmoro mene. (2). yi F Es F is ts Ec Therefore, y= Vi wee sak pd eRe (2a). fe Es From the assumptions made for T-beams, and the conditions of equilibrium, Pee Pe se Pe = Ps ab P cce ein cedtded cele (3). Therefore Pe Ps ab = Se ee ing aes Pee igneanae (4) oe T or, Pe Ps Co (4a) ts ts From Johnson’s Equation 6, in his “Materials of Construction,” p. 20, fe s = ———_. 2 tan. 6 in which @ is the angle of rupture under direct compressive stress. It is usually about 60°, whence fe = 3.464 but it is thought best to assume, for safety, fe s=— P’=Sr= Sr 8 (not strictly true for Sv, as a part of P’’c is not transmitted to the wings; the error is.on the safe side). VARIOUS BEAM THEORIES. 327 Ss=%sxbx’B’Lxi2=3bsL. Svx=%sx2tx%eLxiz2=6tsL. It is evident that, for equal strength in shear, b should be at least twice as great as t, and t practically equal to % b. The equation of the stress-strain curve, referred to A as the origin of co-ordinates, is, fe F= y : ay Hence, : fe? ee f= [— ») : ¥1 Therefore, yu From the equation of the stress-strain curve, and the properties of the horizontal parabola assumed as the curve of stress in the flange, we have y3 */a Pe” = % bi [Han at ( ) |- yi a \ */s */> Da fe yi : —) (- ) | sk do ge se Ble RS Wied B58 (6). yi ¥3 5/2 Sn = 3bs L= Pe” = */s bi fe ya Est yu fe _ S = —, hence ya 5/, 3% b fe L = ‘*/s bi fe yr | ¥ — I1{ —— y1 : bL Therefore, be 732. $$. pg —_. sss eee eee (7). rf (2)"] Substituting this value in Equation 6, we get, Pee" So fe Dale ccs ccisasnes ox aa cb a eadeanwa es ee T eaaeeaients aPaeanas (8). y3 Va Pe = Pe’? + Pe” = % bfe LL + % bfe ys ( 7 Yi y3 3/4 =bfe |%L+%y yi ‘ ‘ t M = as ys Pe’ + | ys + =) Pie Pa Yai ccs ceca: tiecnsctel ered 804 oo we SS (9) 2 328 CONCRETE AND’ REINFORCED CONCRETE. The numbered equations are sufficient for designing. Determine t from the requirements of the floor slab; assume d (if possible, so that d will be at least = 4 t). Compute P,’, Pe” and P,—all in terms of b. Substitute in equation 9, and b may be determined. Ifb > 2 t, t must be increased; in designing T- beams, as in rectangular beams, compute M for a load 214 times greater than the working load. Make F = f,, and =. It will be found that, for similar assumptions as'to the relative values of d and t and the same values of f, and E,, designs of similar cross-section will be obtained for different loads and spans, so that the moment of the stresses may be written, quite accu- t rately, in the form, M =kfetb: (yz: + ys + — 2 It will also be found that b, will be practically equal to b, multiplied by a constant. This enables a design of a certain type to be detailed quite simply and quickly, and also gives a means of quickly determining the approximate stresses in a given de- sign, after the constant k and the ratio of b, to b have been deter- mined for various types of designs, 1. e., for various groups of assumptions as to the values of f, and E, combined, with the various values of t, corresponding to different spans and load- ings. Prof. A. N. Talbot's Beam Formulas.—The following theory of beams developed by Prof. Arthur N. Talbot deserves careful con- sideration, as it is based on data obtained from the latest tests on reinforced concrete beams. Unusual care was taken in con- ducting these tests at the University of Illinois, and it is believed that the data obtained therefrom are by far the most reliable now available. The usual assumptions that the loads are applied at right angles to the length of the beam, that the supports will permit free longitudinal movement, that a plane section before bending remains a plane section after bending, and that the metal and surrounding concrete stretch together, are made. It is further assumed that the tensile strength of the concrete is negligible in the part of the beam where the bending moment is greatest, at least in the calculation of the resisting moment of the beam at the time of maximum load. The analysis is restricted to rectangular beams with reinforcement on the tension side only, and refers generally to simple beams free from end restraints, VARIOUS BEAM THEORIES. 329 Notation.—The following notation will be used: b = breadth of rectangular beam. ! d = distance from the compression face to the center of the metal reinforcement. A = area of cross section of metal reinforcement. A p = —— — ratio of area of metal reinforcement to area of concrete above center of reinforcement. o = circumference or periphery of one reinforcing bar. m = number of reinforcing bars. Es = modulus of elasticity of steel. Ee = initial modulus of elasticity of concrete in compression, a term which will be defined. Es e =: = ratio of two moduli. c { = tensile stress per unit of area in metal reinforcement. c = compressive stress per unit of area in most remote fiber ot concrete. c’ = compressive stress per unit of area which causes failure by crushing. As = deformation per unit of length in the metal reinforcement. Xe = deformation per unit of length in most remote fiber of the concrete. : Ae’ = deformation per tnit of length when crushing failure occurs; i. e., ultimate or crushing deformation. Xe q= = ratio of deformation existing in most remote fiber to e . ultimate or crushing deformation. k = ratio of distance between compression face and neutral axis to distance d. distance from compression face to center of gravity of com- a pressive stresses. d’ = distance from the center of the reinforcement to’ center of gravity of compressive stresses. =X = summation of horizontal compressive stresses. M = resisting moment at the given section. s = horizontal tensile stress per unit of area in the concrete. t = diagonal tensile stress per unit of area in the concrete. u = bond stress per unit of area on the surface of the reinforcing bars. vy = vertical shearing stress and horizontal shearing stress per unit of area in the concrete. Relation between Stress and Deformation for Concrete in Com- pression—Concrete does not possess the property of proportion- ality of stress and deformation for wide ranges of stress as does steel; in other words, the deformation produced by a load is not proportional to the compressive stress. The relation between stress and deformation is not entirely uniform; there are even considerable differences in deformation for the same mixtures. 330 CONCRETE AND REINFORCED CONCRETE. Various curves have been proposed to represent the stress- deformation relation, but the parabola is the most satisfactory general representation. Frequently the parabola expresses the relation almost exactly, and in nearly every case the parabolic relation will fit the stress-deformation diagram very closely throughout the part which is ordinarily developed in beams, the lack of agreement near the crushing point not being of import- ance. The analytical work with the parabola is not complicated, and this curve offers casy comparison with the straight-line rela- tion and easy translation to this relation. Even if the straight- line relation be accepted as sufficient for use with ordinary work- ing stresses, the parabolic or other variable relation must be used in discussing experimental data when any considerable deformation is developed in the concrete. The parabola will be adopted as the basis of the analytical work used in this discus- sion. Figure 186 shows such a stress-deformation curve. For pur- poses of illustration, the crushing strength of the concrete is represented as 2,000 lbs. per sq. in., and the ultimate unit deformations as .002. The relation between proportionate stress or ratio of stress developed to ultimate compressive c . % : strength of the concrete —— and proportionate deformation , c or ratio of deformation developed at the given stress to ultimate or crushing deformation ( = s) which forms the basis of Ne this analysis, is also shown by the figure. Modulus of elasticity is a term which has been used very loosely in connection with reinforced concrete. In the general theory of flexure it is defined to be the ratio of the unit stress to the unit deformation within the elastic limit of the material. As applied in this way to materials having the property of proportionality of stress and deformation, the modulus of elas- ticity is a constant. For materials with a variable stress-deforma- tion relation like concrete it may not be considered proper to call the variable ratio the modulus of elasticity, and such a use in connection with formulas for flexure of concrete may lead to misunderstandings. However, it is important that a definite VARIOUS BEAM THEORIES. 331 expression for this ratio be found. The writer obtains this relation from the initial modulus of elasticity, and uses the term “initial modulus of elasticity” to express the relation which would exist between stress and deformation if the concrete compressed uniformly at the rate it compresses for the lower stresses. The tangent of the angle which the line AC in Fig. 186 makes with the vertical gives this initial modulus of Elasticity E,. The line is tangent ‘to the parabola at A, and its equation is x = E, y. By means of this initial modulus of elasticity the parabolic Propor‘ionate Stress = Ss o-n mM nor Ro co 0 ees a ° Ac @ Proportionate Deformation a 9010 fh Deformation per Unitof Length=Ag¢ P 2° 2 oOo Stress in Pounds per Square Inch =c. Fig. 186.—Stress Deformation Curves for Concrete in Compression. stress-deformation relation may, from the properties of the para- bola, be expressed as Ee Ve = (a —% q) Eckc .....0e (1), c= Ec kc — % Ne in which q is the ratio of the deformation developed to the ultimate or crushing deformation of the concrete. From this the following equation is also true: i — Si 2 ge niaveminciga oteaitnertee-s (2). Cc These relations are fundamental. The values of E,, c, and *« 332 CONCRETE AND REINFORCED CONCRETE. must be obtained experimentally. The line for E, should be taken as the line which will give a relation which will best fit throughout the range used in the test of beams, and a’. should be taken as the abscissa of the vertex of the parabola which fits best, and not necessarily as the actual.crushing deformation of the concrete. It is the general relation which is important and not the values at the point of failure. Many stress-deforma- tion diagrams have been gone over in this way, and this repre- sentation has been found quite satisfactory. It may be noted from Fig. 186 that while 2,000 lbs. per sq. in. will give a deforma-. tion of .002, it will take 1,500 lbs. per sq. in. to produce one- half of that deformation. For small stresses the stress-deforma- tion curve does not differ much from the line of initial modulus of elasticity. El _ [Neutral Axis -¥ — +s 8 -8--8]— Fig. 187. Distribution of Stresses in Beams.—Let Fig. 187 show the section of the beam. kd is the distance of the neutral axis below the top of the beam, k being a ratio. In Fig. 188, the left diagram represents the deformation above and below the neutral axis. Consider that the upper fiber is stressed to the point of failure; the upper deformation will then be the ultimate or crushing deformation. Since the deformations are proportional to the distances from the neutral axis, the curve of compressive stresses shown on the right will be a parabola with its vertex at O. The horizontal distances to the “line for initial modulus . of elasticity” represent the stresses which would exist for the same deformation with a constant modulus of elasticity equal to E,. The stress in the steel is represented by a length propor- VARIOUS BEAM THEORIES. 333 tional to the ratio of the modulus of elasticity of the steel to the initial modulus of elasticity of the concrete e = In like Ec Deformation Compressive Stress ‘g 1 Neutral? Axis — — RSS) )- BSS ity wal Peecmacccast OP sisson J Deformation Tensile Stress ee! Fig. 188.—Stress and Deformation: Distribution at Ultimate Deformation Deformation Compressive Stress keg 24 be SST ESR RSEES EA SOOUSS SEN OND GY seeceee eee fee e eee renee 4 Deformation Tensile Stress of Steel Fig. 189.—Stress and Deformation Distribution at Three-Fourths Ultimate Deformation. manner Fig. 189 gives the stress and deformation distribution for a deformation of the upper fiber equal to three-fourths of the ultimate deformation of the concrete and a stress of fifteen- 334 CONCRETE AND REINFORCED CONCRETE. sixteenths of the crushing stress. Fig. 190 shows a similar distribution for one-half ultimate deformation and three-fourths crushing stress. It will be noted that the parabolic arc appears somewhat different from that in Fig. 188, and that it differs much less from the line for initial modulus of elasticity. Relations in the Stress Diagram.—In deriving formulas for resisting moment, position of neutral axis, and compressive stress at upper fiber, three relations in the stress diagram are needed: (1) the relation of the stress c and the deformation \« at the upper fiber; (2) the total compressive stress, here called > X; and (3) the position of the center of gravity of the compressive Deformation + Compressive Stress. ker ; rene ae area, Re / i = ; : Nel wer Roe kd ? | Neutral Avs Center of Stee! SSS ke Deeeaietpelas Heroemahion Tensile Stress. of Steel. Fig. 190.—Stress and Deformation Distribution at One-Half Ultimate Deformation. stresses given by the distance z. These relations vary for dif- ferent values of the deformation in upper fiber. Basing the variation on the parabolic stress deformation law previously Aa stated, and using g = as the ratio of the deformation de- x. veloped in the upper fiber to the ultimate deformation of the concrete, the following relations are: readily deduced, though their derivation will not be given here. c I a nc ne Weise erakednaiaoa dorekiaes m Eede 2 : a =x Parabolic area = =1—K%q...... * W% EeNckbd Triangular area . ‘e l"ARIOUS BEAM THEORIES. 335 2 4—q q Ear Ue a ectinecey »- (5). kd i2—Adq 3—q Equation (3) gives the ratio of the compressive stress in the upper fiber to the stress which would exist for the same upper fiber deformation with a straight-line stress-deformation relation. Equation (4) gives the ratio of the summation of compressive stresses to the stress which would exist for the same upper deformation fiber with a straight-line stress-deformation relation. Equation (5) gives the ratio of the distance between the com- pression surface and the center of gravity of compressive stresses to the distance between that surface and the neutral axis. Values for several ratios of the deformation developed in the upper fiber to the ultimate or crushing deformation of the con- crete are given in the following table: TABLE LXVII. PROPERTIES OF THE STRESS DIAGRAM. At At % At 4a At 4 ‘eal POUT aoe) ae. gGmete,, gaullimsts | iinelatlon q=I q=% q=% q=% q=o0 c % Ecdec 5 EecXe % Ecdc % Ecde Eeke ZX WEcdckbd % Eetckbd "/y Ecdckbd "/ay Ecdckbd %Eedckbd Zz 3% kd 8/56 kd */oo kd ®/as kd 4% kd Cc 2pt % °/ 8 Ls 10 "(2 i k Figure 191 shows graphically the relations given by equations (3), (4) and (5). It will be seen that the center of gravity of the compressive stresses ranges from 3% distance down to neutral axis (the value for a deformation equal to the ultimate deformation) to 1/, distance down to neutral axis at the lower a rie : limit, (:, — ) The position for q = 34 is °/,,, equal to kd .36. This is not far from the value */,, which has been used in the discussion of the experimental work, and which was obtained by another method of analysis. The position for q = % is .341, and for q = 0 it becomes '/, as in the straight-line relation. The other ratios are less nearly constant. The ratio for compressive stress at most remote fiber to that for direct proportionality with ¢c same deformation ( ) ranges from 14 when ultimate EcAc 336 CONCRETE AND REINFORCED CONCRETE. deformation of concrete is developed to 1 for no deformation. The. range for summation of compressive stress is from ?/, to 1. It should be remembered that these formulas, are not applic- able when tensile stresses of concrete need consideration. Neutral Axis.—The foregoing relations and the analytical condition that the total horizontal compressive stresses and the total horizontal tensile stress are equal will, if tensile stresses in the concrete be neglected, readily enable the position of the 400 20 9 100 30.60 40 20 Bs Ratio of Agto Ne =q Fig. 191.—Diagram Showing Variation of Functions with q. neutral axis to be determined for rectangular beams. From the proportionality of deformation (Figs. 188, 189 and 190). As de aay cadeaeeas ours alaciecnsnesiliah pesineaddaveeee vee (6). 1—k k Equating horizontal stresses, Af = % (1 — % q) Ecdckbd .......... cece eee eee (7). Dividing (7) by (6) and substituting f = Es As, AEs (1 —k) = % (1 — % q) Eck*bd Es A Calling =eand ——p, Ee d pe (I —k) = % (1 —% q) F Solvin= 2pe pre’ pe Sito (8). k= + = \ 1—'%q (1 — % q)* 1— ’%sa VARIOUS BEAM THEORIES. 337 _ This gives the position of the neutral axis after tensile stresses in the concrete have become negligible and before the concrete reaches its ultimate strength. The value of k will vary slightly for the range of q usually considered, probably not more than .o2. For q = I equation (8) becomes: = aor Fg Pie Se PO. dcciinde niin oak uaorion (9), 40 / =k Bh a < oR Proportionate Depth A @ = i. 2. os A Ss. © 3, 10 Proportionate Stress = Sand Proportionate Deformation = Xe =q Fig. 192.—Variation in Position of Neutral Axis for Different Values of q. which is the expression when the concrete is at the limit of its compressive strength. For q = 0, equation (8) becomes: — “t 2 pe t-p'e? — pe .xusiaacereseweasaas (10), which is the same as the value of k derived from a straight-line stress-deformation relation. Fig. 192 shows the variation in k for e = 15 and a 1% rein- forcement (p = .or), given both in terms of q and in terms of c c In this diagram the position of the neutral axis changes from .418 when qo to .484 when the full or crushing deformation 338 CONCRETE AND REINFORCED CONCRETE. is developed. It shows a slow change for increasing values of the compressive stress until two-thirds of the full compressive strength of the concrete is developed. Beyond this the neutral axis lowers rapidly. Ordinarily a 1 per cent. reinforcement will not develop the full compressive strength of concrete, but the diagram serves to illustrate the change in the position of the neutral axis both in this and with other amounts of reinforce- ment. It is seen that the position remains nearly constant during what will be termed the third stage of beam action. Of course for low values of q, the tensile strength of the concrete would modify the position somewhat. For the calculations in this paper and for the reinforcements used, k for q = % gives results which are representative for the range considered, and will be used in the discussion. For q = %, equation (8) becomes k= Spe gat nes psa Sy Fae hea. Seman aeasiintt (11). II 121 EL This equation gives the position of the neutral axis for deformations which correspond closely with those developed under working stresses. Figure 193 gives the position of the neutral axis based upon equation (11), (q = ™%) for e = Io, 12, 15 and 20. Calling the modulus of elasticity of steel, 30,000.000 Ibs. per sq. in., these ratios correspond to initial moduli of elasticity of concrete of 3,000,000, 2,500,000, 2,000,000 and 1,500,000 Ibs. per sq. in., respectively. Resisting Moment.—When the tensile stresses in the concrete are neglected and the center of gravity of the compressive stresses is known, the value of the resisting moment of the beam (which it is readily seen is the moment of the couple formed by the tensile stress in the steel and the resultant of the compressive stresses in the concrete) is easily expressed as the product of the tensile stress in the steel and the distance from the center of the steel to the center of gravity of the compressive stresses. Hence the formula for the resisting moment for a rectangular beam is Mo AP (dS: 2) does eer ews ca came (12). {t was shown that z varies slightly for different compressive 5 VARIOUS BEAM THEORIES. 339 Stresses. The value of z when the concrete at the remote fiber is stressed three-fourths of its ultimate deformation (q = %) is approximately .36 kd; for q = ¥%, .35 kd, and for q = %, .34kd. 20 o /904 Beams a! Average of 9, 1905 Beams, lodded at the one- third joints 02 Average of 4, 1905 Beams, mmiacellanieous loading. 03 Average of 5,1905 Beams, abnormal Concrete. 4 Average of 3, 1905 Beams, loaded at the one-third points. : =k b 3 Depth & Proportionate The position of the neutral axis 1s quer in terms of the distance d, Tom compression face to center of metal The ratio of reinforcement 1s the ratio of the area of reinforce- ment to the area of the concrete above the center of the metal Ratio of Reinforcement =p Fig. 193.—Diagram Showing Position of Neutral Axis. For q = 0, z = '/,kd. This is the position when the straight- line stress-deformation is used; i. e., when the modulus of elas- ticity is constant and equal to the initial modulus of elasticity. 340 CONCRETE AND REINFORCED CONCRETE. When the E, of the concrete is known and the amount of reinforcement is fixed, equation (12) will take the fori OA ar GG ets eae arn ceaes (13), where d’ is the moment arm of the couple and may be expressed as a proportionate part of d. Thus for q = 4, with E, = 2,000,000 lbs. per sq. in. (n == 15) and 1% reinforcement (p = ol), d@? = 53d. For 1.5% reinforcement (p = .015), d’ = - 831d. The values of the resisting moment for these reinforce- ments become .853 Afd and .831 Afd, respectively. This method offers the most convenient way of calculating the resisting moment so far as it is controlled by the tension of the steel within its elastic limit. The position of the neutral axis may well be taken from a diagram like Fig. 193, and the value of d’ is then easily obtained. Generally it will be best to use the resisting moment in terms of the tension in the steel, but if it is desired to express it in terms of the compression in the concrete the following equation may be used. 1—%q m= ("*) wexpaa—o Re (14). I1—%q : At least an approximate value of q will be known which may be used in equation (14). The fractional coefficient is the recip- c rocal of the function 2pf given in Fig. 191. k Compressive Stress at Upper Fiber.—The formulas for the position of the neutral axis and moment of resistance are based upon the assumption that the compressive stress in the upper fiber is within the crushing strength. To determine the value of the upper compressive stress substitute equation (3) in equation (7). This reduces to 2Af I1—%q 2pf 1— eq c= on 15). ‘ kbd 1—%q k 1— %q fs For a deformation of upper fiber equal to three-fourths of the deformation at crushing (o« c= a ). this becomes 16 5 apf es oe For an upper deformation equal to one-half of k VARIOUS BEAM THEORIES. 341 ; , : apf ultimate deformation this becomes ¢ = es aa For the Io k 2 i 3 apf crushing point of the concrete 1t becomes ¢ =—-——. As the 4 k : apf upper deformation decreases, the value of c approaches ae k which is the amount of the stress for a constant modulus of elas- ticity equal to the initial modulus of elasticity. By multiplying apf : a the stress found on the basis of a constant modulus of elasticity and a known position of the neutral axis, by this ratio I1—'%q 1— %q the value of the compressive stress is found. The variation in this ratio may be seen in the upper line in Fig. 191 and also in the last line of Table LX VII. It will be seen that for high compressive stresses the stress developed is much less than that given by the straight-line relation using the value of the initial modulus of elasticity, being only three-fourths as much if the full compressive stress is developed. For low compressive stresses the discrepancy is much less. It should be noted that when the compressive deformation developed is well up to the ultimate, the compressive stress calcu- lated from equation (15) is much less than that found by using apf the formula =e (or any formula based on a straight-line stress- k deformation relation), but when the load develops a deforma- tion which is a small proportion of the ultimate, as may be the case for working loads, the coefficient found in equation (15). will not differ much from unity, and the straight-line formula will be but little in error. When it is desired to check or design a beam, using the above theory, the following relations should be kept in mind. As ex- plained above, in connection with equation (13), q may be taken equal to %4 the ultimate deformation, which condition will exist within the limit of the usual working stresses in the concrete. Then from Table LXVII., z will equal 15/,,kd = .34kd, the 342 CONCRETE AND REINFORCED CONCRETE. value of k being taken from Fig. 193 for the desired ratio of reinforcement p and ratio between moduli of elasticity of the steel and concrete x =o Es Ec Then d, the effective depth of the beam, being assumed, the value of z = .34kd becomes known, and d — z = d’, which is the lever arm between the centers of gravity of the compression and tension forces. Equation (13) may then be solved. Example.—Design a beam of sufficient section to develop a resisting moment of 234,375 in. lbs., using I per cent. of rein- forcement and a unit stress of 16,000 lbs. per sq. in. on the metal. Our equation (13) is M=Aftd; then M 234,375 AS — = ——. fd’ 16,000 d’ d’=d—z. Assume d’ = 12 ins, Now z = .34 kd. From Fig. 192, assuming e = 10, k = 37. Then Z = .34X .37 d = .126d. d’=d — .126d = 874d. But d’ = 12 ins., and d = 14.2 ins. = effective depth of beam. Then 234,375 A = ——— = 1.22 sq. in. 16,000 X 12 p = .O1 = 1.22 sq. in. Then Ac = area of concrete = 122 sq. ins.; Lut d = 14.2. 122 Then b, the width of the beam, = —— = 86 ins. 14.2 VARIOUS BEAM THEORIES. 343 We will therefore have a beam 8.6 ins. wide, 14.2 ins. + 1.8 = 16 ins. deep, assuming that the bars have 1.8 inches of concrete below their centers; two %-in. diam. bars = 1.20 sq. ins., which will be used for the reinforcement. Wason’s Formula.—Mr. Leonard C. Wason, Assoc. M. Am. Soc. C. E., presented an extremely simple formula for the solu- tion of reinforced concrete beams, in the Transactions of the American Society of Civil Engineers, Vol. 46, page 102. This formula is among the earliest used in this country and has the merit of having been long and extensively used. It is stated that beams designed by it when tested had a factor of safety varying from 3 to 5. The formula is based on the following assumption: That there is a perfect bond between the steel and the concrete within the limits of the working stresses of the combination. That the “Kx i fh ' See Bae cm Nevtral__Aus | y i i 4 sd rae, Me mee Fig. 194.—Diagram Illustrating Beam Formula of Mr. L. C. Wason. steel takes the entire tensile stress and the concrete the entire compressive stress. That the neutral axis is assumed to be half way between the center of the reinforcing bars and the top of the beam. That the center of pressure of the concrete under compression is considered as being two-thirds of the height from the neutral axis to the top of the beam. The distance from the center of pressure of the concrete in compression to the center of the reinforcement equals °/,d. In Fig. 194 let = effective depth of beam. 1 = span in inches. Fs = total stress in steel. W = total uniform load in pounds.’ Then, taking the center of pressure as the center of moments, the resisting moment M = 3 d Fs. The bending moment of a beam for a uniformly distributed load 344 CONCRETE AND REINFORCED CONCRETE. M = %W4I1. Equating these two moments and solving for f, we obtain Wi = 6% d Mr. Wason states that the above assumption for the position of the neutral axis is somewhat higher than its position accorcl- ing to theoretical assumption, but that it approximates closely the position as found by actual determinations during the test of beams. 7 Example.—Determine amount of steel required for a beam of 12.5 ft. span to carry a total uniform load of 12,500 lbs., assum- ing effective depth determined in example on page 308, of 14.4 ins., and using a unit stress for the steel of 16,000 Ibs. per sq. in.: 12.5 ft. = 150 inches. 12,500 X 150 Fs = ————_——— = 19,500 lbs. 6% X 14.4 19,500 = 1.22 sq. ins. 16,000 2 bars “/ X “/-in. give an area of 1.32 sq. ins. After determining the total stress in the metal, the area of the reinforcement is determined by dividing the total stress by a safe working stress to determine the area of metal. Bars of proper size are selected to make up this area, a convenient spac- ing selected, and the area of the concrete adjusted to resist the compression. Mr. Wason uses 16,000 lbs. per sq. in. tension on the steel, and for a 1:3:6 concrete an average of 500 lbs. per sq. in. in compression on the concrete, and requires 32 sq. in. of concrete in the‘upper third of the beam for each square inch of steel. This averages very nearly 1 “per cent. of reinforcement. The above ratios are applied to the use of Ransome twisted bars, which have, as explained on page 227, a high elastic limit and give a factor of safety of about 4. In the above problem the total compression is 19,500 Ibs.; this, divided by 500 lbs., gives a required area in the upper third of the beam of 39.00 sq. ins., 39.0 X 3 = 117 sq. ins., total area of beam, 117 sq. ins. + 14.4 ins. depth assumed gives 8.13 ins. width of beam; a width of 8% ins. may be used. VARIOUS BEAM THEORIES. 345 Ransome’s Formula.—Ransome’s formula for a simple beam uniformly loaded is Wi 5S =—_ 7d in which W = total dead and live loads in tons. 1 = span in inches. d = depth of steel below top of beam = effective depth. S = maximum stress in beam, either tension or compression. When the beam is not uniformly loaded the formula becomes BM x8 7d in which B M equal the maximum bending moment in inch tons. In order that the compressive stress per lineal foot resulting from a chosen value for d shall not exceed the safe compressive strength of the concrete there must be 16 sq. ins. of concrete above the bars for each ton of stress. 16S = 124d, from which : S=%d. Substituting this value of S in the above formula we have Wi Sf gia 7d 4 d = — WI. ai Having obtained d, the total stress in tons S = 34 d. Example.—Assume a flat floor slab, having a span of 12 ft. carrying a live load of 150 lbs. per sq. ft. It is necessary to assume the dead weight of the floor. Let this be taken at 75 Ibs. per sq. ft., making a total load of 225 lbs. per sq. ft. The total load W in tons on a strip of floor 1 ft. wide would be ‘ 12 X 225 = 1.35 tons, 2,000 and we have for d, 1X 1.35 X 12 X 12 d =/ —_—_____—__—. = 6.08 inches, 21 The total stress in the bars would equal 34 x 6.08 = 4.56 tons. Assuming an allowable working stress on the metal of 8 tons 346 CONCRETE AND REINFORCED CONCRETE. per sq. in., there will be .57 sq. ins. of metal required, or 4 rods 3% in. square in each foot width of slab. When %4-in. rods are used the distance from center of rod to bottom should be at least ¥\% in., and 34 in. for ¥ in. square rods. For 34-in. rod reinforce- ments we will have a total thickness of 634 ins. Ribbed Floors.—In calculating the beam dimension and amount of reinforcement for ribbed slabs, the formula Wi Se 7d is used. This condition, however, is imposed, that the upper third of the beam, including the flat.slab connecting the ribs, shall contain at least 5 sq. ins. of concrete for each ton of stress given by the formula. This condition prevents the concrete in the top of the slab from being strained beyond its safe compres- sive strength. Example.—Assume a ribbed floor of 20 ft. span, loaded with 200 Ibs. per sq. ft., to find dimensions of floor and size of rein- forcing bar. We will assume the weight of the floor to be 60 lbs. per sq. ft., making the total load 260 Ibs. per sq. ft. It is neces- sary to fix on some spacing of the beams; this is usually taken from 3 to 4 ft. centers. We will take 4 ft. between centers for our beam spacing, and the total load on each beam will be 20 X 4 X 260 L = ————_——_ = 10.4 tons. 2,000 and the total stress is g 10.4 X 20 X 12 356.2 yxd d Tf we use a 144 in. x 114 in. bar having an area of 1.5625 sq. ins., and a safe tensile strength of Io tons per sq. in., the depth d will be 356.2 = ——______ = 22,77 ins. 1.5625 X 10 The minimum thickness of slab to give the required compres- sive strength will be 5 X 1.5625 X 10 48 = 1.63 ins. VARIOUS BEAM THEORIES. 347 This will be less than it will be advisable to use, as from a prac- tical standpoint a thickness of from 2 to 3 ins., at the least, should be used. The slab should be figured as a flat floor spanning from beam to beam. Thus, if the slab be unreinforced, and we assume a unit tensile working strength of 50 lbs. per sq. in. in the con- crete, and if the rib be assumed at 4 ins. thick, we have a clear span of 44 ins. The external moment in in.-lbs. will then be M = ea = 5,244 in. lbs. 12x 8 ; For a rectangular beam the resisting moment I M=S— c S = 50 I 12x d? — = ¥%, bd? = =2d c and M = 100 d? = 5,244 in. lbs., and d = 7.25 ins. which will be the proper thickness of an unreinforced slab be- tween beams spaced 4 ft. center for the live loading of 200 Ibs. per sq. ft. The assumed dead load was, therefore, too low. For such a heavy live load a reinforced slab should be used. The width of beam b and total height h depend upon the size of the bar used and are given in the following table as used by Ransome. Dimensions are given in inches. Sizaofbar 4g in. 34 in, 1 in. 14 in. 14 in. 1% in. 2in h d+% d+11% dt+i1% d+1% d+2% d+2% dt+3 b _ 1% 2% 3 _ 3% 4% 3% 6 Where ribbed floors of long spans are used it is often advis- able to run one or more stiffening ribs at right angles to the main beams. These will stiffen the longitudinal beams laterally and assist in the distribution of stresses in case any heavy con- centrations are brought upon the floor system. These stiffening beams should be reinforced at the bottom, and it is customary to rest the bar directly upon the main bar where they cross. Cantilever Beams.—If a beam is supported at one end only, the stress in the beam is four times that in a beam of equal span 348 CONCRETE AND REINFORCED CONCRETE. supported at both ends. Hence, the formula for cantilever beams uniformly ‘loaded is 4’W 7d when I’ = the length or projection of the beam. In this case the tensiun bar is placed in the top of the beam and the portion below the bar must contain at least 16 sq. ins. of concrete for each ton of stress. Wall and Pier Footings——The general form and arrangement of the Ransome wall and column footing is shown in Figs. 195 and 196. In all cases the width of wall T and load per lineal Stress = Twisted Steel Tension Rods. Fig. 195.—Typical Wall Footing by Mr. E. L. Ransome. foot W and the width of footing T’ will be given. The total stress in the tension bars or the total compression in the concrete per lineal foot is 2WI’ 7d in which W equals the total load in tons, 1’ equals the projection in inches, and d-equals the distance in inches from the top of the footing to the center of the bars. There are two unknown quan- tities, stress S and d. It is therefore necessary to impose another condition, and it is that when the safe compressive strength of the concrete equals 35 tons per sq. ft. there shall be 16 sq. ins. of concrete in the area above the bars for each ton of stress, or 16 x S =12 d, from which S = 34 d. This condition is necessary in order that the concrete shall not be strained beyond its safe l’ARIOUS BEAM THEORIES. 349 compressive strength, and should be modified to suit the strength when the latter does not conform to the value of 35 tons. Sub- stituting this value of S in the above formula and reducing, we have 8 wl d= 2s 21 Having obtained d from this formula, the total stress S in the bars in tons = 34 d. The bars should be arranged as shown in Fig. 195. The sizes of the bars should be so taken that the bars ---- 17 oa reeset * ! Fig. 196.—Typical Column Footing by Mr. E. L. Ransome. will not be spaced more than 12 ins. apart. The total height h of the footing should be at least 3 ins. greater than the depth d. Exampie: Let T = 2 ft., W = 30 tons, and the safe bearing power of soil equal 2.5 tons. Then T’ = 12 ft. and l’ = 5 ft. = 60 ins., and “8 x 30 X 60” aoe d = ——___—_—— = 26.2 ins. = 26% ins., approximately; 21 and stress S = % X 26.2 = 19.65 tons, requiring %-inch square bars, 3'/is ins. centers, assuming a working stress of 10 tons. per sq. inch for the steel. Then the length will be tS T ——= 09% ft. 2 350 CONCRETE AND REINFORCED CONCRETE. Formula for Pier Footings—As in the case of wall footings we have given, the dimensions of the piers to be supported and of the footing T and T’ and the total load W to be carried. The formula for obtaining the total stress S in the tension bars running in each direction is wr 3d in which we have as before the two unknown quantities, S and d. In order that the concrete may not be stressed in compression beyond its safe working strength, we impose the condition d 4S =— (T + 6), 2 d(T +6) —— Substituting this value of S in the above formula and reducing we have 8Wl ‘= V oa 3 (T + 6) Having obtained d by this formula, the total stress S in tons will be from which s=—— xd, from which the size and number of bars running in each direction can be computed. These bars may be in two lengths, as shown in Fig. 196, the shorter length being equal to T +1’. The total height H should not be less than d + 4 ins. Example.—Let T = 20 ins., load W = 100 tons.- Safe bear- ing power of soil equals 2 tons per sq. ft. The required area of base of footing is 50 sq. ft. and the width T’ equals the square root of 50 = 7 ft. 07 ins., or 85 ins. approximately, and 1’ == 32.5 ins. 8 X 100 X 32.5 ; d= a = 18.5 inches. 3X2 The total stress will be 18.5 X 26 = ——— = 60 tons. 8 VARIOUS BEAM THEORIES. 351 requiring 11, 34-in. bars, or 24, %4-in. bars running in each direc- tion. These bars should be spaced equally over area T’, giving fer 34-in. bars a spacing of about 7 ins. and for 14-in. bars of about 3% ins. The total height h = 18.5 + 4 = 2214 ins. Thacher’s Formulas.—Thacher’s empirical formulas are based - on the ultimate safe loads, and have been found to agree quite closely with the results obtained by experiment. These formulas are quite easy to apply and give safe and satisfactory results. The formulas developed below are for ultimate strength, and a factor of safety depending upon the conditions and judgment of the designer should be used. ft -b- ->| | i i H x 4 ' ‘a Neutral Ags it oh eg ; a i y i} @ 09 @] #-X. « Gi k-Fs-af Fig. 197.—Thacher’s Formula, Rectangular Beams, Single Reinforcement. Let Fe = probable crushing strength of the concrete per sq. in. in pounds. fe = compressive stress in pounds per sq. in. on concrete. Fs = tensile strength per sq. in. on steel = ultimate strength per sq. in. on test piece + 10 per cent. fs = tensile stress in pounds per sq. in. on steel. Ee = modulus of elasticity of concrete. Es = modulus of elasticity of steel. e = a = 20, as taken by Mr. Thacher. ec A = area of steel in tension for 1 inch in width of beam. 1 = length of beam in feet = span. M = bending moment in foot pounds for 1 inch in width of beam (ultimate). W = load at center, including weight of beam for 1 inch in width (ultimate). w = uniform load per lineal foot, including weight of beam for 1 inch width (ultimate). w’ = 12 w = uniform load per sq. ft. (ultimate). b, hs, d, x, y and z are as shown in Fig. 197. First Case—Assume a rectangular beam, with reinforcement in tension side only (Fig. 197), and neglecting the tensile strength of the concrete. Assuming that plane sections before bending are plane after bending, we have the relation 352 CONCRETE AND REINFORCED CONCRETE. Fe Fs x er ye ; Ee Es Therefore Fe XS YS —— cea eetitietiouss ssuwes (T 1) Fs or T'sx Beis eased eee ee ems (T 2) ey and Fe d=xty=ye ty, from which 4 YF oe eeecccccccccccceces (T 3) Fe e a Fs also = Yh leis te ne eos (T 4) In order that there be equilibrium, the total compression must equal the total tension, and we have Fe x AFs = AFs or X = 2 —— cocececcseeees (T 5) 2 Fe Substituting the value of Fe found in equation (T 2) in equation (T5), we have x=2Acy. and x? 2Ae Substituting the value of x from equation (T 5), we have m1, ) OTs d=x+y=2 at =) Ja therefore A — 2 [e+ ey iasas v2 wapaeyetere ..(T6). Now x? =xtry=xt 5 2Ae and x t+2Aex=2Aed from which =V2Acdt (Ae)? —€A oo... .ceeeeeee(T7) VARIOUS BEAM THEORIES. 353 Let M = resisting moment of beam. Then taking Me = resisting moment of concrete in compression. Ms = resisting moment of steel in tension. Taking the neutral axis of the beam as the center of moments, x and y are in inches, and Fe x Fe x? Me = x %x = —, alata 2 3 Dividing by 12 to reduce to foot-pounds, Fe x? Me SS 36 and Ms = Fs Ay in inch-pounds, ss Fs Ay or, Ms = in foot-pounds. 12 The total resisting moment of the beam will be M = Me + Ms. Fe x* Fs Ay M = —— + 36 12 Substituting for Fe its value from equation (T 2), we have Fs x® Fs Ay M => ——— 4+ — # 36 ey 12 Fs x? eh A J terterteccaes sud ce vs a adaces (T 8) “36 ey For a simple beam with uniform load 8M M = % wF and w = = Therefore Fs x® w= bec Aye I a dee ety waabtayataica wee e eS .-(T9) 4.5 P ey and 12 Fs x? w =I12w~= . —+3Ay : 45 FP ey For a simple beam loaded at the center, M=% WI, and Fs = = — BGA Hrcsoacanseond Cravocesemeceivs (T 10) 91 ey , To check a simple beam, assume proper values for F,, E,, E.; A, d and 1 are known. Then equation T7 gives the value of x, and equations (T 8), (T9) and (T 10) will give M, W and w, as may be required. Then if the value of F, from equation (T 2) exceeds the assumed or determined ultimate strength of the con- 354 CONCRETE AND REINFORCED CONCRETE. crete in compression the values of M W or w, as determined by equations (T 8), (Tg) and (T10), should be reduced in the ratio that the probable ultimate compressive strength of the con- crcte bears to F,, as found by equation (T 2). To design a beam, values must be assigned for F,, F., Es, Ey, h, z and d; 1 will usually be found by conditions of the problem, as is also sometimes h; z should usually be from 1% to 2 times the diameter of the rods. If h or d is not fixed by existing conditions, a value should be selected by trial to give an economic ae che =| aT ce a [ [eee Tay | Ck : e e Fs and : x=d-—y. : Fe x y Equation (T 13) gives A = ——~————__-, 2 Fs (y = n t) Fst Equation (T 11) gives Fs° = : ¥ and Equations (T 15), (T 16), (T 17) and (T 18) give values of M, w, w’ and W as required. ; Third Case.—Mr. Thacher’s analysis for the solution of a rein- forced T section for a ribbed floor construction is as follows: B L Some pes see eS Py, i x ee ee et a | a; Y j amiss ibe Pt ae ome = wal Fig. 199.—Thacher’s Formula for T-Beams. The slab is first designed as a beam with a span equal to the distance between floor ribs and with the reinforcing bars at right angles to the direction of the length of-the joists. The joist spacing varies with the conditions, and when the spacing is not fixed by limiting conditions the spacing of the ribs, thickness of floor slab and depth of ribs should be so chosen as to give the most economic floor. Several solutions may be necessary to secure this result. In Fig. 199 let B == width of slab = distance center to center of ribs in inches, r = thickness of slab in inches. A,” represents the area of steel which is necessary to develop the same compressive resistance as the wings of the T. This is an imaginary quantity, as no steel reinforcement is used for CONCRETE AND REINFORCED CONCRETE. 358 reinforcing the slab in a longitudinal direction. Mr. Thacher r ‘ takes z == — when r is the thickness of the slab. 2 To Design a Simple Beam.—Having: assumed or determined values for B, r, z, and assumed values for F,, F., e, h and d, as in the previous cases, and noting that As” As —— =n, and As =A, Then (B—b) r As’ d y =—; x=d-y; Fe Fs Fst Fs° = 5 y Febx + 2 As° Fs® As = SSS 2 Fs M = "/12 [% Fe b x? + Fst Ac® t + Fs Asy]; od e I W=— (% Fe b x? + Fs* As® t + Fs Asy); 31 8 , ee (% Feb x? + Fs® Ast t + Fs Asy): _If M, W or w’ is greater than required, As can be reduced propor- tionately. To check a ribbed beam supported at the ends as a simple beam: Assume values of Fs and e as before. Then ‘ (B—b)r As® = ——; e As = area of reinforcing bars; x =V2Ae (dtnz) + [Ae (nt1)f — [Ae (n+ 1)]; 7 tFs y =d—-x; Fo = ; y Fo xc ro ey VARIOUS BEAM THEORIES. 359 Thacher's Constants——The formula for the design of beams can be much simplified by substituting for F., F,, E, and E, their values and reducing. The following table gives the values of Ag, M, W, w, w’ and d at 1 and 6 months for the following values: Figs hs Geass cue can edhccee BS te ema ta ase e Seals 30,000,000 Beep RUE ACE® 6 0.5 a cavenancicnasem ate weave ncheatennta doass qasace emma 64,000 Ee, for 1: 2:4 concrete, one month old.............. 1,460,000 Fe, for 1:2:4 concrete, one month old.............. 2,400 Ee, for I: 2:4 concrete, six months old.............. 2,580,000 Fe, for 1:2: 4 concrete, six months old.............. 3,700 Ec, for 1: 3:6 concrete, one month old.............. 1,220,000 Fe, for 1: 3:6 concrete, one month old.............. 2,050 Ee, for 1: 3:6 concrete, six months old.............. 1,860,000 Fe, for 1:3:6 concrete, six months old.............. 3,100 THACHER'’S CONSTANTS FOR BEAMS. Proportions of Concretp........ 1: 2: 4 ——_7 ——-1: 3:6-———_ Age of Concrete.......csesceees 1lmonth 6months l1month 6 months Area of steel sq. ins. required for 1 in. Fi a d 4 width of beam = A,............- — ae sores ees 142 100 165 109 Ultimate bending moment ft.-lbs. for 1 in. width of beam = M.......... 35.62 d? 51.25 d* 30.62 d? 46.25 d? Baoding weizht Sot for rim, sys at 205.0d? 122.5d? 185.0d 1 1 1 1 Preaking weight per lineal ft. uni- formly distributed for 1 in. width 285.0 d? 4t0.0d* 245.04? 370.0 ds Of beam = Wi... ceeee cece eeereees 2 z a : Breaking weight per sq. ft. uniformly Rue 3 A - distributed = W ateueins eoen aint Se a oe d a d “ qd Effective depth of beam required fora = = es : uniform load of w’ lbs. per sq. ft. =d Iw Pw «jee Pw 3420 4920 2940 4440 The above formulas are for ultimate strength and it is neces- sary to divide the constants by the proper factor of safety to secure the desired working values. If calculations are based on formulas for concrete I month old there will not be sufficient reinforcing metal to develop the full strength of the concrete after the latter gains its full strength. It is therefore preferable to use formulas for concrete 6 months old, using such a factor of safety in 6 months as will give any desired factor of safety in 1 month. A factor of safety of 5 in 6 months will give a factor of about 3.5 in 1 month, which will be ample in almost all cases, Under certain conditions it will be found desirable to use an- other value for the factor of safety. 360 CONCRETE AND REINFORCED CONCRETE. Example 1.—To find the depth of a slab 8 ft. long that will support a uniform load including its own weight of 400 lbs. per sq. ft. with a factor of safety of 5 in 6 months, using 1:2:4 con- crete: Fw’ %.0* X 400 d= = —_——_—— = 5.1 in, h = 5.1 in. + g in. = 6 in. 980 984 d 5.1 As = ——- = —— = 51 100 100 For rods %-in. square, distance center to center 25 = = 4.9 inches. .O51 Example 2.—To find the safe load per square foot on a slab having a clear span of Io ft. and a depth of 8 ins. from top of slab to center of rods, using a 1:3:6 concrete, with a factor of safety of 5 in 6 months: 888 x 8? w= = 568 Ibs. 10” 8 = — = .0734. 109 3 4418 For %-in. round rods the spacing = = 6 in. 0734 Example 3.—To find the width of a beam having a clear span of 16 ft. and effective depth of 15 ins. that will support a load of 500 Ibs. per lin. ft., with a factor of safety of 5 in 6 months, us- ing 1:2:4 concrete: For 1-in. width, 82 d? 82 x 157 w= — = ——— = 7207 ins. wide. r 16" 500 = 6.94 ins. wide. 72.07 The steel, 15 X 6.04 As = ——— = 1.04 gq. ins. 100 Example 4.—To find the breaking load at the center of a beam VARIOUS BEAM THEORIES. 361 12 ft. long, 1614 ins. deep and 6 in. wide, in which d = 15 ins., for a 1:2:4 concrete 1 month old: 6 *« 15 Stecl = = 0.634 sq. ins. 142 [example 5.—To find the safe bending moment M in ft.-lbs. that can be sustained by a beam 22 ins. deep (d = 20 ins.) and 10 ins. wide, factor of safety of 4, concrete 1:3:6, 6 months old: 46.25 X 10 X 20° M = —————- = 46,250 lbs 4 The above formulas for the design of beams assume that the strength of the steel in tension is equal to the strength of the aa J fa ---—4 ieee oe 4d Pee : Fig. 200.—Rectangular Beams, Hennebique’s Formula. concrete in compression, as it is believed that this will give the most economic design. The formulas given above both for the design and review of beams may be applied to any mixture or age of concrete or any grade of strength of steel. For work in which great strength is desired, and the saving of weight essen- tial, a 1:2:4 mixture is recommended. Under certain conditions a 1:3:6 mixture may be used. Hennebique’s Formulas for Beams, Slabs and Columns.—The formulas used by Hennebique for computing the strength of beams and slabs are based on the following assumptions: (1) The tensile stresses are carried entirely by the steel. (2) The strain on the concrete is uniform throughout the whole compressive area. (3) The moments of the elastic forces in compression are equal to those of the elastic forces in tension. (Fig. 200.) 362 CONCRETE AND REINFORCED CONCRETE. Let M = the bending moment in inch pounds; d = effective depth; . A = area of concrete above center of reinforcement; then A= bd; x = distance of neutral axis below top of beam; e = unit working stress of concrete; s = unit working stress of steel; As = area of steel. Then fex b = the total compressive stress on the concrete, and 4s As.= the total tension on the steel. Their respective moments about the neutral axis are: fe b x” sind Teen CS ae, 2 b Each of these quantities is equal to one-half the moment of the ex- ternal forces, or fe b x? M ata ) M / (1) — = —, and fs As —x)=—orx= —.....(1), 2 a feb 2 2 which equation gives the position of the neutral axis, and M M As = a e 7 2 fs (d — x) ( i—) e 2 Is d— Fes cae te caren dk 2). Viteb This equation gives the area required for the reinforcement, or if the area be known, the stress in the steel may be obtained by solving for f,. When this formula is used the depth of the beam, d, is supposed to be known. The last two assumptions on which this theory is founded are evidently inexact. The value x, it will be seen, is independent of the depth d of the beam. When different depths d are assumed, it will be found that working stresses or factors of safety for the concrete and metal will vary considerably. On this account these for- mulas do not prove very satisfactory. Hennebique, however, assumes a possible range of working stresses for the concrete, and for the metal, computes the stresses in his beams, and if the resulting stresses fall within the permissible limits, considers them as satisfactory. Hennebique uses a working stress of 25 kilograms per square centimeter (356 lbs. per sq. in.) for concrete, and from 1,200 to 1,500 kilograms per square centimeter (17,068 to 21,335 lbs, VARIOUS BEAM THEORIES. 363 per sq. in.) for steel. Substituting these values in formulas (1) and (2), viz., £, == 25 kg., and f, = 1,500 kg., we then have Again, assuming a working stress of 350 Ibs. per sq. in. for concrete, and 16,000 lbs. for steel, the empirical formulas (3) and (4) become: Example.—Assuming same data as were used for example on page 307, M = 234,375, assume d= 14.4 in. and b=- 12 ins.: 234,375 . X = .0535 = 7.48 ins. 12 234,375 As = ——______——- = _ 1.05 sq. ins. area of metal required. 32,000 (14.4 — 7.48) Ribbed Slabs.—For ribbed slabs a slight modification of the above formulas is necessary. It is assumed that the area of the slab filling between the beams is added to the compressive area of the beam (Fig. 201). Let b’ == width of slab and g = its thickness. Then, as for beams, M g — = fe b’g SS = 2 2 ‘ g which expression gives the value (: _ *) of the lever arm 2 of the resultant of the compressive forces above an assumed neutral axis. From this assumption we obtain M g x = —— +-, 2 fe b’g 2 304 CONCRETE AND REINFORCED CONCRETE. from which value of x we deduce, d being assumed in the be- ginning, the value (d — x) of the lever arm for the tensile torces, and there results: _M As = 2 b’fe It is customary to limit the width of the slab between beams to a value less than 50 times its thickness, i. e., b’ < 50 g. Shear.—Stirrups are employed in Hennebique beams to rein- force the concrete against shearing stresses. The method em- ployed for calculating the stirrups is as follows: Let S; represent the maximum shear in the beam. It will fgets bl ---+e-2neeeeo noe 1 a aor 9 fs eS ee eN id d-x ; x F i ii e--—@- + -— - —- eee eee Fig. 201.—T-Beams, Hennebique’s Formula. occur at the supports, and is equal to the reaction. It is as- sumed that one-half of the shear is carried by the bent bars and one-half by the stirrups. If S, represents the allowable shearing stress in the metal, and A, the area of metal required, Sr 2Ss This formula gives the total section of the stirrups required in a length of the beam equal to the distance between the center of compression and the center of tension. This distance is as- As = sumed to be equal tod — = See Fig. 201 for ribbed slabs and 2 for slabs and rectangular beams, a — = | When the spacing z 2 ‘of the first two stirrups at the end of the beam differ from this spacing their section is modified to correspond to the spacing used. Furthermore, when a number of stirrups are placed in the same transverse section of a beam, it is considered that each VARIOUS BEAM THEORIES. 365 stirrup is composed of two branches, and if there be n stir- rups the total section for each branch will be As St Zz — = ——— x 2 4 Ss n Fig. 202.—Stirrup Diagram, Hennebique’s Formula. The following analysis will make clear the development of this theory for stirrups. Irom Fig. 202: St Z= AsSsr, 2 and Srz As = = 2 Ser but r is taken equal to a — * and we have for the total sec- 2 tion of a stirrup, i, e., its two branches: Sez se ees g 28s (« — ~) 2 and for a rectangular beam Sez ee 28s d—— Hennebique allows a shearing stress of 800 kilograms per sq. cm. (11,380 Ibs. per sq. in.) for steel. In computing the maximum bending moment at the center for beams under a uniform load w per lineal foot or meter, Henne- bique uses the usual formula, M — \% w IP? for principal beams or girders, but for secondary beams which are more or less con- tinuous over the principal beams he employs the formula M = '/,, w I. In figuring rectangular floor slabs which are 366 CONCRETE AND REINFORCED CONCRETE. approximately square and supported at all four edges, he as- sumes them to be fixed at the edges, and uses the formula M = '/,, w I? to obtain the required maximum bending moment. Columns.—To determine the strengtn ot columns and walls, Hennebique considers that both the concrete and the metal may be strained up to their maximum working value in compression at the same time and simply puts P = fsAs + fe Ac, The working values assumed for steel and concrete in com- pression are respectively f, == 1,000 kg. per sq. cm. (14,200 lbs. per sq. in.) and f, = .25 kg. per sq. cm. (350 lbs. per sq. in.). This formula is inexact as regards the true internal stress in the two materials, for as f, and f, are assumed at 25 kg. and’ 1,000 kg. per sq. cm., we have Es As 1,000 a much higher value for c.than is warranted. A higher stress than 25 kg. will result in the concrete if the steel is strained up to 1,000 kg., and the highest stresses will result in the concrete when high percentages of reinforcement are used. -+-@- Fig. 203.—Diagram, Coignet’s Formula. Coignet’s Formula.—In designing pipes, Coignet uses the fol- lowing formula: ssl As = . 2 fs in which p = pressure in pounds per sq. inch or kilograms per sq. cm., d = internal diameter of pipe, and f, the tensile working stress in Ibs. per sq. inch, or kilograms per sq. cm. of the metal. To calculate the longitudinal rods, Coignet considers the section of concrete included between the adjacent coils as being a slab fixed at its extremities. VARIOUS BEAM THEORIES. 367 Coignet employs the following formulas for computing slabs (Fig. 203): 8 Asfs 5 feb Assuming fs = 1,500 kg. and fe = 40 kg., x = 60 As, b being equal to unity, or bx = 60 As. This engineer also uses the following empirical formula: As = % d. x ="; d. M = 64 d?. Bonna's Formula.—M. Bonna uses reinforcing rods in both the tension and compression flanges of beams. His formulas are as follows: If A, represents the sectional area of the tension bars calculated for the total load, 2/3 A, is used for the section of the upper or compression bars. For a simple beam, M = 1,500 d Ag, as he assumes f, = 1,500 kg., and M As = ————7, 1,500 d’ d’ being the distance between the center of gravity of the two reinforcements. A,’ the section of the upper reinforcement then is M As’ = % As = . 2,250 d’ If f, be assumed at 15,000 lbs. per sq. in., tne above formulas hecome M M As = ——, and As’ = ————_. 15,000 d’ 22,500 d’ This method of computation avoids the necessity of determin- ing the position of the neutral axis, which is always a tedious solution to make. Johnson's Theory.—The following theory for reinforced con- crete L..ms has been developed by Mr. A. L. Johnson, M. Am. Soc. C. E., Consult. Engr. for the Expanded Metal and Corru- gated Bar Co. It is based on the following assumptions: That plain.sections before bending are plane after bending, up to the elastic limit of the metal and up to the full compressive strength of the concrete. It is also assumed that such a quantity of metal is used as will cause the elastic limit in the reinforcement 368 CONCRETE AND REINFORCED CONCRETE. and the compressive strength of the concrete to be reached at the same time. It is assumed that the modulus oi euasticity of steel is constant up to the development of its-elastic limit. When the elastic limit of the steel has been reached, the construction as a whole has reached its maximum carrying capacity, for beyond this point the elongation of the steel will be so great that the concrete will be ruptured, hence a steel with a high elastic limit is desirable in this kind of construction. As regards the con- crete its maximum strength and load carrying capacity will occur when the extreme fibre stress on the concrete becomes equal to the compressive stress, assuming a metal section of sufficient strength is used to develop it. When this occurs, re- ferring to Fig. 204, we assume that the shaded area above the neutral axis represents the complete compressive stress diagram k- b “> “aS 4 4 = ' xi » ‘ a Y2 2 aoa ae a ¥ Fig. 204.—Stress-Strain Diagram for Johnson’s Formula. of the concrete, os being the axis of proportionate elongation, and the neutral axis the axis of stress per square inch. Mr. Johnson states he has found from an examination of a great many such diagrams, that the resultant modulus, represented “by the tangent of the angle nos, is about two-thirds in rock concrete and one-half in cinder concrete, as much as the original modulus, represented by the tangent of the angle mos. Also that the total area for both kinds of concrete is about one- quarter larger than the triangular area nos. These assump- tions seem crude at first, but as a matter of fact. they are not more so than would be any formula intended to represent the compressive stress diagram for a class of concrete. The latter would give all points on the curve, whereas our method gives only the end of the same: but our location of that point is as accurate as can be obtained by any method. The development of the formulas for rectangular beams follows: VARIOUS BEAM THEORIES. 369 Figure 204 shows a cross section of a steel-concrete beam; strain diagram at the ultimate load, the stress diagram corre- sponding to the above strain diagram. Let Es = Modulus of elasticity of steel in pounds per square inch. Ee = Modulus of elasticity of the concrete in compression in pounds per square inch. F = Elastic limit of steel in pounds per square inch. fe = Compressive strength of concrete in pounds per square inch. fe = Tensile strength of concrete in pounds per square inch. b = Width of section in inches. a’ = Area of one bar in square inches. d = Spacing of bars in inches. a® - = Number of square inches of metal per inch of width. a’b —- = Total quantity of metal in width b. d Mo = Moment of ultimate resistance of cross-section in inch pounds. M = Bending moment of external forces in inch pounds. W = Total load on beam in pounds. Ps = Total stress on metal in width b in pounds. Pe = Total comprehensive stress on concrete in width b. Pt = Total tensile stress in concrete in width b A, = Unit elongation of extreme fiber in compression. A» = Unit elongation of steel. e = Distance in inches from extreme fiber on tension side to middle plane of metal reinforcement. This thickness is not figured into the strength of the beam. We can then write the following equations: Pee: Oe) Pea yis ava se, aa ee nae Naseem (1) 2 Ee Ay c= = . But ¥1 AY = Are ye And F 4 = Es Then Fy: hy == Es y2 And 2: FEcy; fe = 3Es ys Or 2 FEe 2 == Vit si Rae eS Ow UN Ves S (2) 370 CONCRETE AND REINFORCED CONCRETE. For the steel, Fa’*b 5 (3) d For the concrete in tension, 8 FEeftby1 Pe = */i ftby2 = t——— ... eee eee eee eens (4) 15 fcEs The empirical constant 8/10 is derived from the results of” M. Considére. We then have, Pie Pia eBoy a apt eesare aceasta seach sf nasa (5) Or, feby. Fa*b 8 FEeftbyr Bo Bean AE errs (6) 8 d .15 fcEs FEe From which : a*b 73 feb, — 64 ftby; \feEs oe (7) d 120 F For the moment of resistance we have, Fa*b 2y1 Sftby, /yz: 2y Mo = (: + ) + [ + =) se ete tibetan (8) d 3 10 2 3 The size of beam needed to develop a required moment of re- sistance can now be readily obtained from equations (2), (7) and (8). From (2) we obtain a numerical ratio between y, and y, when the constants depending only upon the particular materials used are known. Equaticn (7) gives the quantity of metal required in terms of y,, all other factors being known con- stants for the given materials. Then (8) gives the value of the ultimate moment of resistance in terms of y, only. As the mo- ment of resistance is to equal the bending moment of the external proof loads, M, in equation (8) is known, which at once gives the value of y,, from which all other values may be determined. We have found the best average values for the constants for 1: 3:6 rock concrete to be the following: Ee = 3,000,000, fe = 2,000, and fe = 200. For the steel the value of E, varies but little for the different grades of rolled material, but F, or the elastic limit, varies greatly. As before stated in the introduction, we can not utilize any of the }'ARIOUS BEAM THEORIES. 371 strength of the steel beyond the elastic limit, therefore it is de- sirable that this limit should be fairly high. Our corrugated bars have an elastic limit of between 50,000 and 60,000 pounds per square inch. We therefore use for the constants for the steel, Es = 29,000,000, and F = 50,000. With these values equations (2), (7) and (8) reduce to the following respectively : ye = 1.72y1 If b = 12 in. | yi = .368d..........4. (9) a*b 3 2a h a’b —_o oe ande=— | = 0.077h = .64%.. (10) 10 d ; Mo = 2750by,” h = yityzte we have, Mil = 3620 oa ccs (11) There are certain grades of rock that give a much more com- pressible concrete than the above and have at the same time a greater compressive strength. Trap rock falls within this cate- gory as well as certain kinds of western limestone using a well proportioned aggregate and a mix of 1:2:5. For such con- crete we may assume the following constants: Ee = 2,400,000, fe = 2,400, ft = 200. Using the same values for the steel our equations of design tren become: Yo = L15y1 | If b = 12 in. yi = .418h... 0... (12) a°b ania es h a’b i 0263by: + ande=— { =a = 0.132h = 1.1%... (13) 10 Mo = 2620by,? h=yity:te we have, Me = 5505h.......... (14) For a 1: 2:5 mix of cinder concrete we-have Ee = 750,000, fe = 750, and ft = 8o. For this material the equations become: y2 = 0.862y1 | If = i2in, yi = .483h........... (15) ae = 00827by: \ h a" d and e = — —— =. 048h = 4%... (16) { 10 d Mo = 693by:" | h =yityate we have, Mo = 1935h?......-.-- (17) 372 CONCRETE AND REINFORCED CONCRETE. In beams of Tee section (Fig. 205) y, is the same as for rec- tangular sections inasmuch as the position of the neutral axis is determined by the relative values of maximum compressibility FERRE ASRS ae Se gate ese aa | —__ es ME afte pe % : jee Fy b- 3 Fig. 205.—T-Beam Diagram for Johnson’s Formula. of the concrete and extensibility of the steel inside the elastic limit or by the ratio of 4, and 4,. This is, of course, only true at the maximum load. We then have as before, 2FEc “3 feEs y= VALUES OF bi AND t. Let Sv = Total shear in pounds along the two vertical planes of attach- ment between the wings and beam; S» = Total shear in pounds along the horizontal plane of attach- ment between the rib and floor plate; s = Maximum shearing strength of concrete in pounds per square inch ; co 1 = Length of span in feet; Pe’ = Total compression in pounds at maximum load _ between neutral axis and underside of floor plate; Pe’ = Total compression in pounds in flange at maximum load. All other functions are as shown by Tig. 205, and are in inches. There are three methods of failure above the neutral axis: 1. By compression in the flange; 2. By deficiency in S, owing to smallness of t; 3. By deficiency in S, owing to smallness of b. It would be desirable to have equal strength in all these direc- tions, but this is not always possible owing to other considera- tions. Where it is possible we have, Pet SSy i Sapna tee senate ue ennaassAsaecindabeates (19) But- Sw 3bsl. aes ceiesss ers Soeweee eens se aha neanwdawaaioneakns (20) VARIOUS BEAM THEORIES. 373 The shearing stress is a maximum at the ends and ior uni- formly loaded beam varies uniformly to zero at the center. The value S, may be increased about 50 per cent., owing to the metal reinforcement in the underside of floor plate, which is always present in these designs. If vertical shear bars were used the same increase could be made in Sy, but ordinarily these would not be used so we will not separately discuss this condition. Equation (21) then becomes De G's ahd souls os eres aeuaiee ease eRe e Tonos (22) Assuming the compression stress diagram to be a parabola ~ Be a2 85 Gs Ky Fela eae ks seas ene eae (23) This is on the assumption that the outer ends of the wings would be just as heavily stressed as the portion next to the beam. This would not be the case, the stress varying according to the ordinates to a parabola from zero at the outer ends to a maximum at the beam, and we should, therefore, multiply the above value hy 2/3. The portion of this width over the beam itself would not be subject to this modification, but there are other influences tending to offset this so that the above is sufficiently correct. Then Pe’ = */) (1 — K%) febiy: vo. cceeeeceeeeeeeeccecevererees (24) From (20) and (22) we see that if t is not less than z fail- 35 ure will not occur along the vertical sides of beam where wings attach. Now we will assume at once that t will not be allowed to have a value less than this. This leaves us to consider the relation between P.’” and S, only. We then have from (20) and (24) 3bsl = */. (rt — K**) febsyy, from which 27 bsl DD Be ee eee (25) 4 (1 — K*) fey, The theoretical relation between s and f, is fe $= . (see Johnson’s Materials of Construction, p. 29) . (26) 2tan where o is the angle made by the plane of rupture on a com- pression specimen of moderate length with a plane at right angles to the direction of stress. 374 CONCRETE AND REINFORCED CONCRETE. For concrete this angle is about 60°, hence fe SN SS ae esta teinidianrnapieissinaueer& (27) 3.464 But this value is high in view of the liability of concrete to crack and we recommend that twice the strength be provided in the shearing values on this basis that is used in compression. We would then have Sn = 2 Pe’, or gbsl = %. (1 — K*) febrys from which i 27 bsl fae ee 8 (1 — K*4 fey, and substituting the value of s we have with sufficient accuracy, bl by = ————_ _....... - cs eee eee (28) (1 — K") y, We will now insert this value in (24) and proceed to obtain the moment of resistance. At times the above value of b, would be greater than the spacing of the beams, in which case the latter distance would be used for the value of b, in (24), and the other values worked over on this basis. From (24) and (28) then we have, Pee See TEDL Gea iak cents saye a uA dacasouschanseyiyeiad tun ataadnativs (29) also Pel aoe Tt ED YS cap tatiana ene a natn heant lis (30) Then 2fcb /al 3 Pe = te I Pe | tiuckinmiesunsvceeeeon (31) 3 3 FPR SiG) RODS. ccscuts suo sishauayd bveet-s As nas avashavwomenodwnacntens (32) f Fa*b 5 hae sate eematineene 24 aeecenyion ad ( 4 33) But Pe = Pe + Ps 2 he telhefisigete seeds, Bridie cay ou'y vlonan eh eateries wisevai- doe aa ae Je’. From which ' os a’b I [- feb (= 4) —- = —|-—_([— + K® y. — 8 ftby. | ...... 5 d F zi tby | (35) and Kyi (1+ K)ys yo + P% —————— + Pr — + Pays.... (36) 2 2 2 Problem: Required the size of Tee shaped beam necessary to 8 VARIOUS BEAM THEORIES. 375 carry a total ultimate load of 600 pounds per square foot on a span of thirty-two feet, ribs to be nine feet apart. Then I2 X 9 X 600 X 1,024 = Se = 8,300,000 inch pounds. Let us assume a depth of beam h equal to 22 in. Then y, + y, == 20 in. For this spacing of beams the thickness of floor plate should be 4 in. Using special rock concrete we have from (12) 20 yi = — = 9.3 in. and yz = 10.7 in. 2.15 yi—t 5-3 K = — = —— = 157, and K°2 = 143. 1 ‘ Then : o Pe’ = % K'? feby, = % x .43 X 2,400 X 9.3b = 6,400b Pe’ = */y feb] = */y X 2,400 X 32b = 34,100 b and —<——$—= Pe = 40,500 b Pe = 8 ftbyz = 8 X 200 X 10.7b = 1,715b Then —_ Ps = 38,785 b and a’b 38,785 b — = —— = .776b d 50,000 Ky, (1+ K)y, ys Mo = PP’. —— + P’’. —————_- + Pr— + Pays 2 2 2 = 6,400 b X 2.65 + 34,100b x 7.3 + 1,715 b X 5.35 + 38,785 b X 10.7 = 690,130b or, 8,300,000 b = ———— = 12.03 in. 690,130 Substituting in (28) we have 12 X 32 b, = ———— = 72.5 in. or 6 ft. 57 X 9.3 As this value of b,, which we have used in determining the value of P,.” above, is less than the spacing of the beams it is the proper one to have used. It will be noted that t is just one- third of b. From the foregoing we derive the following relations for good 376 CONCRETE AND REINFORCED CONCRETE. grade of 1:2:5 Portland cement rock, concrete, where fp = 2400; f, = 200; E, = 2,400,000 ; E, = 29,000,000 ; F — 50,000. \ P's = 1,600 K*? by.; Pe = 160by2; Pe = 1,066 bl. a’b P’, — Pe + Pe Also —— = ————————— = number of squere inches of metal re- 50,000 quired in rib. ; yi t t yo Mo = Pe’ (—+y2—— } + Pe’ (yi + ys —— — Pir— = 2 2 2 2 ultimate moment of resistance in inch pounds. All measures of length in inches except 1, the length of span, which is in feet. The value of t must not be less than one-third b. The value of b represents the maximum width of flange that can be utilized in figuring the strength of the Tee, and its value 1S? bl oa = SSS a pe a (r— K*!)y, Where this value of b, exceeds materially the distance between the ribs, the above formule can not be used, and the value of P.” would have to be obtained from the general equation (24). SHEAR IN STEEL-CONCRETE BEAMS. Let Mo’ = moment of resistance in inch pounds at 12 in. from end of beam carrying its ultimate load. Mo = ultimate moment of resistance in inch pounds at center. 1 = span of beam in feet. X» = elongation per inch at the plane of the metal, at section 12 in. from end. = width of beam in inches. s = ultimate shearing strength of the concrete, about one-fourth the ultimate compressive strength. Other functions as already given. 4l—4 Then Mo’ = F Mo for uniformly loaded beam...............008 (1) M.’ D5 et Ec by,®> Eeby:* — Es a*by* + PS sia eben oamendemtaearasans (2) 3 y2 3 d 2Es ab bys? = bys? + ya woeieccccccccccccccececcucvccveeveee (3) Ee d VARIOUS BEAM THEORIES. 377 Yar Ny rate wach nattees an Od banners (4) Pa a: irs pishsattoee essed aoa bated pee sew awa (5) anes designing the beam by the beam formula given above, a ——. yi + yz, Ec, Es, and b are known. From (1) we obtain M’. and from (3) and (4), y: and yz From (2) will be obtained sz, which inserted in (5) will give the pull in the bars which has to be absorbed by shearing stress in the concrete over an area = 12b. As it is desirable to take twice the factor of safety in shear that is taken in bending, Ps should not exceed 6bs, where s is taken at one-fourth the compressive strength of the con- crete. If beams are loaded at two points some distance apart the maximum shearing stress is likely to be a very different character. The bending moment being uniform between the loading points, the first cracks on the tension flanige are as apt to occur under one of the loads as in the middle and this will greatly reduce the asl Fig. 206.—Shear Diagram, Johnson’s Formula. strength of the anchorage of the ends of the bars represented by the shearing resistance of the concrete along the plane just above the metal between the crack and the end of the beam. This is especially true as the maximum shearing stress along this plane is likely to be double the average stress. In such cases, as also in cases of uniform load where the shear exceeds the limits above given, the bars should be bent up at the ends, as shown in Figs. 206 and 207. The discussion of formulas 1 to 17, only applies to beams on knife-edge supports and is inadequate when applied to rectangu- lar beams used in flooring where there are haunches on the beams and flooring in the adjacent panels. There is no scientific dis- cussion of such a construction, but we know from experience that it has about twice the carrying capacity of a construction acting as a simple beam resting on knife-edge supports. The haunches on the beams produce a continuous girder action, such that the external bending moment in the middle is only about two-thirds BY 378 CONCRETE AND REINFORCED CONCRETE. as great as if it were free at the ends; also the floor in the adjacent panels produces an interior arching action within the thickness of the slab, increasing the area of the compressive stress diagram, about one-third of this extra compression being counteracted by the adjacent floor panels, instead of by the re- inforcement. The effect of these two elements is to double the Fig. 207.—Shear Diagram, Johnson’s Formula. strength of the beams as used in floors. If the beam does not have haunches projecting below, but is itself the full depth throughout, then only one-third should be added to the value of the moment of resistance. Beams of Tee shape are not greatly strengthened by incorpora- tion in floor panels, inasmuch as most of the compressive strength -comes from the flanges too high up to be affected by the interior arching action. That is to say, P’e would remain practically the same and P’e would be increased probably fifty per cent. But the latter is usually so small as to make this increase of little value. CHAPTER XXI. THEORY OF COLUMNS. Reinforced concrete columns are of two general types: First columns with straight reinforcing rods, and, second, hooped columns. Concrete Columns with Straight Reinforcing Rods.—These may be divided into two classes. First: When light reinforce- ment is used. In this class may be included all columns where the area of the reinforcement is only a small percentage of the cross-section of the column and no appreciable error will result if it be neglected when computing the sectional area of the con- crete. Second: When a higher percentage of metal is used and it becomes necessary to deduct its area from the total area of the piece to obtain the correct area of the concrete. We will assume a column, having a cross-section of any form, round, square, rectangular, etc., and reinforced with straight bars of round, square or any desired section, subjected to com- pression due to a load P, acting along its axis. If the column was composed of homogeneous materials the sectional area re- quired to sustain the load P would be fe Ay te tte Ae o.oo 5 ac kee icone eet (1) Where f, = the allowable working stress on the concrete and {,° that of the metal, A, represents the sectional area of the concrete and A, that of the metal. The deformation due to a load P will cause the displacement of any section taken at right angles to the axis of the column, to a position parallel to itself. In order that the concrete and the metal may act as a homogeneous mate- rial their deformations must be equal, and we have the condition that the stress upon each material must be proportioned to its coefficient of elasticity, or fe fa" Ee Es I when E, and E, are the coefficients of elasticity of the con- crete and the metal respectively. Equation (2) may be written 38c CONCRETE AND REINFORCED CONCRETE. Es fs° = fe ( ) RE er ee ee ee ee ee Cen a ae io a savel3}) Ee Substituting this value of F, in equation (1), there results Es P= fe A + fe As Ee Es =1|a+( ) a | 55 Gane aos is SE Gas BORN (4) Ec The ratio of the coefficient of elasticity of steel to that of con- Es crete is usually expressed by e= Eo and formulas (3) and (4) become fe CRE sec hak la ep asnlemnaal eee eau 5) Pete CA ele) og casera eed aes (6) Columns Heavily Reinforced—When the percentage of metal used is increased it is necessary to determine more closely the sectional area of the concrete. Subtracting from the total sec- tional area the area of the metal the true area of the concrete is obtained, or :\, A — Ag. Substituting this value in equation (6) and reducing Pi te CA + G6 — 1) As) ware as vevexss acces (7) This equation may be used for computations of columns in which the percentage of metals used is greater than 1 per cent. - The above formulas are applicable to columns having a length not exceeding from 20 to 25 times their diameter. When a greater length than this is used, Euler's formula for flexure, given below, should be used. For all practical purposes it will be found that no formula for flexure will be needed, as columns longer than 25 diameters are seldom used. For important work and very heavy loads it will be well to limit the length to 20 di- ameters or less. In classic architecture the total length of the column, including the base and capitol, does not exceed from 10 to 15 diameters. Slender columns have an appearance of weak- ness, and for this. if for no other reason, should often be avoid- ed. Again, great difficulty will be experienced in securing a thoroughly homogeneous concrete when constructing slender columns. It will often be advisable on the score of economy to use larger sections than theoretical requirements call for. THEORY OF COLUMNS. 381 Euler’s formula for long columns with fixed ends is (see Mer- riman’s Mechanics of Materials) : m EI P=4 sg eet (8) in which I = the moment of inertia of the column. E = the coefficient of elasticity and may in the case of reinforced concrete columns be taken as E,, the coefficient of elasticity of the concrete. 1 = the length of the column in inches. For a rectangular column of reinforced concrete I= V2 bd? + e As y’ avi avfaviaaine aneineweing Tey arin Sa Neh Cy (9) y being the distance of the center of the reinforcing bars from the axial plane of the column. For square ended columns formula (8) becomes bd® 47 t+eAsy’ | Ec I2 P= ——__—__................ (10) r Substituting tor e, a value of 10 and for 7? its value, this formula becomes bd* 39.48 {| ——+10Asy’} Ee 12 PS nen. (11) Lr Formula (11) gives the ultimate strength of the column, and to obtain a working formula a suitable factor of safety should be used. For square columns b = d and the expression bd® d* —— becomes ——, 12 12 ana equation (11) becomes dt —+10As “) Ee T2 = 39.48 as a reece enrwen 4 pers (12) For circular columns and columns of polygonal section approxi- mating a circular form, the value of the moment of inertia I when d = the diameter of the columns, becomes I = (0.0491 dé + 10 Asy?) ...ceeeceeceen eens (13) 382 CONCRETE AND REINFORCED CONCRETE. Substituting this value of I in equation (8) it becomes 47 (0.0491 d‘ + cAsy’) Ee = ee 7, pisenciath a (14) - replacing e and w by their numerical values, we obtain for the ultimate strength of round columns (.ogg1 d‘+10 As y’) Ec P = 39.48 steer eect ah alana tateietinees (15) - For heavily reinforced sections Euler’s formula for columns with fixed ends takes the form 47° [(Ie — Is) + eIs] Ec i a ee P When I, —.the moment of inertia of the whole section and J, = the least moment of inertia of the reinforcement with refer- ence to the axial plane of the column and E,, as before, the co- efficient of elasticity of the concrete. Now, I, = A, y? when A, = the area of the metal and y is its distance from the axial plane. I, has the same value for rec- tangular, square and round sections as before, and the equation becomes : For rectangular columns 12 4 P= ——— eee... ieee (17) r bd’ 47 (—— + (e —1) Avy?) Ee For square columns , gt 47 (—+ (e — 1) Avy] Ee 12 PS eee (18) ies and for round columns 47° [.oggt d‘ + (e — 1) As y7] Ec Pos i, (19) r Substituting the values of w and e, as before, formulas (17) (18) and (19) become, respectively : ° For rectangular columns bd® 39.48 2: ee vans Ec P i THEORY OF COLUMNS. 383 For square columns d‘ 39.48 |= + g As | Ee 12 P= Le (21) i eg For round columns . 39.48 [.ogg1 d* + g As y*] Ec cette eee (22) L It should be remembered that formulas (20), (21) and (22) are for the ultimate strength, and when a working formula is desired a proper factor of safety should be introduced. When it is desired to use another value for e than 10, it should be intro- duced in equations (6), (7), (10), (11), (15), (16), (17), (18), and (19). Formulas 20, 21 and 22 may be used to check the columns of existing structures or to design a column to support a given load. When used to check a column, the sectional area of both the concrete and the metal, together with the load, may be given to determine the working stress, f,, in the concrete, or safe working stresses may be assumed and a value for P computed. When the design of a column to support a given load, P, is to be made, a working value for f, is assumed; we have then to determine the vatue of A and A, and the problem becomes a tentative onc. Usually practical considerations fix within narrow limits the size of column desired and the area of steel necessary to sup- plement the concrete or the percentage of steel to be used is fixed upon in advance, and the areas of concrete and steel may be determined by assuming a section and computing its strength by the formula to determine if the working stresses f, and f,° approximate the working stress determined upon for the given structure. Usually a section having the proper work- ing stresses may be found after two or three trials. Examples will be given showing the use of the formulas, both for checking end designing columns. Example 1.—Let it be required .to check the section of the Hennebique column described on page 467. The section of the column is 35 x 35 cm. = 1225 sq. cm. = total area of col. 4 rods 20 mm. diam. = 3.14159 x 10° x 4 = 1257 sq. mm. = 12.57 sq. cm. area of metal. Comparing the total area of reinforcement with the area of column it is observed 384 CONCRETE AND REINFORCED CONCRETE. that the reinforcement is approximately 1 per cent. We will, therefore, use formula (6), P = fe (A + 10 As). The total load was 43,000 kg., and we have 43,000 fe = ee = 318 kg. 1,225 + 10 X 12.57 total compression per sq. cm. on concrete, or approximately 450 Ibs. per sq. in., which, while a little high for the load on column, is at times used by some designers. Example 2.—Determine the safe load which can be carried by the column for a Chicago store building, shown in Fig. 319. The size of the column is 20 x 20 ins. = 400 sq. in. 4 rods 2 +5 ins. diameter — 5.1572 x 4 == 20.6288 sq. ins., or approximately 5 per cent. In this case we will use formula (7). P = f, (A +(e — 1) A,). It is necessary to assume a safe working stress for f,. The concrete used was a 1:2:2 mixture, and its crushing strength may be taken at 3,600 Ibs. Ifa factor of safety of 6 be used, the working strength will be 600 lbs. per sq. in., and we have, substituting in the formula, taking e = Io, P = 609 (400 + 9 X 20.63) = 351,400 = 1757 tons. Example 3.—Let it be required to determine the size of a col- umn 12 ft. long necessary to carry a load of 40 tons, using a 1:2:4 concrete with a working stress of 500 Ibs. per sq. in., re- inforced with 3 per cent. of metal. We will assume that e has a value of 10. We then have P = 40 tons = 80,000 Ibs. ¢ = 500, e = 10, p = .o3, and As = .03 A; and Formula (7) is P= fe [A + (e —1) Asl. Transposing, P ee xX .03 A = 1.27 A. 80,000 . = 127A. 500 A= 126 © sq. ins, Add 2 sq. ins. for chamfers 2 SS As = 126 X 03 = 3.78 “ “ 131.78 sq. ins. THEORY OF COLUMNS. 385 A column 11.5 x 11.5 ins. = 132.5 sq. in. 4 rods 1% ins. in di- ameter = 0.994 x 4 = 3.976 sq. in., giving an area of reinforce- ment slightly in excess of area required. As the column required is only 12 ft. long, it will not be nec- essary to test it by Euler’s formula for bending. Example 4.—What will be the size of column necessary to carry the same load as in the last example, but reinforced with 1 per cent. of metal. As before P 4o tons = 80,000 Ibs. fe = 500 lbs. e = 10. p = .o1, and As = .ot A. As only 1 per cent. of reinforcement is to be «ised, we will em- ploy Formula 6. P = fe (A + eAs) or, 80,000 = 110 A, and 500 A = 145.45 + sq. ins. As = 1.45 + sq. ins. A column 12% x 12% = 150 sq. ins. concrete. Less 2 sq. ins. for chamfers gh ® *e 148 sq. ins. concrete. Four rods 1/,, in. diameter = 1.48 sq. ins. metal. These sec- tions will be adopted. The column with 1 per cent. reinforce- ment will be the more economic of the two. Thus, assuming the cost of the concrete in place at $8.00 per cu. yd. and the cost of metal in place at 3 cts. per lb., we obtain the following costs: With 3% reinforcement: For cost concrete— 11¥%e” x 11%” X 12’ = 11.04 cu. ft. concrete. 11.04 x $8.00 = $3.27. 27 48 ft. 1% diam: rod, at 3.379 lbs. = 162 Ibs. 162 lbs. at $0.03 = $4.86. 3.27 4.86 Total: OSE anisindcd aed aandaes = $8.13 386 CONCRETE AND REINFORCED CONCRETE. For 1% reinforcement: 12%” x 12%” xX 12’ = 12.50 cu. ft. 12.50 X $8.00 27 48 ft. */1e-in. diam. rod, at 1.262 Ibs. = 61 Ibs. Y 61 lbs. at $0.03 = $1.83 Motal cost: sewtwimetaus8e essere ees = $5.49 The saving when I per cent. of reinforcement is used will be $8.13 — $5.49 == $2.64, or a saving of 32.6 per cent. Es The value of the ratio represented by e varies according e to the quality of the concrete used. Values from 6 to 20 are used by different engineers. In general, the value of e may be taken at 10, which value probably represents the approximate value of this ratio for ordinary concrete used in compression. However, if the true value of e varies slightly from the value 10 here chosen, it will not affect materially the working stress of the concrete or the size of the column. For assuming values of e at 8, 10, 15 and 20 and substituting in Formula (6) we obtain for I per cent. of reinforcement: P Tore = 8—=108A x fe P fore = 10 — = 1.10A fe P fore = 15 —= 115A fe P fore = 20 —= 1.20A fe Taking e == 10 as the basic value for e = 8, or a value of 20 per cent. less than 10, we have 1.10 — 1.08 = .o2 decrease, or 02 ; —— = 18 per cent. change in area. 1.10 In a like manner, for e == 15, or an increase in value of 50 per cent. over our basic value, we have an increase in section of 4.54 THEORY OF COLUMNS. 387 per cent., and for e = 20 an increase in section of 9.1 per cent. For a higher percentage of metal than 1 per cent. the change in section will be somewhat greater than that here shown, the _largest increase resulting when the highest percentages of metal are used. This makes a close determination of the value of e de- sirable when high percentages of metal are to be used. The method of reinforcing columns with longitudinal rods has not proved entirely satisfactory for many reasons. It is often impossible to keep the upright rods in proper position dur- ing the construction of the column. Again, rods thus embedded in concrete are not in a position to develop the full strength of the steel, as before the shortening has become great enough to develop the full strength of the concrete the metal has reached its elastic limit. The low stresses in the steel and comparatively low working stresses in the concrete not only do not give an economic section, but when heavy loads are to be carried neces- sitates so large a column as to be very objectionable. While it has been admitted up to the present time that stone mortar and concrete, when subjected to direct compression, al- ways fail by shearing along planes inclined to the direction of stress, recent experiments made by Messrs. Foeppel, in Ger- many, and Mesnager, in France, seem to prove that this method of failure is due to the friction between the planés of the test specimens and the plates transmitting the pressure. The friction between these surfaces was greatly reduced by greasing the sur- faces of the testing machine, and it was found that failure took place not along planes inclined to the axis of pressure, but along planes parallel to the direction of pressure. If these experi- ments are taken as conclusive, it is evident that very little strength is added to the concrete by the use of longitudinal rein- forcement. It is evident that rods in this position cannot pre- vent the separation of the molecules either vertically or obliquely. The total strength will then be that of the concrete, plus that of the steel. Shrinkage Stresses——The tendency of concrete to shrink when setting in air causes high internal stresses, tension in the con- crete and compression in the steel. Considére describes experi- ments made in 1902 at the School of Bridges and Roads at Paris which show to some extent the stresses resulting from the shrinkage of concrete in setting. 388 CONCRETE AND REINFORCED CONCRETE. A bar of 1:3:6 concrete 6 ft. 6 ins. long and 4 ins. square reinforced with 4 rods % in. in diameter, placed near each corner, showed sufficient shrinkage of the concrete at the end of 3 months to cause a compressive stress in the steel of 6,540 Ibs. per sq. in. Similar specimens 8 x 16 ins. in section by 13 ft. long, reinforced with 4 rods 7% in. in diameter, about 14, ins. from the surface, showed sufficient shrinkage to produce compressive stresses in the steel varying from 10,800 to 14,220 lbs. per sq. in. Thus we see that in compression members the stresses induced in the steel by the shrinkage strains become of so great importance that they must not be neglected in computing the strength of the member. Ordinary concrete can stand, without crushing, a reduction in length of from .0007 to .oo1 of its length. Such a deformation in the concrete will cause stresses to be developed in the metal which will vary from 20,000 to 30,000 lbs. per sq. in. for a coefficient of elasticity of 30,000,000 lbs. for the steel. Adding this stress to the previous stress of say for 6,000 to {4,000 Ibs. gives a total stress of from 26,000 to 44,000 lbs. per sq. in. on the metal. These stresses approximate or exceed the elastic limit of mild steel. Therefore, when the concrete is strained at or very near its ultimate strength, the steel will already have been strained beyond safety, and failure will not be delayed hy the steel, but will take place suddenly and without warning. When horizontal ties are employed to bind together the vertical reinforcements at intervals about the thickness of the columns, failure takes place by the buckling outward of the rods between the ties, accompanied by local disintegration of the concrete. Hence the total strength of the column will closely approximate the strength of the concrete, plus that of the longitudinal rods when stressed up to their elastic limit. After the elastic limit of the metal is passed, the value of its coefficient of elasticity is greately reduced and its power of resistance becomes correspond- ingly less. The portion of the load which each will carry, as ex- plained above, will depend upon their respective sectional areas and the moduli of elacticity of the concrete and the steel. When longitudinal reinforcement is used the bars are immedi- ately available for sustaining a certain amount of load as soon as they are built into the column, and before the concrete itself has hardened sufficiently to have acquired much strength. The bars are also available for spanning over places of local weakness. The THEORY OF COLUMNS. 389 adhesive bond between the concrete and the metal permits a trans- mission of stresses from the concrete to the steel, inducing higher stresses in the latter at points where local weakness exists in the concrete. These stresses are again transferred back to the con- crete at a lower point, where it again attains its normal strength through the medium of the bond. It does not seem advisable to depend entirely upon the bond to transmit the stresses from the steel to the concrete at the bottom of the column. A bearing plate or suitable shoe should there- fore be placed under the reinforcement at the foot of the column. Lean mixtures have much less compressive strength and are more compressible than rich mixtures. It follows that the longi- tudinal reinforcement will be subjected to higher stresses at all stages of loading in a column made with a lean concrete mixture than when a rich mixture is used. We may therefore conclude that steel with a high elastic limit is especially desirable for rein- forcing columns when lean mixtures are used. Under working conditions, however, neither the concrete nor the steel is highly strained and the metal often serves to transmit the strain through zones of comparatively low strength which are sometimes present in concrete. This function, which is seldom taken into account when determining the theoretical strength of concrete columns, is one neverthcless which should not be lost sight of in proportioning the columns and would lead to condemn- ing the use of unreinforced or very lightly reinforced concrete columns so much in favor for certain classes of work at the pres- ent time. This point should be emphasized when higher working stresses than 350 or 400 lbs. per sq. in. are used. On account of the uncertain action of columns with straight longitudinal reinforcement, it is desirable to use comparatively low working stresses. Factors of safety ranging from 6 to Io are not too high for this kind of member. Hooped Concrete.—The resisting power of concrete may be augmented by reinforcing it against lateral vielding either bv shearing in a vertical or diagonal direction or by preventing the concrete from spreading laterally as shortening takes place under heavy loads. It has been found that when a block of concrete is subjected to heavy pressure the cohesion between the molecules is lessened as the block decreases in height and increases in size in a direction perpendicular to the’line of pressure. This tendency of 390 CONCRETE AND REINFORCED CONCRETE. | the molecules to flow horizontally is resisted by the cohesion and the friction between the molecules. If the lateral expansion is prevented by surrounding the concrete with a tube of metal or by confining it with spirals or hoops, its resistance to compression will he greatly increased. The maximum degree of efficiency will be reached when the hooping is continuous and of sufficient strength and rigidity to retain the component parts of the concrete within certain definite limits. As has been stated, the leaner mixtures of concrete are most compressible. Hence, only rich mixtures are suitable for use in hooped columns, as a minimum shortening in the column length is desired to bring the hooping into action as the loads are applied. Experiments made at Columbia University by, Prof. Ira H. Woolson show the manner in which concrete confined in tubes be Fig. 208.—View Showing Flow of Concrete Under Heavy Pressure. flows in a lateral direction when subjected to excessive pressure. A series of short columns, 4 ins. in diameter and 12 ins. long, were constructed by filling steel tubes of that size with finely crushed stone concrete and allowing the same to set. The con- crete in the column tested was 17 days old at the time of test and appeared to be very hard. The metal of the tubes was of different thicknesses, varying from 1% in. to 14 in. The heavier metal col- umns carried a load of 150,000 Ibs. (about 12,000 Ibs. per sq. in.) without injury except a slight shortening of less than 1% in. The columns with the light weight tubes began to show a marked de- formation under a load of 120,000 lbs. (9,500.Ibs. per sq. in.) ; this gradually increased until a load of 150,000 Ibs. was applied, when the tests were discontinued. The photograph, Fig. 208, shows what happened in different cases. No. 1 was unaffected by the full load, No. 2 had sustained a THEORY OF COLUMNS. 391 load of 115,000 lbs. (9,000 lbs. per sq. in.). A bulging ring at the top and bottom shows that failure had just begun. Nos. 3 and 4 show excessive deformation due to increase of load. They all compressed 314 ins. and 3% ins., respectively. The diameter had correspondingly increased to about 5 ins. It was supposed that this excessive distortion had completely disintegrated the concrete and left it a powdered mass, but when the tube was sawed apart and removed, the concrete was found to have taken the exact shape of the distorted tube and was solid and perfect in every way possible. This experiment shows con- clusively that the concrete had actually flowed under the pressure like any plastic material. The concrete was apparently perfectly dry and no signs of moisture could be observed. A similar experiment is discussed by Considére. A hooped prism of concrete, a 1: 3.2 cement gravel mixture, was subjected ta a pressure of 7,940 lbs. per sq. in. of the original section. The prism became very much bent, taking the shape of the letter S. The maximum deflection was 0.4 ins. in a length of 13 ins. The curvature was the sharpest at the middle of the specimen, the least radius of curvature being about 2 ft. The stretched fibers showed no transverse cracks, and therefore did not suffer greatly from the extension. The computed shortening of we compression fibers amounted to 17 per cent. The hooping and longitudinal reinforcing were removed and " the concrete core, having a length of 4 ft. 3 ins., could not only be handled without breaking, but when placed on two blocks 3 ft. 7% ins. apart, it required a load of 55 lbs. to break it by bending. One half of the same core not so much bent was put on two supports 201% ins. apart, and required a load of 428 Ibs. to break it. This indicates a tensile resistance at the extreme fiber of 205 lbs. per sq. in. In another experiment a metal tube 7% ins. in diameter was filled with Portland cement and bent so that the radius of curva- ture of its neutral axis was 21.6 ins. The metal shell was then removed and a piece of cement cut out. The cement which had been subjected to this great deformation did not break and only showed a few cracks on the compression side. Another test described by Considére was as follows: A speci- men mixed with the proportions of 1 part of cement to 4.3 parts of sand and gravel withstood a pressure of 10,270 lbs. per sq. in. 392 CONCRETE AND REINFORCED CONCRETE. with a maximum longitudinal shortening of 2.8 per cent. and an average shortening of 2.4 per cent. After the removal of the re- inforcement the concrete core sustained a pressure of 924 Ibs. per sq. in. Another specimen withstood a pressure of 6,970 lbs. per sq. in., with a shortening of 0.6 per cent., and after the re- moval of the reinforcement the plain concrete withstood a pres- sure of 1,420 lbs. per sq. in. Table LXVIII. gives a summary of the results obtained by Considére in 1go1 from tests on specimens of cement mortar 1.6 ins. in diameter, reinforced with a hooping of fine iron wire and without longitudinal reinforcement. The mortar was mixed in the proportions of 675 lbs. of cement per cu. yd. of sand (a 1:4 mix- ture by volume, assuming I cu. ft. of cement weighs 100 lbs.), with the exception of one prism in which the proportion of cement was 730 lbs. per cu. yd. (a 1:3:7 mixture by volurre). The iron wire was drawn cold and had no definite elastic limit, but the stress of 78,200 lbs. per sq. in. corresponded with what was vir- tually the yield point. TABLE LNVIII. PROPERTIES OIF HOOPED CEMENT MORTAR. Specimen: No». scunis cramer diacmgees I 2 3 4 5 Cement per cu. yd. of sand, lbs. ...... 675 675 675 675 730 Proportions by volume .............. Pet ota. Pig. Deg Bes Age of mortar, days.................. 8 14 22 23 100 Percentage of reinforcement in cross SECUIOM: 45.5. Aeatyacapstatescairacecedvgerdaeet sie wyordonancerd 2 3 4 2 3-4 Crushing strength of total section, Ibs. PEE SOe AM wincnnwenameadansonaeee 4,870 6,540 7,360 4,930 10,500 Crushing strength of mortar (not re- inforced) Ibs. per sq. in. ..........., 569 Ir 853 853. 2,420 Increased strength due to hooping...... 4,301 5,829 6,507 4,077 8,080 Calculated resistance of iron as longi- tudinal reinforcement .............. 1,564 2,346 3,128 1,564 2,658 Value of hooping in terms of longi- tudinal reinforcement ............... 27 2.5 2.1 2.6 3.0 The above experiments illustrate to some extent the remark: able ductility of hooped concrete, and the enormous pressure: which it will sustain without apparently losing much of it: original strength. Considere’s Experiments on Hooped Concrete—M. Considére made a large number of experiments to determine the coefficient of elasticity of hooped concrete. Table LXIX. gives details of a few of these experiments. The test specimens were octagonal in sec- THEORY OF COLUMNS. 303 tion, having a diameter of 6 ins. and a length of 4 ft. 3 ins. The prisms were reinforced with helicoidal spirals and longitudinal rods. The amount of reinforcement and proportion of cement, both by weight and by volume, assuming 1 cu. ft. of cement weighs 100 lIbs., are given in Table LXIX. The amount of shortening under given loads is shown in Table LXX. TABLE LXIX. MATERIAL OF TEST PIECES. Weight of Spirals. Longitudinal Rods. Test cementto 1 Proportion Diameter, Spacing, Diameter, No. cu. yd. gravel. by volume. inches. inches. Number. inches. I 840 1: 3.2 wy 0.79 8 0.3125 2 840 1: 3.2 y 0.79 8 0.3125 3 840 1732 % 0.79 20 0.276 Similar results were to be expected inghe various prisms. This, however, was not found to be the case. For specimen No. 1 with the pressures below 2,845 lbs. per sq. in. gave a coefficient ot elasticity of 7,110,000, while No. 2, which was of identical com- position, gave a coefficient of elasticity of 2,845,000 lbs. per sq. in. This difference was due to the quantity of water used for mixing the concrete. The correct amount of water was used for No. 1, while an excessive amount was used for No. 2, giving a soft con- crete, which did not acquire the compactness essential for a high coefficient of elasticity. Thus we see the coefficient of elasticity may vary within wide limits, according to the amount of water used in mixing. Upon plotting the deflection curves it will be found that after a certain pressure has been exceeded a decided change in the in- clination of the curve takes place. - The point of this change may be taken as the elastic limit. Considére found that the elastic limit and the resistance to crushing are almost independent of the amount of water used in mixing, but vary according to the amount of cement used. The coefficient of elasticity was not, however, found to be affected materially by the amount of cement used. — During loading and unloading the deformations show a perma- nent set, which increases if the same load was repeated, but in a less and less degree, and rapidly approaches its final limit. A re- duction in the temporary deformation was observed during the loadings and unloadings following the first, which appreciably in- creases the coefficient of elasticity. It was also observed that the deformation curves for the repeated loadings turn their concave CONCRETE AND REINFORCED CONCRETE. 394 zOIg'O grzoo gri10'0 ‘ur “bs sod ‘sq, OF6‘Z ye ainxapy ‘ut ‘bs sod ‘sq, S€EQ Je ainxa,y ‘ur ‘bs sod ‘sq, gS69 38 9Inxe]JT orér- obZ'g PSfo'0 SLO gSf1" o1z'9 ooor'o $1900 glfo® ofe'e SZg0° L£Z30" 009‘S Stroo gsgo'o ogtro'o Szgit “‘BuUIpvojuA, pue Surpeoy 3s41y S9Zo° ofg0° = zgSo" S60" 60° zZ£Zo" Sggo° zggo. SF go" ozh's oS1‘S = o6g'P “SUIPeOT PU0dIIS Stroo §=6LEb0'.0 = OS £00 gsgo0 = ZgpSo'0-s LEFo'o ogroo §=ogzoo.—s BS I0°0 06th Segie of NE obSo" SPLo obso’ o6r'y bgzo'o oSfo'o of£10'0 SLE goto" zbvgo’ 6rr0" oof 'e Sozo'o g4zo'0 S600'0 oS9‘T coy Seco" £ Sayoul Ul obSo° Z [ Zuruey0ys ee I J "ON 759.L oS9‘t teeeeeeer out bs dad ‘sq, ‘ainssaig S100 g soyour ur eZ4iI00 =z SUIU9}IOYS Z¥oo'o I ‘ON 780.L €So'r stresses ee aT bs dad ‘sq[ ‘ainsseaig “ONIGVOINA AGNV DNIGVOT GaALVdadda AO LOAAAY “XXT TIEVL THEORY OF COLUMNS. 305 side to the axis of pressure, while it is convex toward that axis in the curve of deformations due to first loading. It follows that the coefficient of elasticity, which is graphically represented by the inclination of the tangent to the curve of de- formation, increases with the pressure with a repetition of the loading, instead of decreasing with an increase of pressure, as under the first application of the loading. It is evident that flexure is to be feared in a column under high pressures, and it is therefore unfortunate that the coefficient of elasticity which is directly proportional to the column resistance decreases with the increase of pressure, as is the case under the first application of the load. On the other hand, it is especially fortunate that hooped concrete which has been subjected to a first load has a coefficient of elasticity which increases as the pressure increases, providing the pressure does not exceed that of the first load. To illustrate this point a specially prepared prism was test- ed. This prism was octagonal in section of 4.3 ins. diameter. TABLE LXXI. EFFECT OF REPEATED LOADINGS. First loading and Second. loading and Third loading and Fourth loading and unloading. unloading. unloading. unloading. Load, Shortening, Load, Shortening, Load, Shortening. Load, Shortenin lbs. per lbs. per : Ibs. per lbs. per, sq. in. inches. sq. in. inches. sq. In. inches. sq. In, inches. 128 sili 1,180 0504 1,620 2790 1,620 553 441 .0047 1,620 .0544 3,170 3105 4,720 614 810 0142 1,990 0615 4.720 3400 6,340 638 1,180 .0205 2,360 .0693 5,530 3580 7,100 658 1,620 .0299 3,170 1088 6,340 3980 7,525 669 1,990 —- .0457 3,990 .1560 7,525 6590 7,910 684 2,360 0630 4,720 2240 7,910 .6600 8,710 768 1,620 .0606 5,530 .3600 7,525 6575 10,290 ats 1,180 0599 5,160 .3590 7,100 6580 280 .950 810 0528 4,720 -3386 6,340 .6540 7,910 .950 441.0304 3,170 «3245 4,720 .6410 6,340 -934 128 .0299 1,620 .2980 1,620 .5830 128 795 arene ee 128 ~—-.2410 128 5480 snaae se The concrete was a 1 cement, 1 sand and 3.2 gravel mixture. The gravel varied from 0.2 to I in. in size, and the sand all passed a screen having 0.2 holes. The helicoidal spirals were of iron wire 0.17 in. in diameter, the adjacent coils were approximately 0.82 in. centers and arranged 334 ins. in diameter. Eight longitudinal wires were also used, of the same size and material as the hoop- ing metal. The length of this prism, 51.18 ins. Table LXXI. gives the loading and resulting deformation. 390 CONCRETE AND REINFORCED CONCRETE. After the high pressure of 10,290 lbs. per sq. in. had been ap- plied and removed it was found that the coefficient of elasticity was as high as after the application of the lightest pressure. Considére draws the following conclusions in regard to the co- efficient of elasticity: ‘‘The application of a first pressure on a hooped prism, no matter how high the pressure may be, as long as it is below the breaking load, has the effect of raising its elastic limit up to that pressure. The coefficient of elasticity which is subsequently developed by the hooped concrete under all the variations of the pressures between the lowest and the previously applied load is higher than the highest coefficient of elasticity which the prism had before the test load, and which held true for a low pressure only. The increase in the coefficient of elasticity ot the concrete after the test load, as compared to the coefficient before, is so much greater the less the proportion of cement and the lower the quality of the concrete.” Elastic Behavior of Hooped Concrete——To determine definitely the effect of hooping, it is necessary to test identical prisms with and without hoops. As it is not possible to make identical prisms with and without hoops, one of two methods must be followed in making a test. The test specimens must be prepared as nearly alike as possible and corrected for their differences in the initial values, or a prism may be tested with its spirals and then tested again after the spirals have been removed. By means of such tests Considére determined that the increase of the coefficient of elasticity due to hooping was practically equal to 90 per cent. of the coefficient of elasticity of longitudinal rods having the same weight of metal. It is generally the case that concrete setting in the air shrinks or contracts. On account of this shrinkage or contraction it is evident that the concrete will not bear effectively against the wire hooping until the load has been applied and the swelling has be- gun, thereby bringing the concrete and the spirals into close con- tact. It has been found that the hooping does not come into op- eration until the pressure per square inch reaches a limit of from 1,200 to 1,500 Ibs. per sq. in., depending upon the richness of the concrete. The above condition exists before the application of the first load. After the first load has been applied, however, the con- crete remains in close contact with the spirals and the hoops have their normal effect upon the subsequent application of loads. THEORY OF COLUMNS. 397 Taking into consideration these facts, it would appear that there is considerable difference between the action of hoops and longitudinal reinforcing rods. As has been stated, longitudinal rods are compressed by the shrinking of the concrete, are brought immediately into action upon the application of the loads and rap- idly reach the elastic limit of the metal. For steel this limit is reached when the longitudinal shortening becomes about .o6 per cent. of the length. The hoops compressed by the shrinkage must, on the contrary, first return to a state of molecular equilibrium before they take tension, and this tension only becomes important when their longitudinal deformation, i. e., lengthening, has reached values above 0.06 per cent. of its length. The hoops have only begun to be seriously stressed under a first application of the load in prisms hardened in air when the longitudinal rods have already passed the elastic limit, are almost at their ultimate strength and cannot offer any further resistance. It was observed that the hooping did not produce its normal effect on the elastic behavior of the concrete until the load ap- proached 220 lbs. per sq. in. It was also observed that after the first application of the load a permanent swelling existed in the concrete, which brought the hooping into action immediately upon the application of subsequent loads. The action of the hooping extends through a wider range than that of longitudinal rods, the elongation of the hoops or spirals resulting from the swelling of the concrete, which is small, varying probably from 0.3 to 0.4 of the longitudinal shortening. The stress in the metal being proportional to its deformation within its elastic limit, it is evident that after having begun to deform the deformation is much slower for the hoops than the longi- tudinal rods. As has been explained, this resisting action of the hooping greatly augments the resistance of the column. When concrete is gradually hardened under water it expands, bringing tension upon the spirals and upon the longitudinal rods. The spiral hooping will be brought into play at once when the load is applied, while the tension in the longitudinal rods must first be overcome before the compression is begun. The elastic limit of hooped concrete members under a first load evidently depends upon the elastic limit of concrete, which is reached before that of the metal. It may be admitted that the shortening of the concrete increases greatly under high pressure 398 CONCRETE AND REINFORCED CONCRETE. and that practically the elastic limit is reached when the short- ening becomes equal to from 0.08 to 0.13 per cent. of the length of the member under load, depending upon the character of the concrete. Summarizing, we have the following rules in regard to the co- efficient of elasticity and elastic limit of hooped concrete: (1) For the first load, the coefficient of elasticity of a hooped member is equal to the sum of the coefficients of the concrete, of the longitudinal rods, and of the imaginary longitudinals, whose volume shall be assumed as go per cent. of the hoops or spirals. (2) For pressure less than a previous test load, the coefficient of elasticity of a hooped member is equal to the sum of the co- efficients of the concrete, as increased by the test load, the existing longitudinal rods and of imaginary longitudinals whose volume shall be assumed as double that of the hooping or spirals. (3) The elastic limit of a hooped member, for a first load, is equal to the natural elastic limit of the concrete, increased by the resistance of the reinforcing as found for a shortening of 0.0008 to 0.0013 and computed on the basis indicated above for the co- efficient of elasticity under a first load. Every load has the effect of making the final elastic limit practically equal to the pressure due to this load. , Experiments were made by Considére to determine the increase in strength due to hooping, by confining sand ina tube. It can be easily shown that the resistance given to the sand by the steel is 2.4 times as much as would be offered by longitudinal reinforcing rods of the same weight as the shell when the tensile stress in the former is equal to the compressive stress in the latter. This gives the ratio of the coefficients.of the two types as 2.4 to 1.1. This 2.4 is also the ratio of the crushing resistance of the two types of reinforcement for equal weights of reinforcing metal. This is true because crushing takes placed in hooped members rein- forced longitudinally when the elastic limit of the metal has been reached, which is the same for tension as for compression. Compressive Resistance——The compressive resistance of a hooped member exceeds the sum of the following three elements: (1) The compressive resistance of the concrete without rein- forcement. (2) The compressive resistance of the longitudinal rods stressed to their elastic limit. THEORY OF COLUMNS. 399 (3) The compressive resistance which would have been pro- duced by the imaginary longitudinals at the elastic limit of the hooping metal, the volume of the imaginary longitudinals being taken as 2.4 times that of the hooping metal. An indirect method of determining the strength of a ene reinforced both longitudinally and spirally, is as follows. Let A," equal the sectional area of an imaginary longitudinal rein- forcement equivalent to the hooping. Then the strength P of the column will be P= Fe (Ac +eAs +2.4¢As"). Let F,° = elastic limit of metal in compression and F*, that of hooping in tension and F, the ultimate strength of concrete in compression. Then P = FeAc + I's* As + 2.4 Fs* As", A more direct method of determining the strength of hooped concrete is given on page 402. In the use of the formula there given the strength of the longitudinal rods is neglected, it being assumed that they care for secondary stresses only. Spacing of Hoops.—Experiments were made by Considére to determine the most favorable spacing of the hoops or spirals. It was found that when the spacing of adjacent spirals did not ex- ceed '/, the diameter of the coils, resistances were obtained almost independent of the spacing. These facts, with others which have been observed, lead to the adoption of a spacing of spirals of from 1/, to 1/,) of their diameter when longitudinal reinforcing rods are also used. Numerous experiments have demonstrated that the above ratio holds true almost independently of the abso- lute value of the dimensions. Additional experiments were made by Considére, assisted by Messrs. Mesnager and Mercier, to determine the resistance of concrete subjected to radial pressure. It was found that the com- pressive resistance of a prism of mortar or concrete per unit of area equals 1.5 f, + 4.8 p when f, is the natural unit compressive resistance of the concrete, and p is the unit pressure exerted by the hooping on the whole of its lateral surface. The coefficient 4.8 represents the compressive resistance of a prism of the same dimensions consisting of particles of the same concrete without any cohesion whatever. This resistance is thus due to friction only. 400 CONCRETE AND REINFORCED CONCRETE. The term 1.5 f., which is of greater importance the higher the specific resistance of the material, is due to the cohesion be- tween the particles of the concrete. This cohesion increases as the particles are forced closer together by the increasing pressure. The increase in the resistance due to this cause is produced grad- ually only, and is proportional to the increase of the lateral pres- sure. It reaches its greatest value when the pressure amounts to from 60 to 70 lbs. per sq. in. The coefficient of f, equals unity when the pressure p equals zero, and only becomes equal to 1.5 when p equals from 60 to 70 lbs., and is maintained for all higher values of p. For hooped columns a coefficient value of 1.5 should always be used, as the lateral pressure due to hooping under practical working conditions is never less than 60 lbs. per sq. in. Working Formula for Hooped Concrete——A practical working formula may be developed from the empirical expression for pressure as determined by Considére and given above, together with well-known principles of hydrostatics. Let R = pressure per square inch on prism, d = diameter of prism and hooping, z = distance between adjacent coils of hooping, p external radial unit pressure, the uniform unit pressure exerted by the hooping, f, = natural unit compression stress of concrete, f, = unit tensile stress of hooping, A = sectional area of prism, A, = sectional area of hooping metal, ing. R, == unit compressive resistance of concrete due to hoop- R, = 1.5 f. + 4.8 p. From the principles of hydrostatics we know that the pressure upon a liquid in a cylinder is exerted equally in every direction and tends to tear the shell of the cylinder apart longitudinally. The swelling of concrete under pressure, neglecting the friction between the particles or molecules of the concrete may be con- sidered as acting in the same manner as a liquid retained by a cylinder shell, and the tendency to rupture in a longitudinal di- rection will be resisted by the hooping. Now, the interior pressure due to the swelling which we con- sider as hydraulic pressure, is resisted by an equivalent external pressure p per square inch up to the point of rupture of the hoop- THEORY OF COLUMNS. 401 ing. The force which tends to cause longitudinal rupture is Rdz. This follows from the principle of hydrostatics that the pressure of a liquid in any direction is equal to the pressure on a plane normal to that direction. Now the tensile stress of the hooping which resists the internal stress is 2A,f,. But these two quantities are equal, and we have 2A, f, = Rdz. But that equilibrium shall obtain, the internal pressure R must be resisted by an equivalent external pressure R = p. Then 2 As fs dz p= Substituting this value of p in the equation R, = 1.5 f, + 4.8 p we obtain the equation 9.6 As fs Re = 1.5 fe eee Wa eee eee ea (a). zd The total strength p of the prism will then be 9.6 As fs PAR =A lies. zd but A = % md’, and P = 1.178 fe d? + Lee Mea eee eRe (b). Zz In most cases formula (a) will be used for given values of dz, f,, A, and f,. When the pressure R, is obtained the total strength of column will then be found by multiplying this pres- sure’ by the sectional area of the column. This formula will be found to give rather higher values than have thus far been used in this country. The pressures used for a number of structures are given in another chapter. It will be well when heavy loads are carried and it is desired to use strains approximating those given by this formula to not allow the length to exceed 10 or 12 diameters. The above formula gives high average unit stress on the sec- tional area of the concrete, and it would appear rational to intro- duce a constant in the formula to reduce the stress somewhat. This is necessary when we consider that the stiffness of hooped concrete does not increase as the strength is increased by the 402 CONCRETE AND REINFORCED CONCRETE. hooping. Let Q represent such a constant the formula (a) be- and (b) becomes 9.6 As fs Re = Q (15 1+) isa aries. WS 6igetietrsnemate eerenteite (a). zd and B becomes 7.54 Asfsd P=Q (x78 fe d? ae) z For 1:2:4 concrete Q may be taken as 0.6. Example.—Determine the strength of a column Io ins. in diam- eter, allowing a working strength of 400 lbs. per sq. in. on con- crete, and 15,000 lbs. on steel, using 14-in. round rods for the spirals. Let us assume that the spacing of hoops will be ?/, of the diameter, then z = 1°/, ins. Substituting in formula (a): we have 9.6 X .0625 X 15,000 Re = Q [1.5 x 400 + ————______ 10 — xX 10 7 =Q (600 + 630) = 1,230 Ibs. per sq. inch;or, taking Q at 0.6, Re = 738 lbs. A = 78.54 sq. ins. P = 78.54 X 738 == 57,960 Ibs. Concrete Colurans in the Light of Recent Tests at Watertown Arsenal.—The tests of concrete columns being made at the Watertown Arsenal should, when completed, furnish sufficient data to determine the proper way in which the concrete should be used for columns. The tests thus far made, as reported by James E. Howard in a paper read at the June, 1906, meeting of the American Society of Testing Materials, are of great interest and deserve consideration in this place. The columns tested were 8 ft. in height and from Io to 12 ins. in diameter, and were composed of various mixtures, all being what is known as wet mixtures and all hardened in the air. During testing the columns were loaded with increments of 50 Ibs. per sq. in., measuring the amount of compression under each increment, returning to the initial load and observing the sets. Micrometer observations were made on a gauge length of 50 ins. equally distant from the ends of the columns. Full details of the tests are published in the reports of tests of metals, a Congres- THEORY OF COLUMNS. 403 sional document issued by the Ordnance Dept., U. S. Army. Details of these tests cannot be given in full, but such information as is necessary to illustrate the work being done will be shown. Figure 209 represents the compressive strength of a number of mortar columns, plain and reinforced, with longitudinal bars of ¥-in, twisted steel. The progressive loss in strength of the plain LONGITUDINAL PLAIN REENFORCEMENT = Nn Oo tr Ww WO +r HW HW ai bn ~ ~ ~ _ at - - _ Fig. 209.—Column Tests, Watertown Arsenal. columns as the mixture became leaner should be noted. The ultimate strength of the 1:1 column was not.reached as it ex- ceeded the capacity of the testing machine. This mixture was rot reinforced. Each of the others were reinforced, four with 8 bars each and one with 13. The percentage of reinforcements was about 2.86 and 4.63. The darker shaded lower ends of the <25 HOOPS, 4 ANGLES Fig. 210.—Column Tests, Watertown Arsenal. figures represent the relative amount of the reinforcement. The steel reinforcing bars extend from end to end of the column and had a full bearing at the ends. They had no other lateral sup- port than that afforded by. the mortar in which they were em- bedded. A slight gain due to reinforcement of the richer mix- ture should be noted. Figure 210 shows the strength of a rich and a lean mortar, each 404, CONCRETE AND REINFORCED CONCRETE. of which was reinforced with hoops and longitudinal angle bars ; also corresponding concretes reinforced. The hoops measured 1.5 x 0.12 ins. in cross section, with lapped and riveted joints. The plain 1:1 mortar displayed a compressive strength of 4,320 lbs. per sq. in., which in the hooped columns run to 5,980 Ibs. ; the addition of two parts trap rock to this mortar resulted in a strength of 5,433 lbs. The weaker 1:4 mortar was raised by hooping and angles from 1,050 Ibs. to 2,766 Ibs. per sq. in., which in a corresponding con- crete reached an ultimate strength of 3,002 Ibs. The free span between the hoops, 2% ins., permitted this lean mortar to flake off, while the larger pieces of the stone in the concrete were held in place. The great increase in strength due to hooping is notice- .able in the figure. REENPORCEMENT, HOOPS AND ANGLES 7 47H 1.2.4 CONCRETES Fig. 211.—Column Tests, Watertown Arsenal. Figure 211 shows the results of tests on 1:2: 4 mixtures with various amounts of reinforcement with hooping and longitudinal angle bars. The compressive strength of this group are as fol- lows: Lbs. per sq. in. Plain: Colina? cos cceda decane es ose oS A AS ENS RAS, 1,413 DQ OO PS. ask yivtsrnsects oetaed ac cecees at Sedatdg ove Rvapaucasear tuawaleidcd tue Sone iaa enti 2,232 13 hoops, 4 angle bars ..............-0.. ssdulaneditatibonas bee amaatehediya 3,029 ZB NOODS sig caie eaten ieseaiin sie ney dou trea ale Seen eae a Ee amie 3,428 25 hoops;.4 ‘angle ‘bats: cc kii. saesaad soenienaaasag ees 4,189 A7 HOODS: 3 25 scisasis aden SeOt8 20 44 CRCAE RE Woe Rae Pye a RERES 5,289 Thus both the hoops and the angles contribute toward increas- ing the ultimate strength of the column. Any desired strength may be.attained by means of lateral reinforcement if sufficient metal is used, but it is obvious that a certain amount of longi- tudinal compression of the concrete will be necessary before the lateral reinforcement becomes effective, which in the case of lean mixtures involves considerable deformation in the column. THEORY OF COLUMNS. 405 Figure 212 represents several columns which are strong by reason of their composition or on account of their reinforcement. These columns in composition, reinforcement, and strength were as follows: Lbs. per sq. in, Ted ‘mortar, (plain. 3.8 isscas-cosyvenvenraacce sense ceeesd above 5,011 LeU auCOncnete, Plain cvcavavuceamnmoured neaseuenmenonccantenssies 3,900 1:2 mortar, 8% ins. twisted steel bars..............2-000- 4,200 I:5 mortar, 13% ins. twisted steel bars................--+% 3,905 I:2:4 concrete, 25 hoops and 4 angle bars................- 4,189 1: 3:6 concrete, 25 hoops: and 4 angle bars................5 3,862 1:4:8 concrete, 25 hoops and 4 angle bars................5 3,002 The relative rigidity of these columns, which is not suggested by a comparison with their compressive strengths, is indicated in Fig. 213. The order in which the compression curves appear is the same as shown in Fig. 209, excepting the 1:1 mortar and the 1:1:2 concrete, which change places, the latter appearing ITUDINAL ONC RARS > « HOOPED 0 Fig. 212.—Column Tests, Watertown Arsenal. first on the left of the group. As may be noted, the plain col- umns display the greatest rigidity of the several types here repre- sented. This has been a noticeable feature in the tests as a whole. It is even found that the plain columns are a little more rigid over the range of stresses here plotted than in the same mixtures in which longitudinal rods are used as a means of reinforcement. In so many cases has this occurred that some explanation should be sought why the presence of the steel bars, themselves so much more rigid than the concrete, should not result in increased rig- idity of the column as a whole. It is not improbable that the set- tlement in the height of the column is so far restricted by the steel bars that minute fissures are developed during the early stages of the hardening of the concrete. Internal strains with- out the presence of fissures would hardly account for this be- havior. The hooped columns were found to be decidedly more compressible. than the others. It should be noted that lateral re- inforcement, while effective in raising the ultimate strength of 406 CONCRETE AND REINFORCED CONCRETE. loads once applied, does not result in imparting rigidity to weak concrete. These tests seem to indicate that a high ultimate strength will be reached, frst by the use of rich mortars or concretes, second by means of sufficient longitudinal metal reinforcement, and third by means of sufficient hooping or other external lateral sup- port. It also appears that rigidity of columns is best secured by 05 10 AS .20 Fig. 213.—Column Tests, Watertown Arsenal. the use of rich mixtures, although the same results may be ob- tained by the use of longitudinal steel bars. The use of plenty of cement seems to be the best means of securing a rigid column of high ultimate compressive strength. Hooping, while it increases the ultimate strength, does not increase the rigidity of the mem- ber. It should, however, be remembered that hooping has the great merit of increasing the elasticity of the concrete and pre- venting sudden and dangerous failure, thereby enabling lower factors of safety or higher working stresses to be used. CHAPTER XXII. FOUNDATIONS. The most suitable foundation for use in a given locality, whether it be for a building, bridge or other structure, can not be determined by text-book rules, but is a question of engineering judgment based upon practical experience and cost. The latter item is often the controlling factor in determining the kind of foundation to be used. Concrete has been widely used for foun- dations, and when the economy resulting from the use ‘of rein- forced concrete is more fully understood its use will become more general. It is not possible within the limits of this work more than to lightly touch upon the principles governing the choice of founda- tions to be used in any given case. The character of the under- lying rock or soil determines largely the unit loads which can be safely brought upon it. It is customary to speak of a given soil as having a carrying capacity of a certain number of tons per square foot. Bearing Power of Soils—Firm ledge rock may in general be said to be able to safely carry any load which may be brought upon it. The greatest loads will, however, not exceed from 30 to 50 tons per sq. ft. From this maximum load for ledge rock the carrying capacity decreases as we pass from firm ledge rock to the softer varieties of rock, hardpan, gravel, sand and clay, and finally to semi-fluid materials like mud, silt and quicksand, which have little or no bearing capacity unless special treatment is resorted to. Different classes of soil require different treatment, and when two or more kinds of material are met with in the same founda- tion the problem becomes indeed complex, and trained judgment and experience are needed to determine what is best to use under the given conditions. A careful examination should be made of the soil to determine its nature, its compactness, the amount of water which it contains, etc. A careful survey of the surround- ing conditions often helps to determine what should be adopted for a given foundation. 408 CONCRETE AND REINFORCED CONCRETE. Where the strata are of considerable thickness and uniform in character over extended areas, the bearing powers decrease as follows: Hard ledge rock, soft varieties of rock, hardpan, cement- ed gravel and sand, indurated clay, dry clay and sand, wet clay, moderately wet sand, loam, mud, silt and quicksand. Probably the most generally accepted values for safe bearing power of soils are those recommended by Prof. Ira O. Baker, which are as fol- lows: Minimum load on rock having a hardness equal to the best ashlar masonry, 25 tons per sq. ft,; for rock equal to the best brick masonry, 15 tons; for rock equal to poor brick masonry, 5 tons; for dry clay, 4 tons; for moderately dry clay, 2 tons; for soft clay, I ton; for cemented gravel and coarse sand, 8 tons; for compact and well cemented sand, 4 tons; for clean dry sand, 2 tons, and for quicksand and alluvial soils, not more than 4 a ton per sq. ft. The above values may be increased from 25 to 100 per cent., depending upon circumstances and judgment of the en- gineer. The following are the regulations of the New York Building Code in regard to Bearing Capacity of Soil: “When no test of the sustaining power of the soil is made, dif- ferent soils, excluding mud at the bottom of the footings, shall be deemed to safely sustain the following loads to the superficial foot, namely: Soft clay, 1 ton per sq. ft.; ordinary clay and sand together in layers, wet and springy, 2 tons per sq. ft.; loam, clay or fine sand, firm and dry, 3 tons per sq. ft.; very firm coarse sand, stiff gravel or hard clay, 4 tons per sq. ft., or as otherwise determined by the Commissioners of Buildings having jurisdic- tion.” When it is desired to carry greater loads than the above, it is customary to make a test of the sustaining power of the soil. Where it is possible the loads used in a given locality should be ascertained and a safe precedent followed. The following ex- amples will be of interest in this connection: Soil tests were made to determine the bearing power of the blue clay subsoil at the site of the capitol at Albany, N. Y. It was found to sustain 6 tons per sq. ft. A maximum load of 2 tons was used. The building is situated on a hillside, and cracks in the side walls. show that some settlement has taken place under the wall on the downhill end. A load of 2% tons was used on yellow clay which tested to 13/2 tons for the foundation of the Congressional Library at Washington, D. C. A load of 3 tons was used for the Bismark FOUNDATIONS. 409 Bridge over the Missouri River for the Missouri Pacific R. R. This clay was of a hard variety, resembling rock and tested to 15 tons. A live load of 514 tons was used on sand overlying rock in the foundation of the Brooklyn Bridge, and 3.63 tons was used on coarse gravel 12 ft. above rock for the foundation of the Roeb- ling Suspension Bridge at Cincinnati, O. On London clay a load of 6% tons was used for the Cannon St. Bridge, and 9 tons for the Charing Cross Bridge. Both bridges settled. In the con- struction of the Tower Bridge a test cylinder settled under 6% tons. The loading used was 4 tons. If the skin friction and buoyancy of water are deducted, the bearing capacity will be from I to 2 tons per sq. ft. The soil under Washington Monument is fine sand, and carries a load of 11 tons per sq. ft. This is increased by wind pressure to 14 tons per sq. ft. In the construction of the reinforced concrete building at Cincinnati known as the Pugh Power Building there were no signs of settlement under a test load of 6 tons per sq. ft. on compact gravel, and a soil composed of part gravel and part sand stood a load of 4 tons. Loads of 5 and 3 tons, respectively, were allowed for foundations and foot- ings up to 11 ft. square. Foundations may be built on sand in spite of the Biblical say- ing. Sand, when confined, is practically incompressible, and if it can be kept free from water no danger need be apprehended from building upon it. Likewise, dry clay makes a good foundation, and when possible if it is proposed to build on clay the foundation - should be drained or kept free from the action of water. General Considerations in Regard to Foundations.—In the prep- aration of the foundation bed the excavation should be carried below the frost line. Again, the deeper the foundation is car- ried the less chance there is of displacement due to adjacent ex- cavation, and, in general, the firmer will be the soil. Whether the foundation be on rock or on some kind of earth, the founda- tion bed should be cut horizontal. When the ground has a slope, steps with horizontal benches should be cut to bring the bearing upon a horizontal bed. It is desirable as far as possible to have uniformity of material in the foundation bed. When not possible, some provision should be made so that settlement, if any at all takes place, will be uni- form under the whole foundation. The character of the structure will in a large measure determine the allowable pressure on the 410 CONCRETE AND REINFORCED CONCRETE. foundation bed. Thus, where quiescent loads are to be provided for, higher loads are allowable than when moving loads or impact and vibration will exist. Thus a much less bearing power should be assumed for the piers of a railroad bridge than for an ordinary highway bridge or a building. When plain concrete is used for foundations the usual practice is. to place a bed 1 ft. or more in thickness under the walls or piers and having a sufficient width to properly transmit the loads to the subsoil. If the soil is firm enough to stand, no boxing wili be needed, the excavation simply being made of the required size. Under other conditions forms will be needed to hold and protect the concrete when it is put in place. Pile Foundations—In many situations it is neither desirable, safe or economical to use spread foundations. The materials may be such as are not able to bear the weight of the structure after spreading the footings, or the cost of securing a proper spread of footing may be excessive, or again the subsoil may at some future time be exposed to the scouring action of water, or if of a semi- fluid nature may be disturbed by adjacent excavations. Under such conditions piles are in many cases used, giving a foundation which can be rapidly and economically put in place. Wooden piles must be cut off under water, as when subjected to an at- mosphere which is alternately wet and dry, they will decay. On this account they cannot be used in many situations where otherwise they would be desirable. Concrete piles, on account of their durability, may be used under such conditions, as well as under any in which wooden piles may be driven. Piles are driven usually 2 or 3 feet centers, in clusters or rows, depending upon whether they are to support a pier or a wall. The nature of the soil, loads to be carried, and size and length of pile to some extent govern the spacing of the piles. It has been found, however, that little or no additional bearing power is se- cured if the spacing is much less than 2 ft. centers. Short piles are sometimes used to compact the earth, thereby so increasing its bearing capacity as to enable it to support the weight of the superstructure. Usually, however, dependence alone is placed upon the pile to carry superimposed loads. The nature of the soil, loads to be carried, etc., determine the character of the pile foundation to be used for each case. The Bearing Power of Piles—The bearing power of a pile may FOUNDATIONS. 4il depend upon the friction of the soil through which it is driven, upon the supporting power of the substratum in which its point rests, or upon both. The frictional value will depend upon the kind and nature of the soil through which the pile is driven, and when concrete piles are used, to a certain extent upon the rougn- ness of the surface of the pile. When the pile is driven through soft earth into firm, compact material, it will act as a column, and when the bearing power of the sub-stratum is high, its support- ing power will depend upon its strength as a column. Of course, if driven through a firm, gritty material, the frictional value will be much higher than when the material is soft or semi-fluid, and the supporting power correspondingly increased. When the sup- porting power depends upon friction it is probable that it in- creases for a time after. the driving ceases. Patton states that piles driven in the alluvial soils of the swamps of the South for railroad trestles, when forced to place by the weight of the pile- driver hammer alone, or at most by a few blows with a short fall, after resting a few days were so firmly supported that it was impossible to move them by repeated blows from the pile driver hammer. On the other hand, if the supporting power depends largely upon the resistance to penetration of the sub-stratum into which the pile is driven, it is probable that the safe bearing power will decrease, as most materials require less force to change their form slowly than they will sustain for a short time. The bearing power of a pile in any given soil is no criterion of what a similar pile will carry in any other soil, and experience and experiment must be relied upon in each particular case to deter- mine what are the safe allowable loads. Thus an extended ex- perience in the use of piles enables the engineer to judge closely from the manner in which piles drive in a given soil the allowable loads which may be placed upon them. When experience is lacking it may be supplied by experiment. Thus, by testing one or more piles driven in a given soil by applying a direct load-or pressure upon them. the maximum load which they will carry may be determined, and a safe working load chosen. When the max- imum load is known it may be expressed in terms of the depth driven, kind of soil and size of pile or surface in contact with the soil. The bearing power in a given soil of a pile of any size may thus be determined. An ample factor of safety should be used when the maximum bearing power is known. This may vary 412 CONCRETE AND REINFORCED CONCRETE. from 134 to 10, depending upon the conditions and character of load to be supported. When the approximate bearing power of the sub-stratum intc which the point of the pile is driven is known, together with the , frictional resistance of the surface of the pile in contact with the soil, the relation between these resistances and the weight which the pile will carry may be expressed by a formula. Thus, let W == weight carried by pile, p = bearing power of soil under point of pile, s — surface in square feet of pile in contact with the soil, and f — a factor depending upon the frictional resistance of the material on the surface of the pile, then W =p tfs. If we know p and f in all cases and the load to be carried, we can determine the depth to which a pile or group of piles must be driven to carry the given load. The value of p varies from zero for silt to from 2 to 3 tons for sand, gravel or clay. When the sub-stratum is hardpan or other firm material, a higher value may obtain. The value of { may be determined by experiment. Pat- ton recommends the following values: 100 Ibs. per sq. ft. for softest semi-fluid soils, 200 Ibs. for compact silt and clay, 300 to 500 lbs. for mixed earths with considerable grit, and from 400 to 600 Ibs. in compact sand and sand and gravel. Thus, if a pile is driven through compact silt and clay into a clay sub-stratum, assuming p == 3 tons = 6,000 lbs., and 22 tons is to be carried = 44,000 lbs. if pile is assumed to have an area at the point of .75 sq. ft., p == 4,000 lbs. Assuming { = 500 lbs., we have for value of S: 44,000 = 4,000 + 500 S, or 44,000 — 4,000 = ——____——. = 80 sq. ft. 500 or, assuming an average diameter of 12 ins. the area per lineal foot equals 3.14 sq. ft. and the pile must be driven to a depth of 80 —— = 25.5 ft. 3-14 Formulas in common use for determining the bearing power of piles are in general based upon the relation existing between the supporting power of the pile, the length and size of the pile, the FOUNDATIONS. 413 weight of hammer used in driving, height of fall and distance ‘the pile was moved by the last blow, or average distance of several last blows of pile driver hammer. When this relation can be ex- pressed by an equation, the supporting power can be found by inserting these quantities in the formula and solving it. The re- lation between these quantities must be determined from a con- sideration of the theoretical conditions involved. Numerous for- mulas have been evolved by different engineers which differ greatly as to results obtained. The limits of this work preclude a discussion involving the merits of different formulas. We will therefore only give a single formula, which, on account of its simplicity and the safe results obtained from its use has gained great popularity. This formula is known as the Engineering News Formula, and when used in the following form gives a fac- tor of safety of 6: = 2Wh d+1 in which P = safe load in tons, d is the penetration in inches under the last blow, or, better still, the average of several last blows, W = weight of hammer, and h = height of fall in feet. Thus, if W = 2 tons, h = 20 ft., d = 3 ins., 2X 2X 20 P = ——————_ = 20 tons. 34+ 1 It is probable that the above formula is not in general appli- cable to concrete piles. Reliance should therefore be placed alone on actual tests to determine the bearing power of concrete piles. A number of examples are cited on later pages of this chapter in regard to loads placed upon concrete piles. These should be re- ferred to in this connection. Reinforced Concrete Foundations.—Reinforced concrete is a material well adapted to the construction of foundations for build- ings, bridges, wharves, docks, etc. It is used in the construction of spread foundations for high buildings, and as a capping for timber piles. In the construction of sheeting and bearing piles it possesses many valuable characteristics and undoubtedly will have an extensive use in the future. This material has also been used as a sheathing material for timber piles in teredo-infestéd waters and as a protection for steel piles used in pier construction. Spread Foundations——Spread foundations are either isolated 414 CONCRETE AND REINFORCED CONCRETE. column footings, combined footings for two or more columns, wall footings or continuous footings extending over the whole foundation area. In whichever form it is used, the purpose of the foundation footing is so to distribute the load over the soil that its carrying capacity will not be exceeded. Among the advantages of this material for spread foundations are a reduction in the amount of excavation required, a saving in material and a reduction in the weight of the foundation itself, thereby greatly reducing the cost of the substructure for a given construction. The simplest form of spread foundation, and the earliest used, 1s not, strictly speaking, a reinforced concrete construction, but a steel construction surrounded and protected by concrete. This is the grillage beam foundation. The earliest form of beam grillage consisted of steel railway rails superimposed in layers at right angles to each other and embedded in concrete. A later construc- tion consisted of replacing the top layer of rails with steel J-beams. Sometimes I-beams are used for the whole foundation. The lengths of the successive tiers of beams decrease from the bottom to the top. Usually the column footing consists of a cast shoe resting upon the topmost layer of beams, although either stone footings or built-up steel shoes may be used. The method of construction of grillage beam foundations is as follows: The ground is excavated to the proper depth and care- fully leveled off. If the character of the ground is not such that it will remain vertical without the sides of the pit falling in, box- ing of the exact size of the footing is constructed. This boxing is accurately centered and its sides carefully leveled to the proper elevation. The concrete is then put in and tamped in layers of 6 or 8 ins. and the top leveled off even with the top of the boxing. The steel beams should then be carefully bedded in 1 to 2 Port- land cement mortar so they will be as nearly level as possible. The beams are set one after another and the spacers placed as the work proceeds, or, if they are not used, care is exercised to place the beams parallel and at proper intervals apart. As soon as the beams are in place the spaces between them are filled with con- crete. When the beams are very close together grout may be used. This filling should be carefully done and the concrete well tamped so that the top flanges of the beams will have a firm bearing upon it. A boxing like that used for the footing is FOUNDATIONS. 415 placed about the beams. The spaces at the sides and ends of the beams are filled with concrete, and a coat of mortar is plastered over the top. The next layer of beams is placed in exactly the same manner, and so on until the top layer is set. Upon this the stone or metal base plate or column footing is set in a bed of mor- tar. A layer of at least three inches of concrete should then be spread over the top of the beams, and the whole coated with 1 to 2 Portland cement mortar. This form of foundation has been extensively used for more than 20 years in building construction and is sometimes called Fig. 214.—Beam Grillage Column Footing. the Chicago Foundation. Fig. 214 shows a_ typical column foundation of grillage beams which was used in the construction of the Franklin Building in New York. The bottom tier of beams consists of eleven I-beams 20 ins. x 65 Ibs., 14 ft. long, and the top tier of five I-beams 24 ins. x 100 lbs., 12 ft. long. The simplest form of reinforced concrete spread foundation consists of a simple column or wall footing of concrete reinforced at the lower or tension face by a series of iron or steel rods or some form of netting, as shown by Fig. 215. The Monier construction, when used for spread foundations, consists of the regular Monier network embedded in the tension side of the concrete. In wall foundations the carrying rods are perpendicular to the axis of the wall and should be proportioned to support the load which comes upon the foundation. The dis- tribution rods are placed parallel to the axis of the wall. It is customary to proportion them so that the foundation wall may have a girder action thereby enabling it to span openings in the 416 CONCRETE AND REINFORCED CONCRETE. wall and give an even distribution of the load to the foundation. For column footings both sets of bars are carrying bars. Fig. Fig. 215.—Typical Reinforced Concrete Column Footing. 216 shows a typical column footing. This particular footing was used in the Robert Gair factory building, Brooklyn, N. NY: When heavy loads are to be carried it is customary to use two or more layers of netting, placing one above the other, with lay- ers of concrete between the successive nettings. Expanded metal oa Cement Mortar cae 2k 7g 22” pees toy. - 7 SOE 4-$'fods" 7-3 Rods. ‘4"Concrete 4-3 frods. A t 1 i wo" f 1 1 ' ae Vix S Fig. 216.—Column Footing, Robert , Fig. 217.—Column Footing for Gair Factory, Brooklyn, N. Y. Chicago Store. is used in much the same manner as the Monier netting. The arrangement and location of the bars are practically the same in all systems. The bars are placed at right angles to each other, sometimes diagonal bars are also added and located as near as possible to the lower face of the concrete. A sufficient thickness FOUNDATIONS. 417 of concrete must be placed below the rods to protect them from the soil and water. When great strength is required a reinforce- ment is sometimes placed in the compression side of the footing. Figure 217 shows the reinforced concrete column footing used in a store building in Chicago, designed by Mr. Lee Heidenreich. Two or more columns are sometimes placed upon one. footing. Under these conditions care must be taken in determining the shape of the footing that the load may be distributed uniformly 8, 1d Vertical Rods A Binders every 10”. a os \agt - Opa — 3-SJ 2 Elevation. Tot) a i Bg Rods Elevation. * Pinae err easereascaae YP QP Stae wentccngeeieneded > ' 7C mC. i 1 = jigs Ae Plan Plan. 4 iy yh” - _ If ods» es yy i Sipe 3,15 Rods FRo Stirups A 36". : sap oe eh irons Tory tg SOY Ef Section A-A. Section BB, Section A-A. Section B-B. Fig. 218.—Column Footing for Atlanta, Fig. 219.—Column Footing for Retain- Ga., Terminal Railway Station. ing Wall, Atlanta Terminal Station. to the sub-soil, otherwise it may settle unevenly and bending be brought upon the columns. The spread footing used in the construction of the foundations for the Terminal Station in Atlanta, Ga., is shown in Fig. 218. As will be noted, this footing is modeled somewhat after the type used for the construction of cast-iron shoes. It has a bottom plate strengthened by cross ribs and the compensating flanges at the edge of the footing. This gives quite a shallow footing, with ample strength to secure the desired spread. Another footing of 418 CONCRETE AND REINFORCED CONCRETE. | the same type is shown in Fig. 219. In‘this the shear is taken care of by the arrangement of the rods shown in elevation. Figure 220 shows a reinforced concrete footing, for the Bush Terminal Building, described on another page. This footing, which is 11 x 12 ft. in size, was used as a capping for 18 timber , ' ’ ' ' ‘ ' . ’ » , y ’ » 2s S ’ , , ' ‘ . i , ' , ’ Fig. 220.—Column Footing, Bush Terminal Co. Factory. piles driven about 18 ft. to a firm bearing, each pile being calcu- lated to sustain a load of 20 tons. In the construction of this foot- ing the lower portion of concrete capping having a thickness of 27% ins., was placed around and over the heads of the piles. This part was reinforced with a single layer of 1-in. rods, spaced about 24 ins. center and located near its upper surface. FOUNDATIONS. 419 The upper portion, or the footing proper, has a thickness at the middle of 391% ins., this thickness being reduced at the edges to 12 ins. Near the bottom surface are placed I-in. transverse horizontal bars spaced 634 ins. centers. In a longitudinal direc- tion the reinforcement consists of eight sets of I-in. steel bars fastened together with vertical stirrups in accordance with the Bertine system. In the center of the footing four vertical bars I in. in diameter and 4% ft. long are embedded in the footing a Square I Cylindrical coldcans . “Hooped Column Column t oe Reinforcing omitted. Cross-Section through A-B, being Center f Gravity of Footing, also point of oy lication " OF) Result OF Coluber loads A Dowels: LEE EPLI IIIT I ora pM LI] Fig. 221.—Combined Wall and Column Footing. and extended above its upper surface to form dowels for connect- ing a column to the footing. These footings support the hooped columns described on page 474, and transmit to the soil through the medium of the piles some 360 tons. A typical footing supporting a concrete column used in the Thompson and Norris eight-story factory building at Prince and Concord Sts., Brooklyn, N. Y., is shown in Fig. 287. Two or more columns are sometimes placed on a single footing. Figure 221 is an example of a spread footing supporting a wall 420 CONCRETE AND REINFORCED CONCRETE. aad interior columns. Figure 222 shows a spread footing used to support a 400-ton smokestack and four columns in the same building. The dimensions, details and reinforcements used in both these examples are shown in the drawings. The type of reinforcement used was the Johnson corrugated bar. The sup- porting stratum is a hard, gravelly soil. A special foundation of novel design is shown in Fig. 223. 15-1" Bars 3°C.10C. u'9" Long. SAAS Fe — RWS SS 36- %" Bars 6°C.10C, 10%” Long. 4 Y 4 Y ba i Fi laces Sere oe eas AIM | eee RSS SM Hy 10-I"Bars ey ears 2 . ra AG Gi bars |. ea eers 79¢ Long. Section A-B. Fig. 222.—¥Footing for 400-Ton Smokestack. Bars 5” 79" Long, This foundation was used for the Garage Building for the De- cauville Automobile Co., New York City. The flaring shape given to the footing is for the purpose of distributing the loads uniformly to the soil, 1 ton per sq. ft. bearing being allowed on the soil. The amount of metal in each footing is given on the drawings. It should be noted that vertical shear bars are used FOUNDATIONS. 421 where the columns come upon the footings; see cross sections. Figure 223 also shows a plan and section of a footing carrying four columns, designed for the same building, but not used, as rock LN r eee htt 1aL hear Sars ! 3 pn Seer rer errr rs rs t ‘Sf Bars 814 Bars "0,1 Bars | Section A-B. Section C-D. & ee \ rr O 3} s i yo x_ a ariat He Us ee i iw x g Siew | as ‘s & |e i : FZ Bars,$ C106. R x i ik (©) Concrete a i Ze thich im > | ‘ Ss RN) fa] jal fa : oar; peg 7 |e er Qo i 1 |FBars Bs /{B x a i iFL El) /&& ae a |i bes i Ne ‘Love | lee y ed ska fe ke] [88 | |. 4 > a : Bi |S SH iow i& | ReR) fs S33 8 | 8 && 1 R! i: |@RA) fee SB SS Se |X) EISR) (8 SOR] [SS |S 8% Pa Jee Sd Ss 8 w 8 ie [384 > --- 245f" ; Seton eee ee ee 20070" sigeesesee 4 Section. Fig. 223.—Foundation for Garage, Decauville Automobile Co., New York was found under the part of the building where this footing was to have been used. The footings are sometimes extended to cover ihe entire foun- 422 CONCRETE AND REINFORCED CONCRETE. dation area. An example of a small foundation of this character is that used in the construction of a four-story addition to a resi- dence in New York City. The soil in this locality is filled in to a great depth, the filling consisting of earth and rock, the latter ranging in size from small stoné to rocks of great size, and so poorly packed that local settlement is liable to occur at any time. A spread footing was used and so designed that the portions of the foundation under the walls will act as a cantilever beam or slab should any local settlement take place. Figure 224 shows a 41 Bars, 206 I Te 8 Bott, : Kz6'4 et hye x % BS im 4 : 4,1 Bars, l0 long | f Top & Bottort oO Section A-B. K2g% Section C-D. Fig. 224.—Foundation for New York City Residence. plan and cross-section of the footing, together with spacing and size of reinforcement used.* Another spread foundation covering the entire foundation area, but of different design, is that used in constructing the C. C. Shayne Building, New York City. This foundation was de- signed and built by the Hennebique Construction Co. It is of the ribbed slab type and spans the full width of the building. Details of construction are shown in Fig. 225. A 1:2%4:5 con- crete was used, the stone being trap rock, %4-in. and under. Hennebique uses rod and stirrup reinforcements for column *The writer is indebted to H. C. Miller & Co., of New York, for the de- signs shown in Figs. 223 and 224. FOUNDATIONS. 423 footings. Figure 226 shows a Hennebique column footing with this kind of reinforcement. This particular footing was used in a factory at Lisle, France, and carried a load of 130 metric tons. The reinforcement consisted of two courses of rods at right f Front Wall Peo sige Dna OGE GING C OG VEGETAL a % aq Eee “ Plan. bee Section C-C. Fig. 225.—Foundation for C. C. Shayne Store, New York. angles to each other, with stirrups extending upwards into the concrete from the lower tier of rods. In a later form of con- struction part of the round rods are replaced by flats, as shown in Fig. 227. For heavy foundations this engineer has used a series 1 59° “20x15. : Koo 3 L g IN PIT 1 a ! “18 . om . PK nnnnern erence rn nce = 2 Gh nnn Fig. 226.—Column Footing with Bar and Stirrup Reinforcement (Hennebique). of flats at right angles to each other and decreasing in length toward the top, and without stirrups. A layer of from 6 to 8 ins. cf concrete is placed between each series of rods. A special foundation which has proved efficient in soft ground is obtained by cutting up the foundation area with a series of in- 424 CONCRETE AND REINFORCED CONCRETE. tersecting brick or concrete walls having a covering slab of rein- forced concrete. The series of bottomless boxes thus formed prevent the earth from spreading and the whole foundation acts together as a raft and is able to support heavy loads, although the ground may be very soft. The intersecting walls, if of concrete, may or may not be reinforced. M. Hennebique employs a sys- tem of this kind for spread foundation, using a modified flat ribbed floor slab with the ribs reinforced heavily on the compres- 7 a NG 4 4— ae 4a es il it 1 wes a= eo} eo roe z=) ' ' eres Han og Lat wre Wit Ne a Fig. 227.—Footing by Hennebique, Fig. 228.—Section of Storehouse, with Flat Bar Reinforcement. Newcastle, England. sion side as well as on the tension side. A warehouse for the Co- operative Wholesale Society at Newcastle-on-Tyne has a founda- tion of this character. This building is eight stories in height above the foundation and has a frontage of 92 ft. on the quay on which it abuts, and is 125 ft. deep. The floors are designed to carry 684 lbs. per sq. ft. The site upon which this building had to he constructed offered great difficulties for securing a suitable foundation. The first 18 ft. were of made ground, below this was 18 ft. of silt and quicksand, next came 10 ft. of soft clay, 5 ft. of hard clay and to ft. of silt and sand, and finally gravel. To add to this difficulty, the whole stratification had a decided dip toward the River Tyne, Piles could not be used on account of FOUNDATIONS. 425 the danger of injuring neighboring property. The feasibility of sinking masonry piers to the gravel was considered, but owing to the uncertainty of ever securing a suitable foundation by this means and to the excessive cost, this plan was abandoned and a reinforced concrete raft was constructed. The whole building, as well as the foundation, was of Hennebique construction. Figures 228, 229 and 230 show the character of the construction. Each iu 156" = “18 Bars, 6b. £ Bars, y Iptt wronen+ 148-2 2-2 ------ Fig. 229.—Plan of Floor Panel. column rests on two intersecting beams 2 ft. 5 ins. wide by 2 ft. € ins. deep. These beams divide the area of the building into rec- tangular panels and in conjunction with the concrete floor arches, 7 ins. thick at the center, transmit the column loads over the whole area. } a K------/2 Fig. 252.—Section of Pile for Quay Fig. 250.—Hennebique Type of Wall at Southampton, England. Pile, Showing Driving Cap. struction of a dock at Southampton, England. Figure 252 is the section of a pile used in a quay wall at the same place. The head of the pile is sometimes moulded round and to a smaller diameter than the thickness of the body of the pile, to 440 CONCRETE AND REINFORCED CONCRETE. permit the application of a driving cap. Figure 250 shows the type of cap employed when this form of head is used. The rods sometimes extend beyond the concrete and are bent into a loop, to which a tackle may be hooked for lift- ing them. Figure 253 shows a hollow Hennebique pile, which is much lighter than the ordi- nary pile, and hence more easily handled. The four reinforcing rods are retained, and the diaphragms, which contain forked spacers and wire ties, join them together. Diaphragmn--k; The Hennebique sheet piling is con- structed in the form of rectangular slabs and is usually reinforced with six vertical rods, two being placed in the middle of the slab. The rods are tied together in both directions in the horizontal plane. A semicircular groove is formed down the edge of each pile and the hole formed by two of these grooves, when the piles are driven side by side, is filled with grout. The pile point is hy formed by beveling one of the SER Diaphragm narrow faces so that it forms a SAS wedge with the opposite face. f Figure 254 is a section of Hen- nebique sheet piling used in the /# construction of a bank protection g on the Ghent Terneuzen Canal, |? Belgium. 7: An example of a square pile Wire Tes above and below of the Hennebique type, but of Se arouse Diaphragm. American design, is shown in Fig. 255. This pile was used in the coustruction of the Railway rig. 253.—Hollow Pile of Hennebique Terminal Station at Atlanta, Ga. Type. Four reinforcing rods, 11%4 in. in diameter, are used. These are bound together by */,, in. wire ties, spaced nearer together than in column construction. The tops of the reinforcing rods gener- oe FOUNDATIONS. 447 ally extend to within about 2 ins. of the top of the concrete at the head. The point is formed by an ordinary pile shoe, the straps of which are turned in at the top, to form a hold in the concrete. The reinforcing rods are bent in at the foot and bear against the bottom of the shoe. Figure 256 shows the form of a rectangular pile used in the construction of a wharf at Novorossisk, Russia. The piles were spaced 16 ft. 434 in. centers and supported 1534 x 2534 in. con- ' == == > a ar cy: Cc Fig. 254.—Sheet Piles of Hennebique Construction. crete steel girders. These were connected by five 8 in. x 12 in. stringers, which in turn supported a 4-in. reinforced concrete slab. The load to be carried was 213 Ibs. per sq. ft., each pile carrying the load from 269 sq. ft. of floor, consisting of a total dead and live ioad of about 43 tons. These piles were approxi- mately 16 ins. square and 42 ft. long, and have a‘ reinforcement weighing about 45 lbs. per lin. ft. _ Figure 257 shows the section of a triangular pile used in the 448 CONCRETE AND REINFORCED CONCRETE. s OK # | Zou SAS] PSS 4 * : ESSN FP SE c io; SSS ¥ | ' 1 SESS TY ' SSSY HO SSH] wa ‘ u NESS : 1 y SISSY OL ' : BEA | EL x : 1 ’ JPW Fs I ) TRA SS | NESS fi F °° Yo! reo ; % is tS ia ys &9 x Pee S |7 38 SURCNA Ps © | * : 3” Sf fo 80,76 vt ems : Binders = Ss eee nee ne 19:0” \ ' “T qT iol # { enn e ane --- === --- eee te SL tf <4 1 ni! 4 t- Mt r sins , : 1 Longitudinal Sectional t Transverse Sectional rt Elevation. Elevation. jie-----------9 7 eee ee eh Fig. 272.—Column and Crane Girder, Ontario Power Co.’s Power House. This column is shown in Fig. 273. These columns are designed to resist lateral pressure due to wind. In the Ingalls Building the columns are spaced 16 to 33 ft. centers. The larger columns decrease in size from 34 x 38 ins. at the bottom to 12 x 12 ins. at the top. The concrete footings were built independently of the columns, and are of sufficient size to properly distribute the column loads to the subsoil. Upon the footing was placed a cast-iron base plate having circular projections on top to form 470 CONCRETE AND REINFORCED CONCRETE. seats for the vertical compression rods. The tops of the projec- tions were faced to a true horizontal plane to form a true bearing for the rods, which had their ends also faced. Each column had 4, 6 or 8 plain round reinforcing rods from 2 to 3% ins. in diameter. All joints were carefully made, with the ends of the rods faced. In the lower part of the building these rods extend through one story only, but above the third story they extend the height of two stories. At each splice a sleeve is put around the top of the bar to form a socket for the next bar above. When ready to place the upper bars, they are set in the sleeves, grouted, and the concrete carried above the joint. These large circular bars are to take compression only, and in addition to them each column has from 4 to 10 smaller bars of twisted steel to take the tension due to wind loads. The series of upright rods in each column are surrounded by rectangular hoops of twisted steel, = 80" Fig. 273.—Column for Ingalls Building. spaced at vertical intervals of about 12 ins., the end of each hoop being lapped and bound with wire, while the hoops are secured by wire ties to each of the upright bars with which they come in contact. The function of these steel hoops is primarily to resist the tendency of the compression bars to buckle, but they also greatly increase the shearing strength of the columns. The column loads coming upon the shoes range from 300 to 700 tons. Wall columns are usually of rectangular section, although tee sections are also used. Sometimes, when the loads are light and stiffness with a pilaster effect is desired at the column line, a large hollow section is used. The reinforcing almost always employed consists of straight rods tied together with occasional horizontal ties or bands. Fig. 274 shows cross-sections of hollow side and corner columns used in the construction of the Kelly & Jones factory building, Greensburg, Pa. GENERAL ;BUILDING CONSTRUCTION. 4" Bar. K 1 ae ' v & vy i { bad af ‘we 4 "Bar. OO ex . bf Side Pjer; %" Bar: 2 4g" Bar. 4"Bar. Fig. 274.—Columns, Kelly & Jones’ Factory, wo. % Frods, 8.106. alt. ) ed i s ld Fig. 27(.—Wall Column, Twelve- Story Loft Building. " 4 2 ""Fods-- 5B ax2 Anchors, 56 Ig. Fig. 278.—Knee Brace, Twelve- * Story Loft Building. ® Kon----- 20r-------4 eX 3 "Rods, iy 7 23Z4------4l Regular Intermediate Wall Columns. Fig. 275.—Column, Pacific Borax Co.’s Factory, Fig. 277.—Corner Column, Twelve- Story Loft Building. Sleeve ‘ _ 8"long Gas Fipe pio. £4. No ; ve Pods... Sheet Lead “ “4 Line Fig. 279.—Column Rod Splice, Twelve- Story Loft Building. Rebates for Window Frames 472 CONCRETE AND REINFORCED CONCRETE. Fig. 275 shows another example of a hollow intermediate wall column used in the Pacific Coast Borax Factory Building, Bay- onne, N. J. Fig. 276 shows the section of a rectangular wall column, and Fig. 277 that of a corner column being used in the construction of a 12-story loft building in New York City. Fig. 278 shows the detail of a knee-brace used on all wall columns. Fig. 279 shows a detail of column rod splice. Fig. 280 gives detail of a column footing so designed as to distribute the pressure on the reinforcing rods, while Fig. 281 gives an enlarged detail of one of the cast-iron shoes. Lead “" aan Fig. 281.—Cast-Iron Shoe for Fig. 280.—Column Footing, Twelve- Concrete Column, Twelve- Story Loft Building. Story Loft Building. Fig. 282 shows typical column sections used in the factory of the American Oak Leather Company, Cincinnati, Ohio. The sectional area of metal used for reinforcement was from 1 to 2 per cent. . Hooped Columns.—The columns used in the Kelly & Jones Co.’s reinforced concrete building were among the first hooped columns used in this country. These columns are square in section at top and bottom, with the corners chamfered off to give them an octagonal section throughout the body of the column. Their sizes were 23, 20, 15 and 10 ins. in the first, second, third and fourth floors, respectively. The reinforcement consists of eight /4-in. vertical rods spaced at equal intervals GENERAL BUILDING CONSTRUCTION. 473 in a circle about 14 in. inside of the surface of the concrete. About these rods was placed the hooping, consisting of a helix of 4 ins. pitch, made of 4-in. twisted steel, extending from end to end of the column. The helix and vertical reds were wired together at intersections. Fig. 283 shows section of this column. The columns used in an addition to the Pacific Coast Borax Fac- 44" Haun 12" 0c a OR COLA wiTH 8 BARE ( Q a. J FOR COLS WITH sy eer iar i ETELEAA Fig. 282.—Column, American Oak Leather Co. Factory. tory Building, mentioned on page 275, are similar to those just described. They are-18, 14 and 9 ins. in section, square at the ends and chamfered to an octagonal shape in the middle. Each column is reinforced with eight 14-in. vertical twisted steel rods, equally spaced near the circumference and wrapped with a helix ? : z \k 4 Tivisted Reds \ yne 4'Pitch Sa fi eo wg Vertical a Prods —-..->m Fig. 283.—Hooped Column, Kelly & Jones Factory. of 1%4 x %-in. steel rod with a 4-in pitch (Fig. 284). A different arrangement of the reinforcement was used in the columns for the shops of the United Shoe Machinery Co., Beverly, Mass. Columns of octagonal section, with diameters of 22, 1814, 14 and 8 ins. in the first, second, third and fourth floors, respectively, 474 CONCRETE AND REINFORCED CONCRETE. were reinforced with eight vertical reinforcing bars, 54 in. square, of twisted steel rods, in the angles close to the surface and with an interior coil of 1%4-in. twisted steel hooping, with 4-in. pitch, inserted within the vertical rods. The vertical rods were of one- story lengths, having 12-in. splices wrapped with a coil of IZ x 14-in. steel. A cross-section of this column is shown in Fig. 285. As has been stated in Chapter XXI., the experiments of Considére, supported by tests of other experimenters, show that the best results are obtained, when the pitch of the hooping is from 1-7 to I-10 the diameter of the columns. In the above columns the dis- tance between adjacent coils is in all cases considerably more than this. The amount of metal used is less than is necessary to secure to the fullest extent the benefits of hooping. The above columns show conservative designing, which is commendable, in- asmuch as this form of reinforcing is comparatively new and TEE, yoira 4th” Fig. 284.—Hooped Column, Pacific Fig. 285.—Hooped Column, United Coast Borax Co.’s Factory. Shoe Machinery Co.’s Factory. untried. The column section shown in Fig. 285, as will be noted, has the longitudinal rods outside the hooping. Should the column become overloaded to such an extent as to cause the concrete out- side the hooping to shell off the resisting power of these rods against flexure will be lost at the time when most needed. Again, when in this position the rods cannot assist the hooping in re- straining the concrete from flowing laterally. The Cummings Column.—In place of the spiral steel hooping used in the Considére column, hoops are used by Mr. Robert A. Cummings for column reinforcement. The hoops are made of flat steel bent to a circle, with the ends of each hoop riveted together. One end of the steel is bent outward at right angles to the hoops and projects a uniform distance from the hoops to hold the reinforcement concentrically with the column in a fixed posi- tion in the mould. Vertical reinforcements are also used, and consist usually of angles with small holes punched at intervais GENERAL BUILDING CONSTRUCTION. 475 for staples, = means of which the hoops are easily secured to them. The hoops are spaced at regular intervals of from 2 to 3 ins. The arrangement makes a rigid reinforcement which is easily assembled and placed in the mould in its permanent position (Fig. 286). Expanded Metal Hooping.—A novel application of the hooping principle is shown in the columns recently used in the construc- H Column Splite,Bars 4-4" Splice | nce i Bars 4'Long | t i Ends of Bars Ek Fig. 286.—Cummirgs Column. eee Metat By “Png Lg aE oe ie QL LLL Ze LLLL %4' Bars, spaced same in both eae Fig. 287.—Column, Thompson & Norris Factory. Yertica] Tension Bors tion of the Asia & Norris Factory Building, in Brooklyn, N. Y. A section and elevation of this column is shown in Fig. 287. The hooping consists of No. 10 expanded metal, with a 3-in. mesh. The sheets of metal were accurately curved to cylindrical shape, with the edges overlapped and wired so securely that the bond has sufficient strength to break the body of the metal. This metal was wrapped with No. 24 expanded metal lath with a ¥4-in. mesh. The metal lath retained the concrete when deposited, 476 CONCRETE AND REINFORCED CONCRETE. thereby enabling the columns to be constructed without any other form of mould. Provision was made for bending stresses by four vertical corrugated rods placed inside the curved hooping cylinder and wired to it at equal distances apart. These vertical rods varied in size from 1 in. in the basement to % in. in the sixth story, and are spliced 2 ft. above each floor, the rods being butt- jointed and spliced with four 1%4-in. fish-bars 4 ft. long securely wrapped to them with 3-16-in. wire. These columns vary in size from 28 ins. in diameter at the basement to 12 ins. in the upper stories, the diameter being exclusive of the plaster finish, which was 5% in. thick. The columns are of uniform diameter through- out the height of each story. The concreting was done in the usual manner and finished with a 54-in. face coat of I : 3 cement mortar troweled smooth. The hooping was designed to sustain a . bursting pressure of -1 of the compression due to vertical 4.8 “Expanded ee Metal... roorrugatea i Gars.+ a hy Fig. 288.—Column for Warehouse, Toronto, Canada. load. The latter stress was 750 lbs, giving a tension of 156 lbs. to be provided for by the hooping. An examination of these columns showed that the expanded metal lath did not in all cases fulfill the function for which it was intended. When a wet mixture was used the cement near the perimeter of the column drained out with the excess of water, leaving only the coarse particles adjacent to the metal, thereby destroying the full bearing against the metal which is essential to secure the full strength of a hooped column. A tolerably dry mixture is necessary for columns of this character. To place a dry mixture much care is necessary, and when properly done the saving by the use of expanded metal in place of the usual column mould will not be very great. Fig. 288 shows a section of a column used in a warehouse build- ing in Toronto, Canada. The reinforcement consists of four vertical rods, surrounded on all four sides of the column with expanded metal. When expanded metal is thus placed it is evi- GENERAL BUILDING CONSTRUCTION. 477 dent that it will not, in a strict sense, act as hooping, but prob- ably some additional strength will be secured. It has, however, another and important function, as it acts as a form for the con- crete; and if a moderately dry mixture be used and the mesh of the metal be not too large, no other kind of mould will be neces- sary, thereby reducing considerably the cost of construction. Hooped Cinder Concrete Shells—In the construction of a six- story factory for the Bush Terminal Company, Brooklyn, N. Y., hooped columns of a unique design were used. An outside shell of cinder concrete was used to hold the hooping in place, to act as a form for the concrete core and to protect the metal against fire. p4aa'upngne ‘ ‘High Carbon . sree! He ‘ ~Exparided Metal Lath Fig. 289.—Column for Baek, Terminal Co. Factory. The shell, which has a thickness of about 114 ins., was constructed in sections about 2 ft. long. The reinforcement, which consisted of high carbon steel wires, from 3-16 to 5-16 in. in diameter, with an elastic limit of about 55,000 lbs. per sq. in., was wrapped about a collapsible mandril with a pitch of about 2 to 3% ins. At either end a partial extra turn of the rod was made and wrapped to the outer coil by means of soft wire. A sheet of expanded metal lath was then wrapped about the coil to act as an inner form for the shell. The expanded metal was spliced with a lap of about 4 ins. and the spiral rod and expanded metal wired together where necessary. The metal was then removed from the reel and placed within a mould about 4 ins. greater in diameter than that of the hooping. The annular space between the expanded metal and the mould was then filled with cinder concrete. When the concrete had hardened the shell was removed from the form. 478 CONCRETE AND REINFORCED CONCRETE. In the construction of the column uprights formed of 4 x 4-in. timbers (Fig. 289) were set up at the four sides of the column to support the girder and beam forms framing into it and to keep the rings in place. The shells were put in one after another and the core concrete put in place as one shell was placed upon another. Each shell acted as a unit and no splicing was found necessary between adjacent shells. The core concrete bears directly against the hooping, which supports it against any ten- dency to spread laterally when subjected to stress. A working stress of 1,000 Ibs. per sq. in. was allowed upon these hooped columns. A test load of double this amount was brought upon a number of columns with no signs of failure. The main interior columns for this building have a diameter of 33 ins. in the base- ment, which decreases in successive upper stories to 3014, 29, 2614, 23%, 19 and 12 ins. over all. Fig. 290 shows detail of hooped column recommended by the Monolith Steel Co., of Washington, D. C. As will be seen, the monolith bar is used for vertical reinforcement. The method of attaching the hooping to the vertical rods should be noted. The Use of Metal Columns in Reinforced Concrete Structures. The comparatively low stresses which are used for reinforced concrete columns necessitate a column section of considerable size when used for heavy loads in buildings several stories in height. Economy of space dictates the use of columns of small section. This necessitates the use of metal columns for interior columns. The slow deliveries of structural steel make the use of built-up steel columns in many cases impracticable. This has led to the use of cast-iron columns. It is unfortunate that steel cannot be obtained for several months after being ordered, as built-up steel columns can be used in many situations with economy, and if proper care be used in working up details very satisfactory connections with reinforced concrete girders may be secured. Considerable difficulty has been experienced in securing proper connections of girders and beams to cast-iron columns. It is necessary in almost all cases to secure a rigid connection of girders and beams to columns. The author has seen concrete girders resting on seats cast on the side of the cast-iron columns with no other connection than one or two plain rods hooked through holes in lugs also cast on the side of the column. These connections were used in a building eight stories in height subject GENERAL BUILDING CONSTRUCTION. 479 to more or less vibration from machinery on the floors. Such connections cannot be too severely criticised. It is possible to secure satisfactory connections if sufficient care is taken in work- ing up details. A detail which has been used in several loft buildings consists of cutting away the metal at the middle of the sides of the column and increasing it at the corners, leaving open- Fig. 290.—Hooped Column, Monolith Steel Co. ings through which the girders are run. Suitable seats must be provided and the section increased considerably at the corners to secure sufficient area of metal to transmit the stresses to the main body of the column below. This necessitates a considerable increase in the thickness of metal at these points, causing dan- gerous shrinkage strains. This and the unsatisfactory workman- 480 CONCRETE AND REINFORCED CONCRETE. ship usually obtained when any unusual features are introduced on cats-iron work makes this detail more or less undesirable. Another detail consists of providing suitable seats for carrying the girders and beams and anchoring them to the column and joining them together by running continuity bars through holes cored or drilled in the columns. The comparatively small holes necessary for the rods do not weaken the column section, and as stiff a connection is obtained as if the girders were run through the columns. Fig. 291 shows details of the connections of girders to column being used in the construction of a twelve-story loft building in New York City, This structure was designed by the Trussed Concrete Steel Co., No. 1 Madison Avenue, New York [ L201 4 NG 2x3 Hahn Bars i 2, x2 abn Bars IO I ‘ 7796 é ods ‘3 Foods Fig. 291.—Column and Girder Construction, Twelve-Story Loft Building. City. The Kahn bar was used for reinforcement in this building. A very rigid connection’ is secured by running continuity bars around the columns and extending them seyeral feet into the girders on either side. Fig. 292 shows a detail used when it is necessary to support a reinforced column in the upper stories upon cast-iron columns below. In many cases such construction is desirable, as only comparatively small concrete columns are necessary in the upper stories. Beam, Girder and Slab Construction —When used in floors, rein- forced concrete constructions may be divided into two general classes, viz.: when used as a filling between the heams and girders of a framed steel floor system, and when the construction is entirely of reinforced concrete in the form of a slab with or with- GENERAL BUILDING CONSTRUCTION. 481 out reinforced concrete girders or arches, the whole, in either event, being built as a monolith. A modification of the second class consists of a monolithic construction placed between the main steel girders or beams, the slab, strengthened where neces- sary by reinforced concrete ribs, replacing the small beams and concrete filling slab of the first class. Filling slabs may have either a flat or arched form. The flat slab, forming the floor plate, may have any of the following forms: (1) It may rest direct- ly upon the top flange of the supporting beam; (2) it may be supported by the bottom flange of the floor beams; (3) it may be flush with or embed ’ (6% Bolts the top flange. The slab in SR Ge a & the latter form is sometimes af ge supported by a corbel filling , Ke of concrete resting on the tli bottom flange. av Arched construction may consist (1) of an arch ring sprung from the bottom flange of the beams with some form of filling between the extrados and the level of the floor sur- face; (2) of a flat-topped arch sprung from the bottom flange of the beams, having its flat Fig. 292.—Method of Supporting Con- extrados flush with or above crete Column on a Cast-Iron Column. the top of the beams. Monolithic floors may consist of (1) flat floor slabs of uniform thickness; (2) flat floor slabs, strengthened by reinforced con- crete beams, sometimes called ribbed slabs; (3) arches without ribs, and (4) arches with ribs. The usual type of monolithic ribbed floor consists of heavy reinforced concrete ribs or girders supported by walls and columns and arranged in parallel rows, smaller ribs in parallel rows at right angles to and spanning be- tween the girders, and a slab of uniform thickness supported by the two systems of ribs and girders, the whole being a monolithic 482 CONCRETE AND REINFORCED CONCRETE. construction. For long spans the floor slab is sometimes a flat- topped arch. For heavy loads and long spans the girders are also sometimes arched. There are a large number of systems of reinforcement, some of which have already been described, and many of these may be applied to floor construction in one form or another. The multi- plicity of systems make a description of them all not only impos- Fig. 2938.—Monier Floor Slab Carried on Top Flange of Beam. sible, but undesirable. A few of the principal systems will be used to illustrate their application to various kinds of building construction, and the reader should be able to apply the general principles here set forth to any of the systems not illustrated. Filling Slabs Between Steel Beams.—The simplest form of rein- forced concrete floor consists of a Monier slab resting upon the top flanges of the supporting beams, as shown in Fig. 293. Any one of the various types of reinforcement used for slabs and described in Chapter XIV. may be substituted for the Monier il Pe Fig. 294.—Floor Slab with Curved Fig. 295.—Monier Slab Carried on Expanded Metal Reinforcement. Bottom Flanges of Beams. netting. When it is desired to protect the beam against fire, it is embedded in a mass of concrete, or three reinforced slabs may be used to box in the exposed faces of the beam, as shown in the right-hand portion of Fig. 294. The slab may rest upon the bot- tom flange, as in Fig. 295, and the space to the floor level filled with a weak cinder or coke concrete. The bottom flange of the beam is protected from fire by a layer of concrete. Sometimes both top and bottom slabs are used, with or without a meager con- crete filling between them. Expanded metal, the Clinton wire cloth and other slab rein- GENERAL BUILDING CONSTRUCTION. 483 forcements are used in the same manner as the Monier mesh, and may rest either upon the top or bottom flange of the beams. Fig. 295 is an example of expanded metal construction of this kind. ‘The other systems are similar in all particulars. When a top slab is used an air space below the floor and protection for the bottom flange against fire is sometimes obtained by hanging a thin slab of concrete or plaster reinforced by expanded metal lath or some form of wire fabric from the bottom flanges of the beams. Both the Donath and Miiller systems are used in the same manner. Figs. 105 and 106 show these systems resting upon the bottom flanges of the beams. Fig. 296 is a good example of an expanded metal slab with the reinforcement below the level of ponents Fig. 296.—Floor Slab of Expanded Metal Carried on Lower Beam Flanges. the top flange and supported by haunching resting upon the bot- tom flange of the beam. Expanded metal lath for a protecting ceiling is shown below the beams. Monier slabs between beams are generally used in spans vary- ing from 6 to 8 ft., and sometimes as great as 10 ft. The slabs vary in thickness, according to the loading, from 1% to 4 ins. The carrying bars used vary in diameter from 3-16 in. to % in., and are spaced from 2 to 4 ins. centers; sometimes bars of larger diameter are placed at greater intervals. The spacing bars are usually from ¥ to % in. in diameter, and are spaced from I to 3 ins. apart. Care is taken when placing the carrying bars to have about 3% in. of mortar below them. Expanded metal in this form of slab is used for spans up to 8 484 CONCRETE AND REINFORCED CONCRETE. ft., this being the maximtm length in which the sheet can be obtained. The thickness of the slab varies from 2 to 6 ins., and the meshing varies from 1 to 3 ins., the most common mesh used being 3 ins., made of No. 10 gauge metal. The Miller system (Fig. 106) uses slabs up to 10 ft., with a thickness of from 3 to 6 ins. The carrying bars are flats, placed on edge, from I in. x % in. to I 3-16 ins. x 3-16 in. in size, and the connecting bars are of sheet iron, the same width as the main bars and about No. 22 gauge, or 1-32 in. thick. Fig. 297 shows one type of Roebling floor, which is similar to the Muller system. The reinforcement consists of 2 x 3-16-in. flat bars, usually spaced 16 ins. centers, embedded in cinder con- crete. Several modifications of this general type are used for " zn 4 Oak ce Spruce =e ante ae 2x3 Sleeper Re } §--% gx Stee! Rod Spacer. =~ 2% 2 Hart Bar . Ta - 54: e e Taxi Flat Bar Imnbedded i Concrete a : Part Longitudinal Section. te € i 6 za = 5 Pe a 3 & TS M ” : i ” v2 Ig ation | &° m= 2 x 7 q poem é Tr (fisteg f t tt a é Port Plan. Fig. 297.—Roebling Flat Slab Floor. spans up to 16 ft. and various loadings. The general style of construction will be understood from the figure. The Donath slab (Fig. 105) is formed of small Tee or I-beams, varying from 34 to I 3-16 ins. in depth and spaced up to 8 iss. apart. The transverse ties are of hoop iron. In this system a wire meshing is attached to the bottom of this framework and holds the concrete in place without any further-centering. This slab is usually employed in spans of from 6 to Io ft., and when the I-section is used up to 13 ft. The thickness varies from 3 to 6 ins. The Columbia floor slab, described on page 237, consists of double-cross shaped bars suspended from the top flange of the beam by a stirrup, or, in case of the larger bars, connected to the GENERAL BUILDING CONSTRUCTION. 485 web of the beam by riveted connection angles. The bars are spaced usually 24 ins. apart, but the spacing may change under varying conditions. The larger bars are used in spans up to 24 ft. This, however, is not an economic form of construction above about 16 ft. The thickness of the concrete slab varies with the Fig. 298.—Columbian Slab Floor. span, load and spacing. Tig. 298 shows details of this floor. Stone or slag concrete is employed for the supporting slab. A top dressing of cinder concrete, 2 ins. in thickness, is sometimes used, but no cinders are used in the main slab. The proportions of the mixture employed for stone concrete is usually I : 2: 5, Fig. 299.—American Concrete Steel Co.’s Floor. and for slag the proportions are usually 1 : 214 : 3. A very wet mixture is used. Fig. 29g shows the floor system used by the American Concrete Steel Co., Newark, N. J. This system is used in spans up to 16 ft. The reinforcement consists of 34-in. diameter round bars, threaded at the end and strung between the webs of steel beams. They are held in place by nuts, and serve as tie rods as well as reinforcing rods. A secondary reinforcement of 1%4-in. diameter 486 CONCRETE AND REINFORCED CONCRETE. ; rods is laced diagonally between the main rods and is wired to the latter at intersection points. The main rods are usually spaced 12 ins. centers. A cheaper form consists of using tee bars for the round rods, passing them over the top flange of the steel beams or resting them upon the bottom flange. The steel tees are sometimes hung from the top flange of the beam by nicans of stirrups similar to those used for the Columbian system. The \4-in. secondary diagonal reinforcement is retained in all cases. A modification of the floor construction described in the pre- ceding pages consists in the use of a form of reinforcement simi- lar to that explained in connection with Fig. 114. The reinforce- ment is located at the end of the slab, near the upper surface, and firmly anchored to the wall; it then passes to the lower part of the slab throughout its central portion; then again rises at the beam to the top of the slab, and so on throughout its length. Thus when the floor is continuous over several beams the condition practically amounts to fixing the slab at its points of support. Fig. 300.—International Fence & Fireproofing Co.’s Floor. Fig. 300 shows the floor section employed by the International Fence & Fireproofing Co., using tie-lock fabric, supported by wire cables for the reinforcement. The wire netting has a 6 x 6- in. mesh, and is supported by wire cables spaced from 12 to 18 ins. apart. This form of slab is used for spans of from Io to 20, ft., and having thicknesses up to 6 ins. Care must be taken to firmly anchor the ends of the cables at the wall and girders. The electric welded wire reinforcement is used in a similar manner, the carrying wires being large enough to take care of all tensile strain. This fabric has been used in spans up to 15 ft., with a thickness of slab of 6 ins. Expanded metal may also be used in this curved form. When so used it is customary to lap the sheets at the middle of the slab. In this manner slabs of more than 8-ft. span may be obtained. Load tests on this type of expanded metal slab reinforcement have, however, not proved very satisfactory. When adapted to the Monier netting the curved slab reinforce- GENERAL BUILDING CONSTRUCTION. 487 ment is called the Koenen floor. This slab has been extensively applied by Mr. Koenen in Germany to the construction of floors for warehouses, factories, etc., in spans from 6.5 to 21.5 ft., with a slab thickness up to 8 ins. In the Koenen floor slab the rods ere anchored by being bent up or fastened to transverse wall anchors at the ends. A mortar composed of 1 part cement to 4 parts sand is used by Mr. Koenen. Fig. 301 shows another example of floor construction rein- forced with '4-in. corrugated bars, and is adapted to spans up to 16 ft., with a thickness of from 314 to 7% ins. Arched Floor Slabs.—Arched filling between beams has been extensively used in floor construction, especially when heavy loads Fig. 301.—Slab Floor Reinforced with Corrugated Bars. are to be carried. Fig. 302 shows a flat arch of expanded metal construction. These arches are used in spans up to 10 ft. The Golding system is more frequently used than the form of reinforcement just described, and is well adapted to long spans. This system consists of a floor plate reinforced with expanded metal. The slab is strengthened with concrete arch ribs, spaced from 4 to 6 ft. apart, the rib resting upon and being reinforced by soffit channels laid flat, with their backs down; 6-in. channels, weighing 121% lbs. per ft., are generally used. The channels are sometimes exposed, but are usually surrounded with metal lath and plastered to protect them from fire. The Golding paneled floor is used in spans up to 20 ft. Fig 157 shows this form of arch flooring. The Roebling system of floor arching consists of a wire cloth 438 CONCRETE AND REINFORCED CONCRETE. centering, stiffened by steel rods woven into the mesh; 7-16-in. diameter rods are used for 5 ft. and 9-16 in. for 7-ft. spans. This centering is sprung between and rests upon the bottom flanges of the floor beams. The concrete is deposited upon this wire centering with its top surface flush with the top flanges of the Fig. 302.—Flat Arcu, Expanded Metal Construction. beams. When a flat ceiling is not desired, the bottom flanges of the beams are enveloped with wire cloth and the whole embedded in concrete. When a flat ceiling is required, a clip of special form is attached to the lower flange of the beams and supports flat iron bars set on edge and spaced about 16 ins. centers. Roeb- ling standard wire lath, with 14-in. steel stiffening ribs woven in, ee ee TLS Ga Flooring Zz 3x4 5x4 Sleqvers, Ie IEF & OC é Stee! fodt, ; woven Into Wire Lathing Fig. 303.—Roebling Arch Floor. is laced to these ceiling bars. The whole is plastered over to form the ceiling. This form of construction-is commonly used for factories, ware- houses, etc., in spans up to 7 and 8 ft., and will sustain loads of 4,000 Ibs. per sq. ft., and can be adapted to loads of 10,000 lbs. per sq. ft. A modification of the above system, in which the stiffening rods are replaced by T's, is used in spans up to 16 ft. GENERAL BUILDING CONSTRUCTION. 489 The T-irons are usually spaced 2 ft. centers, and the wire cloth centering laid between the T-iron ribs. Fig. 303 shows the usual type of Roebling floor arch. The thickness of the arch at the crown varies from 2 to 4 ins. The concrete mixture used for Roebling floors is 1 cement, 2 sand and 5 cinders. A1:2%: 6 mixture is also sometimes used. Fig. 304 shows the arched type of floor slab used in the con- struction of the first floor and sidewalk of the Metropolitan Building, New York City, while Fig. 305 shows the flat floor slab used for the upper stories. De Man bars, described on page Fig. 304.—De Man Arch Floor. 227 form the reinforcement, and were made of 1 x 1%-in. steel strap, crimped at regular intervals. The location of the rein- forcement will be understood from the drawing. The bars are spaced from 6 to 12 ins. apart, according to the floor loading. The American Fireproofing Cement Construction Co., of New York City, build this type of floor. When considerable strength is needed Monier arches are used in place of Monier slabs. They usually consist of an arch having a rise of = the span, springing from the lower flanges of the cr spisasngaenoe 60": Fig. 805.—De Man Flat Floor. supporting beams. A single Monier netting, placed near the introdosal face, constitutes the reinforcement. A filling of meager concrete fills the intervening space up to the floor surface. The bottom flange of the beam is protected by a layer of concrete about 114 in. thick. Mr. Wayss, an Austrian engineer, states that it is customary to use Monier arches up to 5 m. (16.4 ft.) span, with a single netting and a thickness of arch ring of 5 cm. (2 ins.) to carry loads up to 1,200 kg. per sq. m. (230 Ibs. per sq. ft.). Fig. 306 shows examples of single and double Monier floor slabs. Sometimes a second reinforcing mesh is used. It may be 490 CONCRETE AND REINFORCED CONCRETE. employed in a second arch ring some distance above the first, with a filling of meager concrete between, but the most common form is to place it near the surface of a flat extrados. Arched floors, with a flat extrados up to 6 m. (20 ft.) span, were used in the construction of Public Buildings at Kameroun. Fig. 307 shows an example of an arch with a reinforced flat extrados which was used in the construction of a warehouse at Trieste. The Melan system (Fig. 308) employs rolled beams for the Fig. 808.-—Melan Arch Floor. Fig. 809.—Wunch Arch Floor. reinforcement, and is most frequently used in spans of from 8 to 14 ft., with a thickness of arch ring of 3 ins. The rise is usually from - to + of the span. The ends of the beams are mitered to bear against the web of the supporting beams, and rest directly upon the bottom flanges. This is not an economic form of construction unless unusually heavy loads are to be carried. The Wiinch system (Fig. 309) uses angles or T’s for rein- forcement. A double reinforcement is used with the ends of the angles or tee irons riveted to the flanges of the beams. This givés a rigid skeleton work, but is expensive. GENERAL BUILDING CONSTRUCTION. 491 Monolithic Floors.—The various systems of floor slabs just described, with few exceptions, may be increased in size to form monolithic floors of considerable span. While these various con- structions may be increased to quite long spans, when so used they are not economical, and hence are not used except in cases where expense is of secondary importance, as when the demand for clear floor space prevents the use of columns, or when limited head-room makes the extra depth necessary for ribs undesirable. When the floor panels can be built in the form of squares or rec- tangles, with their sides of nearly equal length, and are supported : | Fig. 310.—Hennebique Floor Slab with Single Reinforcement. on all four sides, the economic spans will be considerably greater than that of slabs supported only on two sides. . In addition to the systems already described, the Hennebique and Matrai systems, as applied to long spans, deserve mention in this place. The Hennebique monolithic slabs are constructed with three forms of reinforcement; first with single independent bar reinforcements, consisting of alternate straight and bent round rods spaced at equal intervals. Fig. 310 shows the principal char- acteristics of this form. The rods have their ends split to anchor them in the concrete. The size and spacing of the rods depends upon the span and load. They usually have a diameter of from = to 34 in. and are spaced from 4 to 12 ins. centers. When the thickness of the slab is greater than 3 ins. stirrups are em- 492 CONCRETE AND REINFORCED CONCRETE. ployed. The stirrups are of hoop iron, about 34 x ~~ in., and extend up into the slab to within about 3 in. of its top face. The example shown in Fig. 310 was used in the construction of a banquet hall at Basel, Switzerland. The second form of Hennebique slab has a series of straight rods at right angles to the first series, with alternate rods placed pear the top and bottom of the slab. This form and the one yet to be described are more suitable for reinforcing square floor slabs and rectangular slabs having their dimensions practically equal. Stirrups are only placed about the lower bars. In proportioning these slabs they are considered as resting upon four supports. Fig. 311 shows this type of slab. The third form of Hennc- bique floor slab has a lattice reinforcement made up entirely of Fig. 311.—Hennebique Floor Slab with Double Reinforcement. straight rods, with alternate rods placed near the top and bottom of the floor plate. The bottom bars only are provided with stirrups. In the construction of the Matrai system of floors the principle explained. in regard to slab reinforcement on page 244 and illus- trated in Figs. 115 and 158, is extended, and develops very com- plicated systems of wire netting. When used in connection with beams and girders the wires are attached as near as possible to the ends of the beams and girders, in order that their bending moments may be reduced as much as possible and their sections correspondingly reduced. The space to be spanned is divided into rectangular panels by reinforced concrete girders, whose re- inforcement consists of stiffening skeleton work, such as is shown GENERAL BUILDING CONSTRUCTION. 493 in Figs. 91 and 92. These are strengthened by wire cables hung in the form of a catenary. Sometimes cables are strung diag- onally through the panels, as shown in Fig. 312. This figure > 1 (en 7 [eoannnnnnennneeennen 8, Fig. 312.—Matrai Floor. shows the section of a floor used in the construction of the Maison d@’Education de la Legion d’Honneur. The concrete used in this floor was I part cement, 2 parts sand and 4 parts slag. The con- crete acts simply as a filling and protecting material in the Matrai 494 CONCRETE AND REINFORCED CONCRETE. floor system, reliance being placed alone upon the wires and cables to carry the loads. The Mushroom System of Construction —This system is the in- vention of Mr. C. A. P. Turner, M. Am. Soc. C. E. By referring to Figs. 313 and 314, it will be seen that the construction consists of columns, and a floor slab without beams or girders. The mushroom action, so called, ‘s obtained by arranging the reinforc- ing metal as shown in Fig. 314, the top of the column being enlarged to form a capital, as shown in elevation, Fig. 313. The reinforcing rods for the slabs are then strung, as shown in Fig. 314, in a manner similar to that used in the Matrai system, FOOTING i i = 1 itavkewhetashedetectetenhestocstay Fig. 313.—Column in Mushroom System of Construction. as shown in Figs. 115 and 312, which this system in many ways resembles. The arrangement of the reinforcement, as used in the construction of the C. A. Bovey Building, Minneapolis, Minn., is shown in Fig. 315. . The advantages claimed for this method of construction are a reduction in the cost of forms, owing to the flat ceiling used, and an increased strength due to mushroom shape at top of columns. It would appear that an analysis of the stresses in the floor slab would be a rather uncertain and puzzling operation. Mr. Turner states that this system has been successful in competition with wood mill building construction. Ribbed Slabs —The most common form of floor construction GENERAL BUILDING CONSTRUCTION. 495 ' ' t ' 1 ' 1 1 1 1 1 1 D we S = ' 1 t \ ' 1 1 J 1 ‘ 1 ' ; 1 = ca S 4 ! \ v Y Fig. 315.—View of Floor, Mushroom System of Construction. | 496 CONCRETE AND REINFORCED CONCRETE. when the spans are greater than 6 or 8 ft. is that of a concrete slab strengthened at intervals of 4 ft. and upwards by reinforced. con- crete beams, the whole being a monolithic construction and com- monly called ribbed slab floors. In ribbed slab construction the various systems are employed in a similar and often identical manner, usually the only differ- ence being in the manner of reinforcing the slab or beam, or both. These have been fully explained in connection with de- scriptions of reinforcements for slabs and beams. For short spans and light loads the plain floor slab will prove the most Fig. 316.—Typical Column and Floor Construction by Hennebique System. economic, especially as the necessary forms are more simple than those used in the construction of ribbed beams. When the spans kecome somewhat greater, however, the ribbed slab will prove the more’ economic. The spacing of the ribs may be varied in order to secure a paneled effect for the ceiling. In fact, in this respect reinforced concrete construction admits of great flexibility in this regard, and often enables the architect to greatly improve the beauty of the structure. When a flat ceiling is desired, a suspended ceiling may be used similar to that described on page 483. The Hennebique system GENERAL BUILDING CONSTRUCTION. 497 has been extensively applied to the construction of floors. The floor slabs used are from 21% to 6 ins. thick, and are, when possi- ble, made continuous over the ribs or reinforced concrete girders, Fig. 133 shows a typical form of Hennebique floor construction. Two systems of ribs are employed. The main ribs are usually anim OxR 14-19 es “Ay rl B+ 71496 1 to beng he 59 oe. 27 he 25 hea Seg Fig. 317.—Floor for Palais de Justice, Viviers, France. limited to spans of from 16 to 24 ft., although beams with a span of 60 ft. have been built. The secondary ribs are generally not greater than from Io to 12-ft. span, and are usually reinforced with a single rod or pair of rods and with stirrups, which are placed about the bottom rods only. The floor space is divided Fig. 318.—Floor Petit Palais des Beaux Arts, Paris, France. . into square or rectangular panels by these two systems of beams. The reinforcing rods used vary from 14 in. to 2 ins. in diameter, and are spaced so that there will be at least from 1% to 2% ims. of concrete between them, and the rods should not be nearer than within 1 in. of the lower face of the beam. Fig. 316 shows the general features of a Hennebique floor and column construction. . 498 CONCRETE AND REINFORCED CONCRETE. M. Christophe gives excellent examples of this form of construc- tion in his book, “Beton Armé” (see pages 109-111), from which the following figures are taken. The first of these (Fig. 317) is a section of floors used in the construction of the Palais de Justice de Viviers, France. A main rib, heavily reinforced, secondary ribs and floor slab are all used together in this building. Sometimes the secondary ribs are omitted, and we have a con- 42 Rodse B yy 12 O'long : | A ' en a | 3g feds : Z EEE A a S| Ener oe eee 3 ig Rods | BRods,A'C. 6. V6, /"Rods “2 ZB Reds-% ods | er Welded Fabric, ‘ 4k 6 "Mesh. i fais | fi F pal 3 : ; S , Fos = We) YX ly “8 'KBt = 3 103% | i Section of GirderA A. | 3% ge 7 ‘ 5, jg Rods. ig, Rods, 4 C.70€. he HeorFods, — bentup at Walls Section of Girder BB Fig. 319.—Floor for Chicago Store Building. struction like that shown in Fig. 318, which is a section of the floor used in the Petit Palais des Beaux Arts at the Paris Expo- sition of 1900. The floor has a span of 7.35 m. (24.11 ft) for the ribs, which are spaced about 7.5 ft. centers. A modification of the Hennebique construction is shown in Fig. 319, which shows the details of a reinforced concreté store building in Chicago. The reinforcing rods used in the floor girders were 34 and 1 in. in diameter, both tension and compres- sion rods being employed. GENERAL BUILDING CONSTRUCTION. 499 Fig. 320 shows the rods used to form the truss of each girder. These rods are connected by an electrically welded fabric netting, which envelops each girder. The ends of the rods are bent up at right angles to firmly anchor them in the concrete. The main floor rods are = in. in diameter and spaced 4 ins. centers in hoth directions and are carried through the girders. Al :2:2 concrete of Vulcanite Portland cement, sharp torpedo sand and gravel screened to pass a 5-in. mesh was used. Mr. E. T. Ransome has erected a large number of buildings in 1810" -- --- eZ" eae 200° Reinforcing Rods in Girder. Fig. 320.—Girder Reinforcement, Chicago Store Building. this country. Twisted rods are exclusively used by this engineer for reinforcing beams, columns, slabs, etc. In the construction of ribbed floors the ribs are usually reinforced with one or more straight rods in the tension flange. Stirrups of square-twisted rods tie the reinforcement to the concrete and are spaced close together at the ends and further apart toward the center as the shear decreases. Fig. 321 shows a section of a floor in an addition recently made to the esnignee concrete building erected in 1897-8 for the ‘ods, Centers Wall Girder “a, =e cy 'Roi = ods, 42 “Centers a - 5 TWpical Transverse i co FOB nm KS | gag Floor Section. 3 Vertical Rods 34 3 Coll, 4'Pitch wae “Section CC. 2 big Fig. 321.—Floor for Pacific Borax Co.’s Factory. Pacific Coast Borax Factory, Bayonne, N. J. The floors in this addition, of which the above figure is a representative example, are designed for a dead load of 100 lbs. and a uniformly distrib- uted live load of 400 Ibs. per sq. ft. The transverse beams are 4 ft. 114 ins. on centers and span between columns spaced 24 ft. 87% ins. on centers. Twin girders are used at the columns, and are separated by a cleavage plane to allow for expansion. The 500 CONCRETE AND REINFORCED CONCRETE. floor slab is 31% ins. thick and reinforced by %4-in. twisted steel longitudinal bars spaced 414 ins. centers. Another notable example of Ransome construction is that of the Kelley & Jones Co.’s concrete-steel factory building, Greens- burg, Pa. This building is 60 x 300 ft. in plan and four stories high. Fig. 322 shows traverse and longitudinal sections of the floors, walls and roof of this building. The first floor is of con- crete and rests directly upon rammed earth. The upper floors " 74 Bars ze = oy Ses ALE ha “a SHB Saar Hi YS eS Col 4 bar s * s Ursection WW ¥ SE FOr “Bar _t, Gloops ‘ & ee : 3 556, 4 Bars Section SS. “2 bar S CP Geol gy 14" 224 Floor 135 4 U-Bars : S { Ww ISLiik 5a “YC aa : “” ® (aera ae /'Bar Bar 4"U-Bars : « Section V-V LT Jed vaw » Fig, 322.Floor and Wall Details, Kelly & Jones Factory. are designed to carry 250 lbs. per sq. ft., and are divided into panels about 3 ft. 8 ins. wide and 8 ft. 4 ins. long by transverse and longitudinal girders. The 3-in. unreinforced floor slab is supported by 12-in. longitudinal and transverse girders. The main transverse girders are in pairs, supported on each row of columns, and carry 13 lines of longitudinal beams connected by transverse girders at the center of each panel. The longitudinal beams are spaced about 3 ft. to ins. centers, are 3 ins. wide, and reinforced with one 11-in. bar in the lower side and by one 14-in. bar in the upper part of the floor slab. Vertical stirrups of 14-in. GENERAL BUILDING. CONSTRUCTION. 501 . Rib at each Column. 4-4"Vertical Bars ot each Column. Flashing Level of Roof at Down Spouts ™ Force loor Line. t 8- &" Vertical Bars. Bar Coil 4! Pitch, 12'5$" to Finished am Wood Wood Stool and Apron, Finished end S/l-— % Floor Line I ny 8-4Vertical Bars. v, i, 4°P ii ke Column. 4! Bar Coil, 4°Pitch, Part Cross-Section of Main Shop. Fig. 323.—Part Cross-Section of Main Building, United Shoe Machinery Co.’s Works. 502 CONCRETE AND REINFORCED CONCRETE. \ steel bars are used, and are spaced close together at the ends of the beams and further apart near the middle, being spaced to conform with the strain sheet of maximum shears and relieve the concrete of all the computed shearing stress. The main trans- verse girders are 9 ins. wide and reinforced with three 11%-in. rods, and are arranged in pairs 9 ins. in the clear from the center line of the columns. A feature of this building is the absence of reinforcement in the floor slab. The above two examples serve to illustrate the earlier types of reinforced concrete factory building constructed in this country. The shops of the United Shoe Machinery Co., Beverly, Mass., consisting of ten buildings, covering about four acres, are prob- ably the largest single reinforced concrete building construction ever undertaken in this country. The floor space in these build- ings is about 18 acres. The total estimated cost of these buildings exclusive of land, which, with the exception of the roofs of the foundry and forge shops, are entirely of reinforced concrete, is about $1,000,000. The Ransome system of twisted steel bars is used for reinforce- ment. The structural concrete was all mixed 1 : 2 : 4, with screened gravel from 14 to I in. in diameter; Lehigh and Atlas brands of cement were used and the concrete was mixed wet. The buildings were divided into sections 60 ft. in length, and all concrete in each section was built as a monolith. The two largest buildings are 62 ft. wide, 522 ft. long and four stories in height. Fig. 323 is a partial cross-section of one of the main buildings, and shows the type of construction used throughout all the buildings. Fig. 324 shows partial plan of first floor at one end. The arrangement of girders and beams will be understood from the plan. It should be noted that the corner panels are mono- lithic slabs without floor stringers, and have the reinforcing bars crossing the panel in a diagonal direction. This construction stiffens the building throughout the planes of the floors against distortion due to wind pressure, and is used for all floors and the roof at the ends of the buildings. The size and spacing of rods in slabs, beams and girders, as well as general details of con- struction, are shown in the figures. The roof was designed for a live load of 75 lbs. per sq. ft., the third and fourth floors for 200 Ibs., and the second floor for 250 lbs. per sq. ft. Fig. 325 is an excellent example of ribbed floor construction GENERAL BUILDING CONSTRUCTION. 503 as used in factory building. The live load it was designed to carry is 200 Ibs. per sq. ft. The longitudinal beams are spaced 3 ft. 9 ins. centers, and are carried by transverse girders 12 to 15 ft. apart on centers and from 15 to 16 ft. in length. The con- crete used in the construction of this floor was a 1 : 2 : 4 Edison Portland cement, sand and trap-rock crushed to pass a 34-in. screen. This floor was used in the construction of the Thompson & Norris eight-story factory building, in Brooklyn, N. Y. Messrs. H. C. Miller and H. I. Moyer were the engineers in charge of the design and construction of this building. te US Aeon SAE TS De of Ne KOPN Ue OM rc * LN et 2 = CIF 3-4¢-7--> " ( 1 pe —--— 20/0". ea xN “4 ===) Concrete! Muitions, ‘0 "Weer T ad of / ae H] a Ha r i ie---- Bee e ea geet 20 me a se Hot Air Flue Brick Lining Fig. 324.—Part Floor Plan, United Shoe Machinery Co.’s Factory. A form of ribbed floor construction used by the Reinforced Cement Construction Co., New York, is a modification of the de Vailliere system, and consists of straight and round rods similar to those used in the Hennebique system for the beam reinforcements and straight rods at right angles to these for the slab reinforcement. The lower straight rods are rigidly con- nected to the slab reinforcement with twisted rod stirrups, causing the two to act together as a tee-beam. Fig 326 shows the ar- rangement of rods and stirrups. The stirrups are sometimes inclined, upon the supposition that they will thus better care for the shearing stresses. Fig. 327 shows the method in which this system is applied to column, girder, beam and slab construction. 504 CONCRETE AND REINFORCED CONCRETE. This system was used in the construction of the Hugh Bilgrim Machine Shop, Philadelphia, Pa. This building is 120 x 100 ft. in plan, and consists of a main building, 120 x 53 ft., five stories high, and a one-story extension occupying the remaining space. a i £'U-Bars - "Corr. Bars 18"Conters $'Corr. Bars .7 Centers: ae pe Section C-D. 4! Column. See Ree. ~ Girder NS Column: 3-f"Corr Bars V6"Llong, #14! Corr. Bars - <== ze 4 SST Ss ! "Corr. Bars. eee Column Ae L+-ICorr Bars Sof which bend up, dees i Fig. 325.—Floor Construction for Thompson & Norris Factory. The columns were spaced 18 ft. 6 ins. centers transversely and 14 ft. 4 ins. longitudinally. The transverse beams supporting the floor are 6 x 12 ins. in section and spaced 3 ft. 7 ins. centers. The floor slab is 4 ins. thick on the first floor and 3 ins. on all other GENERAL BUILDING CONSTRUCTION. 505 floors. Girders 10 x 14 ins. in section are supported by the columns and carry the transverse floor stringers. Fig. 328 shows the arrangement of the reinforcement for the floor slab, girders and columns. The column sections are 21, 19, 17, 13 and 8 ins. on the first, second, third, fourth and fifth floors, respectively. The first floor was designed for a uniform live load of 300 lbs. per sq. ft., the second floor for 200 lbs. and the other floors for Fig. 326.—Girder and Slab Reinforcement, Reinforced Cement Construction Co.’s System. 150 Ibs. per sq. ft. Round rods with twisted rod stirrups, as shown in Fig. 326, were used for reinforcements. The concrete mixture was I part Alpha Portland cement, 3 parts clean sand and gravel and 5 parts trap-rock, broken to pass a 34-in. ring. Mixing was done by hand. The saw tooth roof used on the rear part of this building is described on page 548. A good example of the adaptability of reinforced concrete to Fig. 327.—Column and Floor Construction, Reinforced Cement Construction Co.'s System. the construction of a building where wide floor space is desired is that of the Robbins automobile garage, in New York City. This is a three-story and basement structure, with reinforced concrete floors and columns and brick enclosure walls. The build- ing is 50 x 100 ft. in plan, with an ell 32.5 x 36 ft. in plan on one side at the rear. The floor space on all three stories is entirely unobstructed. The concrete floor slab of the first story rests on 506 CONCRETE AND REINFORCED CONCRETE. beams and girders carried by reinforced concrete columns built up from the basement floor, while the slabs of the second and third floors and the roof rests on heavy transverse girders which are carried at each end by the reinforced concrete columns built in the outside brick walls. This arrangement is shown by Fig. 329, which is an interior view of one floor. Fig. 330 is a section of one of the main girders, showing details of the reinforcement. In the main part of the building the basement is divided into three bays by the outer walls and two rows of 12 x 12 columns. The Wood Floor or, 2%3" Sleepers 16"C.fo C. laid in 2* Cinder Concrete AY eo a Ve-teRods 7 Cs ‘flee, Reinforced with Rods, moe Is Spaced 6"C foC. Ait strcups made of 2- "9 Rods, Twisted wa sene 14°81 ~~ ------ Ih -| . ‘ Same Flooring as above, ae ms ee rar = = = é fs i ae are “AY Rods a ety oe at Slab Reinforced with i lam = G'°Rods, spaced 6C.toC, | Ri] 2 We : Q c—| y---+ |-0 1 t ee t UY poe) | Section A-B prion i ‘ T fra ae W'Cement Finish ' | | 3"Concrete Z : f= i ees oe = = ED B Section A-B Fig. 328.—Part Section of Hugh Bilgram Machine Shop, Reinforced Cement Construction Co.’s System. columns are spaced 13 ft. 5 ins. centers longitudinally and 17 ft. 3 ins. centers transversely. They carry 6 x 14-in. transverse beams and 8 x 18-in. longitudinal girders, which are built mono- lithic with the floor slab. The second and third floors are carried by 20 x 36-in. transverse girders, spaced 13 ft. 5 ins. centers. These girders are 50 ft. long, with a clear span of 45 ft., and are built monolithic at the ends, with 24 x 26-in. columns carried up from the basement floor. The floor slab between the girders is carried by 6 x I4-in. cross beams 6 ft. 3 ins. centers. The roof GENERAL BUILDING CONSTRUCTION. 507 girders and beams are lighter than the floor slabs, as they are designed for lighter loads. The slabs of the floor and roof are 5 ins. thick. Round rods were used for the reinforcement throughout and arranged according to the de Vailliere system. Fig. 329.—Interior View, Robbins Garage, New York City, Showing Floor Girders and Columns. Te ' ~ bina -¥ehngers pe ae aa Fig. 330.—Section of Main Girder in Robbins Garage, New York City. A.wet concrete was used in proportions of 1 part Vulcanite cement, 2 parts sand and 3 parts of 34-in. broken stone with the dust screened out. The forms were made of 2-in. plank, dressed on one side. Those for the floor and roof slabs were made of tongue and grooved flooring. : Another reinforced concrete building in which the de Valliere system of reinforcement is used by the Reinforced Cement Con- struction Co. is that of the paint and overhauling shop of the Philadelphia Rapid Transit Co. This building is two stories in height and 90 x 389 ft. in size, the first floor having a clear height 508 CONCRETE AND REINFORCED CONCRETE. under beams of 18 ft., and the second floor a clear height at eaves of 15 ft. 2 ins. Five lines of tracks are provided for on the first floor and six on the second floor. To facilitate handling of cars .a transfer table was placed near the rear of the building on both floors in place of the ladder tracks usually employed for entering the various floor tracks from the street. This necessitated girder spans of 48 ft. for supporting the floors. The transfer table is carried on four lines of rails, supported on 18 x 18-in. cross beams, carried by longitudinal girders 18 x 39% ins. in section, having a clear span of 46 ft. between columns. These girders are joined to the columns by special brackets. The columns and girders are’ built together and form a monolithic structure. The general 1-601 >e-60 Ke -60" >i 3" ab- cui D> AHAtT! sar ii tA, tim tt yt a ee Bs {yaar mz Na ee 7 antares d ect tort tog bog ft a tt Ot erin OKIE” 8x16 Beans a = te meds v “Gl Rods “Ie, ip Reds oe i tH i 4 yay 7 i rex /i ” a <8 18 " 1 A r ! an ‘ al ‘ \..-7take-7/9ftoke-79%s| C : rx tg | ae eH ; nso HH iMacs MP ee rl sheet chodete tede tee 4) = x “ IX rt a SS H i. cs {4 4 ko A m3 KH ‘SH E q ae } Fig. 551.—Longitudinal Section, Overhauling Shop, Philadelphia Rapid Transit Co. features of the construction and the arrangement, size and num- ber of roof rods are shown in Fig. 331, which is a longitudinal section of the building. A cross-section of the building, showing details of reinforced concrete construction, plan of roof bars, etc., is shown in Fig. 332. The method of reinforcing brackets on columns in the first story to support the crane girder is also shown in Fig. 332. Another form of ribbed slab construction, used for both roof and floor slabs, was employed in the construction of the Centrai Felt & Paper Factory, at Long Island City, and of the Parkville sub-station of the Brooklyn Rapid Transit Co. The reinforce- ment consists of a straight rod and one or more bent rods in the same vertical plane, there being two or more series of rods parallel GENERAL BUILDING CONSTRUCTION. 509 to each other, and all wired together to make up the skeleton work of one. girder. This makes quite a stiff framework, which is hung in the I Sab abbott 6/4’ Beams S LiTril Half Plan of Transverse Girder. 16”. Half Plan one Bay of Roof. Fig. 332.—Transverse Section, Overhauling Shop, Philadelphia Rapid Transit Co. w 6- Rods 12"0 | Longitudinal Beam ' 40, 14 14" 164 M16" 16416" 18" 18" 18" Zeg6L 7282 9" 1081", HW J2" 120,12, 148, a 4h, pA aaa a ee 16 * Section Z-Z of Column 4-34" Rods Fig. 333.—Roof Girder, Central Felt and Paper Co.’s Factory. Q forms, and the concrete is tamped firmly about the metal. It is claimed that the metal when thus used will not be displaced when the concrete is put in. Compression rods are also sometimes used. 510 CONCRETE AND REINFORCED CONCRETE. The floor slab is reinforced in the usual manner with a series of parallel rods. The connecting rods or stirrups are spaced to correspond to the diagram of shears. Fig. 333 shows the details of a 52-ft. roof girder used in the construction of the Central Pulp & Paper Co.’s building. Wire fabric was used for reinforcing ae pm Se fn fae Rae ee fhe ee eel) ee fw ae im ud Tee. | Wipe pact daosbe Q-1 8 Rods ( 21h Rods, WW 2-12, “Rods. Transverse Section. Saree aie ee Seer w'6"-—- ~- 0: 7 = ay ie ie if 4 rE ge &— Main Rocf FR 0 Girders 5 a Y'Rods. Travelin’ _ Bl Granee Girder t ara ae it oA Eni 4-1"Rods % Ties Pilaster -- 30"-- Peas rt Wall Col. 1 ‘ Lt) ee { Elevation 2! 1 Ww. i@ Pods g! &§ Section xe A-B,. Fig. 335.—Transverse Section of Fig. 334.—Column Bracket for Sub-stalion Building, Brooklyn Crane Run Girders, Central Rapid Transit Co. Felt and Paper Co.’s Factory. the roof slabs. Fig. 334 shows details of wall bracket used for carrying crane-run girders in this building. Fig. 335 shows a transverse section of, wall and roof construction, and Fig. 336 longitudinal sectional elevation of Parkville sub-station, together with framing of roof and crane-run girders. GENERAL BUILDING CONSTRUCTION. SII A long span girder used to support the gallery of the Lyric Theater, Cleveland, Ohio, is shown in Fig. 337. This girder is Longitudinal Sectional Elevation of Part of Building. Fig. 336.—Longitudinal Section, Sub-station Building, Brooklyn Rapid Transit Co. We}, oe 550 har Span Elevation of Main Girder. intorced ogee lol. / % , Teint Concrete Col, jon eeemnmnen mam Gf) an = mane woman nnn Fen Section on Certter Line. Fig. 337.—Long Span Girder Carrying Gallery of Lyric Theatre, Cleveland, O. 55 ft. in clear span, 60 ins. deep and 12 ins. wide at the bottom and 20 ins. at the top. The reinforcement consists of round rods and stirrups, as shown. This girder was tested with a maximum 512 CONCRETE AND REINFORCED CONCRETE. load of 44 tons, giving a total deflection of 43 in. No evidences of cracks or other injuries were visible. The general features of Unit system of construction are shown in Fig. 338. The-details of the Unit girder frame were shown in Figs. 95 and 96. This system is being used in the construction of an eight-story manufacturing building in New York City. The building is approximately 125 x 137.5 ft. in plan. The «all columns are rectangular in section and reinforced with 4, 6 and 8 round rods. The interior columns for the four upper stories are of reinforced concrete of square section reinforced with 4 and 6 round rods. The lower interior columns are of cast iron and have the open section at the beam and column levels described on page 479, permitting the latter to run continuously through them. The first floor is designed for a live load of 200 lbs. per sq. ft. Fig. 338.—Typical Construction Unit Concrete Steel Co.’s System. and the upper floors for 150 lbs. per sq. ft. The slab reinforce- ment consists of 4; in. round rods, spaced 6 ins. centers, the slabs being 5% and 4% ins. thick. The columns are spaced 12 ft. centers longitudinally and 17 ft. 4 ins. transversely. The building recently constructed for the Bush Terminal Com- pany, located in South Brooklyn, N. Y., is an example of a rein- forced concrete building of unusually heavy construction for warehouse and factory purposes. The reinforced concrete details were worked out and the construction supervised by Bertine & Son, under the direction of the then chief engineer of the Bush Terminal Company, Mr. E. P. Goodrich. This building is 600 ft. long, 75 ft. wide and has six stories and a basement. A pile foun- dation was necessary, as the soil in this locality is all made ground. GENERAL BUILDING CONSTRUCTION. 513 Fig. 339.—Column and Floor Con- struction, Bush Terminal Co.’s Factory. Three rows of interior columns and two rows of wall columns extend the full length of the building. Longitudinal wall and floor girders span between the columns, which are spaced 16.5 ft. apart on centers. In a trans- verse direction one line of col- umns is placed on the center line of the building and one row 17 ft. 8 ins. on each side of it, leaving an outside space of 20 ft. between the last row of columns and the exterior of the wall col- umns or piers. The columns are connected longitudinally by mas- sive reinforced concrete girders, which divide the floor space into two center longitudinal panels, 17 ft. 8 ins. wide on ccaters, and two outside panels 18 ft. wide in the clear. The panels extend from end‘to end of the building, a distance of 500 ft., exclusive of the somewhat narrower extension it has at the ends of the building, where there is a_ different ar- tangement of the columns and girders. In the main portion of the building the floors in these lcngi- tudinal panels are carried en- tirely by the longitudinal girders, without any transverse beams or girders. The regular floor slabs are of special construction, dc- signed to economically span the panel width. They have, as shown in the details, a continuous smooth horizontal upper surface 4% ins. thick, strengthened by transverse ribs, 6 ins. deep and 22 ins. apart on centers, which give ) 514 CONCRETE AND REINFORCED CONCRETE. the ceilings a corrugate.! or trcugh-like appearance. These corru- gations are staggered in adjacent panels, so that a cross-section throug: the center of a corrugation in one panel cuts through the center of a rib in the adjacent panels, and vice versa. The floors weigh about 100 lbs. per sq. ft. and are proportioned for a live load of 450 lbs. per sq. ft. (See Fig. 339 for sketch of floor.) The wall and center girders have rectangular cross-sections, and are reinforced with round bars wired together to form a rigid Fig. 340.—Intermediate Girders, Bush Terminal Co.’s Factory. skeleton work of the Bertine system (see Figs. 340, 341). They have a width of 10 ins. and a depth to the floor slab of 30% ins. Reinforcement consists of two 1-in. and twol?sin. round rods horizontal in the lower edge of the beam at the middle part, bent up at an angle to the top of the girder at both ends. In addition to this, there are two }{-in. straight rods extending through the lower part of the girder from end to end. ' The rods are grouped in two sets of three each, vertically on each side of the 4164" Qverall--- Fig. 341.—Wall Girder, Bush Terminal Co.’s Factory. beam, and are connected by 37 vertical stirrups made of -#;-in. rods wired to them and spaced at variable distances, as deter- mined by the diagram of shearing stresses in the beam. The flat roof is proportioned for a uniform live load of 50 Ibs. per sq. ft. and consists of a flat slab of reinforced concrete 3% ins. thick, supported on the reinforced concrete longitudinal gir- ders and on similar transverse girders at the columns and at in- termediate points. The interior columns are of hooped construc- GENERAL BUILDING CONSTRUCTION. 515 tion, and are fully described on page 477. The exterior columns are of rectangular section. The exterior walls are of brick work supported at each story by reinforced concrete girders, which, with the interior girders, are made integral with the floor slabs feo Y aaa ¥ ' ! tL ' MA Ny al vo Q iA~ ' al Ny \ \A \A » 8 i eh a Y y © 2 1 aes ll : Kh --- 1970" ------ NA paca £76" ~-~--pkh---- 1767----4%}----- 190"-~ 8 ' eof ' ' ob ; \ ¥ t ¥ a y Fig. 342.—Cross-Section of Bush Terminal Co.’s Factory. and are banded to them with reinforcing bars. A large portion -of the walls is glazed, so that the brick work is not a large item in the construction. Figure 342 shows a general cross-section of the building. 516 CONCRETE AND REINFORCED CONCRETE. ‘Bars ” 207 Cross Section. - eae oF — Columns Section showing Columns and Wall. * t K/2"4 Detail at Col. Fig. 845. Typical Section. GENERAL BUILDING CONSTRUCTION. 517 Figures 343 to 345 show plans of a one-story power house for the Ridgefield Electric Co., Ridgefield, Conn., designed by Mr. E. S. Ball, Assoc. M. Am. Soc. C. E., of New York. The building is 70 x 25 ft. in plan, and 20 ft. high. The construction consists of 12 x 12-in. wall columns, spaced 7 ft. 10 in. centers, carrying 8- in. cross girders 22 ins. deep at the center and 16 ins. at the ends, reinforced by three 114-in. bars. The cross girders carry the 4-in. roof slab, reinforced by 14-in. rods, spaced 8-in. centers, and run- ning from girder to girder, forming a continuous roof slab. The wall columns are reinforced with four 14-in. vertical rods. The wall slabs were bui!t in place after the construction of the wall columns and roof girders, and are reinforced with rods, as shown. In the end of the building, where the boiler is located, the side wall is 6 ins. thick and reinforced as shown, to act as a storage hin for coal. The general features of the building will be under- é i 5 sbi ot J ' 1 Dyrall of Bectlan AA Iwside View Ourse Pew Fig. 346.—Crane Run Girder, Taylor-Wilson Mfg. Co.’s Shops. stood from the drawings. This building is a good illustration of a type of building of moderate size to which reinforced concrete may with economy be applied. It gives a fireproof structure at a moderate cost., A good example of a reinforced concrete building used to re- place the type of building so commonly used for what is gener- ally called ‘‘mill building construction,” is that used for the shop at McKees Rocks, Pa., for the Taylor-Wilson Manufacturing Co. This structure was designed and built by Mr. Robert A. Cummings, M. Am. Soc. C. E., of Pittsburg, Pa. The column and girder construction is of the Cummings system, described on pages 247 and 474. Figure 346 shows the general system of reinforcement for the crane-run girders. A cross-section of the main girder is shown in Section A-A. A cross-section of the shop is shown in Fig. 347. As will be seen, the main features of the 518 CONCRETE AND REINFORCED CONCRETE. building consist of Cummings columns, the outside column being 12 ins. square and about 16 ft. high. These support the walls of the lean-to. Two rows of interior columns 20 ins. in diameter and the side columns carrying the crane-run girders support the roof. These columns are reinforced with four vertical rods to which are attached a series of hoops 1% ins. wide and \% in. thick, spaced 4 ins. apart. The main girders of the building were designed for a 30-ton crane, and span 20 ft. between columns. A section of this beam is 18 x 36 ins. and has an upper flange, re- inforced as shown in the figure, to take care of the transverse thrust of the crane. The roof construction is a good example of the application of reinforced concrete arch slab. This concrete Fig. 347.—Cross-Section of Taylor-Wilson Mfg. Co.’s Shops. arch spans 54 ft. between supports and was made 4 ins. thick at the crown and Io ins. at the haunches. The arch reinforcement consists of 3g-in. bars 9 ins. on centers, running across the arch ring. These rods are laced together by 1 x % in. band iron, ar- ranged so that in case the rods at the intrados and extrados act in compression, there will be no danger of buckling. The thrust of the arch is taken up by tie rods made up of two 3 x 214 x qy-in. angle irons, spaced to ft. apart. These tie rods are bolted to two 10-in., 15-lb. channels, placed back to back, as shown in Fig. 348. The channels distribute the load due to the thrust between the rods. A light skewback casting was placed in the upper channel to act as a spacing bar for the roof rods and to transfer the thrust of the arch through the medium of the channels to the tie rods. Expansion joints were made every 10 GENERAL BUILDING CONSTRUCTION. 519 Ne Eres SS, SK parai"ling k 3 * = | | Sy YZ A x Hy i ed ! ' RS ae a it! Wit SS LY 4 D7 ~ Lar, 5 { on Vege 1 S - — : Or | | ls “ye =e ah ~ vengsialh “4 K i Me Piste ne a yu15 Ibs, T | hf Hess ae Ht a, abet | ' See eee | WS =—-—+— NS ‘ear t Fig. 348.—Tie Rod Construction for Arched Roof, Taylor-Wilson Mfg. Co.’s Shops. Dotted Lines - of Floor above Section A-B. loth Floor Plan. Fig. 349.—Plan of Tenth Floor of Ingalls Building. . . 1 ye. £ ipbit ' ‘ 1. a Ig Meee GOB E16 gn Mo BOB" hem Bonn dhe nnn pry i 1 = | 1 Width of Girders “A: Floors 3 10 5----- 20" ” he ipa eo---- 75 t-- 2a " Bite Mtic-16" Section across Bullding East and West, : (bet. Columns.) Fig. 350.—Sections of Tenth Floor of Ingalls Building. 520 CONCRETE AND REINFORCED CONCRETE. ft. in the arch to care for the large temperature stress that would naturally be developed in such a large thin area. Probably the most pretentious reinforced concrete building in ' N fia ¢ : ee 6 ae we “AU Bars shi 4 U bas [. [Bea Sd. pi dT 1 ak , : Section’ A-B. Section C-D. Oxia bs f iL va ; Section = Section E-F G-H. Fig. 351.—Typical Girder Construction, Ingalls Building. Spliced with 4,4 Bars wiredon-.. Wind Bars «3 Clwisted) Gearing Bars «:-%: Grovlar} Siooth and |. found, with Faced Ends ? i Nea ZH Concrete AS = Bracket 4 Stee! Hoops _ Twisted -- Ties around} Searing Bars > ke i ype Sleeve Join? Ol Grouted Line Hoops of 4 Twisted Stee? 7 ware Twisted ‘Steel Wind Bars, "trom Face of Goh Wired Splice Cross Section. Fig, 352.—Girder and Column Connection, Ingalls Building. this country is the 16-story Ingalls office building at Cincinnati, Ohio. This building is of Ransome construction. This structure is 213 ft. high from the sidewalk to the cornice, and is 100 x 50% ft. in plan. A row of interior columns running lengthwise of the GENERAL BUILDING CONSTRUCTION. 521 building divide it transversely into two floor bays, one 17.5 ft. and the other 33 ft. wide. Figure 349 is a plan of the tenth floor, and shows the location of columns and main girders, while Fig. 350 shows both longitudinal and transverse sections of the floor. The main girders are 36 ins. deep on the first floor, 34 ins. on the second, and 27 ins. on the floors above, and vary in width from 16 to 20 ins. The depth of the girders includes the thickness of the floor slab, which is 7 ins. on the first floor and 5 ins. on the floors above. The girders are so designed that they are fixed at the walls and columns. The typical girder construction is shown in Fig. 351; they have reinforcing rods and stirrups at both top and bottom. Inclined bars are used to stiffen the column and girder connec- tions to care for bending at the columns due to wind pressure. The connections at the columns are clearly shown in Fig. 352. The following list gives the number and size of reinforcing rods used in the various types of girders: Bars, Size, Length, Bars, Size, Length, Mark. No. ins. ft. Mark. No. ins, ft. I 4 14 10 II 2 % 6 2 2 I 13 12 2 1% 34 3 2 I 934 13 2 14 14 4 2 I 34 14 2 1% 11K 5 2 I 34 15 2 % 5 6 2 % y, 16 2 x 8 7 2 I 8% 17 2 4 7° 8 2 14 10 18 2 I 13 9 2 ay 11% 19 2 I 16 10 2 4, 5% he ate és ; U BARS IN LEFT-HAND SPAN. 4 Type X, %-in., 10 Type X, Y¥-in............ 5 ft. 4 ins. long. ta “Type: Y¥y ritscceccaanseeevercmeteeasnen 7 ft. 8 ins. long. U BARS IN RIGHT-HAND SPAN. LO: DARKS), WA ETM scevssacsuceveth sniebevecrtea toledo Aasarbetselinatsbeweend 4 ft. 4% ins. long. The floors are 7 ins. thick on the first floor and 5 ins. on all others, and are reinforced with a network of two layers of 34-in. twisted rods laid at right angles and spaced from 12 to 16 ins. center. The floors are divided by the longitudinal and transverse girders into panels 16 ft. square, and are figured as a flat floor slab supported on four edges. The floors are calculated for a live load of 200 lbs. on the first floor and 80 Ibs. on the second floor and 60 lbs. per sq. ft. on a!l others. The concrete used was. 522 CONCRETE AND REINFORCED CONCRETE. made of 1 part Lehigh Portland cement, 2 parts sharp sand and A parts I-in. crushed limestone or gravel. Both the stone and gravel were crushed and used without screening. Plain Arch Floors.—Reinforced concrete arches may be used in the construction of monolithic floors of wide spans. The thrust of the arch on the walls and the weight of the spandrel filling largely modify the form and rise of arches in buildings. The Fig. 353.—Arch Slab Floor Carried by Arch Ribs. great weight of the spandrel filling for erches of even moderate rise make the use of a flat arch imperative. A flat extrados with a horizontal reinforcement near its upper surface in addition to the usual intradosal reinforcement is the most common form. The upper reinforcement is supposed to modify the thrust, acting along the theoretical axis of the arch. This type of arch is an 7 ‘ vo ‘Bars 17 Bars ‘ ; fim mm ‘S30KE Kg 7-4 Pea = fd 1 1 £ ' Fig. 354.—Plain Arch Floor, Petit Palais des Beaux Arts, Paris Exposition of 1900. economical form of construction for heavily loaded or wide spar floors. Fig. 353 shows an arch floor of Hennebique construction with a span of 13 ft., supported by 50-ft. arch rib girders. The thickness of the arch is 3%4 ins. at the crown and 8 ins. at the haunches. The dotted lines show the location of the reinforce- ment in the slab. GENERAL BUILDING CONSTRUCTION. 523 The Winch arch, as applied to monolithic floor construction, is entirely analogous to that shown in Fig. 490, the only difference being in the end attachment. The rise of the arch is usually sy of the span. The two reinforcements are rigidly attached at the ends to an anchoring rod placed vertically in the side wall masonry. The Wiinch arch has been more extensively employed in bridge construction than in buildings. Figure 354 shows the section of an arch floor constructed in the Petit Palais des Beaux Arts at the Paris Exposition of 1900. A gallery of 6.10 meters (20 ft.) was spanned by this arch. The thickness at the crown was 3% ins. and 85% ins. at the springing aie = Se —t——-- Section ESF, Fig. 355.—Ribbed Arch Floor for Machine Shops at Nantes, France. paints. These arches were designed to carry a combined dead and live load of 220 lbs. per sq. ft. Ribbed Arch Floors.—Ribbed arches supporting a flat floor plate are more common than plain arch floors. Sometimes plain arches are used to span between arch ribs. Figure 355 shows a good example of a flat floor supported by arch ribs used by Henne- bique in the construction of a machine shop at Nantes, France. The clear arch span is 26 ft., with a rise of 6.5 ft. Figure 356 shows a longitudinal and transverse section of an arch floor, supported by arch ribs, used over a gallery in the Petite Palais des Beaux Arts at Paris. The ribs had a span of 524 CONCRETE AND REINFORCED CONCRETE. ieee ey cae rw ko gaye N6X6 Transverse Section. 10, 8 Bars ~SStimps IB sap a Longitudinal Section Fig. 356.—Ribbed Arch Floor, Petit Palais des Beaux Arts, Paris Exposition of 1900. 234 2U4 US BA3"L-Clip. 23 WOME oo. = ia Tag ty / oer - Section a-a Fig. 357.—Saw-Tooth Roof of Tile and Concrete Construction. GENERAL BUILDING CONSTRUCTION. 525 7.2 meters (27.6 ft.) and are spaced 3.48 meters (11.4 ft.) cen- ters, the latter distance being the span of the plain arches form- ing the floor. The ribs were 10 ins. thick at the crown and 24 ins. at the spring. The arch floor slabs were 27%; ins. thick at the crown = = Roof LEAS EEE st = S pW eee tbececes eee . 4-470 Reinforcement to Fhnor Slab. BT; @ Ties. a t ; ' ' ' i 1 t ‘ t ' ' ZY ' U ‘ ' \ u tg 2. im N Sectio ‘ t Ra retel Sone we, t Fig. 361.—Wall Construction, Central Felt and Paper Co.’s Factory. anchor the partitions securely to them. Figure 360 shows window and wall framing for main shop. ‘ The outer walls of these buildings are 70 per cent. window space, and consist almost entirely of wall columns, girders or belt courses and cornice, so that above the sills of the first-floor win- dows there is practically no wall surface proper. The character of the wall surfaces, belt courses and cornice is shown in Fig. 360. GENERAL BUILDING CONSTRUCTION. 535 Figure 361 shows wali con- struction used for the Central Felt and Paper Co.'s building, Long Island City. The above details show the usual type of wall construction used in. this class of buildings. When broader belt courses and vertical wall slabs are employed with a smaller percentage of window area, it is customary to use both horizontal and vertical rod reinforcement, and place one or more rods near the edge of the slab about all openings. Sometimes electrically welded wire or lock woven fabric is used for wall reinforcement. This material is especially adapted to the construction of thin curtain walls. At the edge of all openings it is customary to bend the fabric back into a U shape to strengthen the con- crete about the opening. ‘Hollow concrete walls were used in the construction of the Pacific Coast Borax Co. build- ing, Bayonne, N. J. The thick- ness of the two faces was 3% ins., with an air space of 9 ins. in the first story. Both the air space and the walls decrease in thickness in the top stories. The Fig. 362.—Section of Wall for GG a ni a a BG Barber Shop =a, reinforcement used is similar to Ingalls Building. that employed in the United States Shoe Machinery Co.’s build- ing. In the Ingalls building the walls are of concrete, 8 ins. thick, faced with marble in the lower stories and terra cotta in the upper stories. The concrete at the floor lines and between the top of the 536 CONCRETE AND REINFORCED CONCRETE. windows in the story below and the bottom of the one above con- sists of deep reinforced concrete girders. The reinforcement consists of two '%4-in. rods placed 2 ins. above the top of the win- dows in the story below, and similar rods below the window sill of the story above. The remainder of the wall was reinforced with Y%-in. horizontal rods spaced 2 ft. apart. Vertical reinforcing rods are also placed 2 ins. from each window opening. The marble and terra cotta facing is supported by projections in the concrete fitting into openings in the facing, forming a sort of dovetailing. Iron anchors tie the two together. Figures 362 and 363 show the details of construction. Fig. 363.—Elevation of Wall for Ingalls Building. Concrete Wall Construction Without Wooden Forms.—The Weiderholt system of construction is one in which no wooden or temporary forms are required. By the use of hollow tile blocks of special shape, a thin shell of fire clay or cement is used as the mould and forms the finished exterior surface. The tile blocks are H-shaped in plan, the two long sides forming the inner and cuter faces of the wall, while the web is reduced as much as pos- sible and only enough material retained to hold the sides together while the concrete is being placed and tamped. By cutting away ‘a portion of the web, space is secured for the horizontal reinforc- ing bars. By reducing the web as much as possible, practically a monolithic wall is secured. The vertical reinforcing bars are em- bedded in the foundation in the usual way and the tiles are laid between them, with horizontal bars at suitable intervals, after which the concrete is placed, the tiling and concreting being car- Stee! Bars GENERAL BUILDING CONSTRUCTION. 537 ried up as the wall progresses. This system is adapted to the construction of walls of buildings, grain and storage bins, chim- neys, etc. When used for chimneys a hard tile may be used, which will protect the concrete from the action of flame from the furnace. This type of construction is to be used for the smokestack of the Martin-Shaughnessy Warehouse Building, St. Louis, Mo. The smokestack will be g1 ft. high; for 50 ft. it will be 3 ft. in diameter inside, with walls 8 ins. thick; in the upper part the thickness of the walls will be reduced to 6 ins., giving an inside diameter of 3 ft. 4 ins. The reinforcement consists of 34-in. square vertical bars, spaced 12 ins. centers, and 4-in. square horizontal bars, 12 ins. centers in the lower section and 24 ins. apart in the upper section. A 1 Portland cement to 3 parts clean river sand will be used for the concrete. Fig. 364 shows the form Vert & Hor, Rods ,$'sq, B°G 106. | Bars to Lap @ at Joints eB" x Hig “x a x & Sectiorr Ld =~ A-B. h6al Wine, Fig. 364.—Wall Construction by the Weiderholt System. of the tile used for walls and chimneys. This system is being introduced by the Atlas Construction Co., St. Louis, Mo. Plaster Partitions—A form of partition extensively used in fireproof hotel and office building construction consists of a single or double mesh of wire netting or expanded metal lath, supported by posts of wood or metal fastened to the framing of the floor or ceiling of a steel building or bedded in the concrete of a reinforced concrete building and plastered over on both sides with an inch or more of mortar. While timber studding has been uséd in this type of wall, metal is most frequently employed. Small channels or round rods, spaced from 12 to 16 ins. centers, depending upon the height of the wall, are used for studding. The wire mesh or expanded metal is placed on both sides of the uprights and wired to them, leaving an air space between when a double wall is desired, or expanded metal lath is woven between 538 CONCRETE AND REINFORCED CONCRETE. the upright rods of a wall of single thickness. Both sides of the partition are then covered with plaster. The Roebling partition, shown in Figs. 365 and 366, are good examples of this type of partition. As will be seen, one of these is a solid partition, while the other is double, with an air space. ' KITA Section C-D, No l8 Gal Wire 1% ayn 4 oes LEB it "Ve./8 Gal. Wire Lacing Enlarged Section A-B. Fig. 365.—Soli@ Wall Construction, Roebling Type. At all openings timber or channel iron casings are provided, to which the mesh is firmly fastened. In Europe a slight modifica- tion of this wall is used, a single Monier netting, with the carry- ing rods horizontal and the distribution rods vertical, being em- ployed. When a thick wall is desired two slabs are built, with an air space between them. GENERAL BUILDING CONSTRUCTION. 539 Walls constructed of cast slabs, strengthened with some form of Monier netting, have been used in a few buildings in Europe, but, as far as the writer knows, have never been employed in this country. Hollow blocks, strung on vertical rods, is another form of wall construction sometimes employed in Europe. In America tron g a8 1 at t Cc % oO Hy 279. Elevation. Staple. Plaster. (hi BxRxg 74 xg Hip Air |\ Space Enlarged Section A-B. Air Space Sees FA Rey Fig. 266.—Hollow Wall Construction, Roebling Type. hollow concrete blocks, laid up in cement, have become quite popular in certain localities for wall construction. Their manu- facture is being developed as a new industry, and undoubtedly this form of building construction will be extensively used, as it is low in first cost and easily and cheaply put in place. Roofs.—Reinforced concrete roof construction is similar in 540 CONCRETE AND REINFORCED CONCRETE. many respects to reinforced floor construction. It may consist . of either reinforced roof slabs supported by steel framework or may be of monolithic construction. Reinforced Concrete Roofs Supported by Steel Framework.— These may be of two kinds—roof slabs moulded in advance and placed upon and attached to the steel framework and carefully jointed together with mortar joints, and roof slabs built in place. Any one of the numerous slab reinforcements already described may be used in the construction of roof slabs. Fig. 367 gives details of a reinforced roof slab of this type used for a warehouse of the Chittenden Power Co., West Rutland, Vt. This construc- tion consisted of slabs 9% x 4 ft. and 3% ins. thick, fastened IRA oe EA Section A-B, hi Part (Entarged.) AZ Vertical Section. Fig. 367.—Slab and Steel Frame Roof, Chittenden Power Co.’s Warehouse. directly to steel roof trusses spaced 9 ft. 8 ins. centers. The slabs were laid with their long sides parallel to the ridge and their ends resting on the double angle top chord of the roof trusses, so that a 2-in. space intervenes between the ends of adjacent slabs, as shown by the section AB ‘n Fig. 367. In constructing the slabs the retnforcement is allowed to project 2 ins. beyond the concrete, and when it is put in place the project- ing edges of the reinforcement lap across the open space. Before filling in this open space short %4-in. rods were driven through the mesh of the expanded metal, which was used for reinforce- ment, and between the back of the angles forming the top chords of the roof trusses. The ends of the rods were then bent over, so as to clamp the reinforcement to the chord. After the clamps are GENERAL BUILDING CONSTRUCTION. 541 placed the space between the ends of the slabs is filled with con- crete, thereby securing a practically continuous slab. The slabs were cast in special wooden forms, having their end-pieces in two parts, to allow the reinforcement to project out of the forms. A %4-in. layer of rich cement mortar is spread in the bottom of the moulds and the reinforcing mesh is laid on this mortar bed. The concrete is then dumped into the forms, thor- cughly tamped and trowelled smooth on its top surface. A stone concrete composed of a 1:2:314 mixture was used. The second form of roof construction of this type consists of N0.20 Gat Iron Flashing Plastic Aspratt. S Concrete _and Expanded Metal : LRing to be put in when, Concrete ia laid ~~, Ce ae Metal Clamps, 4' C106. & Filled with Cement . @0'T,and old ren Rods, 5'Onder Concrete for Root sea RY ‘Stone Cone: cS Smuts aS y td i wag is we “Cinder Concrete for Ceiling Sections of Concrete Beam. me AGE abot Construction for Locomotive Roundhouse, Canadian Pacific Railway. huilding the roof slab in place and surrounding the supporting metal framework with a projecting coat of mortar. This con- struction presents no unusual features, and is essentially the same in all particulars as floor construction supported by steel beams. A gocd example of type of construction is shown in Fig. 368. This shows details of a ribbed slab roof construction used for a round-house roof for the Canadian Pacific Ry., located at Moose Jaw, Assiniboia, Canada. The slab was of cinder concrete 3 ins. thick, reinforced with 3-in. mesh expanded metal, and the cross ribs were of 1:3:5 Portland cement gravel concrete reinforced with 14 and 34-in. bars. 542 CONCRETE AND REINFORCED CONCRETE. Monolithic Roof Construction—In this style of constructicn both the roof slab and the roof framing are of reinforced con- crete. This form of construction has been applied to all kinds of roofs, flat roofs, pitched roofs, arched roofs, domes, etc., some being of very elaborate construction. The flat and pitched roofs closely resemble ribbed floor slab construction. Examples of flat roof construction are shown in Figs. 322, 333 and 323, which show respectively reinforced roofs used in the Kelly & Jones factory building, the Central Felt & Paper Co. building, and the United Shoe Machinery Co. building. The hip roof of the Medical Laboratory for the FARCE SRY OP RRR “fla 7oe LTS Bar 6K Section K-K. Section of Girder «s* Section of Girder “D? 8 Half Inverted Plan. Fig. 369.—Roof Construction for Medical Laboratory Building, Brooklyn Navy Yard. Brooklyn Navy Yard is a good example of pitched roof construc- tion. The slope of the roof makes an angle of 30° with the horizontal. Fig. 369 shows details of this roof. A skylight opening 16 ft. 4 in. x 79 ft. long, was provided in the peak. This required two girder rafters “S” to extend con- tinuously over the peak between the wall plates. The inter- mediate rafter girders were cantilevered out 4 ft. 6 in. from the posts to support the skylight curb. A 1: 3:5 cinder concrete was used throughout this roof, making a very light construction. In laying the cinder concrete a rather dry mixture was used, and it was found that no other precaution was needed to keep it in place until hardened. A slate roof covering was placed over GENERAL BUILDING CONSTRUCTION. 543 the cinder concrete slab. The roof used for a fireproof warehouse at Los Angeles, Cal., is a good example of a reinforced concrete roof of small pitch and wide span. This roof has.a center to center span of 102 ft., and is 150 ft. long. The roof slab is 4 ins. thick and is supported by reinforced concrete girders spaced 16 ft. 6 in. centers. These girders are 6 ft. 6 ins. deep at the center and have a slope of 3 ft. each way from the center. The girders are connected by heavy curved brackets to the concrete wall piers, which are 2 x 2 ft. in sections, and reinforced by five 13 in. outside and two 34 in. inside rods. The girders are 14 in. in thickness and reinforced at the bottom with ten 1% in. rods of medium steel, two of the rods being straight and the others bent into a hog chain form. Stirrups of 1 in. by No. 14 metal anchor the rods securely in Fig. 370.—Roof for Firéproof Warehouse at Los Angeles, Cal. the concrete. Three 114 in, reinforcing rods 66 ft. long are used to reinforce the top of the girder. In addition to the roof load the girders have to carry a 16 ft. gallery on each side of the building. In designing these girders provision was also made for suspended tracks for a light travel- ing crane. Cross beams are provided between the girders dividing the roof into square panels. These beams are 6 x 11 ins. in sections and are reinforced with four 7-in. rods. The rein- forcement of the roof slab consists of 3-in. rods, 5-in. centers running in both directions. This roof is probably the widest span ever constructed in reinforced concrete. Fig. 370 shows a cross section of this building with a side elevation of the girder. The wide span roof construction used for the furnace house of the Northwestern Ohio bottle factory at Toledo, Ohio, is an unusual type of reinforced concrete roof. This building has a total height of 52 ft. above the lowest footing. The roof girders 544 CONCRETE AND REINFORCED CONCRETE. have an out to out span of 65 ft., and are made integral with the wall columns so as to form complete transverse bents 16 ft. apart on centers. The columns on one side of the building are 37% ft. high from the footing to the eaves, and on the other side are 8 ft. shorter. Their upper ends are connected with the lower end of the rafters 8x 8” Column ~at cach truss ie od Dowel soy 1 1 1 1 t | “FF cy 1 “FY ! i 4d 2 RA af ne : . 8-4"B RY Ter 1 7 4 ' bat 1 a M4" pois inteRion WALt 4 { SOLUMA COLUMN ‘i 1 al fd i An fs : Z beh fee ent re tee a Freee omer on - Pe mse ning SOR tg cree HE nee ene ol V LA N LOA © B AR. 2-4"Bars, Is-34”Burs over Doorway "Bare f 0% S-M4"Baraench way ty | [ Fig. 371.—Cross-Section of Bottle Factory at Toledo, 0. by tangent curves, which, with a curve at the peak, give the straight rafters somewhat the effect of an arch. Fig. 371 shows a cross section of the building, while Fig. 372 shows the size and arrangement of the reinforcing bars of the rafter girders and columns. The rafter girders are 18 x 40-in. cross section, and are reinforced by ten 1 in. bars near the top and ten 1 in. bars GENERAL BUILDING CONSTRUCTION. 545 near the bottom surface. The top chord bars are spliced and are made continuous to the foot of each side column. Five I-in. bars making an angle of about 45° with the vertical extend across the foot of the rafter and top of each column, and together with transverse shear bars thoroughly reinforce the curved knee brace. The lower chord bars extend in a single length through both rafters from one knee brace to the other, being curved at the apex of the roof. They are stopped off 5 ft. from the lower RL LE SX $-36"ire “bp DR a yg : a: $ Lie 1o-'" Bare: ‘4 “Ooile Fig. 372.—Reinforcement in Rafters and Columns, Bottle Factory, Toledo, O. end of the rafters, where a set of five I-in. bars in the same plane are lapped over them about 5 ft. and continue to the end of the rafters. The bars in the top chord and in the outer face of the column are made in three lengths, lapping 33 ins. and breaking joints at splices where they are inclosed by Ransome coil couplings of 1%4-in. steel. Five vertical 114-in. bars’ run in a single length from the footing to the top of the rafters to form the reinforcement of the inner face of the wall columns. 546 CONCRETE AND REINFORCED CONCRETE. The column reinforcing rods are held together by a coil of 14-in. bar with a pitch of 18 ins. The coil is made continuous by lapping the rods 12 ins. and wiring the joints. Coils of 1%4-in. rods in five sets connect the top and bottom rods of the rafters, as shown in the cross section and diagram. The pitch of the coils varies from 9 ins. at the crown to 18 ins. at the haunches. The coils are made continuous by lapping their ends 18 ins. and wiring them together. Each coil is given a full turn around the top or bottom pair of bars at every intersection, and the latter are fixed in position by spreaders between them at these points. The rafters are connected by horizontal longitudinal purlins Diamt Galv Irom Vents. “ Wood Floor Coa! Tar Wood Floor —_—_ Zeb Concrete Fig. 873.—Section of Bilgram Machine Shop, Philadelphia, Pa. 4 ft. apart on center. These purlins are 214 ins. wide and 18% ins. deep, including the thickness of the roof slab. They are reinforced with a single 34-in. bar 114 in. from the lower edge, and have %-in. sheer bars to reinforce the webs. Transverse struts connect the purlin at the center of the panels. These are 4 ins. wide and 18% ins. deep, and are reinforced with two 3g-in. bottom bars. These struts are made in two equal parts with a joint at the center line. The roof slab is unreinforced. The rafters, purlins, struts and roof slabs were constructed as a monolith. . A monitor four panels long and 20 ft. wide made entirely of reinforced concrete, with large windows in the walls, is located GENERAL BUILDING CONSTRUCTION. in the center of the roof, Other features of this’ building are shown in the drawing and need no special description. A concrete made of 1:114:3 mixture of Portland ce- ment, sand and broken stone was used for this building. This building affords an ex- ample of a recent type of Ransome construction. A type of roof especially adapt- M-in. . ed for machine shops: and fac- 20" Vent) tories is the saw tooth roof used in the construction of the Bilgram Building, Phila- delphia, Pa. This is shown in Fig. 373. The roof slab is 3 ins. in thickness and supported on inclined 8 x 10 in. rein- forced concrete beams. Galvanized ventilators are placed at the peak of each tooth and the skylights have galvanized iron frames embedded in the concrete. Details of con- struction, with the number and size of rods, are shown in Fig. 374. This building '2- Rods 17° 2-19 Rods ere ey See tail Fig. 874.—Saw Tooth Roof, Bilgram Machine Shop. was constructed by the Reinforced Cement Construction Co., of New York. Fhe Stamford, Conn., factory building, designed by the Rein- forcement Supply Co., and erected by Tucker & Vinton, of New 548 CONCRETE AND REINFORCED CONCRETE. York, embodies some unusual features and is of unusually bold design. This building is approximately 500 x 100 ft. in plan, and is divided into 25 x 50-ft. panels. The saw-tooth roof shown in section in Fig. 375 is supported by 50-ft. longitudinal girders carried by 15 x 15-in. colums. Transverse struts 25-ft. long span between the columns. The columns have an unsupported length of 24 ft. 8 ins. Details of the roof framing, size, number and location of reinforcement are shown in Fig. 375; while details of main roof girder and columns are shown in Figs. 376 and 377. Figure 378 shows a view of the building in the process of construction, part of the forms being still in place. The walls are constructed of ers nant BGs Ec: Detail under Window Frames. Section. Je) Fig. 375.—Section of Saw Tooth Roof for Factory at Stamford, Conn. cement blocks. The Bertine system of reinforcement is used throughout. Reinforced concrete may be used in place of timber or metal for the construction of all kinds of elaborate roofs. In arched roofs, arch ribs or girders similar to those described under arch floors are usually employed for wide spans. For domes, either a spherical shell reinforced with rods, or some form of Monier netting, or a shell with ribs meeting at the center of the top of the dome and reinforced in the usual manner may be used. It is customary in dome construction to support the dome with a circular concrete girder reinforced circumferentially. In Europe, Hennebique, Cottancin, Bonna, and others have GENERAL BUILDING CONSTRUCTION. 549 & oS kK: bh -9 fe pag bene Length 21 t= 8" t% 62". >< 64 ote sete BOB licen csnenenteenee i r rors KN ry os ee sw j IS SHH SARS PS 5 Ie iim 4 og [ans feet SF Ke 5 KANE BA" oe PA" 24H | 9g? \ ‘ Mark. Dia. a. b, e. d, Dia. Length. No. per To- : ins. ft. ins. ft. ins, ins. ins. ins. ft. ins. beam. tal, RODS Rey wees seseex seve I 517 4 ‘ Reo8 wesn seks | ees I 510 4 a Ro wees seee8 “Sewers g gree I 49 7 4 R20 need sewers Sages I 50 5 4 STIRRUPS. s.r I" 711} 3 107; “1 13 ts 811 36 432 S 2 1; - 7 AIt 3 10/5 I iy ts 9 3. «16 192 S 3) ts 7IIf 3 1075 I Gy t 9 5 24 288 S44 ST eadeitaees I abso ts 5 of 16 192 $5 SET tessa I ee as 4114 8 96 . RINGS a, * 3 ia gua I xs 14 8 96 b. 3 1 ts I 2 4 48 c. Bhan I fs 17h 4 48 d. 3° oe 1 ts III 10. 120 Fig. 376.—Details of Main Roof Girder, Stamford, Conn., Factory. see SMS oh ale ie ft ee ed rr er ee x ys on on ° ALD HIS ALS AIH “ee Wes KS 5 15x Details of Columns. Fig. 377.—Details of Columns, Stamford, Conn., Factory. | > 550 CONCRETE AND REINFORCED CONCRETE. executed many bold and elaborate designs for arched, domed and fancy roofs. One of the largest arch roofs ever built was constructed at Basel, Switzerland, for a railway train shed. This building is upward of 650 ft. in length with a width and arch span of 6514 ft. Hennebique constructed an arched roof with a span of 83 ft. on a factory at Rheims, France, in which rein- forced concrete and girders replace the usual steel ones. About half of the width of this roof is taken up by skylights between the arched roof girders. In America among the notable rein- forced concrete roofs are the dome of the University of Ottawa, Fig. 378.—View of Factory at Stamford, Conn., Under Construction. Canada; the dome for the Court House at Mineola, N. Y:, and the dome of the chapel of the U. S. Naval Academy at An- napolis, Md. The dome for the U. S. Naval Academy chapel is about 70 ft. in diameter, and consists of a shell of reinforced concrete covered with terra cotta. Figure 379 shows a plan and section of this building with linear dimensions. The dome springs from a reinforced concrete ring which transfers its weight to 24 supporting columns resting upon another reinforced ring, which in turn is supported by lateral arches carried by 8 main piers in the main wall. The 551 GENERAL BUILDING CONSTRUCTION. AS Section Vertical B. Ca eTee: Ciara ledides ‘Section, Horizontal Fig. 379.—Plan and Sections of Naval Academy Chapel, Annapolis, Md. 552 CONCRETE AND REINFORCED CONCRETE. K 267. > - Section’ C-D.- Lp Rod é ' ' tier ‘together / with Wire Wey Locking: Rode “x” (Enlarged.), Section A-B. Fig. 380.—Piers and Circular Girder Naval Academy Chapel. corbeled top of the main piers with sections of circular girder are shown in Figs. 380 and 381, while half plan and half eleva- tion with sections of same are shown in Fig. 382. The dome is surmounted by a terra cotta lantern weighing 120 tons. This is supported inde- pendently by the pyramidal framing of reinforced concrete, shown in the cross sections, which transfers its weight di- rectly to the walls. No perma- nent falsework was used except a light tower outside the building, which was used for hoisting the material. Details of framing of inner and outer shells are shown in Figs. 383 and 384. The de- tails of falsework and moulds for outer dome shell are shown in Fig. 385. The forms were kept on the concrete only long enough for the latter to harden, and were then raised about two feet and clamped in position for a new batch of material. The moulds for the outside face were first put in place and then those for the inner face hung from them. The rein- forcement and concrete were placed between the mould sides and allowed to harden for a few days. The moulds were then pushed forward and upward to conform with the desired curvature of the dome until, when the work had reached the crown, the men were working on a practically unsupported floor of reinforced concrete. Reinforced Concrete Roof Trusses.—If there is any one place in which reinforced concrete should not be used, it is in the con- GENERAL BUILDING CONSTRUCTION. 553 Section x-y i Section WeZ. Halt Sectional Plan Fig. 382.—Elevation and Plan of Circular Girder, Naval Academy Chapel. 554 CONCRETE AND REINFORCED CONCRETE. struction of roof trusses. It will be found in almost all cases that a more economical construction will be that of the usual type of skeleton steel truss. Where it is not easy to secure the Orx6 Gireular Boar Capping Cypola oS Yr.” Stirreps, vo” every 1 Gates “Srrrups every 8° 1 Fig. 383.—Plan and Section of Inner Dome, Naval Academy Chapel. steel, a wooden truss may be used and will prove more eco- nomical and certainly more satisfactory when it comes to a ques- tion of analysis of the strains in the trusses and the arrangement GENERAL BUILDING CONSTRUCTION 555 Vertical Section A-B. c-D. F i g. 384.—Details of Outer Dome, Naval Academy Chapel. 556 CONCRETE AND REINFORCED CONCRETE. of the details for the joints. Reinforced concrete enthusiasts have applied this form of construction in many cases to roof ee ‘, Ht 5 al ey oy WAZA eee 4 oy 1584 Fig. 385.—Falsework for Constructing Outer Dome, Naval Academy Chapel. trusses. In almost all cases, however, another type of construc- tion could with advantage have been used. For purlins and rafters where the usual reinforced beam may K gig l| 42” = a 2 . #7 HI é [F Brick Wall . 257g 25) i Longitudinal Section B-B yi a _ Bearing Pl, 20138" 4 es ana" fer 410" under each Triss Seat. ae % : : 4’ Rods, ! . l2°C.t0C. : UB Rods, a: 10°C.t0€. : : “Rods Brackets, 1 12107 4 te 4 ” il Moe ce Re AOR alle BB tad le 0g BIOS othe (3103 sal {2 Rods, 9°C.t06 aa 16 , 3g, 4%, Beth es Half Plan showing Ceiling. « Half Plan, showing Roof "(View from beneath.) ! (View from above.) 267 Section C-C, Enlarged. Fig. 386.—Plan of Roof Used at Atlanta, Ga., Terminal Station. be used, and for the roof slab itself, reinforced concrete may prove both satisfactory and economical; but when it comes to complicated truss work, it is the author’s belief that this type GENERAL BUILDING CONSTRUCTION. 557 of construction should be avoided, as there is little assurance that satisfactory connections will be made to care for the stresses at the joints. However, this treatise will not be complete unless a few examples of this type of construction be shown. In the construction of the Atlanta Terminal Station, reinforced concrete was used throughout for roof trusses, walls, floor beams, girders, columns, retaining walls, etc. Fig. 386 shows the roof construction of one of the buildings. The span between walls is 29 ft. 4 ins. The trusses were spaced about 13 ft. 10 ins. centers. Fig. 387 shows the general details, together with the reinforcing rods used for the main truss. For the main waiting room of this building trusses of 56 ft. 4 in. span were used. The details of construction, sizes of members, reinforcement, etc., are shown in Fig. 388. pe 4 Section of Section Section Top Chord . D-D. E-E Fig. 387.—Details for Main Truss for Roof Shown in Fig. 386. Stairways.—The strength, fireproofing qualities and edse with which it may be moulded into any desired form, makes reinforced concrete an excellent material for the construction of stairways. While reinforced concrete slabs moulded in advance and sup- ported by a wooden or metal framework, are sometimes used in place of metal or stone for treads and risers in stairways, the more usual method is to mould the steps in the top surface of an inclined slab which may or may not have ribs of reinforced concrete for string pieces. In the New York Rapid Transit subway stations two types of stairways are used. The first, details of which are shown in Fig. 389, is used for narrow stairways. This stairway is supported independently of the walls of the station. Two flights, with an intermediate landing supported 558 CONCRETE AND REINFORCED CONCRETE. “WOT}EIS [LUlUAAL vIUe[Zy 3% pasM uvdg 3J-YYy JO SSNLL JOOU—HRE “SlA hf UOIZIES 1DD1449,4 aKa r sdauys S 26 —p-— 290 ~— he 19 ==) 1D YPM sassny P Yoljesyu05 PUKY Oe psoys woyog ur Spoy jo spug jo u01498uULIO+ becom ! SS 3 bt A ce hacberdackei WN belt oe \F - mn Z << Leds ssopiig 2. ff of LL? fh i he. ‘aa fA i MeHES [L 9-9 ra rig 9-8 oy v = u0lj3ag 1G dae & re 014905 : ee ites ‘sedans *, GENERAL BUILDING CONSTRUCTION. 559 by four posts, are used. The construction consists of a plate notched on the top to form the steps, and plain on the under side, carried by and built in one piece with two reinforced con- crete string girders, one on each edge. These are supported on columns and on top and bottom supports. The string is rein- forced with one bar near its lower edge; a 34-in. rod reinforces each tread, as shown in the drawing. The second type, used for wide stairways, is shown in Fig. 390. This stairway also consists of two flights and an intermediate ianding, but is without string girders. One side of this stairway 8%6'Columm. _ PX6%Co!. eye c ; i All eu al ora WW n-—~ == DS 5S She = == Gp nne K K i < | ! i 8 Section x 6-H . his sedis 8 | Cement aa 4 f is ‘aad Be 8x8 Col, § " % 4,3 Bars ae = &,, : 8 SIS - FOR cone Pky D vey ee § + , Section Section A-B. c-D. Fig. 389.—Narrow Stairway Construction, New York Rapid Transit R.R. is supported throughout its height by the side walls and sup- porting columns are only used on one side. The stair plate is reinforced with longitudinal bars on the tension side, supple- mented with short compression bars at points directly over the columns. Two heavy bars run transversely through the plate over the column. The reinforcement consists of cold twisted square steel ‘rods with an elastic limit of about 60,000 Ibs. A 1:3:5 Portland cement concrete of 34-in. broken stone or gravel was used. The panel faces and tread surfaces are finished with 1 in. of 1:2 560 CONCRETE AND REINFORCED CONCRETE. cement and sand mortar laid with the concrete. Safety metal treads are fastened by lugs embedded in the tread surface. The stairways used in the Medical Laboratory Building in the Brooklyn Navy Yard consist of slabs having plain bottoms and tops notched to form the treads and risers. They are ail in straight runs with landings intermediate between floors. The reinforcement consisted of 1%4-in. rods spaced 6 ins. apart, reach- ing from floor to landing, and 1%4-in. transverse rods 12-in. cen- ters between partitions. The stairways used in both the Pacific Coast Borax Co. build- t s 106". Abiaicnindracetn Sa | 5 v “8 Bars section A-B. 36" hoo i210" He. ' 1 ! ' ' i ~---=-) wb bars 6.106. : FL 24.93, Fig. 390.—Wide Stairway Construction, New York Rapid Transit R.R. ing and the Kelly & Jones building, mentioned on pages 499 and 500, were made with triangular horizontal steps moulded in the shops and put in position after sufficiently hardened. They were supported at each end on inclined string pieces of reinforced concrete. The details of a portion of one section are shown in Fig. 391. In the Kelly & Jones building the string pieces were inclined girders about 3 ft. deep and five ft. apart over all, and have their lower flanges flush with the under sides of the stairs and their upper edges moulded to serve as hand rails. The inner face of the 2-in. solid web is plain and the outer face is paneled. They are reinforced by a single 1-in. bar in the lower GENERAL BUILDING CONSTRUCTION. ‘501 flange and a %-in. bar in the upper flange. The lower flange is also reinforced by a 4 x § in. rectangular coil of %4-in. twisted ait qT To J he # i i ye IA! | OF XN ? A ' | No Xt A! ee ee U-Bar in every ae = nae Alternate Step . \ Ne * Detail of Concrete Steps in Stairway, Fig. 391.—Stairway with Separately Molded Steps, Pacific Borax Co.’s Factory. 74! Bars (Ce —$—$——$— r ae > ——— 7 + | ieee Ye" Coil 4" Pitch full Length of Stringer fe Section 2-Z Main Stairway Fig. 392.—Stairway for Kelly & Jones Factory. steel with a 4-in. pitch enclosing the tension rod from end to end. Stirrups are provided about the lower bars to take care of 562 CONCRETE AND REINFORCED CONCRETE. the shear in the stringer. The lower flange of the stringer pro- jects inward to form a seat for the steps (Fig. 392). A stairway of the Hennebique construction is shown in Fig. 393. The reinforcement consists of the usual straight and bent rods used in floor slabs, and stirrups at each step to tie the rein- Fig. 393.—Stairway for New York City Residence. forcement to it. This particular form of construction was used in the residence of Mr. W. C. Sheldon, New York. When overhanging stairs are desired they are cantilevered out as shown in section (Fig. 394). A large reinforcing rod is placed near the outer edge of the slab and firmly anchored at its ends. This Fig. 394.—Overhanging Stairway Construction. rod is passed through the loop at the end of the double canti- lever reinforcement. Small longitudinal rods near the bottom of the slab rest upon the bottom portion of the cantilever reinforce- ment. Stirrups are placed at increasing intervals apart from the support toward the end. Shaft Hangers——It is essential to provide some means of attaching machinery and shafting to the ceilings of factory build- GENERAL BUILDING CONSTRUCTION. 563 ings. Wood and iron construction present no special difficulties, but special arrangements are necessary when reinforced concrete is used. It is desirable that the system adopted be as flexible Wood Fillers ------ Angles." Cast Iron Clamp--* Anchor Bolt" A “T"Headed Attaching \ Bolt, in Slot Fig. 395.—View of Angle Slot Hanger Construction for Shafting. as possibie in order to secure great freedom in the location of individual machines. This is especially desirable, as methods of manufacture as well as modern machinery are constantly being improved, and so great are the Lp ety, % hy Cols gts changes that new machinery or zw. ie a ie G C4 Concrete acd = DEA! Washer | | ae one i Pig, 37sec of or Pane an entire change in the arrangement of the old is often neces- sary. The method of attachment used in the United Shoe Ma- chinery Co.’s building described on page 502 is the most flexible known to the author, and is the invention of Mr. H. P. Jones, of Yonkers, N. Y. ‘ 564. CONCRETE AND REINFORCED CONCRETE. To provide fastenings for shafting, “machinery, etc., anchor bolts 3 ft. on center were built into all transverse floor and roof girders. A transverse line of bolts alternately spaced 1 ft. and 6 ft. centers was built in the middle of each floor and roof panel. The bolts built into the girders had their upper ends bent at right angles and have nuts on their lower ends en- gaging cast-iron saddles that clamp against pairs of 21%4 x 2 x fs in. angles with wood fillers, Figs. 395 and 396 show this S : SS = SS 3 7 Ss ~ \ AS SSS) SPER ~ RON ‘ RR WON ANS, SSNS Ss SSSAY AM x ROS SSS SSS SNS SSS ‘A. iz e : CGS BZ Cirder Vee Lee: iy ‘A ~ ss SS S SS . @s Ss S SS WS ANS . S < NS SS LOY SS S ~ NN Bolt for Attaching Hangers ere" hp CNN EG eel CO PNR GLEE Tay CL SSOS SSS SSS Soa <> SoS Ss ZSESe oS 4 I Z2 |UKA Holding Down a ee wi Hf tf NES Sane A tee SS ll iy tli Late Se Sa eT 4 ga § Bott 4%a" F' Bolts Core for Wall Column. Mould for Corner Wall Column. Fig. 411.—Core for Hollow Column, Kelly & Jones Factory, Greensburg, Pa. l ia ; Bs 24-4 SI } - ey! ete at ee IL rm ie == 15"— 4 - $ J a —¥ fr HARLAN ul be? ne Wes es co oe & aa WLLL ui ‘ S| 1 Reh ON 1 ! S| NONE | FAS! N ZN 5 S|! N Nis ' ' S Ad \ NN * \ oa WLLL i tl | 20"Centers, fetal A. a | (rr mM cn ry 2 Nailed. Vea? te td oH iz Mould for Wall Column. Fig. 412.—T-shaped Column Form, Parkville Sub-station, Brooklyn Fig. 418.—Column Form for Atlantic Rapid Transit Co. City Hotel. mould was used in the construction of a water tower at Borden- town, N. J. When fluted columns or other special surfaces are desired the 582 CONCRETE AND REINFORCED CONCRETE. interior of the mould is covered with strips of wood or plaster o1 Paris to secure the desired surface. Moulds are sometimes removed in from two to six days after the concrete is put in, but it is desirable to leave them in place fur two weeks, and if possible for a longer time. Hooped columns are sometimes constructed without special forms. The method of moulding columns reinforced with expanded metal, surrounded by metal lath, which acts as a mould fer retaining the concrete, is fully explained on page 475 in connection with a description of the Thompson & Norris Building. Another method used in the con- struction of hooped columns for the Bush Terminal Co.'s building is described on page 477. In this column concrete shells are used _} 2’Bo1r 2 Bor | ja 1x12 Plarh 26 Timber 5 x ae y x uy 2%2’Imber D Fig. 414.—Column Form for Water Tower, Bordentown, N. J. to act as a form for the core concrete and to hold the reinforcing metal in its correct position. Centering for Floor Slabs Between Beams.—The coustruc- tion of centers for slabs and arches used as a floor filling between beams is a comparatively simple process. The centers usually consist of flat or curved lagging carried on straight or archea joists suspended from the steel beams or girders. When the floor slab rests upon the top flanges of the beams the lagging joist may rest upon the bottom flange of the beams, as shown in Fig. 415. When the filling slab consists of either a flat floor plate or floor arch and rests upon the bottom flange of the beams the lagging is sometimes hung from the bottom flanges by hook bolts, as shown in Fig. 416. When hook bolts are used to support PRACTICAL CONSTRUCTION. 583 forms from bottom flange of beams and the bottom flange of beam is protected by a layer of concrete, the hook bolts have to be sawed off flush with the face of concrete. This may be avoided by using the form of*hanger shown in Fig. 417. By greasing the bolt before it is put in place it may be unscrewed and removed. Another form used for the floor filling between steel beams is shown in Fig. 418. This form has the lagging supported by the Fig. 415.—Form for Floor Slab on Top ~ Flanges of Beam. Fig. 416.—Form for Floor Slab on Fig. 417.—Hanger for Floor Bottom Flanges of Beam. Slab Forms. main timber A, which is 2 x 4 ins. for spans not exceeding 6 ft., and the whole is carried by the 2 x 3-in. timber B, resting upon the bottom flange of the beams. This latter piece is secured at the outer end by a cleat C nailed to A and at the inner end by cleat D, also nailed to timber A. The cleat D serves to support the battered boards and cross cleat G, carrying lagging below bottom_ flange of beam. The nail F is only partly driven, and when it is Fig. 418.—Center for Floor Slab Between Steel Beams. desired to remove the form it is withdrawn and cleat C knocked off and B withdrawn. : When the lower flange is not fireproofed the battered lagging rests against the lower flange and part of the timbering is dis- pensed with. For larger beams the spacing block K shown in the right-hand part of Fig. 418 is used. For small beams B may be omitted and A allowed to rest directly upon the flange of the 584 CONCRETE AND REINFORCED CONCRETE. beam. When this is done it is necessary to saw in two the timber A to strike the forms. Wire ties are sometimes used to support the lagging, being attached to the beams through holes punched in the top flanges, and pass around and support scantling, which in turn support the lagging. ; When two Monier slabs are used it is at times customary to fabricate the lower slab in advance, then block it up to the level of the under side of the top flange, construct the top plate upon it as a center, and when the top slab has sufficiently hardened lower the bottom slab to its seat upon the bottom flange of the beams and plaster over the exposed bottom flange to protect it against fire. This leaves an air space between the two slabs. Sometimes this space is filled with a meager concrete up to the level of the second slab and the latter constructed upon it as a center. In the construction of the Donath, Roebling and some forms of arched expanded metal floors the concrete is supported directly upon the metallic reinforcing web, and false centers are unneces- sary. After putting the centering in place the usual procedure, when the expanded metal and various forms of Monier lattice systems are used, is to place the reinforcement directly upon the lagging, then deposit a single laver of concrete upon top of it. Some- times an effort is made to draw the netting up into the concrete ‘by means of hooks and work the concrete under and around the metal. These are very unsatisfactory methods, as in the first case it is necessary to leave the meshing more or less exposed or plaster it over afterwards, and in the second case the final location of the meshing is very uncertain. A better method is to place a thin layer of concrete upon the centering, lay the netting upon this, and then deposit the con- crete, ramming it into place until the level of the second rein- forcement is reached; put it in place and cover it with concrete until the proper thickness is secured, or when a single reinforce- ment is used carrv the concrete to the top at once. This method is always employed when single bar reinforcements are used, care being taken to properlv space the rods. Jn the Columbia, Miiller, Wiinch and Melan systems, owing to the stiffness of the rein- forcement, it is not difficult to locate it in the proper position, PRACTICAL CONSTRUCTION. 585 Upon, the correct location of the reinforcement in the slab, and the placing of the concrete in such a manner that it will act as a monolith, the strength of the floor slab and the utility of the con- struction depends. These requirements are essential to secure the strength and stability of the construction, and too much care cannot be taken to see that they are properly carried out. Care should also be taken when expanded metal or wire mesh reinforcements are used to cut the sheets to the proper length. If they are too long, the workmen sometimes, instead of cutting them to proper dimensions, try to force the sheet down into place, and the resulting location of the metal and its utility as a ten- sion member becomes of doubtful value at best. When no ceiling plate is used the lagging must be dressed smooth, or objectionable marks will be left upon the concrete. The surface of the lagging should be coated with soft soap or grease to prevent the concrete from adhering to the boards ; some- times oiled paper is used. This is very important, as every pre- caution must be taken to keep the centers from sticking to the concrete; otherwise difficulty will be experienced in striking the centers, and if force be used the concrete will be permanently injured. Under no consideration should the lagging be jarred loose by blows from a crowbar or sledge. Monolithic Floor Construction.—The ordinary type of mono- lithic floor consists of main girders spanning between walls and columns and supporting floor ribs at right angles to them; these latter in turn support a flat floor slab. Two methods of construction are employed: First, the forms for the girders are built up to the level of the bottom of the cross beams, and the concreting brought up to the same level; then the forms for the cross beams and girders are carried up to the bottom of the floor slab and concreted to the same level, after which the slab forms are constructed and the concreting finished. Second, the entire construction of the given floor or floor section is built up as one continuous operation and make a perfect mono- lith. The first method is commonly used in Europe, but in this country the more truly monolithic construction of the second method is most frequently used, and deserves its well merited popularity. While the methods in both cases are essentially simi- lar, and the forms used vary but little in general detail, both 586 CONCRETE AND REINFORCED CONCRETE. methods will be described and illustrative examples given of forms used on important constructions. he moulds for the girders are usually supported at their ends by the column and wall moulds. Either extensions of the frames are run out or cleats are nailed on the sides of the forms to sup- port the ends of the boxes. Between columns the mould boxes are supported by posts resting upon double wedges for adjusting their height. The Hennebique type of mould is constructed of a bottom piece B (Fig. 419), and supported at intermediate points by vertical posts and at the ends by the column and wall moulds. Two side pieces B’ reach up to the level of the under side of the secondary beams. These side pieces are held together by clamps, as shown in Fig. 420. The clamp shown is for use in small beam LLL LLL LLZEEB c Fig. 419.—Hennebique Form for Slab and Girder Floors. and column construction. It consists of the hook A, made from a 4 x 1%4-in. iron flat by bending one end to a curve, as shown. The dog B is of square iron, with one end slightly bent to form the jaw, and has a hole at the other end somewhat larger than the shank of the hook piece A. The dog is slipped upon the shank and tightened by hammering on the lower end until it jams. The outward pressure of the form boards upon the upper end causes it to bind and prevents it slipping back. If need be, a wedge of wood may be driven in to assist in tightening the clamp. This form of clamp is used in both column and beam construction. It is usually desirable to construct the bottom of the girder or beam mould of one piece of timber, but when the beams are large PRACTICAL CONSTRUCTION. 587 and the span wide two or more pieces may be used, care being taken to so fasten them together that the top surface of adjacent pieces will remain flush at splice points. Care must be taken that the top edges of the side pieces B’ are level with the lower side of the cross beams, as the sides of the boxes for these will rest upon the top edges. Chamfers for the bottom of the beams or girders are formed by lightly nailing triangular strips in the bottom corners. When this portion of the form’ has been constructed it is cus- tomary to tamp concrete in the bottom of the form to the thick- ness desired below the reinforcement, place the reinforcing rods in position, together with the stirrups, and hold the latter in End POON Elevation a om | | 1) Side Elevation. Fig. 420.—Hennebique Clamp for Floor Girder Floors. c place with small mounds of concrete; then bring the concrete up to the bottom level of the cross beams. The bottom and sides of the moulds for the cross beams are now put in place. The bottom C is supported at the ends by cleats nailed to the sides of the main beams, and intermediate posts support it at frequent intervals. The side pieces C’ rest on the side of the girder moulds, and are held together by clamps at the bottom and pieces of board nailed to the top edges. The level of the top of the sides C’ of the secondary beams and the additional side pieces B” of the primary beams are made so that when the bottom boards of the 588 CONCRETE AND REINFORCED CONCRETE. floor lagging rest upon them their top surface will be at the cor- rect elevations of the under sides of the floor slabs. The planks forming the top side pieces of the primary beams are held together by pieces nailed to the side and distance pieces nailed to their top edges. The main and secondary beams are now moulded up to the level of the under side of the floor beams. The floor centering is next put in place and the concreting con- tinued as rapidly as possible. The floor lagging is supported on the top edges of the sides of the principal beam boxes and runs parallel with the secondary beams. The edges of the outside plank in each panel rest upon and are even with the inside of the cross beam sides. Cross timbers, supported at the ends by cleats nailed to the sides of the cross beam boxes, or sometimes supported by posts, are placed at proper intervals to keep the floor planks from sagging. Fig. 421—Girder Form Used in Ingalls Building, Cincinnati, O. Care should be taken to keep the beam and girder boxes in line, and in all cases proper spacing should be rigidly maintained. Fig. 421 shows a girder form used in the construction of the Ingalls Building. These moulds were carried on timbers between column moulds and by posts at the center span. It is sometimes desired to remove the sides of the beam and girder moulds before the floor is constructed. In order to do this the sides of the boxes are run up to the level of the under side of the floor. When the concrete is sufficiently hard the sides of the boxes are removed and the floor lagging put in place between the beams. The lagging is held at the proper eleva tion by cross pieces resting upon timbers clamped at the proper height to the side of the cross beams and supported by props. Another method is to lay transverse lagging upon longitudinal timbers supported by posts. Fig. 422 shows a form of indepen- PRACTICAL CONSTRUCTION. 589 dent mould for a floor panel. When in place the concreting is carried on as before. Many modifications of the above described type of floor forms are used. Fig. 423 shows a modification of the Hennebique forms, in which the clips are omitted and a slightly different arrange- ‘ment of the side plank and lagging used. The parts are fastened together with wood or lag screws. Fig. 422.—Independent Mold for. Floor Panel. The methods of construction used in the United Shoe Machinery Co.’s building are a good example of the best practice in reinforced concrete building construction. The following description of the manner of conducting this work is slightly condensed from an article in “Engineering News” by George P. Carver, Resident Engineer for this work. After the foundation walls and footings for the columns had Fig. 423.—Modification of the Hennebique Forms with Clamps Omitted. been completed the clay sub-grade of the floor was leveled and well tamped and a 4-in. layer of concrete laid and rolled for the sub-floor. When the sub-floor had.set, spiral coil and rod rein- forcements for the lower ‘intermediate columns were set up and inclosed in a column form set to line and temporarily braced. The lower columns were 22 ins. and octagonal in shape. The exterior columns on one side of each building were constructed to act as 590 CONCRETE AND REINFORCED CONCRETE. hot-air flues. Before setting the forms for these columns a hollow brick lining was built up to the grade of the next floor and the brick lining was mopped with asphalt. This lining was then encased in a rectangular wooden form, allowing from 8 to 12 ins. thickness of concrete around the brick. The columns were rein- forced with vertical rods and hoops placed at intervals through- out the height. The column forms used in this building are described on page 577. When all the column forms had been set and temporarily braced the forms for the girders were set up, resting upon tall horses spaced about 3 ft. centers, the ends of the girder forms fitting with the top of the column forms. Figure 424 shows details and material for the beam and girder forms. 3'Floor Fig, 424.—Girder Form, United Shoe Machinery Co.’s Factory, Beverly, Mass. These girder forms consisted of a bottom board set on the horses and sides made up of short pieces, having U-shaped open- ings for the beam forms, which were set in a manner similar to the girder forms. The girder forms extended entirely across the building on each row of columns, which were 2o ft. apart. Mid- way between these girders was placed a bridging beam form entirely across the floor, and between the girder and bridging beams running across the building were set the floor beam forms, about 10 ft. long, spaced between 3 and 4 ft. apart. The forms for the floor slab and beams consisted of bottomless boxes made with outer dimensions exactly conforming to the clear distance between beams and girders. They were spaced to secure the proper location of girders and beams and with their upper PRACTICAL CONSTRUCTION. 591 surtace in the plane of the lower surface of the floor slab. Their ends and sides thus formed the vertical sides of mould for the floor beam and girders, The bottoms of these moulds were made hy horizontal strips, being fitted between the adjacent boxes. The boxes are supported on their lower edges by the column moulds and on intermediate supports under the beams, as indicated in the cross section. The upper sides of the boxes are formed with 5 x 114-in. boards laid lengthwise, battened. together on the under side and supported on cross strips 3 ft. apart. The upper edges are rounded to a 134-in. radius, and small triangular shaped wood fillets were placed in the lower angles of the beam and girder moulds to prevent sharp corners on the concrete. Splayed joints between the sheathing boards were used to prevent damage from swelling. The beams and girders were so located as to secure uniform distances between them, thereby enabling the moulds to be used several times. Moulds were pro- vided to construct a complete floor. The sides of the beam and girder forms were temporarily held apart by strips of the required length. These were taken out as the concrete was poured. When the column, girder, beam and floor forms were all set and secured to line and grade the columns were poured up to the level of the bottom of the girders and allowed to set. The columns were poured in the following manner: A mixing board was placed in close proximity to the column to be poured and a bucket of con- crete from the cableway was dumped upon this board. In this © connection it is necessary to state that a mixing plant was erected at one side of the work, a large Ransome mixing machine being used, and’the concrete conveyed to the particular portion of the work under construction by means of a cableway. The concrete was usually very wet and of 1 : 2 : 4 mixture of small crushed stone or gravel. Previous to pouring a column the form was cleaned of all small blocks of wood, shavings and sweepings which had gotten into it. A stream of water from a 34-in. hose was then turned into the column. The first I or 2 ins. of material put into the column form consisted of a mixture of I to 114 grout, to make a good bond between the old and new concrete. The con- crete from the mixing board was shoveled on top of this grout, and men with 14-ft. cutting tools made of wood and pointed with metal worked the concrete in between the reinforcement and the form, while a man with a heavy tamping tool rammed the con- 592 CONCRETE AND REINFORCED CONCRETE. crete inside the coil. Good results were obtained, and very few voids showed in the concrete when the forms were removed. In the bottom of.the girder forms and on a beveled wood strip 1/2 in. high, to form a slot in the bottom of the girder, holes were bored, 34-in. in diameter, over which were set small castings holding 34-in. anchor bolts, which projected down through the forms the required distance, for use later as a means of supporting shaft hangers. For a detailed description of the shaft hangers used see page 563. All surfaces coming in contact with the concrete were oiled to enable the forms to be readily removed. After the system of anchor bolts for. the shaft hangers had been installed the forms were treated with a coating of crude oil and the steel placed in the bottom of the beam and girder forms. A small supporting template of concrete was made the width and shape of the beam and 134 ins. thick and grooved on top in as many places as there were rods for the form. These blocks were used to hold the steel in position and keep it the correct distance from the sides and bottom of the forms, and were left in the forms. The rods placed in-the bottom of the beam and girder forms vary in size from 14 to 1 in., according to the depth and width of the beam. These bottom rods are of a sufficient length to have a bearing on the columns at either end, where they are lapped and fitted with a coil coupling, which consists of a coiled spring of flat band steel : loosely placed around the lapped ends of the rods. In connection with these bottom rods are placed U-shaped bar stirrups, the lowest part of which are under the tension rods. These U-bars for the most part were 14-in. twisted steel rods, and were usually four in number at each end of a beam, to strengthen the beam for vertical shearing strains. They are placed at increasing distances from the column toward the center of the heam, as 8, 12, 16 and 20 ins., these distances depending upon the depth of the beam. The U-bars were secured to the tension rods with wire, and were held in place by a line of wire running between the tops of the same. Great care was taken in the inspection of this. work to see that the steel was clean and free from rust scales. A thin coat of rust was thought to do no harm, and probably 90 per cent. of the. steel had a thin coat of rust; but if the steel was coated with rust scales before placing it in the forms it was treated in a pickling bath of PRACTICAL CONSTRUCTION. 593 sulphuric acid anc water, which effectively removed the rust. In some instances the rust was removed by the use of a wire blush. When the tension members and the U-bars were in place con- creting was commenced. Usually a gang of twenty-five or thirty men handled the concrete, which was delivered in buckets by the cableway. Sections 50 and 60 ft. long were poured at one time, this being the distance between the expansion joints, as explained on page 566. When the pouring was begun a 1:1%4 mixture of grout was first used to fill in around the steel in the bottoms of the forms. This grout was well worked in and cut with tools so that every part of the steel rods would be covered with concrete. The 1; 2:4 fine gravel or crushed stone mixture was then shoveled from the mixing boards into the beams and girders on top of the steel and continually cut and tamped with a tool shaped like a hoe with the blade turned down in line with the handle. In this manner the concrete was brought up to the top of the beam, when the cantilever rods were placed. These rods were laid along the beam, the centers of the rods being on the tops of the columns and with their ends abutting. After placing these cantilever rods and embedding them in the concrete, the beams and girders being brought to this height, a layer of concrete, varying in thickness from 1% to 34 in., was spread over the floor area, and on this were laid 14-in. rods, spaced 1 ft. centers and running across the floor. The ends of these rods lapped 9 ins. usually over a beam. On top _of these rods were placed a layer of concrete of sufficient depth to bring the floor slab up to within 1 in. of the finished grade. This layer was well rolled with a metal sheathed roller about 30 ins. in diameter and weighing 250 lbs. The wearing surface was laid on this base within an hour or two after the floor -was poured. The wearing surface was screeded to a level surface and then troweled until a smooth surface was obtained. In hot or rainy ‘weather the floor surface was protected by a canvas covering spread over a temporary framework over, the section being fin- ished. After the wearing surface had set it was spread over with a layer of wet sand, the sand being kept wet continually for a period of about ten days. The moulds were removed at the end of fourteen days, cleaned, repaired and set up for the next floor.. Intermediate posts were retained under the middle of the beams for several days longer A very careful supervision was carried on by a corps of able 504 CONCRETE AND REINFORCED CONCRETE. inspectors. This resulted in securing a very satisfactory class of werk. Figure 425 shows a girder and column forms used in the con- Hide Section A-B Fig. 425.—Girder and Column Form for Minneapolis Warehouse. struction of a warehouse at Minneapolis, Minn. The materials used are fully shown in the figure. These forms were light in weight and easily erected and taken down. Fig. 426.—Slab and Girder Floor Mold, Central Felt and Paper Co.’s Factory. Figure 426 shows girder and floor mould used in the construc- tion of the Central Felt & Paper Co.’s factory, Long Island City, N. Y. Details of the construction are shown clearly in the sketch. By the withdrawal of the lag screws the bottom pieces were easily PRACTICAL CONSTRUCTION. 595 detached from the vertical sides. Both the bottom and side pieces were supported independently on transverse cap planks resting upon 6-in. x 8-in. posts spaced 6 to 8 ft. apart on the center line of the girders. The bottom piece consisted of a single plank from t to 3 ins. thickness; the side pieces of 4 x %-in. boards nailed to 2 x 4-in. top and bottom hori- zontal pieces. A third 2 x 4-in. 2 horizontal piece was placed near ae ® the top to support the joist : : i x carrying the lagging of the floor slab mould. Vertical _ strips under the ends of these joists transmitted their load to the lower horizontal strips and post J lI I SECTION 68 | F ! 4 é a = Se Sa all = all a P= caps. The lower edges of the ‘ side pieces were temporarily * 7 screwed to the bottom pieces, 4 = | and the upper edges spaced by cross-ties, from which the rein- forcing rods were hung until the concreting was begun. The 5% first boards of the floor slab lagging were nailed to the edges of the side pieces and to the ends of the joist; the other boards were laid loose. After the floor slab concrete had set about seven days, the floor joists were turned on their side faces and the lagging lowered a few inches below the ceiling. A few days later the side: pieces af the girders a Fig. 427.—Beam Mold and Slab Cen- unscrewed and removed, the ter, Atlantic City Hotel. bottom pieces being left in place some three weeks longer, until the concrete had thoroughly hardened. In this construction the reinforcing rods were wired together and fixed firmly in place in the moulds before the concreting was begun and so held that they would not be displaced by ramming. [ | | | | WINDSTRUT SECTION AA 596 CONCRETE AND REINFORCED CONCRETE. Figure 427 shows beam moulds and centering used for support- ing the hollow tile and reinforced concrete floor construction used 4 Fig. 428.—Girder Forms, Central Pennsylvania Traction Co.’s Car Barns. 7", 4 xe thick ©. \ Bi ms pore. ‘ VA / / = ‘24 8 Flaned Boards Bk 7 Te Kb" J Bien gS « Gy Bx 1 AY r FR “Nails Clinchea ul MF age BxA" Fig. 429.—Slab and Girder Floor Forms of Unit Concrete Steel Frame Co. in the construction of an Atlantic City hotel, designed by the Trussed Concrete-Steel Co., Detroit, Mich. Figure 428 shows the forms and centering supporting them used in the construction of the shops and car houses of the Central Pennsylvania Traction Co., Harrisburg, Pa. PRACTICAL CONSTRUCTION. 597 The framing of forms for columns, girders, beams and slabs shown in Fig. 429 are recommended by the Unit Concrete-Steel Frame Co., of Philadelphia, Pa., to whom the author is indebted. for the drawings. The method of framing and wedging scaf- folding to support forms is also shown. The posts may be loosened by knocking out the wedges upon which they rest. The side pieces of girder forms are also released by driving out the bottom wedges. The side pieces may then be removed and the bottom plates left in place. Fig. 430.—Slab and Girder Floor Forms, Pacific Borax Co.’s Factory. Fig. 430 shows the form of moulds employed in the construction of the floors in the extension to the Pacific Borax Co.'s building, Bayonne, N. J. The mould consisted of collapsible bottomless boxes having solid sides and tops, and exactly corresponding in shape and dimensions to the cavity of the panel between each pair of girders and floor beams, which they connected. . A number of these moulds were set side by side, with their ends resting on stringers carried by column moulds and with spaces hetween each equal in width to the thickness of the floor beams. Floor. ee Ex 5L"Sheeting y a x hangs a yo bees” = eens: i Bata in, reed ee 2K h.- poet 368 —-—3 Fig. 481.—Slab «od Girder Floor Mold, Kelly & Jones' Factory. The bottoms of these spaces were closed by. boards, resting in cleats nailed to the side of the boxes. To collapse the mould it was cut in half diagonally. These two parts are clamped together by a slotted plate, which, when loosened, allows the parts to slide past each other and partly collapse the mould. Another form of collapsible mould, used in the Kelly & Jones factory building, mentioned on page 500, is shown jin Fig, 431. This mould is in reality a core between the beams and girders, 598 CONCRETE AND REINFORCED CONCRETE. and consists of a horizontal top and four vertical sides connected with rounded and beveled corners. The side pieces are nailed to vertical cleats and have stiffening strips on the lower edges. The moulds are made in two equal parts, with a hinged joint through the longitudinal center line of the upper surface. When: put in position the upper surfaces are in the same horizontal plane and the mould is held open by transverse struts between the lower edges. The bottom of the beams are formed by horizontal boards resting upon the flange pieces of the sides of the mould boxes. These boxes are supported in the usual manner by the column mould at the ends and intermediate posts. When it is desired to remove the moulds the cross bars are Fig. 432.—Method of Stopping Work on Concrete Slab. knocked loose in the bottom of the mould, and a few taps cause it to close enough on its center hinges to collapse. When freeing itself from the concrete it fell and was caught on horizontal ropes stretched for the purpose. When provision is to be made for expansion in the floor a joint is sometimes made in the floor slab on the center line of a beam or girder, and when double girders are constructed for the same purpose only a slight modification of the usual type of mould is needed. In the case of twin girders a partition cutting off half of the mould is used. The concrete is put in up to this partition, which is removed when it has sufficiently hardened; then the concreting is continued. To make a more positive clearage plane, paper or canvas may be placed at the division plane against the PRACTICAL CONSTRUCTION. 599 concrete first put in and the concrete laid up against it. This will break any possible surface bonding. Concreting.—While no special instructions, other than those already set forth, need be given for concreting floors, it will be well to emphasize a few points, as careful and conscientious work is necessary to secure good results. The mixing should be thorough. A wet mixture is to be preferred, but there is danger in using too much water. Care should be taken in placing the concrete. Tamping should not be neglected, and when the mix- ture is too wet to successfully tamp it may be cut and spaded, either with an ordinary spade or one made for the purpose. A special tool, having a 6 x 8 x \%-in. blade attached to a 5-ft. gas- pipe handle, is used by Ransome companies in much of their work. When the concrete is tolerably dry it is sometimes compacted ec Finish of Slab I Ly Tem porm 7 res rj Wobd Block Swe Ree oy gees aie & Gol. Rods-4-- os Fig. 433.—Method of Stopping Work on Beams and Girders. by rolling. In the Kelly & Jones factory, at Greensburg, Pa., a 3 x 3-ft. 250-lb. wooden roller was first used; then a 2 WY x 2Y- ft. 700-Ib. iron roller, for compacting the floor slab. Very satis- factory results were reported. In stopping the work for the night the concreting of principal beams should be left off over a column as near the center line as possible. Secondary beams should be left off at the principal beams, but in all cases the principal beams should be moulded through at one time. In like manner the concreting of the floor slab should be left off at. center line of the beams. The method recommended by the Unit Concrete-Steel Frame Co. for stopping off concreting when work cannot be carried on continuously is shown in Figs. 432, 433 and 434. Fig. 432 is a part plan and Figs. 433 and 434 are sections showing manner in which concrete work should be stopped. It is desirable to make the operation of 600 CONCRETE AND REINFORCED CONCRETE. ms concreting as nearly céntinuous as possible, as only by so doing will a perfect monolith be secured. In no case should the con- crete be stopped before the full thickness of the floor slab is secured over the entire surface laid for the day’s work. The concrete in the floor slab should be permitted to set for at ns and or Bei Order \Col Concert at least to ‘Orr inish of Stab, a tH Fig. 484.—Arrangement of Forms for Stopping Concrete Work. least a week before removing the frames; two weeks. would be better. When the lagging is removed an occasional plank near the center of the span should be left in and supported by a post. The sides of beam moulds may be removed soon after the floor slab moulds are taken down, but the bottoms of the beam moulds Fig. 435.—Under Side of Floor System with Molds Removed and Post Supports. should be left in place for three or four weeks, after removing while the beams and girders should be supported by props until the concrete is six or eight weeks old. Fig. 435 shows the under side of a floor system with the moulds removed, but supported by occasional posts. It is advisable when the floor surface is exposed to the rays of the sun in warm weather PRACTICAL CONSTRUCTION. 601 to cover it with cloth or burlap, kept continuously wet or kept well sprinkled ; otherwise bad shrinkage cracks will be formed. Finish of Floors.—This will depend on the purpose of the floor. Tiling or mosaic work may be laid on the top surface of the concrete, with a plaster bed, in the usual manner. For ordinary factory floors a finish of rich cement mortar from 14 to I in. in thickness, trowelled smooth, is sometimes used. If a better finish and a harder surface is desired, a granolithic finish may be used. This, if possible, should be laid while the concrete is still soft. If a top surface of wood is desired, nailing strips are set in the con- crete or upon it, with a filling of cinder concrete between them, and the floor surface nailed to them. The methods to be used in finishing a concrete floor surface are similar in all respects to that used for finishing sidewalks, and fully described on page 127. Fig. 486.—Potter’s Wall Form. The Construction of Walls and Partitions.—Forms for walls and partitions may be constructed as in columns, between timber sides extending the entire height of the wall. The reinforcing rods or network are first put in: place, the walls of the mould erected, and the concrete, mixed wet, is then put in and rammed with long slender rammers to force it around the metal. Forms of this kind consist of uprights, placed at fairly close intervals, which hold the sheathing in place. Struts and crossties are used to keep the uprights in line and the sheathing at proper intervals apart. Bolts and wire ties, extending through the wall, are used for this purpose. Hennebique sometimes uses a modification of this method. The mould on one side is built in panels all the way up, and the other side is brought up as the concreting proceeds. The longitudinal rods are placed as the concrete is brought up to the proper elevation. This method enables the concrete to be placed in layers of moderate thickness and to be thoroughly rammed as 602 CONCRETE AND REINFORCED CONCRETE. it is put in. The construction of the above type of wall mould consumes a large amount of lumber, which is of little value after being once used. They are frequently used when timber is cheap, as the cost of erection is quite low. A form of wall mould described by Thomas Potter in his work on “Concrete; Its Use in Building,” is shown in Fig. 436. These forms consist of pairs of vertical posts placed at convenient intervals and connected by tie-bolts passing through conical washers to preserve proper spacing between them. Movable frames, consisting of sheathing boards nailed to battens, of the proper length to fit between the upright posts, are put in place and held flush with the inner side of the posts by battens nailed to the side of the posts. Through tie-bolts, also surrounded by conical washers at each batten, maintain the proper thickness of wall between posts. In concreting several sections of sheathing are ly Fig. 487.—Wall Forms Used in Ransome System of Construction. used, the lower one being removed from the hardened concrete and placed on top of the one last set, and the concrete is then carried on up. To remove a section the bolts are withdrawn, the tapered spacers driven out and the holes filled with mortar. Narrow sheathing boards should be used to prevent warping; they should be surfaced to give the concrete a smooth surface and closely jointed to prevent leaking. In the construction of wall moulds of all kinds it will be well to splay the edges of the boards as done in column moulds, and shown in Fig. 406, page 574. In the Ransome constructions the sides of the form are carried up as the work proceeds, the planks forming them being held in place by vertical uprights... The uprights, or standards, are slotted, as shown in Fig. 437. These uprights are kept at proper intervals apart by spacing pieces, which are removed as the concrete is brought up. Through-bolts passing through the ‘slots hold the PRACTICAL CONSTRUCTION. 603 standards firmly against the portion of the wall already built and the spacing pieces placed between them. The sheathing boards are put in position between the standards as the work progresses. When near the’ top the bolts are loosened in one pair of the standards, pushed up, releasing the lower boards, and the bolts again tightened. When a bolt reaches the lower limit of a slot it is removed and placed at the top of the slot, and so on. The holes left by the withdrawal of the bolts are filled with mortar. Fig. 489.—Wall Mold for Central Felt Fig. 438.—Form for Wall and Paper Co.’s_ Factory, Long Molding. Island City, N. Y. When mouldings in the wall are desired the methods followed are similar to that shown in Fig. 438. Fig. 439 shows a type of mould similar to the one just described. This mould was used in the construction of a wall for the Central Felt & Paper Co.’s building. Each panel of this mould con- sisted of two vertical side pieces, 3 ft. high and 16 ft. long. The first course was seated on the foundation and held together by braces. After the concrete had hardened sufficiently the sides were loosened and pushed up until the lower edges lapped slightly 604 CONCRETE AND REINFORCED CONCKETE. on the concrete already laid. In this position they were sup- ported by bolts passing through pasteboard sleeves resting upoa the top of the concrete, and their upper edges were held at the proper distance apart by battens nailed to their top edge, about 4 ft. apart. In the use of this type of mould special care must be taken to make a perfect joint between the old and new concrete. Again, great care must be exercised to keep the moulds in line wheh they are raised, or the wall will be constructed out of line. When hollow concrete walls are constructed, core boxes, in addition to the usual side moulds, must be employed. These must he made collapsible, so that they can be removed without injuring the concrete. Cross ribs connect the two sides of the wall at frequent intervals, and the whole makes a very rigid wall construction. Collapsible forms similar in design to those shown in Fig. 411, and used for hollow columns, may be used. When hollow reinforced concrete walls of light construction are to be built, forms like that shown in Fig. 440 may be used. In this form the bolts do not pass through the concrete, but rest upon the top of the core, and the forms are raised when the concrete reaches the level of the bolts. The core boxes are slightly tapered to keep them from slipping down. Where the wall forms are erected complete before concreting is begun it will be advisable to use a tolerable wet mixture, but where movable panels are used for forms a dry concrete should be used, as it will harden much more quickly than wet concrete, thereby enabling the wall to be carried up more rapidly, and when the cement is tolerably quick setting the operation of con- creting may be carried on continuously. For walls a concrete having a 1:214:5 or 1:3:5 mixture will usually be found satisfactory. The stone should not be greater than 34 or I in. in diameter. Wall Mould Ties.——Various kinds of ties, some of which have heen patented, have been devised to hold the sides of wall moulds together. These are generally better adapted to use in thick walls than in thin walls, such as are used for reinforced concrete work. Bolts with or without sleeves will usually be found satisfactory. These special ties usually consist of the shank of a bolt threaded at both ends, having a special nut or threaded casting at each end. When the form is removed these nuts or castings are screwed off, leaving the bolt in the wall. Another device consists of either PRACTICAL CONSTRUCTION. 605 ordinary nuts or special castings placed in and near the faces of the wall and connected by wire ties. Bolts passing through the timbers of the frames are screwed into these nuts and tightened by means of nuts and washers on the outer ends of the bolts. OB Elevation. Vert. Section. i Fig. 440.—Form for Hollow Walls. When these nuts are loosened the bolts unthread from the buried nuts or castings and the latter are left in the wall. Fig. 441 shows two kinds of wall ties. Through-bolts will generally give less trouble and prove much more satisfactory. Roof Construction.—The methods used in the construction of “2 Nall Wires I Details showing Arrangement of Wires, (Enlarged.) Fig. 441.—Example of Wall Form Ties. roofs are similar to those used on floors. When thie roofs are flat or only have a slight slope, the methods used are identical with those employed for floors. If the roof has a moderately steep pitch, a dry concrete must be used, as this will stand at quite a steep slope. If a wet con- ° 606 CONCRETE AND REINFORCED CONCRETE. crete is desired, forms similar to those used for walls must be employed. Concrete roofs may, like floors, be either supported by a frame- work of steel or may consist of a reinforced slab supported by reinforced concrete rafters and purlins. A roof constructed of the first kind is described on page 541, and was used for a roundhouse for the Canadian Pacific Railway. Fig. 442 shows forms used in this construction which con- sisted of a reinforced concrete roof plate supported by reinforced concrete purlins, spanning between and supported by 18-in. J-beam rafters. The details of the forms are clearly shown in Part Side Elevation. Cross Section, Fig. 442.—Form for Slab and Girder Roof. the sketch. The manner in which they are hung from the top flanges of the beams should be noted. For steep roofs, domes and other complicated roofs, the moulds are in each case a subject for special study in the draughting room and careful work for the carpenter. In such cases the inner moulds require complicated framing, and when special paneling is desired, or for any other cause outside moulds are needed, they are built up of light timber in panels of convenient widths, or are sometimes made of plaster of Paris, strengthened with wire mesh- ing. Lugs are supplied to keep the moulds at proper distances apart, and ties or bolts are used to hold them together. When an entire outer section is put in place, the concreting is hrought up in the usual manner, a wet mixture being used. After the concrete has hardened the outer moulds are removed and any inequalities filled with cement mortar. CHAPTER XXV. RETAINING WALLS. Retaining walls of reinforced concrete may be used with economy in many localities to replace walls built of ‘cut stone, rubble or concrete. The amount of saving depends, of course, upon the relative price of stone, sand, gravel and cement, and at times may amount to as much as 50 per cent. The cost of forms, as is always the case in reinforced concrete work, will to a large extent determine the amount of saving, and when properly designed should not greatly exceed the cost of forms for a solid concrete wall with a gravity section. It will be found that reduc- ing the sections to a minimum thickness will increase both the cost for forms and for depositing the concrete. Slightly thicker sections, when used, will often prove more economical, as the slight increase in concrete yardage will be offset by the saving on the other items. The usual form of retaining wall used for walls built of brick, stone or concrete is what is called a gravity section, i. e., when the resistance to the overturning of the wall due to its weight counterbalances the overturning moment due to earth pressure against the back of the wall. Reinforced concrete walls do not depend upon the weight of the masonry alone to resist overturning, but substitute for it the weight of the earth resting upon a broad base formed by a slab of reinforced concrete at the heel of the wall, and sometimes a horizontal beam or beams be- tween the buttresses at the back of the wall. The function of these horizontal beams is similar to that of the relieving arches sometimes used with masonry retaining walls. The economy of the reinforced concrete wall is due to the ability of a wall of thin section to resist the bending moments and shears caused by the earth thrusts when acting as cantilever and simple beams and as slabs supported on two and four sides. The weight of the earth on and vertically above the reinforced slab forming the heel of the retaining wall, multiplied by the distance of its center of pressure from the toe of the wall, gives 608 CONCRETE AND REINFORCED CONCRETE. the moment of resisting to overturning due to the weight of the earth. This, plus the resistance to overturning due to the weight of the wall itself, gives the total resistance to overturning, and must equal the total overturning moment due to earth pressure multiplied by a suitable factor of security. Sometimes the weight of the wall itself is neglected when computing the resistance to overturning. This is on the side of safety. The scope of this work precludes a discussion of the methods employed for determining the pressure of earth against the back of retaining walls. This pressure varies according to the nature of the earth, its height above the wall, the amount of moisture it contains, etc. The reader is referred to Merriman’s “Walls and Dams,” Howe’s “Retaining Walls for Earth,” Baker’s “Masonry Construction,” Trautwine’s “Engineers’ Pocket Book,” and other works on the subject for discussions on earth pressure and methods of determining thrust against walls. In designing reinforced concrete retaining walls provision must be made against sliding. This may be done by providing a wall buried in the earth below the bottom plane of the base, as shown at the toe of the wall in Fig. 446 and at the heel of the wall in Fig. 447. At times it will be necessary to drive piles, preferably under the toe of the wall, to increase the supporting power of the soil at this point and to anchor the wall against sliding by burying the heads of the piles in the concrete footing. This is shown in Fig. 449, which shows a retaining wall at Seattle, Wash. Reinforced concrete retaining walls may, in general, be divided into two classes: Walls with an inverted T-section and walls with counter forts. Inverted T-Section Walls——These walls are simple in form and easy to construct. They consist, as shown by Fig. 445, page 610, of a thin reinforced vertical wall rigidly attached to a base formed by a reinforced concrete slab. The vertical slab acts as a canti- lever beam. The earth pressure increases from zero at the top to a maximum at the upper face of the base, where the bending moment 1s a maximum, The wall proper is usually increased in thickness from about 6 to 8 ins. at the top to a maximum thick- ness at the top face of the base. At the latter point there must be sufficient concrete and metal to resist the stresses due to shear and bending moment. The base at the heel acts as a cantilever, RETAINING WALLS, 609 and must resist the weight of the superimposed earth resting upon it; while the portion of the base in front of the wall, forming the toe, also acts as a cantilever and resists the upward thrust of the earth caused by the tendency of the wall to overturn about the point of the toe. Hence the base must be reinforced at both top and bottom. Care must be taken that the maximum pressure at the toe does not exceed the safe bearing power of the soil upon which the wall rests. Having found the moments of the wall at the section-where it 4 Ka I a 3", = 4 fod kz 1 aw (8 wel |e S Sell |S I & S38 Atay 1 dk is) sa ls i | $28 |§ Ssh [8 =e $ ea le ot Le ios. i 2 sSl a a8 sk ‘260, S os Bs, ! 8 ra ‘$0 ~ PQ \ : fot BY a : ef ¥ : . t ‘ ‘4%, > Rartiabove Acbrsta i,t a ' Whee Wall 6,500 83M. fogs el ets s Si ' { rs ro s 6,500 Ibs. i oes = 3 i dlalals H i 2 Fods,| == | ‘ 9°C. 106. SF, I Libpt 3 in Heel Ax a i Hf pha } o YF | eis | @ ay f q T e is ' 4 S Spacing of Rods. feeieeeed 7g 1A Ls , Psy ‘ i i= ‘Si 16" Po sees wets How Ke--8 yt e se { fetcereceo reece 14/0" ~a-----~—------->} Fig. 446.—Retaining Wall with Counterforts. varying in thickness from 4 to 6 ins. at the top to 8 or Io ins. at the bottom, and vertical ribs or counterforts spaced 6 or 8 ft. centers, connecting the base plate and vertical wall. The econ- omy of material for this type of wall is greater than -for the wall of T-section, and increases as the height increases, but the cost of the forms is greater. In this type of wall the overturning moment and the bending moment produced by the resultant hori- 612° CONCRETE AND REINFORCED CONCRETE. zontal thrust at the plane of the top of the base are resisted entirely by the counterforts. The horizontal earth pressure be- tween the counterforts is transmitted by the thin vertical wall slab to the counterforts. When a horizontal beam is used at the top to | forma coping, the vertical wall may be figured, as a slab sup- ported on four edges. However, in this type of wall, as in the T-section, a minimum thickness of slab will not always prove the most economical. Fig. 447.—Retaining Wall with Counterforts Designed by Hennebique. The base plate at the back of the wall between the counterforts should be designed as a floor slab, supported by the counterforts, to carry the weight of the earth and superimposed loads coming upon it, while the portion of the base in front of the wall should be designed as a cantilever beam fixed at the wall to resist the reaction of the ground. It should be remembered that the maxi- mum pressure at the toe must not exceed the safe bearing power of the soil. Fig. 446 shows the design of a wall made by the St. RETAINING WALLS. 613 Louis Expanded Metal Co., and Fig. 447 a wall of Hennebique construction. Sufficient metal must be placed in the back of the counterforts to care for all tensile stresses due to overturning. Horizontal reinforcing rods are placed at frequent intervals throughout the height of the counterfort to tie the face slab to it, while occa- sional vertical rods will assist in carrying the tensile strains to 2 Corr. Bars, Spaced le” Bars, looped over Reinforcement, in Face about every 4’ a a Corr Bars, Spaced 9 0" 3 4 Elevation, Fig. 448.—Retaining Wall, Great dite tos Seattle, Wash. the base. The amount of reinforcements necessary for the wall and base slabs and girders is determined and the rods located in the manner usually employed for slabs and beams; this has been explained in Chapter XIX. In addition to the amount of longi- tudinal reinforcement necessary to care for tratsverse strains, provision should be made for temperature and shrinkage strains, or when this is not done the wall should be built in sections of about 50 ft., with expansion joints between adjacent sections. 614 CONCRETE AND REINFORCED CONCRETE. The questions of temperature and shrinkage strains will be dis- cussed further on in this chapter. A good example of a high reinforced concrete retaining wall of the counterfort type is the wall adopted for the terminal yard at Seattle, Wash., by the Great Northern Railway. This wall supports a street, and varies in height from 2 to 37.8 ft., and will be approximately 2,000 ft. in length. Mr. C. F. Graff, of the engineering staff of the Great Northern Railway, states that a comparison of cost between a plain concrete wall of gravity sec- \ SBars- FER x t ' i : & N ¥t HAS Re * k WS Seay OSS ! ao \ ea pe ay i\ 3 } \ an Raa 4\ a mnt \ we S Sie a eS ek Section at Portal. 20" Fig. 449.—Retaining Wall, Great Worthen: Ry., Seattle, Wash. tion and a wall of the counterfort type (Fig. 448) gave the fol- lowing saving for walls of heights varying from 10 to 40 ft., assuming a section of wall 1 ft. long and figuring the amount of steel used at 41% cts. a pound, evaluated in terms of concrete at $6 per cu. yd., in place: TABLE LXXII. Height of Wall. Cu. ft. Concrete, Cu. ft. Concrete. Saving. Feet. Plain Wall. Reinforced Wall. per cent. 10 44 34.9 20.4 20 II0 69.9 30.4 30 226 127.8 43.4 40 306.4 218.0 45.0 RETAINING WALLS. 615 It was assumed in the above estimate that the extra cost for forms and a higher grade of concrete for a reinforced wall was counterbalanced by the saving in piling necessary for the plain concreté wall. Fig. 449 shows elevation section and plan of the wall at its highest end where it joins the portal. At the highest point the wall is 37 ft. 7 ins. in height. Fig. 449A shows an elevation and section of the wall where it is 31 ft. 7 ins. in height. The general dimensions and reinforcement employed are shown on the draw- ing. In computing sections of face and base of wall they were considered as composed of a series of independent beams lying side by side, giving an additional factor of safety, as there is in reality a supported slab action. ieee SY Thars ~eomtE at 676" Fig. 449A.—Retaining Wall, Great Northern Ry., Seattle, Wash. Piles were driven, as shown in the part plan (Fig. 449), to com- pact the earth, to support the toe of the wall and to prevent the structure from sliding forward. Scaffolding was put up to facil- itate the erection of the steel skeleton work. Near the top of this scafolding the two top I-in. horizontal face bars were se- curely fastened in exact line and elevation, and the long diagonal 114-in. bars running down the back of each rib were hooked on these and swung into proper ‘posi- tion at the bottom. Some of these bars were 42 ft. in length, and were kept from sagging by wooden cross pieces nailed to the 616 CONCRETE AND REINFORCED CONCRETE. falsework. The 14-in. vertical face bars were then hung from the top horizontal ones and held in place in a similar manner. Next the vertical bars in each rib were placed, being styck in the ground at the bottom and held at the top by wire tied to the scaffolding. In construction 3 ins. of concrete was first placed above the 8 etude esiSelaies % v é £ — ; 8 3 P64 B = Q Section C- 8, 14 Bars Top of Fail _ & x & % : RS SO Section F-F ae NB EA . ye ' KiB ° 5D tone Bars Section M-M Fig. 450.—Retaining Wall, Brooklyn Grade Crossing Commission. top of the piles, the horizontal longitudinal rods were put in place, and then the concreting carried up throughout the whole section. As the work was brought up the horizontal bars in the face and ribs were put in place, care being taken in all cases to bed them in fresh concrete. The laps where the rods were spliced were made at the ribs, a 2-ft. lap being used for the base and 114-ft. lap for the face wall. Corrugated bars were used throughout. A 1:2:4 mixture of Portland cement, sand and trap-rock was RETAINING WALLS. 617 used for the concrete. -A fairly wet mixture was employed, being deposited in 6-in. layers and thoroughly tamped. Fig. 450 shows a design of a proposed retaining wall for the Brooklyn Grade Crossing Commission by H. C. Miller & Co. The reinforcing metal is St. Louis Expanded Metal Co.’s corrugated bars. The total height of this wall is 24 ft. 7 ins., and the but- tresses are spaced 15 ft. centers. The dimensions, reinforcement and general features of construction are clearly shown by the Garriage Drivel Station Buildi Gioor Noor ce - 4. .f Rod. Rods. ef Roas.. =| A- RS = LA “St Ground | 4. Stirrups re | 2 Pods We ati ge Sosa Ps Elo Horizontal : Section A-A Horizontal Section B-B. Fig. 451.—Retaining Wall with Counterforts, Atlanta Terminal Station. drawing. This wall is exceptionally well designed, and uses a minimum amount of material. In the construction of the Terminal Railway Station at Atlanta, Ga., several modifications of the usual type of wall with counter- forts were used. Fig. 451 shows two sections of a wall 194 ft. long and 22 ft. 6% ins. high. The spacing of the counterforts varies from 4 to 6 ft. On another part of this work the wall shown in plan, elevation and section in Fig. 452 was used. Figures 453 and 453A show the details of a wall used to protect the end and side of a building from an embankment filling. As will be seen, the usual solid buttress is here replaced by a skeleton 618 CONCRETE AND REINFORCED CONCRETE. buttress. The details of construction are clearly shown in Figs. 453 and 453A. Fig. 454 shows a modification of the usual type of wall with counterforts. This wall is of Hennebique construction, and was used to support the sides of a sunken street near the Gardens of the Trocadero, at the Paris Exposition of 1900. The wall was M N 6. wy : o Elevation. 500" [opposed 3 ; kj04 BOE geeage i 4 22°Rods’ fe Ele a a m4 a a «-2,I"Rods Section | us 2 Stirrups..-\ * at Bracketsit Section Q-R. eee eae ef 888 =I ji Small Buttresses. Large Buttresses. Sectional Plan ST. Fig. 452.—Retaining Wall with Counterforts, Atlanta Terminal Station. _ built in sections about 20 ft. in length, each section or panel being made up of a facing strengthened at its back by three buttresses. Two horizontal beams connected the facing and buttresses. Shal- low buttresses below the street level were used to strengthen the base slab at the toe of the wall. Two separate beams, at different levels, which act as relieving arches, reduce largely the thrust of 619 RETAINING WALLS. ag ‘WOT}B1S JVUlUlIeL BEY ‘sJojrojuNoD pemVIg GYM [1BM SUlUlejoU— ECF ‘31 0,89 ‘peBunjug ‘uoljsesS |PLUOZIWOY os 1 IY --— AE He, 9,£-—-Hk at a Ht [el 33) * Baal jhe, —oe Soe Tt orem LLL Kei MG ee NSDL twsosenia| $o ubid > “SMIN "OND wet A1ana SPY 1 pe = ne ow ee ee 620 CONCRETE AND REINFORCED CONCRETE. the earth upon the vertical face of the wall and assist in sustain- ing the earth by the weight of the earth coming upon the beams. This arrangement also greatly reduces the amount of excavation necessary in building the wall. The vertical face was reinforced xe SF 3 nniesanscies ipa tieasa oe G \.. tical Section S-T Vertical Section Q-R. Fig. 453A.—Details of Counterforts Shown in Fig. 453. with two series of vertical bars, combined with one series of horizontal bars, with increasing spacing toward the top of the wall. The vertical bars were bent over at right angles at the top to support the reinforced coping. The reinforcements of the RETAINING WALLS, 621 buttresses consisted of inclined bars tied together by straps and supported by horizontal bars. The horizontal beams had rein- forcing bars, run in both directions and spaced about 8 in. centers. The beams were further strengthened by flanges at their edges. The arrangement of the reinforcement and general features of construction are shown in Fig. 454. Braced Walls—Reinforced slabs are frequently used for area and cellar walls. When so used they are braced at both top and _ kbe Coping ys AN : t 1 WS as | TNs et rid \ \Ak rs SHAY | yy RS pasta \ KG oi 1% es 5 8 SATA S SU yaa Aa 8 tt Nae S Hor. \ Beart x SIRE Wid ==k=—- SIN + 284-2179 + See : Sigh | Sir i Si Vertical Section. Horizontal Section A-B. Fig. 454.—Retaining Wall for Sunken Street, Paris, France. bottom, and may be considered when they are figured as slabs supported at top and bottom and loaded with a uniformly increas- ing load from top to bottom. Expansion and Contraction.—Some provision should be made against cracks due to shrinkage and temperature stresses in walls, dams, pipes, sewers, etc. Unless special provision be made, points of failure or cracks will occur at intervals such that the frictional and other resistances to movement of the section be- tween the cracks are greater than the tensile strength of the wall. 622 CONCRETE AND REINFORCED CONCRETE. Two methods may be used to avoid unsightly shrinkage cracks: First, the wall may be divided into sections of about 50 ft. and provided with expansion joints to allow for movement and to localize any possible cracking; second, sufficient longitudinal reinforcement may be provided to care for all stresses due to expansion and contraction, and cracking will be avoided. The steel, when so used, equalizes the strain between different sections along the length of the structure and causes it to stretch as a homogeneous material, thereby avoiding dangerous local cracks. When steel is properly distributed through the wall it will stretch about ten times as much without visible cracking as when na steel is present. . As already explained, cracks first become visible in the under side of a reinforced concrete beam when the elongation becomes equal to from 0.001 to 0.0013 of its length. The coeffi- cient of expansion of concrete may be taken at 0.0000055. To pro- duce an elongation of 0.001 will require a change of temperature 001 of ———— = 182° F. The maximum range of temperature .0000055 under ordinary conditions will not exceed 125° F., and is probably considerably less than this. Assuming 75° as a probable varia- tion under ordinary conditions, the total change of length due to 75° change of temperature will be 0.0000055 x 75 == 0.0004125 part of its length. If it be assumed that the wall is fixed at both ends and subjected to a fall of 75° F., the resulting thermal stress in the steel will be equal to that required to stretch the wall 0,0004125 times its length, i. e., 0.0004125 times the modulus of elasticity of the steel. This will give a thermal stress in the steel of 0.0004125 x 30,000,000 == 12,375 lbs. per sq. in. If the modulus of elasticity of the concrete is 3,000,000, the thermal stress in the concrete will be 0.0004125 x 3,000,000 == 1237.5 lbs. per sq. in., or about three times its ultimate strength. If no reinforcement is used, the concrete will crack. The maximum stress coming upon the steel when reinforcement is used will be its own thermal stress of 12,375 lbs. plus the strength of the concrete at its elastic limit. This limit may be taken at its ultimate strength. : Assuming an elastic limit of steel at 34,000 lbs. and the ultimate tensile strength of concrete at 300 lbs., and taking a wall with a RETAINING WALLS. 623 sectional area ot 700 sq. ins., the area of metal required to care ; . 300 X roo for the thermal stress in the concrete will equal 34,000 a 12,375 == 1.39 sq. ins., or 1.39 per cent.. If steel having an elastic limit ; 300 X 100 of 54,000 lbs. is used, we have —_-______ = 0.75 per cent. 54,000 — 12,375 Stresses in Concrete Due to Setting—As has been stated, the contraction of concrete when setting in air, or expansion when setting in water, may amount to from 0.0002 to 0.0005 of their length. Assuming that when the concrete sets in the air its shrinkage amounts to 0.00035 part of ‘its length, the tensile stress resulting will amount to 0.00035 x 3,000,000 == 1,050 lbs. per sq. in. Unless the concrete is reinforced, cracks will open up along the length of the wall if it is not free to move. The number and amount of the cracks will depend upon the amount and character of friction on the foundation, the strength of the concrete, etc. The greater the friction, the shorter the intervals between the cracks, and the stronger the concrete the farther apart will be the cracks. A thorough distribution of steel: reinforcement through- out the wall will prevent cracking, and if the steel is fixed at the end of the wall it cannot change in length, and the summation of the stress on the steel due to the shrinkage of the concrete will become equal to zero. Where the section of the concrete is weakest the steel will be in tension, and where strongest the steel will be in compression, and the algebraic sum of all the stresses will become equal to zero. The maximum stress which may come upon the steel will be equal to the ultimate tensile stress of the concrete, and the maximum compressive stress in the steel will be that due to the total deformation, i. e., 0.00035 x 30,000,000 == 10,500 lbs. per sq. in. The amount of steel necessary to care for the shrinkage stresses alone, assuming, as before, 300 lbs. ulti- mate tensile stress in concrete and 34,000 lbs. per sq. in. as the elastic limit, and assuming a wall section of 100 sq. ins. will be, as 300 X 100 5 before ——____-. =: 0.88 sq. in., or 0.88 per cent. 34,000 Thermal and Shrinkage Stresses Combined.—It is probable that the thermal stress in the steel due to its contraction will neutralize 624 CONCRETE AND REINFORCED CONCRETE. t the compressive stresses due to the shrinkage of the concrete. It is usually assumed that the maximum tensile stress in the steel can never exceed its own thermal stress, which, under the condi- tions fixed above, is 12,375 Ibs. per sq. in. plus the ultimate strength of the concrete. Otherwise the concrete would fail. Under this supposition, it will not be necessary to take into account the tensile stress due to shrinkage. In any event, by keeping the wall wet during the setting of the cement, all danger due to shrinkage strains may be avoided and thermal stresses only need to be provided for by reinforcement. CHAPTER XXVI. DAMS. Reinforced concrete is particularly adapted to the construction of dams. When so used there is a great saving in material, and on this account a reduction in cost of, in some cases, as much as 20 per cent. Again the space under the apron may be utilized for storage or power house purposes, as for the location of tur- bines, electric generators, etc. Another advantage is that of se- curing a practically impervious curtain face wall, without any of the dangerous leaks so troublesome to locate in some masonry structures. If sufficient number of reinforcing rods are used and run in every direction there will be little or no danger of crack- ing in the deck concrete. The usual type of reinforced concrete dam consists of an in- clined slab of reinforced concrete extending from the heel to the crest,-and spanning between and supported by transverse but- tresses of concrete, resting upon the foundation. Another in- clined slab may or may not be used to form an apron or spillway. The deck is usually increased in thickness. from the crest to the heel on account of the increase in pressure as the water deepens. Sometimes a greater economy in material will result if a design consisting of longitudinal beams spaced closer together toward the bottom, be used to span between the buttresses and support a thin reinforced deck slab spanning between the beams. Less ma- terial will be used, but the cost of forms for this kind of structure is considerably greater than for the first type. An objection to this type is the thin deck slab used, which is liable to be injured by the pounding of floating ice or driftwood during floods. Fig- ure 455 shows a design of such a dam. A dam of this type may prove economical under certain conditions, as in tropical coun- tries where the cost of cement is high. The principles governing the design of reinforced concrete dams are the same as those used for the design of masonry dams. These are fully explained in such text books as Wegmann’s 626 CONCRETE AND REINFORCED CONCRETE. “Design and Construction of Dams,” Baker’s “Masonry Con- struction,” etc. However, as reinforced concrete dams are usually of triangular cross-section, they have a much wider base than masonry structures, which greatly increases their resistance to overturning. This resistance is further increased by the weight of the water above the face or deck, which usually has an inclination of from 30° to 45° with the hori- zontal. An increase in the height of the water flowing over a masonry or solid dam increases the pressure thereon and causes the line of pressure to rise, thereby greatly increasing the overturning moment on the dam without in any way increasing the resisting moment to the same. In a triangular dam, with a broad base, sometimes called a gravity dam, as in hollow rein- we es — 4 Distributin 1 Rods, — — paced l2"C.t0 C.- 28 EK Rubble Concrete Piers, Spaced 12'0°C.toC. Fig. 455.—Open Front Type Dam. forced concrete dams, when the head of water flowing over the dam is increased, the lines of pressure become more and more nearly vertical, the overturning moment is actually reduced, and the stability is in no way endangered. Until recently, wooden dams have been the only gravity dams used, but their short life and the increasing cost of lumber now, from the standpoint of economy, in most cases forbid their use. For the methods of determining the pressure on the face or deck of an inclined dam, together with the center of pressure, see Chapter IT. of Merriman’s Hydraulics. Again, hollow dams have only a fraction of the weight of solid masonry dams, and hence possess much less resistance to overturning due to the weight of the dam than all masonry structures. The reduction in weight must also be considered when comput- DAMS. 627 ing the resistance to sliding. In some cases it will be advisable to fill the hollow dam with sand, gravel, earth or a meager concrete. A 1:12 or 1:15 mixture will answer the purpose. In the latter event the dam and filling may be so constructed that they will act as a solid mass. ‘ After obtaining the pressure at various depths the problem of determining the thickness of slab needed, and, when used, the size of beams becomes simply a matter of determining the strength of a slab or beam acting under a uniform load. The methods used are the same as those explained in connection with the theory of slabs and beams. The great reduction in weight and the broad base obtained by the use of this type Of structure peculiarly fits it for situations Fig. 456.—Dam at Theresa, N. Y. having poor foundations. Thus, by the use or spread footings of reinforced concrete under the buttresses, the pressure carried by the latter can be so distributed as to bring a safe load per square foot on a clay or clay and gravel soil. When still less satisfactory soils are met with, foundation piles may be used to support the buttresses. On account of the reduction in weight when this type cf structure is used, fewer piles will be necessary than when a solid masonry dam is used, and a great reduction in cost secured. This item alone may at times warrant the adoption of a reinforced concrete dam. . When the foundation is on rock, no provision is necessary against sliding, if the surface of the rock is rough. If it is smooth it is customary to anchor the buttresses to the rock by dowel pins or anchor bolts, or sometimes a heavy cut-off wall, 628 CONCRETE AND REINFORCED CONCRETE. sunk in the rock at the heel of the dam, serves to anchor it and to cut off leakage underneath the dam. On foundations other than rock, walls buried in the earth arid anchored to the buttresses, may be used to prevent sliding, or a few piles having their heads buried in the concrete of the but- tresses will suffice to hold the structure securely in place. Where a pile foundation is used, no danger of sliding will result. Some- times the cut-off wall at the heel or toe may be relied upon alone to prevent sliding. Shrinkage and temperature cracks may be prevented by the use of sufficient reinforcement. The methods of obtaining the proper sections for the steel have been explained in connection with retaining walls. The particular form of reinforced concrete gravity dam to be Follway hock Line Fig. 457.—Half Open Type of Dam. adopted will depend largely upon local conditions. The open front dam shown in Fig. 456 is used for dams having a moder- ate height when located on a ledge of rock of sufficient hardness to resist the erosive action of the overflow of water and ice. A slight modification of this type consists of extending the slab or apron a slight distance beyond the crest to pitch the ice and water far downstream, away from the foot of the dam. If the apron is carried down to within 6 or 8 ft. of the base and curved to the bucket form shown in Fig. 457, the half-apron dam is secured. This form of bucket near the toe gives the water a high initial velocity in a horizontal direction and discharges it far below the toe of the dam. When both the back and front of the dam are covered, what is known as the curtain dam is obtained. (See Fig. 458.) The DAMS, 629 pitch of the apron is generally easier than that given to the apron of a solid dam. Vents are placed in the apron just below the crest, for the purpose of admitting air behind the sheet of water to kill the partial vacuum which would otherwise form under high velocities of overflow during flood, and which is the cause of the “trembling” of dams. If the dam is high, and the foundation on ledge rock, the floor shown in Fig. 458, as well as the cut-off wall at the toe, are omit- ted. When the foundation is on cemented sand, clay, or hard- pan, sheet piling is driven to a sufficient depth at the heel and toe of the dam to insure tightness by puddling, and the concrete placed over and about the head of the piling. Draught holes are placed in the toe to carry off all seepage. Weep holes may be placed in the floor to prevent upward pressure on the floor. This Fig. 458.—Curtain Type of Dam. arrangement of the foundation prevents any upward pressure from within or below which might endanger the safety of the dam. A modification of the type shown in F ig. 456 is the form shown in Fig. 459. This type is designed for low heads on alluvial and clay foundations. The floor takes up the effect of the falling water and delivers the water parallel to the bed of the stream and prevents gouging out the bed of the stream below the dam. The sheet piling at heel and toe act as a cut-off and help anchor the dam. The light weight, together with the broad base of a rein- forced dam of this type greatly reduces the pressure upon the subsoil, thereby enabling such a dam to be used in locations where the weight of a solid dam would make its use prohibitive. The dam shown in Fig. 459 was designed for a 5-ft. head on a New 630 CONCRETE AND REINFORCED CONCRETE. Jersey stream, where the foundation is strictly mud, without a trace of rock or gravel. The concrete floor is reinforced in both directions and on both edges, so that the whole dam acts as a unit. The inclined deck is somewhat steeper than generally used, and is braced by buttresses in the usual manner. The overflow is taken directly on the floor of the dam. The dam built in the Fall of 1904 at Fenelon Falls, Ont., is a good example of a reinforced concrete dam of moderate height. This dam is to ft, high and 194 ft. long, and rests upon a smooth limestone ledge. It was built complete in the remarkably short period of 22 ordinary working days. The dam consists of triangular buttresses 12 ins. in thickness, spaced Io ft. centers and anchored by steel dowels to the ledge, supporting an in- Fig. 459.—Open Front Dam with Floor and Buttresses for Alluvial Streams. clined deck varying in thickness from 7 ins. at the top to Io ins. at the bottom, where it increases in thickness to form a cut-off wall. Figure 460 shows a cross-section of the dam. No reinforcement is used in the buttresses. The deck is rein- forced with 7 and 34-in. Thacher bars, spaced from 6 to 7 ins. centers, extending between the buttresses. A secondary rein- forcement of fence wire is provided to prevent hair cracks. ‘The deck is figured for a factor of safety of 5, using Thacher’s formulas. The maximum load coming upon the buttresses is 4.5 tons per sq. ft. This dam forms a portion of a horseshoe dam, the water flow- ing past the face of the dam. To protect the buttresses from drift ice and logs, a reinforced concrete facing slab, shown in the draw- “ing, was provided along the back face of the buttresses. DAMS. 621 The dam was completed Noy. 11, 1904, and the full head of water turned on 18 days after the last concrete was laid. This dam was designed ‘and built by the Ambursen Hydraulic Con- struction Co., Boston, Mass. Another small reinforced concrete dam, which was among the first to be constructed, was built for a small water power plant at Theresa, N. Y. This dam is 11 ft. high, 120 ft. long and was built on solid rock. Concrete buttresses, 12 ins. thick, spaced 6 ft. centers and anchored to the rock foundation with 1%-in. anchor bolts 3 ft. long, support a concrete slab reinforced with 34-in. Thacher bars and expanded metal. The crest is strength- ened by a 6 x 8-in. reinforced beam. Figure 456 shows a trans- verse section, with general dimensions, spacing of rods, etc. A Log Fender Fig. 400.—Dam at Fenelon Falls, Ontario. concrete composed of 1 part Portland cement, 2 parts sand and 4 parts broken limestone, was used for the deck slab, and a 1: 3:6 mixture for the heel and buttresses. It is stated that about 125 cu. yds. of concrete was required for this dam. The reinforced concrete dam constructed for the American Wood Board Co., on the Batten Kil River, near Schuylerville, N. Y., is a good example of a hollow reinforced concrete dam of Somewhat greater height than those already described. The crest of this dam has an average height of 25 ft. above the bed of the river and a maximum height in the channel of 28 ft., with a length of 250 ft. between abutments. The foundation is of Hud- son River shale, moderately firm in texture, but not strong enough to withstand erosion due to sheer overflow. Figure 461 shows a cross-section, a partial front view and partial longitudinal sec- tion on the center line. The general dimensions, details and reinforcing material used are given on these sections. — The form of dam used is such that when its weight was calcu- 632 CONCRETE AND REINFORCED CONCRETE. lated and combined with the water pressure the resultant lines of pressure were found to be more nearly vertical as they approach the crest of the dam, and in all cases to fall well within the base, *2"iron Pipe slorctec. = a —— et eee e | , #1 ¥ E1,134:00 Ytron Conduit (oS See SS Wr Bls/ire. A gpaentashlasie i, O / 8 Ng on Wy Po fz PHOS / ¥o, s ™ ' . *y f A oy OL ea 8 N; f As = x pj Peat * ; 7 SKE. Ss athe __ ‘ys > S “sy - ce Comore" a SOFFSpF ET 728.00 NN . fe y al she%3e"| J» Ay RS ee, ae AS oP St a S, a s SAN \ a o. N “at ceEna'o’ TI ise ELNG.S Tle er Rock Line £10880 2.62004 Psiot7-- 2e%90" i Cross-Section 36° won --- ++ rat em ome errata nnn -— --- 3} Perce te ween ns Cannan nn -- ene 52'0” y £E113400 : Se Ree ge ‘71 yl 34% Sq Bars | oo ‘ 3'Vent | er ‘5 bem t i. ' Le ” \ t 4". pee =! ' ! 1 ‘ Bena fe ee Se. feo i)! ~---~foanmnm BY" ----- Mees, BO hin Partial Front View Partial Segtion on Center Line Fig. 461.—Elevation and Sections of Schuylerville Dam. assuring the absolute stability of the structure under any flood. The angles of these resultants were greater than the angle of fric- tion between the dam and its base, thereby doing away with any possibility of sliding. The buttresses in this dam are 8 ft. 1 in. centers, and have a thickness of 12, 15 and 18 ins. from the top downward in three benches of approximately equal height. DAMS. 633 Reinforcing rods were placed vertically, horizontally and along the edges, as shown in the drawings. The concrete used for the buttresses was a 1:3:6 mixture, the stone being 214 ins. and under in size. The maximum load coming upon the buttresses at any point is 5 tons per sq. ft. No excavation was done for the buttresses, but the rock was thoroughly cleaned off by means of a water jet before depositing the concrete. A trench about 3 ft. wide and deep receives the solid concrete cut-off wall forming the heel of the dam. Three longitudinal beams of reinforced con- crete extend between the buttresses, adding greatly to the stability cf the structure. These beams are shown in both the elevation and cross sections. The crest is 24 ins. thick in the thickest part, and it was planned to contain sockets for flash boards, but these, through an oversight, were omitted. The deck or face is 9 ins, thick immediately below the crest, and increases to 11 ins. at the bottom. The apron has a uniform thickness of 8 ins. from the crest to the curve of the toe, where the thickness of the toe con- crete increases. Johnson corrugated bars, spaced as shown on the drawing, were used for reinforcement. The sizes and spacing of the bars ‘for the deck were so proportioned as to give a factor of safety of 5 with concrete six months old when the crest is under a 5-ft. flood. Un- derneath the bars and supporting them is a netting of wire mesh. The deck and apron were laid of 1: 2: 4 concrete, with aggregates below 34-in., using as wet a mixture as possible. No special fin- ish was given to the surface, and when the dam was filled no perceptible leak could be found. The rock at the site of the dam slopes slightly toward its toe and drain openings were provided by which its drainage is as- sured at ordinary stages of water. During the flood, however, the height of the water is always the same inside the dam as be- low it, there being free communication through the drain open- ings. The shale foundation is seamed with minute cracks, which in the case of a solid dam might allow sufficient leakage to create an upward pressure on the base of the dam and endanger its sta- hility. The possible leakage can cause no trouble, for as soon as the water appears below the cut-off wall it is drained off. The 3-in. vent openings shown below the crest in each bay serve to admit air behind the over-fall, thus breaking the partial vacuum and preventing the trembling of the dam. Openings are provided 634 CONCRETE AND REINFORCED CONCRETE. through the buttresses at the top and bottom to allow easy access to all bays. A bridgeway through the top openings affords a passageway through the dam underneath the crest. This foot- way, which is 16 ft. above the river bed, is dry and well ventilated, is lit by an incandescent lamp in each bay and is used as a pas- sageway from the mill on the north bank to the railway station on the south bank of the river. In the construction of this dam cofferdams were used, which inclosed all but about 70 ft. of the site near the south end, which was left for a by-pass. The portion of the dam within the coffer- dam was all completed except a portion of the deck and apron walls in the lower part of six bays near the middle of the river, which were left for sluiceways when the dam site at the south shore was shut off by a second cofferdam. After the south portion was completed and the cofferdam was removed the sluiceways were closed. The method of closing the sluiceways is unique. The deck and buttresses of the six bays forming the sluiceways were extended, as shown in plan and vertical section in Fig. 462, to form a hori- zontal shelf through which the openings forming the sluiceways were left. Grooves were formed in the buttresses and in the concrete foot- ing. Rough gates of 6-in. timbers were prepared for temporarily closing the bays, and two loose-fitting forms, as shown in the fig- ure, were provided for the construction of the permanent wall of the open bays. A lattice work built up in advance by wiring to- gether horizontal and vertical reinforcing bars of sufficient length to bear on the concrete at the sides and top was used for the wall reinforcement. When everything was ready one of the openings was closed by placing the timber gate in place, the forms and rein- forcement put in place, and the concrete deposited. A second opening ‘was closed in the same manner, and lastly the four re- maining openings closed at the same time and in a similar man- ner. Soft coal ashes were dumped in the stream above to close any temporary leaks in the wooden gates. Two 3-in. pipe drains were set in holes previously prepared in the bottom edge of each form to carry away any water leaking past the gates, thereby preventing damage to the green concrete. When the concrete was sufficiently hard the holes were closed with two soft pine plugs, enclosing a plug of concrete. Flash boards were set to di- DAMS. 635 vert the water from the openings in the apron, and under this protection forms were set and the concrete put in place. Figure 463 shows a design of device for holding a flash-board on hollow concrete dams, but, on account of an oversight, omitted when the Schuylerville dam was constructed. The rod is operated from within the dam; by reversing the hook the rod Stop Logs Buttress Sectional Plan Fig. 462.—Details of Schuylerville Dam. ca be drawn down and the hook will rest in the socket and the boards will then float away. An inverse operation enables the boards to be placed in position. Mr. Geo. F. Hardy, of New York City, was consulting en- gineer, and Tucker & Vinton general contractors for this struc- 636 CONCRETE AND REINFORCED CONCRETE. ture. The author is indebted to the latter for information in re- gard to this dam. Danville Dam.—Figure 464 shows the method used for increas- ing the height of an old masonry dam at Danville, Ky. The ma- Fig. 463.—Scheme for Flashboards on Reinforced Concrete Dams. sonry section had already been strengthened by placing a heavy bank of quarry gravel and clay above it., As it was desired to raise the height of the dam 4 ft., the buttresses and reinforced siab construction shown in the figure was adopted. Openings Air Vent SSS Fig. 464.—Dam at Danville, Ky. were left below the apron to equalize the tail water, and an air inlet is provided by a 6-in. pipe carried out through the abutment and extending above high water mark. The open space within a hollow dam may be utilized for the location of machinery, as turbines, electric generators, etc. While DAMS. 637 if the machinery operating gates, flash boards, etc., are located within the dam, access may be always readily had to them. Figure 465 shows the cross-section of a dam designed by Et 1380 102.0 re : ee SSS —— low Water EL9B0 Fig. 465.—Dam at Cannon Falls, Me. the Ambursen Hydraulic Construction Co. for the Cannon Electric Power Co., Cannon Falls, Minn. As will be noted, the penstock, turbines, generators, operating machinery for gates and tail race are all located within the body of the dam. : || Na <. SS |! | Clear Water Chamber ~ Intake Fig. 466.—Intake and Gate House for Dam at Walton, N. H. _ Figure 466 shows an intake and gate house used on a dam con- structed at Walton, N. H. As will be seen, the gate house is lo- cated all within and in one panel of the dam. CHAPTER XXVII. CONDUITS AND SEWERS. Sewers and water conduits may be built of both plain and reinforced concrete in sizes ranging from a few inches to many feet in diameter. This material has been used much more exten- sively in Europe for aqueducts and sewers than in this country. Two types of construction are employed, viz.: pipes moulded in advance and laid in much the same manner as cast iron pipes, and conduits moulded in place. American practice has been almost -exclusively confined to the latter type of construc- tion, although the first mentioned type has been employed in a few cases, and will undoubtedly have wider use in the future. The use of reinforced concrete in place of plain concrete, brick, vitrified pipe, or metal pipe, is dictated entirely by economy and increased stability. Pipe moulded in advance is used in Europe from a few inches in diameter up to 614 ft. and sometimes 71% ft. in diameter, and 10 or 12 ft. in length. Monolithic conduits constructed in place possess many advan- tages, and it is probable that only the smaller sizes of pipes moulded in advance will become popular, as it is impossible to devise satisfactory forms for building conduits in place of a diameter less than about 3 ft. Much less material is needed to construct pipes moulded before being laid than those moulded in place, as the thickness of the shell rarely exceeds 214 to 3%4 ins., and pipes up to 9 or Io ins. are usually from 34 in. to 2 ins. in thickness, while 6 inches is about the thinnest shell that can be successfully used in conduits ‘constructed in place. , Sewers constructed of concrete have been built for from 50 te 70 per cent. of the cost of brick sewers of the same size. When reinforced concrete is used the added cost of the metal is counterbalanced by the greater strength and the saving in con- crete, which at times is as much as 50 per cent. This construc- CONDUITS AND SEWERS. 639 tion should prove under almost all circumstances as cheap as plain concrete sewers. Reinforced concrete, besides being a cheap material, possesses other advantages for use in conduits, some of which are as follows: It is stronger than either brick or plain concrete, and may be used in lighter sections. It may be strongly reinforced along the length of the pipe and used where there is danger of settlement, without the heavy and expensive foundations usually recessary in such cases. The hardness and smoothness of the surface obtainable with concrete reduces the friction to a mini- mum and renders it less liable to erosion than other materials. Concrete sewers built at Duluth, Minn., show very little wear after twenty years’ use. Conduits may be made practically water-tight under ordinary heads with little trouble, and when especial care is taken will withstand heads of from 50 to 75 ft. Some twenty to twenty-five years ago a number of concrete sewers were constructed in this country but did not prove very satisfactory, owing probaly to the inferior quality of the cement of that time. The great improvement in the quality of cement now used will, however, probably enable concrete to success- fully withstand any wear that may come upon it, especially if a granolithic lining be used for a wearing surface. Some engineers fear concrete will not stand attrition due to possible gravel or small stone carried by water at high velocity, and line their sewers when of large diameter with vitrified brick, and when of small diameter with sections of vitrified clay pipe. Better workmanship is obtained in constructing reinforced concrete sewers than in unreinforced sewers. Concrete sewers are usually built in monolithic lemgths of not ever 50 ft. to avoid shrinkage cracks, but if the section of the longitudinal reinforcement be designed to care for shrinkage and temperature stresses, monoliths of any desired length may be built. . The amount of steel required to care for these stresses may be determined as explained on page 621 in connection with retaining walls. There are no fixed rules for determining the stresses, sections and reinforcement in conduits under the uncertain loadings due to earth pressure and possible superimposed loads. The maximum moving load, together with the weight of the 640 CONCRETE AND REINFORCED CONCRETE. material that may come upon the roof of the conduit, should be taken as the maximum loading, although the actual load in many cases will be less than this. In case the fill over the top of the conduit is small, an addition should be made to the moving load for impact. Whether the roof should be considered as an arch or slab in figuring the stress will depend upon the form of cross section used and the supporting material. In any case, the judgment of the designer will have to be depended upon for the proper treat- ment of the problem under the existing conditions. The stresses in the sides of conduits under internal pressure must be entirely taken up by the circumferential reinforcement. The manner of determining the stresses and sections of metal necessary to care for them is as follows: Let p be the intensity of the internal pressure in pounds per sq. in. d the internal diameter of the conduit in inches. T the tension in the shell per lineal in. = —. If fs is the allowable working stress per sq. in. in steel, 2 a area of the steel required for each longitudinal foot of the concrete will be ir As = . fs or, 6 pd As = fs The reinforcement for sewers and conduits may consist of circumferential rods in the form of hoops or spirals. When hoops are used they should be welded or fully spliced. The rods of adjacent spirals should also be spliced. Longitudinal rods either inside or outside the hooping, depending upon whether the pressure is from within or without, and wired to the hoop- ing at intersecting points, are usually employed. These act as distribution rods, take up shrinkage and temperature strains, and strengthen the pipe longitudinally. When cross strains come upon the pipe provision must be made for an ample section in the longitudinal reinforcement. Expanded metal and various forms of Monier netting are often used for reinforcements in pipe construction. Pipe Cast in Advance for Conduits and Sewers.—The successful manufacture and use in Europe of reinforced pipe cast in short CONDUITS AND SEWERS. 641 lengths would indicate that the attention of American engineers should be called to the subject, as undoubtedly there are many cases in which it may also be economically used in this country. The author only knows of two firms in this country who make concrete pipe. In Europe pipes are generally manufactured at special plants, where the apparatus and process used are controiied by patents. While’ it is undoubtedly true that the cost of manufacture is thereby reduced to a minimum, it is not essential that such apparatus be used, as pipes can be constructed by the use of simple methods at a cost considerably lower than vitrified clay pipe, cast iron pipe, or concrete pipe cast in place. Monier Pipes——The Monier reinforcements for pipes. are formed of longitudinal and spiral rods tied together at their inter- sections. The rods used vary in size from 3 in. to I in, and are usually spaced evenly. The pipes are molded vertically and are of sufficient thickness to permit ramming. A collapsible core and outside casing is used to form the mould. If the shell is too thin to be molded in this way, it is formed in the following manner: The reinforcement is placed on a collapsible core of the size of the internal diameter of the pipe. The concrete is mixed stiff and thrown hard against the core, and passing through the reinforcement forms a layer behind the net work, which is shaken during the process. When the first layer is partly set another layer is added in the same manner, but the net work is not again shaken. This process is continued until a proper thickness is secured. The successive layers are about 36 of an in. in thickness. The inside and outside is then finished with thin layers of mortar floated on. Wayss & Co., of Berlin, Germany, employ special molding machinery. The pipes are formed on a rotating drum of sheet iron or wood covered with zinc. The mortar is applied to the drum through a hopper at its upper surface, and the mortar’ is spread evenly over the drum by rollers. A special arrangement prevents the mortar from breaking away from the lower part of the drum during rotation. After one coat nas been put on, the reinforcing network is wound around it and another layer ot mortar added and the process continued until the desired thick- ness is secured. 642 CONCRETE AND REINFORCED CONCRETE. The Pavin de La Farge pipes are constructed according to one of the first two methods used for Monier pipes. These pipes are reinforced with longitudinal bars about which are circumferential bars wound in the form of spirals for the smaller size pipes, but for the larger size circular hoops are formed by welding the ends of the hooping bars together. The reinforcements for horseshoe conduits and other sections are made in much the same way. The pipes are usually constructed in sections of from 3 to 6.5 ft. in length. The sections are con- Fig. 467.—Joint for Pavin de La Farge Pipe. nected by collars of reinforced concrete and expansion joints formed by a plain collar and two iron angle collars. The angle collars are secured by bolts and the joint is made by two rings of India rubber, which are pressed between the angle rings and the plain collar when tightened up, as shown in F ig. 467. Bordenave Pipes—The reinforcement for the Bordenave pipe is bent by machinery, and wound in helical rolls, which are placed on a core and adjusted until the required pitch is obtained. The longitudinals are then placed inside or outside the spirals depending upon whether the pressure is from within or without, CONDUITS AND SEWERS. 043 and tied to them in the proper positions with pieces of wire. Small I-sections and-round rods are used for both spiral and longitudinal reinforcements. The casting is done from a covered platform on which the concrete is mixed. This platform is mounted on a framework which runs on a track over the molding floor, and which carries hoisting apparatus for handling the molds. A core, which is adjustable in diameter and collapsible, together with an outside hollow cylinder divided in halves is used to form the mold. The reinforcing coil described above is set on end, the core placed within it and adjusted to the proper diameter. The outside mold is then clasped in place and the mold is filled with liquid mortar through a special funnel fixed to the platform. Before the mortar is entirely set the funnel is removed and the top of the pipe formed by hand. When the mortar has hardened the shell is removed and the core collapsed and withdrawn. The pipe is left standing for a time and then removed and stacked until used. A quick setting cement is used in the manufacture of these pipes. Among other notable works in which the Bordenave pipe has been used is that for the water works at Bone, Algeria, built in 1893. Eighteen and a half miles of conduit about 24 ins. in diameter was built, much of it being under a head of from 50 to 80 feet. Figure 468 shows the arrangement of the reinforce- ment used in this pipe. For a pressure head of 50 feet ft. the coils of the circumferential reinforcements were spaced about 3% ins. apart, and for a head of 80 ft. about 2 ins. apart. The longitudinal reinforcements were spaced about 314 ins. apart cir- cumferentially. The shell was about 134 ins. thick. The rein- forcements used were small .47 in. x 2 in. I’s, and weighed about 0.142 lbs. per ft. The joints were spliced with collars of the same construction as the pipe, as shown in Fig. 468. These were slipped over the adjacent ends and fastened by filling the annular space between the collar and pipe with mortar. Bonna Pipe-——The Bonna pipes are reinforced with a bar having a section the form of a cross. This gives a large area for adhesion. Either a spiral or hooped circular reinforcement is used, depending upon the size of the pipe. Figure 168, page 269. shows a simple spiral wound pipe reinforcement. When hoops 644 CONCRETE AND REINFORCED GONCRETE. are employed they are cut to the proper length, bent into hoops and the ends fastened together with a riveted joint. A series of hoops are placed upright at proper distances apart in frames, and the longitudinal bars having notches cut in their sides at <7 a vache 9,84’ -------------- Fig. 468.—Bordenave Construction for Pipe. proper intervals apart to receive the hoops, are placed in position, and all firmly wired together. For high pressure, two series of reinforcing skeletons are employed with a sheet steel tube between them. These tubes are also used inside pipes with a single reinforcing skeleton work, in which case they act as a mandrel on which the pipe is molded. CONDUITS AND SEWERS. 645 The steel sheet tubes are usually formed of three pieces having their edges bent in the form of clips, as shown in Fig. 469. These clips are hooked together and clasped tightly by special machinery. The joints are sometimes soldered to make them entirely watertight. For pressures up to 50 ft. the steel tubes are formed of metal of about No. 10 gauge, and for pressure greater than 50 ft. about No, 7 gauge is employed. The pipes are molded in a manner similar to that used in casting the Bordenave pipe. The cores are of sheet iron and col- lapsible. The outside mold is made of sheet steel in halves, and held together by hoops. _When an inside shell is used it is employed for a core. A liquid mortar formed of a mixture of quick and slow setting cement is poured in much the same manner Fig. 469.—Steel Lining Fig. 470.—Joint for Unlined Bonna Pipe. for Bonna Pipe. as in the Bordenave system. While the liquid mortar is being poured the sides of the molds are pounded with a wooden mallet to drive out the air and consolidate the mortar. In some cases a steel core with both inside and outside reinforcements is used. In this case the steel shell is put in place, the inside and cutside reinforcements put inside and outside the shell; a col- lapsible core put inside and a sheet steel mold outside, and the pipe poured as before. A traveling platform and apparatus for pouring the concrete are provided as in the Bordenave system. M. Bonna built a number of large sewers in Paris. In the Mery, Prerielage and Treil districts alone about 75 miles of pine was laid. These pipes vary from 12 to 43 ins. in diameter, and in some cases 6.5 pipes were used. The pipes were constructed in lengths of about 8 ft. and laid 646 CONCRETE AND REINFORCED CONCRETE. by setting them end to end and joining them with special collar joints. Figure 470 shows joint used for joining pipe without interior tube, and Fig. 471 shows detail of joint for pipe with interior tube. The cost of the conduit having a diameter of about 6 ft. was Fig. 471.—Joint for Lined Bonna Pipe. approximately $18 per lineal ft. for the lined pipe, and about $12 per lineal ft. for the unlined pipe. U.S. Reclamation Pipe Tests —Experiments were made in 1904 by the U. S. Reclamation Service upon large reinforced pipes to determine their fitness as service conduits for irrigation work. An attempt was made to determine the various conditions which should be considered in the construction of large pipes. A num- ber of pipes 20 ft. in length and 5 ft. in diameter were built and tested. These pipes were reinforced with 34-in. round circum- ferential rods spaced 234 ins. centers, and held in place by 8 longitudinal rods 14 in. in diameter wired to them. The following general precautions should be considered in manufacturing and use of reinforced concrete pipe: (1) Do not allow the sun’s rays to touch the concrete when it is being mixed and placed in the forms. If necessary, build a shed over the work to insure this precaution. CONDUITS AND SEWERS. 647 (2) If the reinforced concrete pige cannot be made contin- uously by machine, do as much of the hand tamping as possible ir radial directions. When the tamping must be done at right angles to the radius of the pipe, either in longitudinal or circum- ferential directions, avoid as far as possible the formation of seams or cleavage planes, from delays in placing the forms and adding fresh material. By making the concrete very wet, delays will not. be so dangerous as in the case of dry concrete. (3) Be careful in tamping not to spring the longitudinal rods, and use as few of these as will suffice to hold the circumferential rods in place, except in case of vertical curves in the pipe, when additional rods or steel cables must be used on the longer sides cf the curved part of the pipe. (4) Do not depend upon the tensile strength of the concrete but make the steel rods of such size and distance apart as will insure no greater stretch of the steel than 0.04 in. in any rod from the maximum pressure to which the pipe is subjected. (5) Make pipe 1% in. larger inside diameter than required, to allow of putting two coats of plaster on the inside. (6) As soon as the pipe is completed give the inside one coat of plaster 14 in. thick, composed of 1 of cement to 114 of sand, and a small quantity of lime paste, thoroughly cooled, to retard setting. Keep pipe well wet ahead of the plastering. When this coat, which may be left rough, is dry, put on another coat abouit \% in. thick of plaster composed of 1 part of sand to 1 part of cement. This coat should be troweled to a smooth surface, and when it is dry give the entire surface of the pipe a thick wash of fine cement and water. (7) Provide for drainage of water which may leak through when the pipe is first filled, so that sufficient water may not remain in the trench to soften the ground under the pipe. (8) Bury the pipe under ground so that there will be no place less than 2 ft. between the top of the pipe and the natural surface of the ground. (9) In very cold climates provide means for draining the pipe so that it can be emptied at the end of each irrigating season. (10) A soap and alum mixture may be used to advantage in the making of the concrete, but reliance for impermeability must be placed on the plastering rather than on the material of the pipe. (11) Do not use reinforced concrete pipes for heads over 70 ft., \ 648 CONCRETE AND REINFORCED CONCRETE. except for short distances, where 100-ft. head might be allowed by taking special precautions. - Jackson Pipe—The Reinforced Concrete Pipe Co., of Jackson, Mich., manufactures and sells a reinforced concrete pipe (Fig. 472). This pipe was used in the construction of sewers at St. Joseph, Mo. The thickness of the wall of the pipe is 4 ins. for 36-in., 4% ins. for the 42-in., 5 ins. for the 48-in., and 7 ins. for the 72-in. pipe. Each pipe section is reinforced longitudinally by 5 bars, except the 72-in. pipe, which has 7 longitudinal bars. Two transverse circular bands, each placed 9 ins. from the ends of the section, are also used and the longitudinal bars pushed through slots punched in the hoops. The pipe is manufactured Fig. 472.—View of Jackson Pipes. in 3-{t. sections. The thickness of one end of each section is reduced by a rectangular rebate, and by a beveled edge, both ex- tending around the circumference. The other end is correspond- ingly flanged, so that when two sections are placed end to end they fit together. The longitudinal reinforcing bars in each section extend with hooked ends into the rebated space which forms the outside groove when two sections are placed together. The sections are then interlocked with a tieband passing completely around the section of the grooves at the joint and through the hooked ends , CONDUITS AND SEIVERS. 649 of the longitudinal reinforcing bars. After the sections have been thus interlocked the joint is enclosed, except some 20 ins. on the top, with a galvanized iron shield. The inner surface is sur- rounded with a galvanized iron mold and the joint poured with 1:2 Portland cement mortar. In the process of manufacture of the pipe a bottom plate of cast iron is used, shaped so as to give the desired flange sec- tions at the bottom end of the pipe. The inside form or core is in four sections of rolled sheet steel. The longitudinal rein- forcing rods are inserted in receiving sockets in the plate and the outer case is then added together with lower and upper flange mold. The reinforcing bars are held in place by clips at the top. The circular reinforcing bars are slot punched to receive the longitudinal rods. When the forms are in position the concrete—usually a 1: 2:3 mixture—is placed in small quantities and thoroughly tamped. Wilson & Baillie Cement Pipe—The manufacture of cement pipe is not a new industry. As early as 1825 Portland cement pipe was made in England, and since that time it has been used j to a limited extent in continental Europe. Cement pipe was first introduced in Brooklyn, N. Y., about 1860, and when proper materials have been used, no failures have been known. Among the advantages of this class of pipe are the convenience of making repairs, the facility with which the pipe may be laid to line and grade, and the ease of making joints. Another advantage lies in the fact that the flat base gives a uniform bearing throughout, rendering the use of a concrete cradle unnecessary, the pipe possessing sufficient inherent strength to withstand any pressure that may be brought to bear upon it. The early pipes laid in Brooklyn, N. Y., and other cities were all made by hand. The forms in many cases consisted of a solid core and a shallow flask in two parts. The flask was clamped together, placed on a plate or ring and lowered over the core. A tray was fitted on top of the collar and concrete shoveled into the tray and spaded and tamped into place with an iron rammer. The mix consisted of one part Rosendale cement, and three parts of coarse sand, mixed with about 25 per cent. water to the consistency of a thick paste. Owing to the difficulty of thoroughly mixing and tamping the ingredients, great trouble was experienced in turning out 650 CONCRETE AND REINFORCED CONCRETE. homogeneous pipe of equal density throughout. Up to 1890, all the cement pipe laid in Brooklyn, N. Y., had been made by hand, at which time the Wilson & Baillie Manufacturing Co., who had been experimenting for a number of years, intro- duced a machine-made ptpe. In the manufacture of the machine- made pipe, the cement, sand, broken trap rock and water were measured, and thoroughly mixed in a mill, evenly fed to the moulds and rammed by machinery regulated to produce con- tinuous and uniform blows of any impact desired. The result Fig. 475.—Machine Head Down Shell Machine with Pipe Complete. in, Place, is a product perfectly homogeneous and of equa! and great density throughout. Figure 473 shows the machine with head down, shell in place, ready for making a 12-in. round flat base pipe. It also shows the pipe complete, rammed up in the shell. Figure 474 shows the core withdrawn, head raised, shell and pipe removed and the machine in position to receive an empty shell. A machine similar to the one shown is used for the manu- facture of egg shape pipe. Described briefly, it consists in the main of a base with a revolving table and two upright columns, about four feet apart, bolted to the base by flanges and carrying a cross .piece on top for the bearings of the gears. There is one large central shaft running tothe central head with a key way CONDUITS AND SEWERS. 651 from end to end, and a key in a cogwheel to set same. This shaft actuates a barrel cam inside of the frame which imparts the tamping or up and down movement to the rammers. The head or frame has a vertical movement in slides secured to the columns, allowing the head to move up and down as the pipe is being formed. By means of a slide with a roller, a small shaft, running parallel to the large central shaft, moves a second cam which has therexact opposite of an egg shape. Attached to cam No. 2 is a lever, the lower end of which is secured to a finger slide. The slide extends into the head which acts as a guide and the finger projects downward and through a shoe Fig. 474.—Machine Ready for Another Pipe. carrying the rammers, while the shoe itself is held on a hori- zontal slide attached to the drum slide which does the tamping. As the upper cam revolves it causes the upper slide to move in and out, and also imparts, by the lever, the opposite movement to the lower finger slide. The latter propels the shoe carrying the rammers, and thus causes the rammers to conform to the irregular shape of the pipe which is revolving on the table. For making egg shape pipe there are eight tampers made of the best tooled steel, each running two hundred tamps per minute. As there is only one rammer. down at a time, the weight of the head must be borne entirely by the density of the material forming the pipe and this results in an even and regular 652 CONCRETE AND REINFORCED CONCRETE product such as has been impossible, heretofore, to achieve by hand. The mixing of the concrete is done mechanically, a cube mixer being used which discharges about 30 inches above the floor, the feeding point being on the floor above. Over the mixer is a hopper into which the crushed stone and sand are discharged by bucket conveyor from the ground. The cement is distributed -into the hopper, through the mass. The whole is discharged into the mixer dry, where it receives several revolutions before the water is added, which is allowed to enter in the usual way through the hollow shaft of the mixer. The proportions used in the mix are one and one-half parts Portland cement, one part sand, and three parts trap rock screenings, containing 20 per Fig. 475.—Showing Manner of Stripping Shell from Pipe. cent. of stone dust. The amount of water used in the mass will vary from Io per cent. to 15 per cent., according to the dryness of the ballast. Water is measured in a marked tank and is in control of the man who opens and closes the mixer. The mix is known as a “dry mix,” but will ball in the hand with some pres- sure. The mixed concrete is delivered to the machines in barrows and is fed into the hopper by two men, one on either side. As soon as the flask is full and the core automatically lifted clear, the flask is taken up by a pipe truck having arms with sockets to engage the lugs on either side of the flask and wheeled into th< stripping rooms where it is allowed to stand about thirty minutes before being stripped. Figure 475 shows the manner in which a shell is stripped from CONDUITS AND SEIVERS. 653 the 12-in. round flat base pipe, and also a similar view for a 24-in. egg shape flat base pipe. After the pipes have set over- night a spray of water is turned on and the pipes kept damp until the expiration of six days, when they are removed from under cover and placed in a yard. At the end of 30 days they are crystallized sufficiently to be handled in the work. Spurs for house connections are made as follows: A hole is cut at the proper point on the side of the pipe and a center is placed in the interior; cement mortar is then spread over the form and the connection piece is bedded in place and a heavy band of mortar is wiped around the joint on the outside. After the center is removed, the inside joint is finished with a trowel. Fig. 476.—Cement Pipe with Connection for Lateral. Figure 476 shows 15-in. egg shaped pipe with manner of making house connections. In order to meet hydrostatic tests, the interior of the pipes are coated with California maltha reduced in bisulphide of carbon. Satisfactory results in this direction have also been obtained by using silicate of soda as a bath into which the pipes are plunged. These pipes are all 3 ft. in length, with hub joints, with the exception of the 6-in. size, which is 2 ft. 3 ins. long. The thick- ness of walls is as follows: 6-inch round pipe ...........cc cece eee eens %4 inch. OHUCH POUNE PIPES sccosecsancv acd dn dA s wmvsiaietnauenne we 12-inch round flat base pipe ...............5- ris “ 15-inch egg shape flat base .................. 1% “ 18-inch egg shape flat base ............0.0005 1% “ 24-inch egg shape flat base ................. 2 a 654 CONCRETE AND REINFORCED CONCRETE. Collars are of the following dimensions: ’ Fs ; ed 6-inch collars 1°/i in. deep with joint of Ve inch. i ie Phe “ “ “ 1B 9 “ “ I hs “e oe “ +e 3 16 ce oo eee S. Se ‘ ‘ i “ a aie 2 : . ae A 24 “ “ 1% “ ‘“ “ “ yu Figure 477 shows a length of 24-in. egg shape flat base pipe. Some interesting tests have been made on the crushing strength Fig. 477.—Egg-Shaped Cement Pipe. of machine-made cement pipe during the past year, a summary of which follows: Size and Description. Breaking Weight. 12-inch round and flat base ................ 10,624 lbs. 18-inch egg a BG GEE” | src amatai tatty ache *18,785 “ 18- “ ed ne Dy se emueetes So a eH ee 12,287 18- “ ie e BH NO seca cpauaRtuisein Baus aoys T13,190 “ 24- “ sf as PAS CET cael Mansi tated eyga 20,547. * *Cracked at 14,155 lbs.; additional required to crush. jCracked at ',717 lbs., additional required to crush. . In making the tests, a wooden beam, 20 ft. long, was used, with a 2-ft. fulcrum. The pressure was applied to a saddle having a rubber gasket between it and the pipe so as to give the saddle an even bearing and thus do away with any concen- trated pressure. CONDUITS AND SEIIERS. 655 Some vitrified pipe tests at the same time showed the following results : Size and Deseription. Breaking Weight. 12-inch double strength shale ................ 7,750 lbs. 12-inch single strength vitrified .............. 7,544 “ 12-inch standard Akron (average of 3)........ 5,500 “ TAANEH Witt HEM os.ccosaccesdeaue ah gare.a a acd seanvduarononace oes 7,859 “ 18-inch Akron double strength .............. . 8842 “ It is probable that the old aversion to cement pipe will be gradually dissipated by the introduction of an improved machine- made product, and that the use of such pipe will be largely in- creased during the next few years. Reinforced Concrete Conduits Built in Place.—Great care must be taken in the construction of sewers and aqueducts in order that they be strong and as nearly impervious as possible. The centers must be smooth, strong and rigid,,and so constructed that they are easily assembled and taken down. Examples will be given to illustrate the most successful appli- cations of reinforced concrete to various forms of concrete sewers and aqueduct construction. The method of construction and a description of the forms used are given in connection with the description of various structures. Simplon Aqueduct.—The aqueduct which carries water from the Rhone to the power works of the Simplon tunnel at Breig, Switzerland, is of Hennebique construction. It is rectangular in. sections and 1.86 miles in length, with a fall of 6.35 ft. per mile. It is carried on supports spaced about 16 ft. 5 in. centers. Figure 478 shows transverse and longitudinal sections of half a bay, giving details, general dimensions, and materials used. Sizes and dimensions given in this figure are in the metric system. The inside dimensions are about 6 ft. 3 ins. by 6 ft. 3 ins., and the side walls are about 4 ins. thick. The bottom has a thickness of about 4 ins. at the sides and is thickened toward the center to nearly 6 ins. The roof is thickened in the same manner from 3% to. 434 ins. The vertical reinforcing rods in the walls are about 3%-in. diameter, and are spaced 7%-in. centers. Three longi- tudinal rods were used at the top, bottom and sides, the top and bottom rods being about 5¢-in. diameter, and the side rods 3; in. in diameter.. A 5-in. trussing rod which at the center of the bay is at the bottom of the sides, is bent upward, runs to the top at the supports. 656 CONCRETE AND REINFORCED CONCRETE. The bottom reinforcement consists of two sets of rods about 3% and 7; in. in diameter, both sets being spaced 7% in. apart. The 3%-in. rods are bent up and form the side reinforce- ment, and the #;-in. rods are also bent up and extend 1 ft. 6 in. into the sides. There are two longitudinal rods 5-16 in. in diameter spaced evenly on each side of the center. The top is reinforced by % and #s-in. rods spaced 7%-in. centers, and located as shown in the figure. Stirrups of 34 x gy-in. hoop iron are placed about all rods. The roof was designed to carry a load of 165 lbs. per sq. ft. and an internal pressure of 62 Ibs. per sq. ft. Provision for seh ) 1 6 eke Ne \ ‘ pa \ nt vf \ i ; i } ae ' 1 aN” 1 ie 6.239" .-------- fi i YY i I wd och S ee ee gs ee y | 4a “| ‘ 1 1 aN! i 4; PP ETRERIRCRTROTBLETE! gj Vay Vga yy wy i" Re gi te 14 ya a gt a aN et a tk Oh by do op M chy Hg uN gf I ( Vat as ou ad ad gu ae 1 @ i toed PB OY ae os tt Fale baal aed Sets EE f= 1 pats | Fig. 478.—Aqueduct for Simplon Tunnel Water Power Plant. expansion was made by open joints over the piers. These were filled after the concrete had set and before the water was turned into the flume. When filled with water very little expansion or contraction can occur. The cost of this aqueduct was about $5.90 per linear foot. Salt Lake City Aqueduct.—A reinforced concrete aqueduct 38,000 ft. long has been constructed at Salt Lake City in order to secure an added water supply. It is partly in excavation, partly in tunnel and partly above ground, thus giving three types of construction. The aqueduct is built on a hydraulic grade and will not be CONDUITS AND SEWERS. 657 subjected to internal pressure other than the weight of the water flowing in it. Figure 479 shows normal section in excavation, and consists of a roof slab modified to suit depth of fill. The thickness is soa Ss * NS S e 8 "kp eee ian, Fig. 479.—Section of Salt Lake City Conduit in Excavation. 4 ins. for 5 ft. fill with Ransome twisted bars as shown; 5 ins. for 5 ft. to ro ft. fill, reinforced with 14-in. bars spaced 9-in. centefs. For a covering exceeding Io ft. a 6-in. slab reinforced with 14-in. bars spaced 6 ins. apart is used. A Elevation. Section C-D. . Fig. 480.—Section of Salt Lake City Conduit on Piers. The tunnel section is in rock and consists of a concrete lining for sides and bottom and brick arch for top. It was deemed unwise to build on an embankment, and section shown in Fig. 658 CONCRETE AND REINFORCED CONCRETE. 480 on concrete piers, spaced 15 ft. centers with additional rein- forcement was used. But joints were used at each pier, and joints grouted in cold weather so as to throw the conduit into compression to care for expansion. The interior of the conduit was coated with a grout of a 1:1 Portland cement and fine sand. The concrete used was a 1:214:4 mixture of Portland cement, sand and broken stone or gravel. The engineer in charge was Mr. Geo. W. Riter, City Engr. of Salt Lake City. Cedar Grove Reservoir Conduit, Newark, N. J.—A 5 ft. rein- forced concrete conduit 4,000 ft. in length was employed in the construction of the Cedar Grove reservoir for the Newark, N. J., water works, and extended from the regulating inlet gate chamber at the north end of the reservoir to the inlet stand pipe at the south end. Another line consisting of a double conduit 1,500 ft. long Fig. 481.—Conduits, Cedar Grove Reservoir, Newark, N. J. extended from the outlet gate chamber to the outlet channel. Figs. 481 and 481A show cross sections of these two conduits. The reinforcement consisted of a circumferential ring of No. 10 gauge 3-in. mesh expanded metal with lapped joints. A 1:2:5 Portland cement concrete with 1%4-in. broken stone was used. The center used in the construction of the single conduit is shown in Fig. 481A. These centers were built in sections 16 ft. long, and were supported on brick piers resting upon foundation concrete as shown by the drawing. The forms were set up and the lagging put in complete, except for a manhole at the middle of the crown. Through these holes the concrete for the inverts was passed to the men working on the inside of the form. After the invert concrete was put in the manholes were closed and the concreting completed in the usual manner. To collapse the forms the bolts holding the bottom cross pieces were withdrawn, CONDUITS ‘AND SEWERS. 659 the cross pieces removed and the feet of the ribs slightly drawn together. A certain amount of play was allowed in the joints to make them slightly flexible. The centers were struck in about 36 hours after the concrete was laid. The method of building the double conduit is shown in Fig. 482. Reinforced Concrete Conduit for the Jersey City Water Supply Co.—The conduit for the Jersey City Water Supply Co. is an excellent example of reinforced concrete construction. Some three and a half miles of reinforced conduit 8% ft. in diameter was used. Four principal types of reinforced sections were employed. Fig. 483 shows sections used in rock, in stiff earth and x axa. ‘Lagging f bo'leng Same as other. Side Outside Form Boards, oREkab long BK6 xB "Posts, every a ‘o” Fig. 481A.—Forms for Single Conduit, Cedar Grove Reservoir. rock, in soft earth bottom and on foundation embankment. These various sections were reinforced with transverse 3g-in. square steel rods bent in the form shown in the drawing, spaced 1 ft. apart, and 1%4-in. longitudinal twisted rods placed 2 ft. apart and wired to the transverse rods. The general dimensions and thickness of concrete used is shown in the drawings. About 90% of the conduit was built in open trench of the type for stiff earth and rock. This section was used for all depths of cover up to about 10 ft. In a few pieces amounting to 826 lin. it. when the cover was about 15 ft. the heavy rock section was used. 660 CONCRETE AND REINFORCED CONCRETE, Fig. 482.—Forms for Double Conduit, Cedar Grove Reservoir. In the construction of both these types the transverse rods were made of such lengths as to extend 1 ft. below the bottom of the outside forms, below which the concrete was built against the hard earth or rock sides of the trench. 7 Longitudinal 4" Twisted GF Stet! Rodse'opart “Twisted Steel ds apart ir Ends lapped by, Vand Weed fy 3'Mesh,#10 Expanded Metal \ v ‘Line of a Cross-Section? CH 58" —-J Sections in Stiff Earth and Rack | Cover, 2 ae 3. FDp-207 Ho3° Lopped /' and Wired Concrete Fig. +83.—Sections of Jersey City Water Works Conduit. CONDUITS AND SEIWERS. 661 The soft ground section shown was used for short lengths where the bottom of the trench was in soft earth. Concrete 6 ins. in thickness at the middle and from 8 to 18 ins. thick at the sides, according to the conditions, in which 3-in. mesh No. 10 expanded metal was imbedded, was placed as a foundation and the conduit built upon it as shown in the sections. Some 420 ft. of this type of section was employed, the 3-in. transverse reinforcing rods in these last two types completely encircling the base of the conduit. In all cases where the rods were spliced a lap of 1 ft. was made and the ends wired together. . Fig. 484.—Center for Jersey City Water Works Conduit. A very dense concrete weighing from 156 to 160 Ibs per cu. ft. was used. It was composed of 1 part Atlas Portland cement, and 7 parts of aggregate consisting of a carefully balanced mixture of sand and crushed trap rock, crusher run of 2 ins. maximum size stone. A very wet mixture was used, it being of such a consistency that it would just flow through chutes with a slope of I vertical to 8 horizontal. The concrete was run through chutes from the mixer to watertight dished boxes, from which it was shoveled with coal scoops into the forms. Two types of centers, as shown in Figs. 484 and 485, were employed. That shown in Fig. 484 was 662 CONCRETE AND REINFORCED CONCRETE covered with thin sheet steel. All centers were made of eleven (11) segments each weighing about 200 Ibs. The specifications required that the conduit should. be built in monolithic sections not exceeding 20 ft. in length, but sections 50 ft. long were used where the top of the conduit was not over 18 ins. above the undisturbed ground. Where the trench was near the required width no back forms were used. When it was necessary to use them they were built up in sections 2 ft. wide and 12.5 feet long. No outside forms were employed for a width of about 5 ft. at the. top of the arch. The forms were built up of 7%-in. lagging’ with ribs and bracing as shown in the illustration. Fig. 1!85.—Center for Jersey City Water Works Conduit. The general method of construction was about as follows: Forms were set up for the sections to be built, making a con- tinuous inner mold for the conduit, except for about 6 ft. in- the lowest part of the invert. These forms were supported on 6 in blocks of concrete which were built into the work. Each 12.5 ft. section of the inside forms had a scuttle about 2 ft. square at the crown of the arch. After having been set the forms were greased with cheap vaseline cut with kerosene, and the twisted rods put in position and wired together. The concrete was deposited on the outside, and by means of tamping bars forced CONDUITS AND SEWERS. 663 under the forms until it appeared on the inside and filled the entire space between the ground and the forms. Concrete was then thrown through the scuttles and screeded into shape and finished smooth by troweling while the mortar was plastic. The scuttles were then closed and the work of making the concrete shell continued. Outside forms were added as the work pro- gressed until all the concrete had been placed, except about 5 ft. along the crown; this was completed without the aid of an outside form. Care was taken to keep the forms clean. At the end of Concrere. ot Lu | « \ o,f ! ey \ raat “Sars 4/5"——-- / - \ i Expanded Metal | | | Granolithic 6" Mesh, 23" rly \ 1/16 °8 td \ { r Se of cy Fig. 486.—Cross-Section of 9-Ft. Concrete Sewer, Torresdale Filler Conduits. each day’s work a groove was formed in the face of the concrete around its whole ring to bond with the concrete next laid. The reinforcing rods extend across these joints. Fine cracks were found to girdle many of these joints, but were observed nowhere else. The leakage, however, was not serious, and after a time the cracks silted up. Little or no brushing or plastering of the concrete surface was done and the interior of the conduit was found to bé smoother than average brick work in similar con- struction. The speed of construction was quite rapid. Between July 25 and November 14, 1903, 18,500 ft. of conduit was built. 664 CONCRETE AND REINFORCED CONCRETE. On one section a force of 38 men averaged 39.8 ft. of conduit per day for 65 days. The Torresdale Filter Conduits—Large reinforced concrete conduits and sewers were used in the construction of the Torres- dale filters for the Philadelphia water supply. The effluent conduit, 2,200 ft. long, has the form of cross sections shown in Fig. 486 for the 9 ft. sections. It is in successive portions 72, 9 and 10 ft. in height. The discharge conduit 850 ft. in length is also ten (10) ft. in height. These conduits will be under a head of 20 ft. Two sizes of concrete sewers were used; first, a 6-ft. reinforced section 1,800 ft. in length and an 814-ft. sewer 300 ft. in length reinforced, as shown in Fig. 487, with two layers of 3-in. mesh No. 10 expanded metal; one was placed 06" > Fig. 487.—Cross-Section of 81%4-Ft. Sewer, Torresdale Filler Conduits. 2% ins. from the interior surface and the other 2% ins. from the outside. , The reinforcement for the discharge conduit consisted of one layer of 6-in. mesh No. 4 expanded metal cut double width, but as it proved difficult to cut such heavy metal, two layers of No. 4 metal 6 in. mesh wired together was used for the filtered water conduit. The position of the metal is shown in the drawings. Adjacent sheets were lapped with not less than 6 ins. The 6-in. metal proved much more satisfactory than the 3-in., as the latter had a tendency to screen the mortar from the stone. Some diffi- culty was experienced in properly placing and ramming the concrete in the bottom and lower portion of the circular sections. much better work resulting when the “horseshoe” section with its comparatively flat bottom was used, as the metal could be kept closer to shape and the concrete more thoroughly rammed. CONDUITS AND SEWERS. 665 The general character of the forms and centers used for bott the conduit and sewers are clearly shown in Figs. 488 to 492. ° gee 2 “Space for dropping Center AG Medges le'Long, 6'Wide Tapered 3"*to2" | Fest Board 2'x10” tL Outside covered with py Tin or Sheet-lron Fig. 488.—Form for 6-Ft. Sewer. The 9-ft. form was the last built and proved the best. The forms were covered with No. 27 galvanized sheet iron, which Dressed "Space lagging 3 pe ang" v Fest Board Bibs 2"Thick Spaced 2/8"C.toC. or Sheet Iron 3 Bolts ‘o"Long Fig. 489.—Form for 8%-Ft. Sewer. gave a smooth surface to the concrete and greatly lengthened the life of the forms. Their surface was cleaned and oiled each Dressed | 4 bagging Vez j Y Ribs and Braces HSperced 18°C toC pi 2 Bolts \ JZ tside covered with Form 13'0" Long.) Sx, a Tin or Sheettron Fig. 490.—Form for 71%4-Ft. Sewer. time before being used. The bracing inside the forms was arranged to allow a-center to be taken apart after the concrete 666 CONCRETE AND REINFORCED CONCRETE. had been placed for at least 60 hours, and brought forward through the form already in place for further use. The straight portions of the conduit were built in mogoliths 12 ft. to 13 ft. 6 ins. in length with a bonding groove in the end of each section, and with the expanded metal extending from one section to the next. All conduits have an inch granolithic finish on the interior surfaces composed of 1 part Portland cement, 1 part sand, and T part grit, mixed to the consistency of stiff grout and poured just in advance of the placing of each layer of concrete with an inch space between the inside forms and sheets of iron, with lugs which were gradually withdrawn as the concrete was placed. Very smooth surfaces were thus secured. call alll Sec Wedges Tapered 3"t02" * Dressed 4 ya a ee nies 7 ‘ thea y utside covel Haggg eA? a A with Tin or Sheet-lrorm. Ribs 2Pces I" Thick Ribs and Braces spaced 2/0"C.t0€. Fig. 491. Sete ra for 10-Ft. Sewer. The concrete was mixed rather wet and placed in 6-in. layers. The manner of building a section was as follows: A bulkhead (Fig. 493) was set up the length of the form in advance of the end of the section already built, and the bottom concrete filled in to within 1 in. of the invert face. The bottom section of the form, which is in two pieces, is then set, its rear end being bolted to the face of the last form used and its front end resting in the bulkhead. About 2 tons of pig iron were then placed on the invert form to keep it from floating, and the granolithic mixture was then poured through four spouts at the corners into the space between the concrete and the form. The centérs were then put in place and the face finish and concrete. put in as already explained. The bulkhead had a slot permitting the expanded metal to pro- ject 6 ins. from the face of the concrete to tie the adjacent CONDUITS AND oEWERS. 667 sections together, and also a rib to form a depression into which the concrete of the next section was rammed. /8'Centers. gix3 ‘Lagging, : ~. Covered with ' Xp m Galv. Sheet Iron, ' ; Y i 2x 6 Braces-/8'Centers. 3 -/éRibs. ° + Bolts with tron Pipe L Separators. Fig. 493.—Bulkhead Form, Torresdale Conduits. It was found that the different sized sections could be built in about the same time, it taking usually from 8 to 10 hours to build a section. One foreman and 18 men on top of the 668 CONCRETE AND REINFORCED CONCRETE. trench mixed and handled the concrete and granolithic mortar, while 1 foreman, 1 carpenter, and 7 men in the trench set the forms, placed and rammed the concrete, etc. It required 20 cu. yds. of concrete and 1,200 sq. ft. of ex- panded metal and 125 bags of cement to build a section 13% ft. long. The cost of the conduit, excluding the cost of excavation and the contractor’s profit, but including forms, expanded metal, materials for concrete and labor, is stated as about $10.50 per cu. yd, The cost per linear ft., exclusive of excavation and ae engineering supervision of the different sizes of conduit and sewers, was as follows: Cost per Size. lineal ft. 6 feCB is ion ert ads axon ates etpahion Hany toeei eg eeeMae eae Yl $7.24 vio feet Woh ceavcassxbeteesi@ingee ees PE eReee es Reese ee SS 19.85 S&S. feet. dianiéter: 3 s.252242 oe auger ag ee cubs 24 ee Meo Sonn bonnes 22.523 8% feet Ge A ee Ne aun ir ch, Duca eae dG, tuche, Ceieamaanaap Pande RRR ER 21.59 G2 HEEL RIG ais ois. qus tageresirentrecunt sisr-0i eaays org raph Srweeranouns dw RG ceee huGN Ee aise 23.94 TO, MESS Schaal be Reteiteetetan hook aes aur a ent aeas donee 20.37 The Providence Sewer.—Figure 494 shows a section of a rein- forced concrete sewer in Brooks Street, Providence, R. I.; 520 it. of it is 56 in. in diameter, 830 ft. is 48 in. in diameter, and 2,150 ft. is 36 in. in diameter. The reinforcement consists of expanded metal No. 14 gauge, 4 in. mesh. A piece 18 ins. wide is placed in the concrete at the sides of the sewer with about half its width helow the springing line. The crown reinforcement laps 6 ins. on these side pieces. The minimum thickness used for the concrete was 4 ins. The invert for about one-fourth the circumference of the sewer was lined with granolithic work similar to that used on sidewalks. Sheet steel was used for inside forms for both upper and lower CONDUITS AND SEWERS. 669 halves of the sewer. Sections 8 ft. long were lubricated with crude oil before setting them in place. The forms were left in place 24 hours, and 32 ft. of sewer was made a day with a gang of 10 men, the bottom half being kept 1 day ahead of the arch. The Harrisburg Intercepting Sewer.—The Harrisburg sewer is a good example of a reinforced concrete sewer with a horseshoe section. A description of the method of: construction used will serve as a good illustration of sewer construction in which the invert is laid by a template. A typical section of this sewer is shown in Fig. 495. The invert is the arc of u circle with a tangent at an inclina- tion of 3 to 1 on each side. The arch is a parabola, The upper ‘J Fig. 495.—Harrisburg Intercepting Sewer. 7,600 ft. of this sewer is 3 ft. 9 ins. high by 5 ft. 134 ins. wide at thé base of the arch, and has an area of 12.278 ft. The lower portion is 5 ft. high by 6 ft. wide, inclosing an area of 16.335 sq. ft. The general dimensions and thickness of the con- crete are shown in the drawing for the 6-ft. section. The same thickness of concrete and same reinforcement are used for the 5 ft. 1%4 in. section, the general dimensions alone being changed. No. 10 gauge 3-in. mesh expanded metal, located as shown, was used for the reinforcement. The metal, as will be seen, is not placed so that it will provide the greatest tensile strength, but it was considered that the section would have ample strength. After the ditch was excavated to sub-grade the bottom was shaped to the proper profile and section. A small trench was then dug in the center, below sub-grade, and the underdrain laid with its top about 3 ins. below the invert concrete. A wooden template conforming to the shape of the invert was then accurately set to grade and line, about 12 ft. beyond the end 670 CONCRETE AND REINFORCED CONCRETE. of the completed invert, and the intervening section laid in the following, manner: The concrete below the line at which the expanded metal was to be placed was thrown in and tamped. The metal previously bent to the proper shape, was then placed with its ends extending up at both sides for lap with the arch metal, and the top course of concrete put in place. Before ram- ming it was roughly shaped by means of’a 14-ft. straight edge, one end resting on the finished invert and the other on the tem- plate. After careful ramming the concrete was covered with a Y-in. coat of 1:1 cement mortar trued by the straightedge and troweled smooth. Each 12-ft. section as it was completed was tested for grade by the inspector. The arch centers were 24% x 2% x \% in. steel angles bent to the proper shape and spaced 3 ft. 4 in. apart, the ends resting on wooden wedges placed on the side slopes of the invert. Two-inch planed pine lagging 10 ft. long was laid loose on these centers and coated with soft soap. The arch metal previously bent to shape was placed over this lagging and held at proper distances from it by block- ing it out with small stones. . A 1:21%4:4% hand mixed Portland cement (Giant Portland brand) concrete was used. A Ransome mixer was tried, but owing to the small quantities of concrete needed for the sewer sections, it was found more economical to do the mixing by hand. From the mixing board the concrete was passed through a chutg into a box supported on the lower bracing, from which it was shoveled into place. Wet concrete was used and forced through the metal against the arch center. The outside arch lagging was built up of rough lumber,against outside pine ribs. After three days the wedges were removed from under the steel ribs and the centering collapsed. The inside and outside was then gone over carefully and all imperfections in the concrete filled with 1:1 mortar. The back fill was kept 48 hours behind the arch construction. It is stated that the labor cost was approximately 53 per cent. of the total cost of the sewer. This sewer stood without injury a severe test accidentally brought upon it at a time when the concrete was less than two weeks old. A loaded coal train was derailed on a siding cross- ing the sewer at an angle of about 20° at a time when the siding was supposed to be temporarily abandoned. The ties were buried CONDUITS AND SEWERS. 671 , out of sight in the soft clay filling by the weight of the train. The cars were left in position for several weeks, but no evidence of failure could be found in the sewer underneath. Portland Concrete ae, = Section in Light Cutting Section in Deep Cutting. ke- Prors| Section in Deep Cutting. Section through Morsh. Fig. 496.—Price’s Run Sewer, Wilmington, Delaware. Wilmington Sewer.—The Price’s Run sewer at Wilmington, Del., is a notable example. of reinforced concrete sewer con- 672 CONCRETE AND REINFORCED CONCRETE. struction on account of the light sections used. Circular sections 9 ft. 3 ins., 6 ft. 6 ins., 5 ft. and 4 ft. 9 ins. were used. Two kinds. of reinforcement, expanded metal and wire-woven fabric were employed. Fig. 496 gives cross sections and general dimen- sions of a g ft. 3 in., 6 ft. 6 in. and 6 ft. sewer, two types being used. The section in “light cutting” was built above the natural sur- face of the ground, while sections in “deep cutting” were built in deep trenches. .The “section through marsh,” as shown in the figure, was supported on piles from 8 to 36 ft. long, four piles to the bent, with bents spaced 4 ft. centers. Caps of 10 X I2-in. yellow pine rested upon the piles and supported a flooring made of 3 x 12-in. hemlock plank laid with broken joints. The reinforcement for the 9 ft. 3 in. sewer was 6-in. mesh No. 6 gauge expanded metal cut in 8 x 5% ft. sheets and placed in a single layer about the sewer. It was located 2 ins. from the inner face and held carefully in position while the concrete was rammed in place. The sheets were lapped one mesh at both ends and sides. It was only found necessary to wire fast the top sheet. Wire-woven fabric was used for part of thé work. This material was furnished in continuous rolls about 100 ft. long and 5% ft. in width. The wire was No. 8 gauge with a No. 6 wire for selvage, and the mesh was 6 x 4 ins. The fabric was cut in lengths to entirely surround the sewer and embedded in the concrete as the latter was rammed in place, as was done with the expanded metal, except over the centers, when the fabric, being more pliable than the expanded metal, was held the proper distance from the wooden center by means of 2-in. blocks, which were removed as the concrete was placed. The wire fabric being in one length was more easily placed than the expanded metal, but the latter, being stiffer, was more easily maintained in proper position. The two kinds of metal were used for the purpose of determining the relative values of each. The expanded metal cost delivered 4 cents per sq. ft., and the wire- woven fabric 2% cents per sq. ft. The molds were built of 4-in. lagging as the concrete was put in, and the concrete rammed in 4-in. layers. The bottom ef the invert was smoothed up with a coat of plaster. The concrete was mixed moderately dry, and for the invert CONDUITS -AND SEWERS. 673 was composed of 1 part Portland cement, 2 parts stone dust ana 6 parts 114-in. stone. For the arch a 34-in. stone was used witn a 1:2:5 mixture. As smooth work and as good results were obtained when 114-in. stone was used as when 34-in. was em- ‘ployed. The stone was a blue’ granite well selected as to size. The section used for this sewer, while only 8 ins. in thickness for the crown of the 9 ft. 3 in. sewer, stood without injury the dumping upon it of a cubic yard of earth and rock from heights of from 3 to Io ft., together with a weight of 25 ft. of loose earth fill. The section through the marsh with a crown thickness of g ins., which is above the natural surface and without any earth cover- ing, was upon two occasions subjected to severe pounding of tons of ice resulting from the breaking up of the ice on the Brandywine River, without any apparent injury. This would seem to indicate that this sewer section was of ample strength. Cleveland, 0., Sewers——Probably more reinforced concrete sewers have been built in Cleveland, Ohio, than in any other American city. The first sewer built of reinforced concrete is known as the main intercepting sewer, and extends along the lake front. The first section built was 334 miles in length and is 1314 feet in diameter. The reinforcement consists of longi- tudinal and transverse steel rods arranged according to what is known as the Parmally system. One section about 2 miles long, is from 35 to 44 feet deep and only 17 feet in the clear from the center line of the Lake Shore & Michigan Southern Railway tracks. This portion was built in open trench. Considerable difficulty was experienced in the construction of this section, as water and quicksand were encountered. Nine-inch sheet piling 28 ft. long was first driven with steam hammers on both sides of the trench, the excavation made by cable machinery and the piles braced by 10 x 10-in. and 8 x 8-in. wale and strut timbers put in position; ordinary sub-strutting and bracing was used in the bottom of the trench. ‘ Figure 497 shows section of the main intercepting sewer. The invert was built of natural cement concrete, and the two anchor rods of 214 x ¥4-in. soft steel shown at the sides and spaced 15 ins. centers in staggering rows bonded the invert to the crown and strengthened the sides against lateral pressure. The invert was 674 CONCRETE AND REINFORCED CONCRETE. lined with 2 courses of shale brick. The arch centering was placed in the usual manner and the lagging was covered with building paper waterproofed with paraffine. This paper did not ° prove entirely satisfactory, as it became soaked and swelled, giving more or less of a rough surface. After the centering. was placed 2%4 x %4-in. curved transverse bars were bolted to the anchor bars to make an inner and outer skeleton, the first adjacent and parallel to the intrados, and the second flattened on top at the level of the crown. To these bars were bolted ihe PPortland Cement, Mortar x4 Portland Cement Concrete Portland Cement Mortar ek Sheet Pung, - is SSS ~ ae x * > \> SS SS S a x Ne. ¥ yy" ML Uk ULM LEE ll MT “Section of Main intercepting Sewer Fig. 497.—Main Intercepting Sewer, Cleveland, O. 8 lines of horizontal longitudinal 11% x %4-in. bars. Portland cement mortar 3 ins. thick was then laid on the lagging enclosing the inner row of bars and formed a finished surface for the arch soffit, through which none of the concrete stoné could pene- trate. Before this mortar set concrete was rammed in between it and the sheeting to a height of 18 ins. above the springing line, and the remainder of the concrete rammed in place against the 3 ins. of mortar without the use of outside forms. The upper surface of the concrete was finished with 1 in. of Portland cement mortar. The arch concrete was made of 1:3:714 mixture with CONDUITS AND SEWERS. 675 1% in. screened broken stone. When the voids in the stone exceeded 40 per cent. the proportion was 1:3:6. Back filling was commenced as soon as the concrete was from 6 to 12 hours old, but the centers were not removed for two weeks. The section shown in Fig. 498 was used for the Gilbert street sewer. Round bars instead of flat ones were used, the connections being made by hooking the bars together instead of bolting them. As will be seen, the arrangement of the bars is somewhat differ- ent from that shown in Fig. 497, in which flat bars were used. The primary bars are nearly horizontal at the crown where they Fig. 498.—Gilbert Street Sewer, Cleveland, 0. pass near the intrados and thence extend through the arch to the extrados along the haunches and then back again through the arch to the intrados, where they are anchored to the vertical side walls 2 ft. above the springing line. These bars do not have sufficient section to take the total tensile stress at the crown, and, as will be seen, are supplemented by secondary bars which alternate with them and are bent to segmental curves with the ends radial, giving a firm anchorage in the concrete. Both sets of bars are 5% in. in diameter and are 6 ins. apart on center at the crown. The 4-in. longitudinal bars are wired to the trans- verse bars at intersections. 676 CONCRETE AND REINFORCED CONCRETE. Comparative bids for the intercepting sewer of reinforced con- crete as compared with the ordinary brick-lined concrete sewer showed a saving of from 19.7 to 22.4 per cent. of the cost in favor of reinforced concrete sewer. S al ee er i! (a) _———— & rota t 4 ‘4 ' i ; eee --h= — 1 Peay ia 1 et : 1 yay 8 i { rat : : tay : tay ot ; Cc \ : : 1 iid : 2 5 ae i ogg ; iret 5 2 \ | Q > cs hie . a” a Z2=S wh u 2 a i 3 et ae 5 ' ai o { a Si 3 | Hilt v7 oe t 4 ‘ ti 0 a: 1 tay ot te SY a tila g be Hae zg tat Ltt tee gop n STO RS] 5 | ri : At yt E ee ee Sey Pre o [4 na & = \ > a = oO a 3 ” PE be - Cc a ° wa ji 6 t ay o o> a “ig eS BG a \ ‘ &s 00 \ 3S 9 & \ Be $N 0 2 ° NS Sy, ‘A = United Shoe Machinery Company’s Sewer.—Figure 499 shows a unique form of sewer designed for use over a fill made on 5 or 6 ft. of mud in the bottom of the Bass River, Beverly, Mass. A line of piles 8 ft. centers was driven to support this sewer CONDUITS AND SEWERS. 677. and keep. it in line. The lower part of the sewer was designed as a reinforced beam I0 ins. square to span between adjacent piles. The beam and invert were constructed as a monolith. The molds were of 2-in. lumber in 8-ft. lengths, with a rib at each end and one in the middle. These were held in place by blocks on the sides of the piles. The earth formed the bottom of the form. After the outside form was in place the metal was placed, the concrete poured in and brought up to an inch or so below the floor line. Then the inside form was put in place arid ‘the concreting continued to the top of the invert. The forms used for molding the arch pieces are shown in Fig. 500. The arch ring was constructed in advance in 2-ft. lengths, and was rein- forced with %4-in. twisted steel rods spaced 12-ins. centers. These sections were set in cement mortar, completing the sewer. Brooklyn, N. Y., Sewers.—Reinforced concrete was used in the OW ° a /°\__,Twisted Steel P i 0) Rods Fig. 500.—Arch Form for Sewer at Beverly, Mass. construction of 600 ft. of 10-ft. sewer on Foster Avenue, between East Nineteenth and East Twenty-first Streets, Brooklyn, N. Y. The depth of earth over the arch at this place ranged from 1 ft. 6 ins. to 3 ft. Figure 501 shows the massive cross section used. The rein- forcement consists of three 7%-ins. corrugated steel bars arranged as shown on the drawing. The reinforcing rods were spaced 1 ft. centers along the sewer. No longitudinal rods were used. The concrete is 12 ins. thick at the crown, 3 ft. thick at the spring- ing line, and 8 ins. at the invert. The sewer rests upon a timber foundation platform made of two layers of 4-in. plank. Below the springing line the sewer is lined with a 4-in. ring of hard burned bricks. Above the springing line the arch is faced with 1 in. of mortar composed of I part Portland cement and 2 parts sand placed against the forms when the concrete CONDUITS AND SEWERS. 679 The sewer runs through a sandy soil having good drainage. Only the arch of the sewer is reinforced. The reinforcement consists of ,% x I-in. steel bands spaced 12 ins. centers, and placed 3 ins. inside the intrados of the arch. The arch ring is g ins. in thickness. The reinforcing bars are in three pieces; 1 piece on each side extends from 15 ins. below to 6 ins. above the Fig. 502.—Invert Form, South Bend, Ind., Sewer. springing line of the arch, with a piece in the arch joining these side pieces. The 3 pieces are fastened together with cotter pins. The arrangement of the rods and forms used are shown in Figs. 502-4. The sewer was built in 12-ft. lengths. After the trench was “Sheeting / Side Pieces of : Hy. Reinforcement Bands sl Fig. 503.—Side Forms, South Bend, Ind., Sewer. graded 4 braces were nailed across the trench between the lowest ranges of the trench sheeting. A -vertical row of lagging acts as a partial outside form for the bottom concrete. The template for the invert of the sewer barrel was suspended from the 4 cross braces as shown in Fig. 502. The concrete was car- ried up to the top of the template on the side, after which the 680 CONCRETE AND REINFORCED CONCRETE. template was removed. The side pieces of the reinforcement were then set and the side forms shown in Fig. 503 put in posi- tion. These sections extend up to the springing lines of the arch and were placed as soon as the invert template was removed~ A notched brace at the bottom and a brace piece at the top hold these in place. The concrete is then carried up to the springing 2x1 Bands OO TECH. Ge oe \ Joint ‘ Sia ee eee (fase Fig. 504.—Arch Forms, South Bend, Ind., Sewer, line as shown in Fig. 504, and the upper section of the forms put in place, the remaining reinforcements put in place and the concreting completed. Curves in the sewer were made in chords of arc Io ft. long, an additional face being provided to overcome the friction at the angles between the straight chord sections. In this way expensive forms for curves in the sewer pipe were avoided. A 1 cement, 3 sand, and 6 gravel mixture was used for the invert and trench wall of the arch, while a 1: 2:4 mixture was used for the arch ring. After the sewer barrel was finished it was coated with %4 in. of 1 to 1 cement mortar up to the springing lines of the arch. The contract price for the construction of the 72-in. sewer, including excavation to an average depth of 18 ft. and back fill, was $9.75 per lin. ft., while the contract price for the 66-in. sewer was $9.50 per lin. ft. Des Moines, Ia., Sewer.—Figure 505 shows two sections of cir- cular sewer 7 ft. in diameter and flat sewer 5 x 10 ft. in sections, recently constructed at Des Moines, Ia. The flat section was used where only a limited clearance was available. The details of construction are clearly shown in the figures. Special Moulds for Small Sewers.—A centering suitable for sewers and conduits of small size was used in the construction CONDUITS AND SEIVERS. 681 of a 30-in. composition sewer at Medford, Mass. The crown of this sewer, occupying about 120° of arc, was of brick and the remainder of the sewer of concrete. The concrete portion was constructed as a monolith. The forms (Fig. 506) were con- structed in 10-ft. lengths and made in halves separating on a vertical line through their center, and were connected by clamps and held at a proper distance apart by iron dogs in the end Reg. 93 Cu.¥d Concrete per Lin. Peet lease wecteaban SIN hesaieok he ““Y4"Oorr Bars 12”Centers Fig. 505.—Sewer at Des Moines, Iowa. ribs. of each form. After smearing the forms as usual they were set in the trench and the concrete deposited and rammed. When it had partly set the dogs. were removed and replaced by turn- buckles, which were slowly turned, so that the upper portions of the forrns approached each other slightly, thereby sepa- rating them from the green concrete without injuring it. The forms were then withdrawn. The arch center was then put in place and the brickwork laid. These centers were also in 10-ft. lengths. The lagging was 7% in, thick by 144 in. wide, 632 CONCRETE AND REINFORCED CONCRETE. with one edge beveled to make a tight surface. Ribs of 2-in. plank spaced 2 ft. centers supported the lagging. It is stated that the total cost of this sewer, exclusive of manholes, was $2.18 per lin. ft. A novel patent sewer form adapted to the construction of medium and small sized sewers is shown in Fig. 507. This form consists of sheet steel plates bent to the required shape and held together by clips made by bending the edges of the plates to Fig. 506.—Form for Sewer Invert at Medford, Mass. the shape shown in the figure. These clips are held in place by filling the spaces inside them with paraffine or clay. The outside ef the form is coated with grease or may be wrapped with paper or burlap in the usual manner. The trench is excavated to the size desired for the outside of the sewer and if necessary, cutside forms of the usual type are employed. The bottom con- crete and reinforcement, if any is used, put in place, the form put together, lowered in place and the remaining concrete deposited. When it is desired to remove the forms the paraffine is melted CONDUITS AND SEIVERS. 683 ‘ in some manner, or if clay is used, it is washed out and the form collapses and is removed. Another patent steel form described in Engineering News, October 20, 1904, is shown in Fig. 508. This form consists of a steel shell bent to the shape of the conduit desired and braced internally by turnbuckle rods hooked into suitable eyes and bearings. The shell is made in two parts, an upper part or center, and a lower part or invert form. Near its top edge on both sides the invert form is provided with hook- eyes which are headed through the shell with countersunk heads. The bottom edges of the arch have plates riveted on their inside. which lap past the edges of the invert form and have slots WY: Concrete, Big. 507.—Stecl Forms for Fig. 508.-—-Blaw Collapsible Steel Sewers, Centering for Sewers. through which the hook-eyes pass. Cotters through the hook- eyes clamp the arch center and invert together. The turnbuckle rods brace the shell internally and preserve its shape under load. These forms are usually made in 5-ft. sections. The Blaw Col- lapsible Steel Centering Co., Pittsburg, Pa., control the patents and manufacture this form. : A patent form used in the construction of a 5-ft. egg-shaped sewer at Washington, D. C., is shown in Fig. 509. Forms of similar construction have been successfully used for building sewers as small as 8 ins. The centering consists of a wooden form made in two parts firmly attached together when in use, about which is wrapped a thin steel strip about 6 ins. in 684 CONCRETE AND REINFORCED CONCRETE. width, forming a continuous coil or covering upon the surface cf the forms. After the strip is in place it is smeared with oil and the form is lowered into the trench, the concrete put in, the wooden form collapsed and removed. The steel strip, which is usually of No. 20 gauge metal, is left in place to support the concrete until it has set, when'it is removed by pulling on one end of the strip. The centering, usually in 16-ft. lengths, is made of Fig 509.—Spirally Wrapped Sheet Steel Form for Sewers. lagging nailed to ribs spaced about 2-ft. centers. Wedge timbers marked A and B in the drawing, are provided to keep the forms the proper distance apart. The two halves are locked together by latches on the outside of the end ribs. A hole C is provided in the centering through which a square gudgeon-timber is passed lengthwise of the centering. The ends of this timber are rounded and the form is mounted on .bearings carried by trestles. The sheet steel covering is wound upon the form by revolving it on CONDUITS AND SEWERS. 685 its bearings. When it is desired to collapse the centering the wedge timbers are driven in and the upper and lower parts close together and are then withdrawn. Fig. 510.—The Ransome Concrete Pipe Mold. The Ransome Pipe Mold has been successfully used for the con- struction of small concrete pipe varying from 4 ins. to 24 ins. in diameter. This device consists of a form made of sheet steel, having an inner core 10 ft. in length. One end of this core 686 CONCRETE AND REINFORCED CONCRETE. is surrounded by a short steel shield that serves as the outer form of the cement pipe. The mortar for the pipe is packed in between the inner core and this outer shield by a man who uses a small rammer for this purpose. lig. 510 shows this mold being used in the construction of pipe. A man standing in the foreground keeps moving the mold forward slowly by means of a lever. This lever is provided with a dog operating in a clutch, which rotates a small drum on which a wire is wound. The wire rope is anchored into a dead man in the trench ahead. As the mold is moved forward it leaves behind it the cement pipe, which is still green. The cement mortar is mixed with a small amount of water, so that it possesses sufficient cohesion to hold together when unsupported by the core. To protect the pipe until it hardens it has been found advis- able to pack a little earth around its sides and over the top. This is done by a third man in the trench, who packs the filling upon the part of the pipe where it is still supported by the core. It has been found that the pipe does not cave in unless a heavy body falls upon it before the cement has hardened. It is stated that a pipe does not break down under its own weight even when made as large as three feet in diameter. When it is desired to connect a branch pipe to the main one, a hole is cut in the side of the green pipe before the core has keen pulled ahead. A branch of the proper pattern is shoved up tightly against the pipe, and the collar of the branch is plas- tered with cement mortar, producing a strong watertight con- nection. The itemized cost for the construction of an 8-in. cement pipe built at Despatch, N. Y., for the oe -Armstrong Piano Co., is given as follows: 6 men at $1.70 per day, 10 hours........-e.eeeeeee $10.20 TD POREMIAIL -cxssansenosners dare voebani yen rboaan ie gm Gnd ae ree Etnee 2.00 2 barnels: cenrent: at: $26 0 eas ncn scans oedema: 3.75 33 cubic: yards'of sand at S085 casei dacaneuraners 2.80 Weate sree aa ans deat ste nssuas aundeans obaleum parece ee 0.15 Total for 300 lineal feet................ $18.90 This is equivalent to 6.3 cents per lin. ft. of pipe. It is found that a gang of six men would average about 300 lin. ft. per day. CONDUITS AND SEII’ERS. 687 In the construction of a 12-in. pipe, the cost was as follows: 7 wien..at $1.70 per day pave cciereswsaies 1 foreman. scons oa soeumnyanses 13 barrels of cement at $1.33 12 cubic yards of fine gravel, at $1.80............ 9.60 Total for 400 lineal feet of pipe..... Paints $41.00 This is equivalent to 10% cents per ft. It is stated that the cost of vitrified clay pipe, 8 ins. in diameter. under like conditions, is about 1714 cents, and the cost of 12-in. vitrified pipe will be about 35 cents, showing a great saving when cement pipe is used. In making estimates on the cost of cement pipe, however, the cost of the cement and the labor items should be carefully con- sidered when comparing it with some other form of pipe. But under almost all conditions it will be found that cement pipe can be constructed at great saving over other forms. As to durability, the cement pipe is as strong, or stronger, than vitrified clay pipe. The pipe which is constructed continuously is desirable on account of the lack of joints, there being no joints for leakage unless the pipe is injured in some manner. This pipe has been successfully used for sewers, water mains, etc. CHAPTER XXVIII. TANK AND RESERVOIR CONSTRUCTION. As has been stated, the first application of reinforced concrete by Joseph Monier was in the construction of tubs and basins for use in horticulture. Monier later becamc bolder and used this new material in the construction of water tanks and reser- voirs, some of large size. The use became greatly extended and reinforced concrete is to-day almost exclusively used for tanks, reservoirs, etc., in Europe. The many good qualities of reinforced concrete make it an especially valuable material for the construction of large and small tanks, both rectangular and circular—for reservoir, stor- age bins for cement, coal, grain, sand, etc. It is also used as a lining for reservoirs constructed of masonry or earth, and for reservoir roofs. Tanks and reservoirs may be buried under the ground, placed directly upon the ground, or supported at any desired elevation upon towers of steel, masonry or reinforced concrete. The posi- tion of the tank modifies to some extent the structural details adopted, as does the shape, whether circular or rectangular. The general system of reinforcement consists, however, of a network of rods, the size and spacing of the rods varying with the loads to be carried. When rectangular tanks are constructed, the sides consist of reinforced slabs, sometimes strengthened with ribs or beams. The horizontal rods of circular tanks and reservoirs are spliced by lapping or welded into hoops. The tank bottoms may or-may not be reinforced, depending upon the nature of the sub- soil; when they rest upon the ground they are usually approxi- mately flat, only having enough slope to drain them properly. When tanks are elevated, the bottoms are either of spherical or conical shape, usually with the convex surface upwards, although it is sometimes placed downwards. The horizontal rings or hoops forming the reinforcement for circular tanks are placed close together at the bottom and spac- TANK AND RESERVOIR CONSTRUCTION. 689 ing gradually increased toward the top, while the vertical rods are spaced uniformly ‘around the tank, the two sets being wired ~ together at intersections. In rectangular tanks horizontal and vertical rods are also used and spaced similarly to those of cir- cular tanks. At the corners formed by adjacent sides the hori- zontal rods are usually bent around to make the reinforcement continuous, thereby making the tank as strong at this point as at any point in the side wall. The vertical rods and bottom rods may be bent in the same manner to form a solid junction between the side walls and tank bottom. Roofs for tanks may be either flat or ribbed slabs, spherical or parabolic arches, spherical arches being preferred when any great load is to be carried on the cover. For flat, ribbed slabs arid par- abolic arches the usual types of reinforcement are used, While for spherical arches concentric rings, with radial rods wired together, give a satisfactory means of reinforcement. The Monier type of reinforcement, with varying spacing of the rods, is almost uni- versally employed in tank and reservoir construction. For small rectangular tanks the arrangement of the reinforce- ment is quite simple, a Monier mesh being placed in each side and the bottom, with sufficient lap at side wall and side and bottom wall junctions. Electrically welded wire, lock woven fabric and expanded metal are easily put in position and give a most satis- factory reinforcement. When tanks of somewhat greater size are used and it is desired to put a roof over them, girders are used with the roof slab. | Figure 511 shows a tank of the latter type constructed for the Pittsburg Lamp, Brass & Gas Company. This tank is 17 ft. wide, 65 ft. long and 11 ft. 6 ins. deep. It is located in a court between two buildings and it was found necessary to take care of the foundations of the walls of these buildings. To do this the side vertical beams shown on the drawings were used, although these are not an essential part of the tank proper. Milford, 0., Standpipe.—The standpipe at Milford, Ohio, is an example of the use of reinforced concrete to replace the usual standpipe built of steel. This structure is 81 ft. high from base to under side of roof. The roof is dome-shaped, with a rise of 3 ft., making a total height of 84 ft. The outside diameter is 15 ft. 6 ins. The shell at the base has a thickness of 9 ins. This 690 CONCRETE AND REINFORCED CONCRETE. thickness is maintained to a height of 30 ft., where it reduces to 7 ins. and again at the height of 55 ft. to 5 ins. The reduction in thickness is made on the inside of the pipe. Both an inside and outside ladder is provided. The foundation is octagonal, with an inscribed diameter of 20 ft., and is 6 ft. deep. It was constructed of concrete composed of I part of cement to 7 parts of gravel, while the concrete for the standpipe proper was I part of cement to 3 parts clean, sharp sand. On top of the foundation concrete 1 x 1 x % T-bars were laid radiating from the center to within 6 ins. of the outer edge. The shell was started directly on these T-bars and, after being = ye > : Ts ‘.— By A A Be 188 . at 8 " 5 “ne &: a der be bi j 5 2 ae WB # Plan. i KO" KDA ORD KID aL Longitudinal Section. Fig. 511.—Rectangular Tank, Pittsburg Lamp, Brass and Gas Co.’s Works. KedsDA KD" DH kOe carried up a sufficient distance, the base outside the shell was cov- ered with concrete 16 ins. deep, and the base inside the shell was covered with a 6-in. layer of 1 cement and 3 sand mortar. The shell is reinforced by a network composed of verticals spaced 18 ins. apart around the structure and horizontal rings, six to the foot for 30 ft., then five to the foot for 25 ft., and then four to the foot for the remainder of the height. Both vertical and horizontal reinforcements consist of 1 x I x %-in. T-bars con- nected at intersections by clamps stamped out of sheet metal, sim- ilar in form to the Streeter clip which is used for con- necting structural steel work. The reinforcement was located 3 ins. inside the outside face of the shell. TANK AND RESERVOIR CONSTRUCTION. 691 The forms used in the construction of this standpipe were made of 1% flooring 3 ins. wide and 3 ft. long for staves, nailed to 4 X 4-in. circular ribs. The topmost rib extended 1 in. above the top of the staves, so as to form a rabbet to receive the bottom of the riext form. Three sets of forms were used, each consisting of an outer and inner form and each divided into eight sections for convenience in handling. The sections-of each ring of the out- side forms were held together with latches, and those of the in- side forms were bolted together. An average height of about 5 ft. a day was constructed. This standpipe was designed and constructed under the supervision of Mr. J. L. H. Barr, of Ba- tavia, O. The Fort Revere Tower.—A good example of a standpipe and Fig. 512.—Horizontal Section of Base of Fort Revere Water Tower. water tower construction of Hennebique design is that con- structed at Fort Revere, Boston Harbor, Mass. The original de- sign was for a masonry tower and steel standpipe, but a bid for the work in reinforced concrete by the Hennebique Construction Co. that was 30 per cent. lower than any bid on the original de- sign led to the adoption of reinforced concrete. The tower is octagonal in form and consists of eight reinforced concrete piers resting upon a reinforced moulded base about 12 ft. high. The filling between the piers consists of brick. The pier support a reinforced concrete floor at an elevation of about 2 ft. above the top of the standpipe. This floor is a ribbed slab 3 ins. thick, having ribs 6 ins. wide and 12 ins. deep. Above this floor is an observatory with a wooden roof. The total height of the 692 CONCRETE AND REINFORCED CONCRETE. structure is about 93 ft. The piers are reinforced with six 34-in. rods. Horizontal and vertical sections of the base are shown in Figs. 512 and 513, while a vertical section of the tower proper is shown in Fig. 514. The interior diameter of the tower is about 25 ft., while the diameter of the standpipe is 20 ft., the space be- tween the two being occupied by a spiral staircase. The stand- pipe has a height of 50 ft. The shell is 714 ins. thick at the bot- tom and 4% ins. at the top. The bottom of the tank is 4 ins. thick. Figs. 515 and 516 show plan and section of the bottom and section of the side wall at the bottom. Both the wall and floor are coated on the inside with 1 in. of I to 1 mortar to pre- vent leakage. The arrangement of the reinforcement and method Lech . 7 Lhd : Brice Ke3/° Bars of, Po om Osts 3 » Stirrups on. y Vertical Bars Stirrups ¥ 20°C.t0C. Bar Z° spare iticcsacaseesal !’Cement Fig. 518.—Vertical Section of Base of Fort Revere Water Tower. of bonding together the walls and bottom are shown in the figures. The wall is reinforced with two sets of vertical and horizontal rods. The upright rods, which are ’/,,-in. in diameter, are 2 ins. apart transversely and are staggered, the rods in each set being spaced about 16 ins. apart circumferentially, making one vertical rod every 8 ins. about the circumference of the shell. The two sets of horizontal bars each encircle one of the sets of vertical bars and are made of %4-in. diameter rods with welded joints for the lower two-thirds of the tank and 3%-in. rods with lapped joints wired together for the upper one-third. The vertical spacing of the hoops increases as the height of the shell increases. For the ¥-in. hoops there are 23 spaces of 134 ins.; 41 spaces of 2 ins.; 34 spaces of 21% ins.; 22 spaces of 3 ins.; 13 spaces of 3% ins., and 23 spaces of 334 ins. [or the 3£-in. hoops there are 9 spaces TANK AND RESERVOIR CONSTRUCTION. 693 Fig. 514.—Vertical Section Fort Revere Water Tower 694 CONCRETE AND REINFORCED CONCRETE. of 3-in.; 6 spaces of 3% ins., and 6 spaces of 334 ins., the inner and outer hoops at each level up to this elevation being in the same horizontal plane. For the remaining 16 ft., the two sets of ———~ ae a] —- 8 Se Te SE sg be eS 5 4°C.t06. Section at Bottom. so SSE Mn LS 1 WL 3 ae Wil a x x iC nee Wt n0, a or rates " Ae (Hit HH oy Plan at Bottom. Fig. 515.—Plan and Section of Buttress, Fort Revere Water Tower Tanke hoops are staggered and the spacing between adjacent hoops varies from 2 to 74 ins. The bottom of the standpipe is reinforced with two sets of 14-in. rods, spaced 4 ins. centers, and crossing one another at right an- TANK AND RESERVOIR CONSTRUCTION. 695 gles. The rods are bent up at their ends, and extend into the wall for a height of about 12 ins. The junction of the walls with the bottom is further reinforced with a set of 34-in. rods extend- ing about 20 ins. radially into the floor slab and running up to a height of about 24 ins. in the wall. These rods are placed in the center of the thickness of the wall and floor slabs and are bent at an angle of 135°, passing near the inner surface of the concrete, which is thickened at this point. A circular hoop is placed at this angle and stirrups of 1 x 14-in. steel, 7 ins. long, spaced 8 ins. centers, placed about the 3g-in. anchor rods, tie the whole firmly together. , The Fast Orange Reservoir—The reservoir for the East Orange Water Supply is 139 x 240 ft. in plan on the inside and has a capacity of 5,000,000 gallons with a depth of water of 20 ft. The % Cirevlor Bar YN Stirrups, ‘emeor Fig. 516.—Section of Tank at Bottom Corner, Fort Revere Water Tower. interior height from floor to roof is 21 ft. 4 ins. The reservoir is divided by a partition wall into two equal and nearly square basins so arranged that each is independent of the other and one may be shut off and emptied while the other is in use. The exterior walls are formed of a reinforced slab 12 ins. in thickness, braced by counterforts or buttresses spaced 10 ‘ft. cen- ters. The buttresses are 12 ins. thick and 7 ft. wide at the bot- tom and were constructed as integral parts of the wall monolith. : The reinforcement for the walls and buttresses is given in Fig. 517. The division wall is 14 ins. thick and has buttresses 6 ft. wide on both sides, also spaced to ft. centers. The floor concrete is 8 ins. thick, except under the wall but- tresses, where it is 12 ins. thick. The floor reinforcement consists of %-in. corrugated bars, spaced 6 ins. centers. The floor ex- tends 7 feet beyond the walls on all four sides. Under the outer e ey 696 CONCRETE AND REINFORCED CONCRETE. edge on each side there is a beam 12 ins. wide and 30 ins. deep formed in a trench. These beams are reinforced by four I-in. rods placed 1 in. above their bottoms. Similar beams are con- structed beneath the floor at the toes of the division wall bottoms. # Pods 3"C.t06, e f "Rods H"Ctoc, & 6" > 5* 1” Bods 24"Ct0C zm az, & te é poinalaas : $a, ecer : oe aR! ME g ab 27x12" mg ETT Se ~ ali ee ee rt rr 4S : | Re | Ss ‘ ; fk ae ae Mh Pe od 7%! Baks 54°C.t0¢. ; 8" i; ait FA 7 lek or alizl &/" Bars. Giiwis or 2 Rods IiCto6, verticer! pen ee re. 70 a 6 “i Y Rods 6"C.t0C, @ bars Vertical § 4 4 Roads 6'C.10C, ‘Rods 2'°C.to Vertical 5 “Roads } Otel JS fods 24"C toc: - $' Bars to. 4-I"Bars. Horizonte! Section A-B. Horizontal Section c-O, Wall, Buitresses, Colummns,Beams and Flooring. Center Wau, Fig. 517.—Details of Walls and Buttress, East Orange Reservoir. One-half inch réds 6 in. centers and 4 ft. long were placed under the exterior walls and columns. . The roof is a flat concrete slab 6 ins. thick for 10 ft. from the exterior walls, and 5 ins. thick over the remaining area, and is reinforced with 14-in. steel bars spaced 24 ins. centers longi- tudinally and 3% and 3 ins. transversely in the 5 and 6-in. slabs TANK AND RESERVOIR CONSTRUCTION. 697 respectively. This slab is supported by the walls and columns, spaced 10 ft. on centers, carrying girders 12 ins. wide and 16 ins. deep below the under side of the roof slab. The columns are 12 ins. square and are reinforced with four 14-in. vertical bars tied together in the usual manner with ,%-in. tie wires. The columns are connected to the girders with a corbelling 3 ft. long. The girders are reinforced with four 7-in. bars, two being straight and two bent, as shown, with four additional 7-in. rods 5 it. long over the top of each column. Stirrups are also used to re- inforce the girders against shear. Expansion joints were formed in the exterior and division walls of the reservoir at intervals of about 50 ft. by inserting a plate of steel 14-in. thick and 6 ins. wide 21 ft. long, covered with two sheets of lead %-in. thick bent in U-shape and fitting tightly to the steel plate. These were also used as division planes at which the work was stopped and started. ~ The reservoir is waterproofed by covering the water sides of the floor and walls with a 1-in. coating of 1:2 Portland cement mortar mixed with a solution of light soft soap in the proportion of 114 Ibs. to 15 gallons of water and having 3 lbs. of powdered alum incorporated with each bag of cement. This mortar coating was deposited as the concrete was put in place. Fort Meade Reservoir.—An excellent example of reinforced concrete reservoir construction is the 500,000-gallon reservoir recently constructed for the United States Cavalry Post at Fort Meade, S. D. This reservoir is built on a hill 200 ft. above the post and serves as a distributing reservoir. The reservoir is divided into two compartments, each 50 ft. by 60 ft. and 16 ft. in height from top of floor to under side of roof slab. The corners are rounded and a division wall separates the two compartments, each of which was designed to hold 250,000 gallons when filled to top of overflow pipes. The bottom of the reservoir floor was fixed at about 9 ft. below the ground surface. This required considerable excavation to secure the proper depth. The material encountered in the exca- vation consisted mainly of coarse gravel, mixed with fine sand and clav. This afforded an excellent foundation when confined, as it was, at the bottom of a deep cutting. After the excavation was completed to sub-grade the entire bottom was rolled with a heavy roller, thoroughly compacting the material. The footing 698 CONCRETE AND REINFORCED CONCRETE. excavations were afterward dug to the proper size and depth without disturbing the adjacent materials. The floor is 10 ins. thick and is reinforced with 34-in. longi- tudinal and transverse rods spaced 12 ins. centers. The floor division and side walls are designed to resist the pressure of the earth when either or both are empty as well as the pressure re- sulting when either or both compartments are filled. The roof is designed for an ultimate load of 800 lbs. per sq. ft., the actual ae Expanded Metal | kg eso = se] aS Hoes z Sens s! s e Bars, 2 bent up a Bars . Neo 6 HM | i 150 i -- 156 eustbecueens aa ee ees) OO Riad awnee eee ere ae WV 3 Corr Bars, 2C#s. § Corr. Bars, 9°Cts Dabo kk-- 5'07*->4 a oe ‘Cts. ‘ No.16, 621 24"Mesh, Expanded Meta! Earth, Fill g ft a ae aks aa posto mae . Seo teen oe ea eee py ee es ne & i rz Bars? Beam 6%la" \—( 8-IBars, ‘4 bentup } Ang Habe - 16'8" ! lea" | 16'8". s & Halls ® a ES £8 is ¢ =F g 50'0 — 8 x s € by 8 a gi S D ds Hl & %Corr. Bars Sig gs : § s Ea] Wired every 14° SHS Pe aoe a es io SH. Ss ys ae Bars, 12"Cte: 8 F Saltes” ~ Se ee Lipset = 34 "Corr Bars, 6" Se -50" 4 Fig. 518.—Reservoir at Fort Meade, South Dakota. load consisting of 12 ft. of earth fill and 100 lbs. snow load. The concrete footings are 5 ft. square and 12 ins. deep below the bot- tom of the regular floor. The wall footings are 5 ft. wide, the full length of the walls. All footings are proportioned for a uniform pressure for the sub-soil of 1.5 tons per sq. ft. As shown in the section (Fig. 518), the footings are reinforced with a grille of 34-in. corrugated bars. No evidence of settlement was observed. The columns are 14 ins. square and are reinforced against flexure for four 34-in. bars, one placed in each corner and the four TANK AND RESERVOIR CONSTRUCTION. 699 tied together with iron wire at intervals not greater than the diam- eter of the column. The columns are designed to carry the total load with an average unit stress of 500 lbs. per sq. in. The ex- terior walls, as well as the division wall, are considered as vertical beams and reinforced accordingly with vertical bars, while hori- zontal bars are provided to care for temperature stresses. Each compartment is divided into three transverse bays, and three longitudinal bays extend through both compartments. The roof slab and beams are carried directly by three longitudinal 12 x 22-in. girders, which rest directly on the columns and side and division walls. The girders are considered as acting as T-beams. The girder reinforcement consists of eight 1-in. corru- gated bars placed in two rows near the bottom of the beam. The upper bars are bent up over the supports to.better resist the shear- ing stresses. The four bottom rods extend the full length of the beam in one plane. The roof beams are 6 x 14 ins. in cross- section, and are each reinforced with four 7-in. bars. The roof slab is 3 ins. thick and is reinforced with 2%4-in mesh, No. 16 expanded metal. The concrete was a 1:2:4 mixture with all stone crushed to a size no larger than a 34-in. cube, crusher-run stone being used. An effort was made to secure as dense a concrete as possible, and a very wet mixture was used. The concrete was not tamped but was spaded to allow the air bubbles to escape. A specially de- signed spading bar was used with a blade or paddle 6 x 3 x 34-in., mounted on a 34-in. round iron handle 5 ft. long. The bottom excavation for the reservoir was made practically level and the concrete placed directly upon it. The excavation for the wall and column footings were made slightly larger than the footing dimensions and a 2-in. plank placed on edge around their sides before placing the concrete. The lagging for the wall forms consisted of 2-in. plank dressed on one side and nailed to 4 X 4-in. uprights 4 ft. on centers in pairs on each side of the wall. The lagging in the forms for the round corners of the outside wall were thin boards bent to the required curve and nailed to posts 2 ft. apart. The posts were held in place by out- side struts and by connecting wires passing through the wall space between the edges of adjacent planks. The column forms were made of three side pieces of 2-in. timber extending from the floor to the girder forms, the fourth 700 CONCRETE AND REINFORCED CONCRETE. side being left open to receive the concrete. These forms were braced: at the bottom by struts extending on all four sides to a firm bearing. At the top they were held in place by braces ex- tending to-adjacent columns and to the walls. The girder and beam forms were open troughs .of the required dimensions, made of 2-in. plank with the smooth side in. For the roof slab a close floor of 2-in. plank with the smooth side upward was used. The slab centering and the girder and beam forms were supported by posts resting upon the floor below.. For the footings under the walls and columns a thin layer of cement was first spread over the bottom and the lower reinforcing bars prop- erly spaced were pressed into the concrete to the required depth. The upper bars were then placed crosswise over the lower ones and covered with concrete, care being taken not to displace the bars in placing the concrete. In placing the floor reinforcement practically the same method of procedure was followed. Before concreting the walls and columns the reinforcement was erected in place forming a steel skeleton, around which the concrete was placed. The four column reinforcing bars were held at proper distances apart by wooden plates, through which holes were bored to receive the bars. These plates were moved up out of the way as the concreting progressed. The column bars were wired to- gether every 14 ins. in height, the wiring being done ahead of the concreting. The vertical bars in the walls were spaced by means of planks, forming templates through which holes had been bored at proper distances apart to receive the bars. Each row of bars was spaced by an independent template that was moved upward as the work progressed and that was kept high enough to allow room below for placing and tamping the concrete. The horizontal bars were wired to the vertical bars, each bar being secured in its proper position as the concrete was put in. The girder reinforcing bars were blocked up and the blocking removed as che concrete was put in place. The expanded metal used for reinforcing the floor slab was laid directly upon the centering and after being covered by some con- ercte roughly shoveled over was raised slightly by means of hand hooks to insure the metal being slightly above the bottom of the slab and entirely surrounded by concréte. The walls were built up as near as possible to a uniform TANK AND RESERVOIR CONSTRUCTION. 701 height all around, no part being at any time carried higher than 4 ft. above any adjacent part. At places where the work was stopped for the night or temporarily, stop boards were used to square up the ends of the concrete. These boards were placed vertically and were not over 4 ft. in height and extended the full width of the wall. These stop boards consisted of a 2-in. plank, to the center of which was nailed a 4 x 4-in. cleat. The cleat formed a recess in the concrete into which the fresh concrete flowed, forming a tenon when the work was continued. This made a firm bond between the new and the old concrete. Care was taken in all cases to brush off all loose materials from the old concrete and wash over its surface with cement grout before depositing fresh concrete. Besides using great care to get a dense concrete, the interior surface of the reservoir was coated over with a coating of 1 cement to 7 sand mortar. This was put on in two coats and the whole brushed over with a coat of grout. In this work the column and wall forms were usually removed from 7 to.10 days after the concrete was deposited. The girder and roof forms and centers were usually left in place from two to three weeks. The Bloomington, Ill., Reservoir—A reinforced concrete res- ervoir of 10,000,000 gallons capacity was recently constructed at Bloomington, Ill. This reservoir is 300 ft. in diameter and has side walls 15 ft. high, vertical on the back, and with a batter of 2 ft. on the front face. Figure 519 shows a section of the wall, which is 1 ft. thick at the top and 3 ft. thick at the bottom, and is built with a footing 10 ft. wide. This footing has a toe on the inner side 4 ft. deep below the bottom of the reservoir and 2 ft. wide. It is reinforced near the bottom with transverse 34-in. cor- rugated bars placed 9 ins. centers. Every fourth bar is to ft. long and is bent down into the concrete toe of the footing. The other bars are 4 ft. long and have one end just inside the back of the footing. The footing is also reinforced near its upper surface on the water side with 34-in. bars placed 6 ins. centers. These bars are alternately 4 and 6 ft. long, and all extend 18 ins. into the concrete under the wall. The wall proper is reinforced with vertical 34-in. bars near its inner face. These bars extend down into the footing and their spacing is reduced from 4 to 6 and then to 12 ins. on centers 702. CONCRETE AND REINFORCED CONCRETE. Fence fosts 100" to0 1 1 ke --- fads Part Plan ! J --20% ~~ - - -- -4’Barsie'G-------> 1§10"- -- -------- 2 < Fig. 520.—Forms for Reservoir a at Bloomington, Tl. ' T t | Crot SOc a : | ars 2, | ne | angveteucsepr=- aa 30" ~~~ ke 20" > uy Fig, 519.—Section of Wall for Reservoir at Bloomington, Il. TANK AND RESERVOIR CONSTRUCTION. 703 from the bottom of the wall to the top. The wall is also rein- forced for temperature stresses near both faces by 34-in. hori- zontal bars. These are placed varying distances apart, depending on the liability of extreme changes of temperature, and on the back face are omitted below the frost line. The wall was built entirely without expansion joints. The surface of the bottom of this reservoir is a segment of a sphere the depth of the reservoir, varying from 15 ft. at the wall to 25 ft. at the middle. The floor is 6 ins. thick and is reinforced with a lattice work of 14-in. round rods, spaced 6 ins. centers in both directions. The forms used in the construction of this reservoir were built in sections. Figure 520 shows the detail of a single section. The forms consisted of planks for lagging, nailed to vertical posts, which were accurately set and firmly braced. The forms were made in lengths equal to one one-hundredth of the circumference of the reservoir. Twenty-one of these form sections were built and all set up at once. The wall.when started was built con- tinuously in both directions from the starting point. The lagging consisted of I-in. boards and was nailed to the vertical posts and was carried up just ahead of the concrete filling. The footing was built without forms up to its junction with the wall proper. A layer of concrete 2% ins. thick was first laid in the footing trench, the lower reinforcing bars put in place, the verti- cal bars set in position and the concrete filled in up to the level of . the top layer of reinforcing bars; these were then put in place and the footing completed. The wall forms were then put in posi- tion as shown in the figure and the concreting continued to the top. A facing of gravel concrete, made of 1 part cement to 4 parts fine gravel, with no pebbles larger than 1 in., was placed on the front face of the wall. A sheet-iron form similar to that described on page 118 was used for depositing this facing. Both faces of the wall were painted with a I to I mixture of cement and sand; the inner face was also painted with a 1 to 1 mixture of waterproof Star Stettin Portland cement and sand. The Failure of a Reinforced Concrete Reservoir Covering at Madrid, Spain—The use of groined, parabolic and segmental arches in reinforced concrete for reservoir covers leads to ex- 704 CONCRETE AND REINFORCED CONCRETE. tremely thin sections and a great saving in materials. Great care, however, should be used in the design when such thin sections are to be used, and precautions taken to avoid types of construction where the strength of any one part depends upon that of every other part, for if local failure takes place it may be followed by a collapse of the whole structure. Care should be taken to brace and stiffen the cover in both transverse and longitudinal direc- tions, and extremely slender sections in columns, beams and arch “4 }--/ot —---.- 602 —-- —- jei<-----------— 84g ---——-- 400 -4 pr-- > 408 — ab -— 403 1 Fig. 521.—Plan and Sections of Reservoir at Madrid, Spain. covering avoided. Temperature stresses also should not be over- looked. The failure of the Madrid reservoir covering will serve to illustrate the features of bad design to be avoided. The Madrid reservoir has a capacity of about 106 million gallons, and was divided into four compartments of about 210 x 85 meters each, with a depth of 6.65 meters (about 690 x 280 x 22 ft.). Transverse and longitudinal sections of the reservoir are shown in Figure 521. The columns supporting the roof were TANK AND RESERVOIR CONSTRUCTION. 705 é 0.25 x 0.25 meters (9.84 x 9.84 ins.), and 8.4 meters (27 ft. 634 ins.) high to the springing line of the arches, giving a ratio of diameter to length of 1 to 34. The columns were spaced 6.02 x 4.03 meters (about 20 x 13 ft.) apart from center to center. These columns rested upon but were not rigidly attached to rein- forced concrete bases. The columns were reinforced with four rods about 5£-in. in diameter, and rested upon flats buried about 3 ins. in the reinforced concrete bases. The covering consisted of parabolic segmental arches having a span of 5.77 m. (19 ft.), and a rise of 0.58 m. (2 ft. 234-in.), and had a thickness at the crown of .o5 m. (2 ins.). Parallel with the arches the columns are connected below the springing line by a reinforced concrete beam 0.5 m. deep (195% ins.), having a single tensile reinforcing rod 37 mm. (about 1% ins.) and 3 compression rods 15 mm. (about 5% in.) in diameter. These upper and lower bars are connected by vertical ‘and diagonal rods 4, 5 and 6 mm. in diameter. No ties were used to con- nect the columns in a direction at right angles. to these girders. The arch reinforcement consisted of rods about 4 in. in diameter tied together with 1% in. diameter rods. A 1:4% or 1:5 Portland cement concrete was used. The details of the roof construction are shown in Fig. 522. The roof of one section of the reservoir had been completed and was tested by loading one line of arches, a width of 4 meters, on April 7, 1905, with 0.8 meters of sand; over 250 lbs. per sq. ft. On April 9 the covering collapsed killing 30 men and wounding 60 others. The collapse was sudden and without warning. The collapse was probably due to several causes. The test load was undoubtedly excessive for such a slender arch covering, probably causing the loaded crown to sink and the adjacent panels to rise. The extremely slender columns used, the absence of any rigid attachment at the base and entire absence of all transverse bracing probably all contributed to the failure of the roof covering. The temperature stress due to hot weather un- doubtedly was a contributing cause to the collapse. It is stated that the excessive expansion of the concrete in a line of girders in one of the unfinished sections forced the beams out of line 2 ft. or more a few days after the collapse of the finished section. This deflection became so great that the columns and line of girders collapsed. 706 CONCRETE AND REINFORCED CONCRETE. The stability of this structure depended upon every part main- taining perfect rigidity vertically and horizontally without the slightest deviation, for as soon as any movement took place in any single member the others were caused to move in their turn, bringing on a general collapse. It would appear from the above data that this structure was not carefully designed, many of mm pian 5 LONG Hornontal Section AB, showing Junction of Lower Girder Rods ot Columns, felaees jam 16mm Diam Rod's 040 Flat Bars 0~g0n3 . * Floor of Reservar C~ = Sechon ¢-D Horizontal and Vertical Secton of Cowmn, of Column Footing, THE THIRD MADRID RESERVOIR. ke 0425 --->f 1 i Abutment on Walls AOI! ods, 2mm 4 EZ J IZA eee (ocagpueMwpecd Forked Rods 6mm Diam x 2m tong Rods in Compression Scarfing Rods Hmm x 4 20Long (Simm & 2m tong ! acs oo aad » Om a 2 x S, 7 (oss L050 Rods 1n Compression 16mm Diam Rods. O05 kk - —-499-—-~--- 19 = 37mm Diamx 4 20tong tongitudinct Sectigny at Center of Arch and i i i dea Longitudinal Section of Girder. Fig. 522.—Roof Construction for Reservoir at Madrid, Spain. the conditions affecting it when in the process of construction being entirely neglected. Then, too, the extremely slender sec- tion used and the lack of rigidity of the completed structure made its successful completion, at the best, a precarious piece of construction. TANK AND RESERVOIR CONSTRUCTION. 707 Grain Elevator Bins.—Reinforced concrete has been practically the only material used in Europe for many years in the con- struction of grain elevators. These bins are usually rectangular in shape and are supported on reinforced concrete columns. In this country both circular and rectangular bins have been built. Grain elevators are usually what are known as terminal elevators, viz., they are located at the terminal of a railway, grain being unloaded at such a point, cleaned, mixed and stored preparatory to being shipped by vessel to some distant point. This class of clevator requires a working floor story of 20 or 25 ft. between the bottom of the bins and the level of the railway tracks, two of which usually run through the house to permit the cars to ke unloaded directly into the elevator bins. The machinery for unloading, cleaning and the mixing machinery are located on this floor. To secure the proper head room columns of upwards of 20 ft. in length must be used to support the girders carrying the bins proper, and must be so spaced as to allow the passage of the cars underneath. These requirements and others to secure the proper location of a line of cars so that a number of cars may be conveniently unloaded at one time fix closely the size of bin and the particular form of construction to be adopted. The Canadian Pacific Grain Elevator, Port Arthur, Ont.—The Canadian Pacific elevator, which was completed in 1904, has a capacity of 443,000 bushels and consists of nine circular bins 30 ft. in diameter and go ft. high, and four inner bins formed by the walls of the circular bins. The centers of the bins are at the intersection of three longitudinal and three transverse lines 30 ft. apart in both directions. Fig. 523 is a part plan showing the arrangement of four circular bins and one inner bin of approximately rectangular form. The walls are of reinforced concrete 9 ins. thick on foundations 24 ins. thick carried down ta offset footings resting on hard- pan. The conical tank bottoms are seated on rammed sand fill. Under the center of each row there is a concrete-lined conveyor tunnel 7 ft. wide, 7 ft. high and about 86 ft. long. The walls of the cylindrical bins have a uniform thickness of 9 ins., except where the adjacent bins are tangent, and the acute ‘angles between the convex surfaces are filled in solid with a width of 7 ft. and a maximum thickness of 214 ft. The concrete 708 CONCRETE AND REINFORCED CONCRETE. used was composed of 1 part Portland cement, 3 parts sand and 5 parts Lake Superior gravel. The horizontal reinforcement consists of hooping bars spaced 12 ins. apart vertically, the size of the bars decreasing from the bottom upwards. These bars are in pairs, one near each surface of the shell. For the first 15 ft. above the base their cross- section is I sq. in., for the next 31 ft. it is 0.88 sq. in., for the next 14 Roas usedin rausirg Concrete Formas and remaining in Walt f oot SSP rsats = 30 Gt aia=ss= | NS ee ae oe ee ae BE Chay, as Vertical Rods i ras SS ee Galv Wire x (4"Vertical Rod. Net, 24Mesh Fig. 523.—Part Plan of Grain Elevator at Port Arthur, Ont. 20 ft. it is 0.75 sq. in., and above that it is 0.50 sq. in. Besides the horizontal bars there are in each bin 27 vertical bars, % in. in diameter, spaced equally distant apart. Where the walls are thickened at the contact points of tangencies they are reinforced by horizontal layers of 2-in. mesh galvanized wire netting 12 ins. apart vertically. At these points they are also reinforced by two horizontal 114 x 36 in. contact anchors 12 ins. apart vertically, which hook over the hoop bands. TANK AND RESERVOIR CONSTRUCTION. 709 The spaces enclosed between the convex surfaces of each group of four bins are also used for grain storage, forming quadrilateral bins with sides concave outwards. In other ele- vators, notably the elevators at Duluth, Minn., no prov.sion was made for strengthening the convex circular walls of the en- closing bins against pressure when the circular bins were empty, with the result that they collapsed. A description of the Duluth failure is given below. To care for the unbalanced pressure, caused by the filling of these bins when the main circular ,bins are empty, tension rcds were passed through the opposite walls near each corner, as shown on the partial plan (Fig. 523). These tie rods have a diameter of 134 ins. up to a height of 20 ft., 154 ins. for the next 30 ft., 1% ins. for the next 20 ft. and 1% ins. from that point to the top. Their screw ends have nuts bearing on beveled washers, which are seated on flat steel tie-plates, which distribute the pressure over the cylindrical walls and con- nect the ends of adjacent rods. The bottoms of the circular bins are approximately conical surfaces, and consist of 3 ins. of con- crete finished with 1% ins. of Portland cement mortar. The concrete was laid directly on well rammed sand, and is without reinforcement. The sides deviate from a true cone, converging tea flat chute 10 ft. long and 1 ft. wide, with a 15 x 15-in. gate near the centers, through which the contents are aischarged to the conveyor belt in the tunnel below. The rectangular inner bins have their bottoms highest in the center and slope to ‘outlets at one corner of each, from which the grain is carried by chutes to the center of the tunnel over the conveyor belts. The concrete walls of the bins were made in movable cylin- drical forms 4 ft. high. The curved surface of the forms were made of 2-in. vertical planks, spiked to inside and outside cir- cular horizontal ribs. The ribs were made like ordinary arch centers, with four thicknesses of 2 x 8-in. scarf planks bolted together to break joints and make complete circles inside the tank and circular segments of 270° or jess on the outsides of the tanks. The moulds were faced on the inside with No. 28 galvanized steel and were maintained in concentric positicns with a fixed distance between them by means of eight U-shaped steel yokes in radial planes. Each voke consisted of an inside and outside vertical post. with radial web and flanges engaging the inner and outer faces of the circular chords. 710 CONCRETE AND REINFORCED CONCRETE. The posts project about 2 ft. above the tops of the moulds, and were rigidly connected there by means of heavy braces and an adjustable tension rod. These yokes were bolted to the inner and outer chords of the moulds and held them rigidly together. The lower ends of the vertical yoke posts were seated on jack screws, which were supported on falsework built up inside the tanks as the walls progressed. The Failure of the Duluth, Minn., Grain Elevator.—The arrangement of the bins of the Duluth elevator resembles some- what that of the Canadian Pacific elevator, described above. There was this difference, however: The sides of adjacent circu- a2 bins were not tangent, and did not have either the thickened buttresses between adjacent bins or tie rods to resist the thrust of the grain from within the inner rectangular bin. Fig. 524.—Diagram Showing Failure of Grain Elevator at Duluth, Minu. Figure 524 shows the arrangement of the enclosing walls, the entire absence of anything like a buttress, there only being a thin connecting wall, while in the Canadian Pacific elevator the walls are tangent and thickened. Failure took place by the crushing of the arched enclosure, there being no skewback to resist the thrust when pressure was brought upon the sides of the bin. The manne. of failure is shown by the dotted lines in the figure. The Duluth elevator consists of a series of circular bins about 33 ft. in diameter and 104 ft. in height. The first failure occurred on December 12, 1900, and a second failure occurred on April 16, 1903. The sides of the bins were 12 ins. in thick- ness at the bottom and 9 ins. at the top. The reinforcement consisted of 114 x 3@-in. steel bands spaced about 12 ins. centers. It is stated that the gravel concrete used for side walls was found to contain a high percentage of voids, and also showed evidences TANK AND RESERVOIR CONSTRUCTION. 71 of containing a considerable percentage of foreign matter, as chips, bark, etc., which was gathered up with the gravel when the concrete was mixed. The lesson to be drawn from the above failures is that careful designing is necessary for success in this type of structure. No possible arrangement of loading should be overlooked while making the design, ‘and, lastly, good materials should be used in fabricating the concrete. Sand Storage Bins.—Two sand storage bins, having a capacity of 1,140 tons, or 850 cu. yds. each, of dry sand, were designed and constructed by the Turner Construction Co. for J. B. King & Co., at Hempstead Harbor, Long Island, in 1904. The combined weight of the bins and sand, which amounts to about 1,355 tons, is carried on fifteen columns. The tank, which is 27 ft. high and 30 ft. in diameter, is supported at a height of about 2o ft. above the pile foundation. The columns are arranged in two concentric arches, with a central column under the apex of the conical bottom of the bin. Each column has a square concrete footing 15 ins. thick and 4% or 5% ft. long on each side, de- pending upon whether it is designed for five or cight piles. The pile foundation consists of 96 12-in. piles about 25 ft. long. The column footings are connected by radial and circum- ferential beams of concrete reinforced with pairs of 3-in. bars, as indicated on the plans, and the center group is connected by a horizontal concrete diaphragm 14 ins. thick. The footing under each column is reinforced by six longitudinal and six transverse 34-in. bars 5 ft. 3 ins. long. The center coiumn and the six columns of the inner ring are each 22 ins. square, and are reinforced with four 34-in. vertical bars, while the outer columns are 22 x 18 ins., with four 34-in. vertical bars. The sections and details of tops of columns are shown in Fig. 525. The upper ends of all except the center columns engage the lower surface of two annular reinforced girders made by thickening the bottom of the bin, and are integral with it. Great pains were taken to make this conical sur- face and its girders monolithic, and the concrete for them was all placed in one day. In calculating the bottom and sides of the bins, fluid pressure for dry sand weighing too lbs. per cu. ft. was assumed. The side walls of the bin are reinforced by horizontal circular rings, each ring being made of several rods, overlapping about 712 rter Flan of ions and for Conical Annular Girders Omitted, Oo tty ‘i ip SO shoe eg ee a ze Le Q'G"-4 Quarter Plan of Bin, ‘Bottom. Annular Girders. a SE este! ge pe ze: s a or PE otc s0'ot* —-------- nie OE 5 OK ee S Bap oe: p Raye Bs & 4X ep oe Se oe oe . - te" ae See. " for Chute. 4 ae (- § Bar, 9'Long, between the! Bars, ¥ "Bars, Curved to Circl Re RR tigen 7 Bgrs: Center Lines L he Bs ‘1 Opening} Sil 31 Bark, Blong. le%ley e & Lapse 19" 0] 7 & 228 SEL oo gees = 4 Lot ue @ ab. Tred aa Rs 4H See? Sad wd WS wd be ie pen ” 3 a ed both directionsy 6-4" Bars bath directions Ecctional Elevation. | Quarter Blan of Reintoreenert Quarter Plan of Reinforcement Omitted. CONCRETE AND REINFORCED CONCKETE. Section 6B 1 Section of rior Columns. Sect nice, « a 5 Section of 434! Bars Wy x YES er and wa oe paces Es v_Intermediate Columns fe 2241 & ¥ oy LX eT ¢ VY NA weet mee" ColumA chor, i Knee Braces Center Colump of Annular Bin Knee Broces Exterior Calumn Joint Supports Fig. 525.—Details of Sand Storage Bins at Hempstead, Long Island, TANK AND RESERVOIR CONSTRUCTION. 713 24 ins. and wired together so as to be thoroughly spliced by the concrete. The sectional area of these rods is varied to conform with the different pressures assumed at different heights of the bin, by changing the number and size of the bars in 214-ft. vertical zones of the wall, as shown in vertical section. The walls are also reinforced by two sets of vertical rods, the lower set consisting of larger bars than the upper set and over- lapping them 6 ins. at a point a little below the center of the bin. The vertical walls of the bin were made in 5-ft. courses, which were additionally bonded together b-- 34-in. vertical dowels 2 ft. long, set in the center of the wall, 214 ft. apart. The walls have a uniform thickness of Io ins. in the vertical sides. The bottom is 13 ins. thick, and is reinforced by horizontal circular and inclined radial rods, as shown in drawing. The moulds for each bin were made with planed vertical staves 11% ins. thick, forming panels 5 ft. high and about 8 ft. long. The staves were nailed to 2 x 10-in. horizontal segmental ribs, one at the upper edge, one at the lower edge and one at the center of each panel. The positions of these ribs were displaced 2 ins. vertically in adjacent panels, and tuey were extended bevond the edges of the panels so as to overlap each other and receive the splice bolts by which they were fastened together. The ribs were braced bv inside and outside vertical standards 4 ft. apart on centers, each made with a pair of 2 x 6-in. strips 6 ft. long, blocked 1 in. apart and tied together by temporary radial bolts through the moulds. These bolts pass through sleeves of 16-gauge block sheet iron, bent cold, permanently -bedded in the concrete and eventually filled with mortar. Enough moulds were made for a complete course about one tank. After the concrete was about 24 hours old, the tie-bolts were removed from the moulds and they were lifted by a small hoist until the lower edges engaged the top of the concrete for about 2 ins. and the vertical standards engaged it about 1 ft. They were then supported on bolts through the upper part of the concrete. Each 5-ft. course was made monolithic by continuous concret- ing in one day’s work. The conical hopper bottom was also built monolithic in one day’s continuous concreting and was constructed without an inside mould. All the work was done from outside platforms, supported at the level of the top of the forms by falsework built up from the 714 CONCRETE AND REINFORCED CONCRETE. ground level. No scaffold or platform was provided on the inside of the bin. Coal Pocket for Pennsylvania Cement Co.—Figure 526 is a view of a coal pocket of simple design. The construction consists of transverse buttresses 9 ft. 6 ins. centers supporting a 6-in.. slab reinforced with 1%4-in. corrugated rods spaced from 4 to 7 ins. centers. The 4-in. roof is reinforced with ™%4-in. transverse bars spaced 8 ins. and 14-in. longitudinal bars 2 ft. on centers. The roof is supported by longitudinal beams and struts reinforced in the usual manner. The roof is sloped so that it will not be Fig. 526.—Coal Pockets, Pennsylvania Cement Co. subjected to internal pressure. The roof house contains the conveying machinery for filling the coal pocket, while the tunnel beneath the pocket contains conveying machinery for removing the coal. Atlantic City Coal Pocket.—Figure 527 shows details of a coal bin for the Water Department of Atlantic City, N. J., at Absecon Pumping Station. The total height from top of foundation to top of roof is 44 ft. 714 ins.; the outside diameter is 36 ft. and inside diameter is 30 ft. A feature to be noted is the annular form of the foundation. The sides and bottom are 9 ins. thick. The bottom is reinforced with 14-in. annular bars, spaced 12 ins. TANK AND RESERVOIR CONSTRUCTION. 715 centers, and 34-in. radial bars 18 ft. long, 2 ft. of which is in the side wall and 16 ft. in bottom and spaced 15 ins. centers and 34- in. radial bars between the forms, also spaced 15 ins. centers, ¥-in. vertical bars, 22 ft. long, spaced 3 ft. centers, having the lower 3 ft. bent into the bottom, with y4-in. bars, 10 ft. long, to form the vertical reinforcement, while 3 and )4-in. bars, spaced from 2 to 6 ins. centers, as shown, form the horizontal reinforce- ment of the side walls. The roof is pyramidal in form, having a 10-in. 25-lb. I-beam Ban k- 74%" i Ma—a-en ~-Ad Tf -—- - ------ * C . aD El evanion Half Section AAS Half Section BB Half SectionGC / ,One Sixth Plan @ of Conical Bottom of Bin £Annvlar //) \ Bars, eH One Third Plan METERS Elevation of Inner Arch 5 oO Half Plan of Annular Plan of Pyramidal Roof Foundations Fig. 527.—Coal Pockets at Atlantic City, N. J. at each angle framed as shown in Fig. 527. The roof is rein- forced with 14-in. bars bent over the I-beam flanges and spaced as shown. The general details of construction are shown on the drawings. Concrete Gas Holder Tank.—Concrete has‘been used both in Europe and this country in the construction of gas holder tanks. The half section of tank, recently constructed by the Cen- tral Union Gas Company at the foot ‘of 136th Street, near Locust Avenue, New York City, is shown in Figs. 528 and 529. This tank has an extreme diameter of 189 ft., and a depth of 41/% it. CONCRETE AND REINFORCED CONCRETE 716 gna Bri IGG 5 IEEE =o wir 12'S rye. ZL. Sr ihieiag § % TT sai | a ain | ° ie : te RG eniz beens ”“ ' 4 ee tae daa Ly } 7 4 Ag Gi | ; p KKK x _| si ey Fig. 528.—Part Transverse Section of \ iy Gas Holder Tank, New York City. Figure 529 shows a partial section Ce - of the monolithic concrete exterior e py wall, which is 42% ft. high from the a bottom of the footing and 5% ft. thick i Le at the base. Concentric with this i wall is an inner one 166 ft. in ex- i a ‘ ternal diameter and about 1614 ft. oF high above the footing. The top of S lt _y this wall is continuous with a con- s \ crete lining 12 ins. thick, which forms ' » the bottom of the tank, and is ap- t proximately a truncated cone. The “le e-xt-]--¥ annular space between the inner and outer walls serves to hold the water. » which forms a seal for the bottom | ; ! of the telescopic cylindrical steel gas \ "ee holder shell. J | % The outer wall is reinforced in the Sm ? upper part with six sets of hori- : ve ee zontal circular bands of square Concrete \ twisted steel bars. Each bar of the i upper and two lower sets has a sec- x tional area of 1.25 sq. ins., while the rove Level intermediate sets have an area 0.75 1 ; Fig. 529.—Wall for Gas Holder Tank at New York City. sq. in. for each bar. Jn each set there are four complete rings or hoops, each made up of several pieces of twisted steel, with their ends lapping TANK. AND RESERVOIR CONSTRUCTION. 717 about 32 ins., and rigidly clamped together by U-bolts, with tie pieces screwed close against the bars. The splices in adjacent bars are made to break joints at least 2 ft. As shown in the figure, the hoops were not placed in the same horizontal plane. The top of the wall is finished with a 6-in. coping reinforced by a continuous horizontal sheet of 3 in. No. 10 expanded metal. On top of the wall there are horizontal seats for the 20 vertical 3M orr 6x3 Pl Anchored hor: Bars Ca ehrore, Hush » x reo U 5 on Inside baa Ng Corr Bar = i > _ & ‘ 3 ' : sg y 3 x yee. 8 - 4 he: LL. Cl Plate PAXTY : k 4 Bolts, gx70" i) Fier H- 4-38 Corr Bars ineach Pilaster 447 "Rad-------->\ S Part Section of gs Tank Wall. ee Ss nat Showing Corr. Bars 17 Top Side of Floor. , f Corr. Bars Go. fLlevation. Part Sectional Plan. Center Pier Fig. 530.—Details of Gas Holder Tank at Dubuque, Ia. columns of the gas holder guide frame. At each seat are four vertical anchor bolts, 21%4 in. in diameter and 19 and 20 ft. long. These rods have at their lower ends forged heads engaging sockets in wrought iron ancl.or plates bedded in the concrete. The upper ends of the rods are in sleeves 4 ft. long and 4 ins. in diameter, so as to provide for a slight lateral movement and allow for adjustment to the front framework. Radial brick landing piers, with granite caps, are provided on the bottom of the tank, as shown in the figure. A 1:2:4 Portland cement con- 718 CONCRETE AND REINFORCED CONCRETE. crete, with an upper finish of 114 ins. of 1:2 cement mortar was used. Gas Holder Tank, Dubuque, Ia—The construction details of a gas holder tank, recently constructed for the Key City Gas Co., Dubuque, Ia., are shown in Fig. 530. This tank is 84 ft. in diam- eter and 21 ft. 5 ins. deep. The bottom of the tank is 5 ft. below the level of the ground, and rests upon a pile foundation. The floor is 16 ins. thick, and rests directly upon piles spaced 4 ft. 6 ins. centers. Under the walls the concrete is 28 ins. thick, and the pile foundation is reduced to 2 ft. 6 ins. Rein- _ gtkb Dagens 4 ax6 Se. : Ae, he i 2'Aante SOE Ow Pyles t Fig. 581.—Mcthod of Bracing Wall Forms, Dubuque Gas. Holder Tank. forced concrete tunnels are run under the floor for inlet and out- let pipes. The wall of the tank is 18 ins. thick at the bottom and 12 ins. at the top. A center pier, also of reinforced concret’, as shown, is also used. A 1:2'4:5 concrete of limestone, all pass- ing a 2-in. ring, was used for the floor, while a 1:2: 4 mixture was used for the walls. The size and location of reinforcing rods are shown in Fig. 530. The method of bracing wall forms is shown in Fig. 531; while one panel of the inside forms is shown in Fig. 532. The outside forms were similar, but were concave instead of convex. 1!ANK AND RESERVOIR CONSTRUCTION. 719 The circumferential bars for the walls were used in 30-ft. lengths, and spliced by lapping 3 ft. Mr. John E Conzelman, Asst. Engr. of the St. Louis Ex- panded Meta! and Corrugated Bar Co., who designed and built this structure, states in Engineering News, August 9, 1906, that % 1 ¥ iby x oP i ye z SS LKb | Ss x | 4 nN Ueto GQ tan nnn. V3. } & ‘Zholedj x?" } dole i y oy hod with lye End Fig, 3..—Wall Forms for Dubuque Gas Holder dank. the cost of unloading steel and placing it in structure was $7 per ton; that the labor of mixing and placing concrete amounted to 3.4 hrs. per cu. yd. for the floor, and 5.2 hrs. per cu. yd. for the wail (including pilasters and piers). The cost ot forms averaged 9 cts. per sq. ft. of wall. CHAPTER XXIX. 1 CHIMNEYS, TUNNELS, SUBWAYS, RAILROAD TIES, FENCE POSTS, PIERS AND WHAKVES. Chimneys.—lor high chimney construction reinforced con- crete is not only superior to brick or steel as regards stability and strength, but it possesses great durability with practically no mainten:nce charges. Many chimneys have been constructed of this material in the past few years, and the popularity of this type of construction is increasing. Examples of a number of structures will be given, together with a description of the general methods of construction. The reinforced concrete chimney for the forge shop of the United Shoe Machinery Co., at Beverley, Mass., is a good ex- ample of a chimney of rectangular section, adapted to industrial works, when a chimney of moderate height is needed. This chimney is 77.ft. 10 ins. in height and tapers from 9g ft. 3 ins. x 10 ft. at the base to 7 x 6 it. at the top. It is divided into two portions by an interior concrete diapuragm, reinforced by hori- zontal 4-in. bars spaced 18 ins. apart up to 25 ft. above the footing. One side of the chimney is again subdivided by a longitudinal diaphragm, making two flues, one of which is used for furnaces and the other for an induced draught. The upper 45 ft. of the chimney is unlined, while the portion below is lined with firebrick. The walls have a thickness varying from 18 ins. at the base to 9 ins. at the top, and are reinforced by six vertical Ys-in. bars lapped 18 ins. at the joints and spliced to make them continuous from the base to the top; 4-in. horizontal bars bent to form rectangular frames connect the vertical bars. These horizontal bars are placed 1 in. from the outside of the concrete, and 12 ins. apart vertically throughout the full height of the chimney. The foundation is a mass of concrete 6 ft. 6 ins. deep, and is stepped off to form a base 13 x 14 ft. Figure 533 shows the general features of the chimney. Most notable among the early chimneys built of reinforced CHIMNEYS, TUNNELS, SUBWAYS, ETC. 721 concrete is that for the Pacific Electric Ry., Los Angeles, Cal. This chimney is of Ransome construction, and was peenee by Mr. Carl Leonardt, of Los An- geles, and merits description, as it possesses a number of features not commonly met with in this type of construction. The Los Angeles chimney is 18¢ ft. in height above its base, off Tested Steel ings, 18° Apart | > > ; I 5 1 1 k--- G3°--- re is ar en F \ "Bars 12"opart | Full Height of Cumney "" 1 WY = | ! | 4! Bars ; \ ee 4 e \ 1 fi | ‘ Fd i 2 Furnace Five ; In ® i ‘ | induced a ; | Orr tf) ly | gy | : | + 2 Bote fer , re ler Foom Floor - | a | § | Sh: % \ oh ie | oH. gO SS { & y 301 Rails: S| | Sectiona! | Elevation » ee ¥ s S ~ ° Lt 3 Bars. iW Hei 15h] 8 Hy t I I > t-- 4-%"Bars 8 Furnace His Se em : Section G-n. Fig. 533.—Rectangular Bihniaes United Fig. 534.—Chimney for Power Shoe Machinery Co.’s Forge Shop, House, Pacific Electric Ry. Beverly, Mass. Los Angeles, Cal. 722 CONCRETE AND REINFORCED CONCRETE. which is 15 ft. 6 ins. below the level of the ground. This chimney is rectangular in section to a height of 36 ft. above the grade, at which point it assumes a circular form, with an exterior diameter of 15 ft. 2 ins., the inner diameter being about 11 ft. The rectangular form for the lower portion’ of the chimney was necessitated by the entrance of two flues from ‘opposite sides. ‘he construction of the chimney is further shown in the accom- Vertical Section. . Fig. 535.—To-ver and Falsework for Fig. 536.—Moulds for Shells, Los Building Los Angeles Chimney. Angeles Chimney. panying figures. It consists of two concentric walls independent of each other from base to top, and separated by an air space of I1 ins. to 16 ins., increasing in width toward the top. The ouver shell above the rectangular part is 9 ins., 6 ims. and 5 ins., CHIMNEYS, TUNNELS, SUBWAYS, ETC. 723 respectively, up to the cap in sections of about equal height; while the inner shell is 5 ins., 414 ins. and 4 ins. thick, respec- tively, from bottom to top in corresponding sections. The inner shell ends 4 ft. below the cap, and is free to elongate by heat independently of the outer shell. As shown in the sections, Fig. 534, it will be seen that at intervals of 30 ins., measured around the chimney, the air space is contracted for a length of 6 ins., and reduced to the width of 2% ins.; at every 5 ft. in height -this is again reduced to 34 in. by the introduction of a concrete brick in the wall. In this manner the oscillations of either shell independent of the other is checked, and the outer shell may sway in the wind 34 in. without bringing pressure upon the inner shell. / Ransome square cold twisted steel bars were used for the vertical and horizontal reinforcements in each shell. The hori- zontal reinforcements consist of 14-in. bars placed at intervals averaging 18 ins. in the inner shell and 24 ins. in the outer; 34-in. vertical bars were placed 1 ft. apart in the lower one-third of the shell above the flues, 2 ft. apart in the middle and 4 ft. apart at the top section of the outer shell. In the inner shell 14-in. bars were used, spaced about 3 ft. apart in the circumference of the shell. The concrete for the outer shell consisted of 1 part Port- land cement and 2 parts sand and 6 parts crushed granite, but that for the inner shell consisted of 1 part Portland cement, 2 parts sand and 4 parts broken sandstone. In the construction of this chimney a temporary tower of timber (Fig. 535) was erected inside the chimney, its top being kept well above the highest level of the concrete, and from this tower the moulds are hung by adjustable suspender rods. All material was hoisted up the shaft by an electric hoist. The tower scaffolding consisted of four 4 x 6-in. timbers having up- rights with 2 x 10-in. horizontal bars bolted thereto every 5 ft., and r x 6-in. cross-pieces. The head or top scaffolding was formed of 6 x 14-in: timbers, to which hoisting rods were at- tached. To avoid the labor of dismantling this head scaffolding for each set of moulds, telescope scaffolding was placed inside the main upright scaffolding, which enabled the workmen to disconnect the head scaffolding, raise the entire head intact, and put ‘in extensions to the uprights, all of which could be done in about 214 hours. The cross beams at the top of the tower sup- 724 CONCRETE AND REINFORCED CONCRETE. porting the moulds consisted of two pairs of beams about 16 ft. long, each cantilevered about 5 ft. beyond the sides of the tower. The inner and outer moulds were each suspended from these cross beams by four equally spaced vertical rods having threaded tops, which engaged screw wheels bearing on the beams. A light working platform projected out from the outside mould near the TIN EE ANE S top, and the concrete plat- S; form was hung from _ this mould a little below to catch dropping material or a fallen workman. Inside the chim- ¥ ney a staging was supported | from the tower, on which the a. workmen stood in placing and ! tamping the concrete. The 2 key Nailed to Topoft> . Wedge Spreader x1 4x4 Srop Blocks Walled to Lowest Cleat NGHLILLIF EL (Ea | 3Fx24" ss tit ee LE “20% i Bio's eso eee ee lly ka" ul eel : “Ss Stop Blocks 1). Side Elevation. Section. Fig. 537.—Joints for Hoops for Shell Fig. 588.—Core Boxes Used with Moulds, Los Angeles Chimney. Shell Moulds, Los Angeles, Cal. shell moulds are shown in Fig. 536. These were made with vertical wooden staves 12 ft. long beveled to an angle of 10 de- grees on both edges, so as to be in contact on the face next the concrete, and having a V-shaped opening on the opposite face. The staves were locked together with bands built up of 3-in. strips of Oregon fir to a thickness of 5 ins. and a width of 4 ins. The ends of these bands were connected by specially designed 725 ETC. Detail of Base. \ SUBIVAYS, TUNNELS, CHIMNEYS, Plan of Foundation. Beverly, Mass. SSA SAE SNS wy ISS SEES BW Se WN ‘ Ws Niece Ses tr ¢ ‘ My io a 8 $ C ‘ 5 ae 7 5 ct z ‘s $ 8 8 D 2S a S BF. uote Bees ass & : ea wer ® Sg LV s = Be Sik ~o 2s She sj SS Bs 3 OEE a iS Ee suog-o¢ | sog-ay A || sung Hog | sg-z ~ 9:0" + 0:51 rAR— Q | ? L. nana nnn 3 $782 = 22-2 z TTIW LBS SRS 539.-. Chimney for United Shoe Machinery Co.’s Works, Porras nnn nn nn nS ne ne nn =21:¢¢t - : Mena nen enn en ne nnn weet an Fig. 726 CONCRETE AND REINFORCED CONCRETE. jaw-forgings and sleeve nuts (Fig. 537). Six hoops were used for each mould, being located outside the stave in the outside mould and inside the staves for the inside moulds. To attach the moulds to the supporting beams 114 x 14-in. bars, with an eye at the top and a length of 12 ft., were bolted to each hoop in a vertical position at the four points of the circumference directly between the suspender bars. A detail of the core-boxes for forming the spaces between the inner and outer shells is shown in Fig. 538. The concreting was done in five sections, one section being completed every day. Probably more reinforced concrete chimneys have been con structed by the Weber Steel Concrete Chimney Co., of Chicago, than by any other concern in the world. The author is indebted to the company for the following information. The featurcs claimed for this chimney are possessed to a greater or less ex- tent by all reinforced concrete chimneys, and may with much advantage be enumerated in this place. In the construction of these chimneys the work is’ carried on continuously from the foundation to the top, thereby forming a monolith. The chimney is airtight, and this, with the smooth inner shell, gives a high working capacity. The construction of reinforced concrete chimneys proceeds with greater rapidity than brick chimneys. Another feature is their light weight, they being lighter than brick, and hence requiring smaller foundations. A concrete chimney resists the influence of chimney gas and of heating better than one made of other materials. The use of concrete gives an opportunity for improving the appearance of the chimney without excessive cost for ornamentation. Figure 539 shows the details of a chimney of moderate height built for the United Shoe Machinery Company, Beverly, Mass., while Fig. 540 is a view of the chimney completed. This chim- ney is 142 ft. I in. in height from the bottom of the foundation to the top, and 6 ft. in diameter. The foundation extends about 16 ft. below ground. The shell is double to the height of 48 ft. above ground. The inner shell is 4 ins. thick, while the outer one is 6 ins., and the upper portion of the chimney shell is § ins. in thickness. The reinforcing bars consist of 11% x 1'4 x 3/,, ins. vertical and 1 x 1 x %-in. horizontal T-bars. The number of bars in the circumference of the chimney shell and the method of arranging the bars in the base, together with the details of con- CHIMNEYS, TUNNELS, SUBWAYS, ETC. 727 struction, are shown in Fig. 539. The horizontal rings are spaced 1 ft. 6 ins. centers in the inner shell and 3 ft. centers in the outer and upper single shells. Another example of Webcr chimney (Fig. 541) is the one used for the Butte Reduction Works, at Butte, Montana, to carry off the gases and fumes from the copper smelting furnaces. This chimney is the largest reinforced concrete chimney that has thus far been built. It stands on a base of slag 12% ft. high, making its top 352% ft. above the surface grade. The shell has an inner diameter of 10 ft. This chimney was designed to resist Fig. 540.—View of United Shoe Machinery Co.’s Chimney. the pressure of the wind blowing at a velocity of too miles an hour. The base is 421% ft. square, 8 it. thick, and made of 1: 3:5 concrete reinforced as shown in the drawings. The shell is double to a height of 101 ft., and above this point the single shell rises 231 ft., making a total height above the slag base of 340 ft. The outer shell is 9 ins. thick, and the inner one 5 ins., with an air space of 4 ins. between. The single upper shell is 7 ins. thick. A 1:4 concrete is used for all the shells. The reinforcing bars ‘in the base and for the verticals are 11% x 114 x 3/,,-in. T-bars, while the horizontal rings are 1 x 1 x %-in. T-bars. A working stress of 16,000 lbs. per sq. in. was used for the steel. The rein- CONCRETE AND REINFORCED CONCRETE. 728 Section A-A. i-.09 of Offset. Detail Section “SIDg [0,434 = "G4 B-B and C-C, 02 04 v0 ‘fe \ 9% 9,9) Sbuly /R{UoZLIOY |. —_ l ' Y meee A | | t | | | | t 0" opt L.| ; al | a x GA 9A GAGA BA BA BA GA GAGA GA GA YA GA BA UA YA OA BAYA GAGA ON-G, SuPg [O24 0; OE OF j09 08 O01 O2i Vii OD Obl OB) OW We Ob OR 082 DOE ME OPE OOF OOP ey OPY 09 | OF PaaS OE HOE OO LOOP OOR, OOOO LOOPS OOP OON: OOP SOOT O07 | | L...---- ss wOlE2 4 Wool lT SIT DENI Op€ uoyopunay fo asbg o nOCEE « 1,256 OPED Of Base Fig. 541.—Chimney for the Butte Reduction Works, Butte, Mont. CHIMNEYS, TUNNELS, SUBITAYS, ETC. 729 forcement in the base consists of two layers of 20 bars each, crossing at right angles, and two layers of 13 bars each, running diagonally. In the outer shell and the single shell,- which is above, the reinforcement consists of 460 vertical bars at the bottom, decreasing gradually to 20 at the top. The inner shell has 20 vertical bars throughout its entire height. The chimney is so designed that no wind strain comes on the inner shell. The horizontal reinforcing rings are spaced 3 ft. apart in the outer. and single shells and 18 ins. apart in the inner shell. In the construction of Weber chimneys the forms consist of ed Bhi tat l Fig. 542.—View Showing Forms for Weber Chimney. two rings of six sections, each about 3 ft. wide, fastened to- gether with patented iron fastenings. The moulds are held in place by friction on the concrete only, and are disconnected before ‘hauling up to the position required for the next course. The flat top ring shown in Fig. 542 is a patented guide ring to hold the vertical steel rods in alignment through hoies in it. The ring is made of two 34-in. layers of wood, and is pushed on ahead of the centers. It also carries the beam for the hoisting pullev. All materials are hoisted inside of the chimney, no interior scaf- folding whatever being needed. For the double shell one form \ 730 CONCRETE AND REINFORCED CONCRETE, or ring a day is filled, while for the single shell two forms a day are usually filled. The T-section reinforcements are spliced by lapping about 2 ft. The character of the forms is shown in Figs. 542 and 543. Tunnels.—Concrete, both plain and reinforced, has been ex- tensively used for tunnel and subway construction during the past few years. The principles of design and methods of con- Fig. 548.—View Showing Forms for Weber Chimncy. struction are similar to those for sewer and water conduits. The larger sections used and general conditions met with in this class of work make the stresses to be dealt with large and the con- struction correspondingly more difficult. The term tunnel is usually applied to construction under cover, in which the tunnel bore is advanced by drifting, the surface of the ground above not being disturbed. On the othér hand, a subway is usually distinguished from a tunnel as being a con- CHIMNEYS, TUNNELS, SUBWAYS, ETC. 731 struction in open cut. The tunnel usually consists of a single arch spanning the opening, while to save head room the roof of a subway is usually flat, being supported by roof beams or girders, sometimes carried at an intermediate point or points by columns. The New York Subway.—The original section for the New York Subway consists of steel bents spaced 5 ft. on centers, having jack arches of concrete sprung between the beams to form the roof and side walls. The bents consisted of a roof beam 26 ft. long for a double track section, supported by two side and one intermediate column, The foundation of the columns and floor of the sub- Stree ¥ Cross - Section Hl Plan Fig. 544.Subway Consiruction New York Rapid Transit R.R. way also consists of concrete. The size of roof beam is governed by the height of cover, a 15-in. 60-lb. beam being used for ordi- nary conditions where the cover varies from 5 to 10 ft. The side column consists of a 12-in. 40-lb. I-beam, while the center column is made up of four angles of special section and one plate. In the construction of Contract No. 2, known as the Brooklyn Extension, the standard section is reinforced concrete for the roof and side walls and a steel column similar to that used in the original section to support the roof slab at mid span. The thickness of roof slab and amount of reinforcement varies with 732 CONCRETE AND REINFORCED CONCRETE. the cover. For a 5-ft. covér the slab is 18% ins. thick, and is reinforced with 1%4-in. square rods spaced about 8-in. centers. Two 1%-in. diameter rods connect the center column to a two- angle post or wall reinforcement spaced also 5-ft. centers. Three 54-in. diameter rods connect the center columns together at the top. / The side walls for a 5-ft. cover have a thickness of 14 ins. eedoteupporting | laggi Bulb L.col. Waterproofing y Ro ds, en is ee spaced 7 space A ‘S. Te Gee 1010" ee | [- ean? Bi: 7 A z [2 ry i bP 4 a Ss 4 4 voRods & eG 2! spaced 7 Sao 44 88 ON B ae Le ee s Be as 2 Ry = 8” ER 2 at ae EB ga j ey ne ae Kg z 4 Z SA t Surface, TET, Yt LSA Waterproofing , 14" Rods spaced 7” , 26" 2-1f"Rods . e 2g josie? J \ | { 4 4 2, Y ; ay q zy 4 3 Z eS fy be Ba 5 4 ie i a o 4 eS" wit |. ee dt 2 as “TTS” ye SS Apa 8 b 2 oY t Pe abe dhe 20” ee ts 72 a4" g 4g a 2a" s Ie ; Ys oe ENCE RUN a fe eee eae Fig. 545.—Forms for Reinforced Concrete Subway, New York Rapid Transit R.R. and have square vertical rods between angle uprights spaced about I-ft. centers. The arrangement of the reinforcement, together with general features, will be understood by consulting Fig. 544. The arrangement of the centering used in the con- struction of a section at Battery Park loop is shown in Fig. 545. The Philadelphia Subway.—In the construction of the Phila- delphia subway the roof beams and interior columns similar to 73: TUNNELS, SUBWAYS, ETC. CHIMNEYS, ‘ABMQGNS ABMTIVY SUeLL “yousg ume Didey eIydiepeltyd Jo steeq—yre “Sa ew wee eed, Buynogs UDid = 1DUO} 8S ‘uoWondsuED weBun, YGnay, UoH2aG ss0ID 734 CONCRETE AND REINFORCED CONCRETE. those used for the original New York subway section are retained The side walls are, however, reinforced with 1-in. diameter ver- tical round rods, spaced about 1 ft. centers and horizontal rods 54-in. diameter spaced about 16 ins. centers. A bulkhead of con- crete reinforced with longitudinal rods about 5% ft. high joined the posts in pairs. This bulkhead is intended to prevent the knocking out of the interior posts in case of a derailment. These details are all shown by Fig. 546. Aspen Tunnel, Union Pacific R. R.—In the construction of the Aspen Tunnel, on the Union Pacific R. R., at certain points, un- usual pressures occurred on account of the unstable nature of the Horizontal, Section. Cross Section. Fig. 547.—Aspen Tunnel, Union Pacific Ry. rock. The tunnel lining used consisted of concrete stiffened with steel ribs spaced from 12 to 24 ins. centers. These ribs consist of 12-in. 55-lb. I-beams, in,three sections, bent to the required curve and riveted together. The ribs are embedded in the concrete, which reaches from 4 ins. to 634 ins. inside the ribs and extend backwards to the wall of the excavation. The construction is shown by Fig. 547. The invert is a mass of con- crete reinforced with old rails placed transversely to the axis of the tunnel. The East Boston Tunwel—This tunnel was constructed with the aid of compressed air. The lining is of concrete, 2 ft. 9 ins. CHIMNEYS, TUNNELS, SUBWAYS, ETC. 735 thick at the side and crown, while the invert is 2 ft. thick, and with the exception of a twisted bar at the crown is unreinforced. The centering was a steel framework, as shown in Fig. 548, for a part of the work; the framework for the remainder was of wood. In the construction of this tunnel two side drifts 8 ft. square were first driven a certain distance and solidly timbered. The bottom of the drifts were then excavated, and the side founda- tions of concrete were placed in lengths of from 16 to 20 it. After the foundations had set the interior forms for the side walls were placed upon them, and the concrete side walls, 3 ft. ! “3 ec 3 S| | /H Fig. 548.—Section of East Boston Tunnel, Showing Reinforcement and Forms. thick, built up to within 16 ins. of the springing line of the arch. This work was kept upwards of 100 ft. in advance of the shield. The shield moved upon rollers traveling upon these side walls as a track. ; The main excavation was made under the shield, and the con- crete placed in sections 214 ft. long under the tail end of the shield. Sixteen cast-iron rods, 3 ins. in diameter and 2% ft. long, were placed in the concrete the entire length of the tunnel, and the shield was pushed forward by means of hydraulic jacks pushing against the cast-iron rod. A 4-in. lagging was placed over the rib-centering. The centering consisted of steel ribs 736 CONCRETE AND REINFORCED CONCRETE. spaced 2% it. on centers. A 1 cement and 2 sand Portland ce- ment grout was forced in on top of the arch to form a water- East Wai, vost Wau Fig. 549.-—Cross-Section of Ossining Tunnel, N. Y. C. & H. R. R. R. proofing film about 114 ins. thick. The invert was laid as the shield moved forward. ; The Ossining Tunnel—The improvements comprised in the i Tiehions -- Katerprooting £ = So eT ee, x- [- % ExyandedMetak a Section X-X Fig. 550.—Part Longitudinal Section of Ossining Tunnel. electrification of the metropolitan zone of the New York Central Railroad necessitated a change from a double track tunnel to a four-track tunnel at Ossining, New York. The tunnel is con- CHIMNEYS, TUNNELS, SUBII'AYS, ETC. 737 structed on the bank of the river, the ground dipping sharply to the water’s edge. The rock is of a micaceous variety, with an irregular stratification, dipping approximately at an angle of 45°. A portion of the tracks: at this point is in open cut, and a portion in a tunnel. When in open cut the sides are lined with concrete, and when necessary the concrete lining becomes a re- taining wall. ‘Figures 549 and 550 show a section of the tunnel, together with details of construction. The columns, which are of a built- up, Z-bar section, surrounded by expanded metal and concrete, are spaced about 12 ft. 6 ins. centers on the longitudinal axis of the tunnel, and are arranged in groups of 4 or 5, with their bases united by a solid collision wall of concrete reinforced with horizontal rods to form piers intended to deflect the cars and Fig. 551.—Section of Ossining Improvement, Showing Retaining Wall Work. diminish impact in case of a derailment. The tops of the columns are connected by two longitudinal 24-in. I-beams encased in con- crete. These beams support 20 and 24-in. I-beams spaced about 4 ft. on centers. Jack arches of concrete are sprung between these transverse beams forming the roof of the tunnel. The con- crete has a minimum thickness of 6 ins. This arch construction is stiffened by a series of ribs about 12 ins. wide the full depth of the cover, and spaced about 4 ft. 6 ins. on centers. The roof and walls are waterproofed with a coating of tar about 14 in. thick. ; Figure 551 shows a section of the concrete retaining wall used for an open cut section of this work. A section of the old tunnel which was removed is shown in dotted lines. Railway Ties.-Railway engineers have been experimenting for years to find a substitute for wooden cross ties which wil! 738 CONCRETE AND REINFORCED CONCRETE. possess all the good points of the wood tie, and, while cheap in first cost, will be more permanent. Reinforced concrete ties have been tested to a limited extent on short stretches of track, and, while the experimental sections are not long enough and have not been tested freely enough as yet to warrant final conclusions, the success of the concrete tie has. however, been great enough to promise that ultimately a satisfactory design will be secured. ~~ sooo" A Sectional Side Elevation. KO} ke /50 EH we 1600" R Teo Plans Fig. 552.—Cross-Tie Used on a French Railway. Figures 552 and 553 show details of a cross tie used on a French railway of one metre gauge, from Vairon to Saint Béron. Sixty cross ties were tested for a year, and proved so successful that 250 more were ordered put in to continue the test on a larger scale. These ties are about 7 x 514 ins. x 6 ft. The reinforcement consists of three’ trusslike frames, each formed of a k4z " ¥ Section C-D, Section A~v. Fig. 553.—Rail Fastening Used with Tie Shown by Fig. 552. single rod, as shown in Fig. 552. The upper and lower parts of each frame are tied together and the three frames are tied to- gether across the tie. A depression is provided for the rail seat and wedge-shaped holes are moulded through the body of the tie for wooden plugs, in which screw bolts for the rail fastenings are driven (Fig. 553). Wooden tie plates are placed under the CHIMNEYS. TUNNELS, SUBWAYS, ETC. 739 rail when it is set. These ties weigh about 230 pounds atid cost in the neighborhood of go cents. Ulster and Delaware R. R. Tie—Fig. 554 shows details of a tie which has been successfully tested on the Ulster and Delaware Railroad. The reinforcement consists of a steel angle with both legs turned down; holes properly spaced are punched through. the ke sg" 48%! CL Clip---». als pe ae ea aera See ee eat angle irom, gxtex 70" “63 K 80". ‘ Section Elevation. through Bolt. 7H%859'P). ¥ go ! Tl wk | 1S) ha k--/0't-->4 Plan. Fig. 554.—Cross-Tie, Ulster & Delaware R. R. angle for the bolts which form the rail fastening A square headed bolt 34 x 3% ins. is used and the two legs of the angle hold it firmly in place and keep it from turning when the nuts are tightened. An iron tie plate is used. The nuts of the bolts, contrary to expectation, did not work loose, but after 18 months of continuous : a om, ie °° a ts } h ° Fig. 555.—Cross-Tie, Hecla Belt Line Ry., Hecla, Mich. tise were as tight as the day the tie was put in, and, moreover, no attention had been given to them since the ties were installed. These ties were made of a 1: 2: 4 Portland cement concrete and cost 42 cents to manufacture exclusive of the metal. The weight of the tie is about 450 ibs. The principal objection to this tie appears to be the impossibility of renewing or replacing a bolt in case one is injured. 740 CONCRETE AND REINFORCED CONCRETE. Hecla Belt Railway Tie—A reinforced concrete tie tested on the Hecla Belt Line R. R., in Bay City, Mich., is shown in Fig. 555. The reinforcement consists of a lower flat bar and a twisted upper bar with flat ends, which extend outside of the concrete resting upon and holding in place wooden spiking blocks partly embedded in the concrete underneath the rails. Holes are punched in the top plate for spiking. The Kimball R. R. Tie—A cross tie of rather elaborate design is shown in Fig. 556. This tie is being tested on the Pere Marquette R. R. It consists of two rectangular blocks of con- crete, each 7 x 9 ins. in cross section and 3 ft. long, reinforced and connected by two steel channels placed 2 ins. back to back. Hard Hard Wood. q 13" Elm Pegs gree tas ye Concrete. - w ve 3x/fa" Channel. Fig. 556.—Cross-Tie, Pere Marquette R. R. wood blocks 3 x 9 ins. x 1 ft. 6 ins. bolted to the concrete serve as spiking pieces. Cast-iron sockets moulded in the concrete hold the bolts for fastening the spiking pieces and space the channels. Wooden plugs set in holes moulded in the concrete receive the ends of the spikes. Exposed portions of the channels are coy- ered with neat cement grout, Buhrer Tie.—Figure 5 57 shows a concrete and steel cross-tie. of which upwards of 3,000 are in use on the Lake Shore and Mich- igan Southern Railway. As will be seen, this tie consists of a piece of an old 65-Ib. rail turned upside down and imbedded in the con- crete. A portion of the bottom is shaped not unlike an ordinary wooden tie. The flange of the old rail forms the seat for the track rail and to it are attached the rail fastenings. These ties weigh CHIMNEYS, TUNNELS, SUBWAYS, ETC. 741 about 400 Ibs. It is stated that under ordinary conditions this tie has proved very satisfactory. In designing a tie provision should be made for the renewal of the fastenings in case they are injured in any way. The simpler the details and construction the greater will be the chance of success, The great weight of the concrete ties, while making them diffi- ee Elevation. f. KB ogy x : e cos en AB ToPa ee Vay Plain Lug. Lke-gtal ; Jojnt Lug, Section AB. Kg eer Section C-D. Section E-F. Fig. 557.—Cross-Tie, Lake Shore & Michigan Southern Ry. cult to handle and surface, will when they are once in the tracks contribute greatly to its rigidity and permanence and will un- doubtely reduce ihe maintenance charges for surfacing and lining track. Reinforced Concrete Fence Posts.—Fence posts may be con- structed of reinforced concrete and in many situations will in the long run prove less costly than wooden posts. The reinforced 742 CONCRETE AND REINFORCED CONCRETE. concrete post will not be affected by the weather and, hence, will last longer than either wood or iron. A concrete post may be cor- sructed in advance and put in place after it has hardened and set sufficiently hard as not to be injured by handling. Posts may also be moulded in place, but the length of time which they must stand before the removal of the forms requires the use of a large number of forms, making this method of manufacture expensive. For the sake of ecenomy the post is usually tapered. It is customary to reinforce them with wire or light rods, one rod being placed near each corner. To provide a means for fastening the fence wires the simplest and most satisfactory method is to use large staples Fig. 558.—View Showing Reinforced Concrete Posts in fence. having their ends bent so as to hook firmly into the concrete. These are put in their proper positions when the concrete is placed in the moulds. Figure 558 shows a braced corner post and line of reinforced concrete posts moulded in place. Figure 559 shows view of mould for corner post and braces and Fig. 560 detail of mould for corner post and brace. These forms are patented by the Stiner Cement Fence Post Co., of Indianapolis, Ind. The moulds for the line posts are similar in construction (Fig. 561). The corner post here shown is 10 x Io ins. at the top, 12 x 12 ins. at the ground, § ft. high, and extends about 3% ft. into the ground. The hole in 742 CHIMNEYS, TUNNELS, SUBWAYS, ETC. Fig. 559.—View of Mould for Corner Post. Y ae g oN \ 9g Ye ! wa in A gimmie 9 la alah acter aaah ales piesa naive et eae ee EE FE ogee an st ~N a XZ a ' wv = * 5 © mx yo. x © : LY x x : YF t La yw ; 4 x x % al o=N a Vg yw ae Sy # rc Xo ° = Fig. 560.—Details of Mould for Corner Post. 744 CONCRETE AND REINFORCED CONCRETE. the ground may be flared outward as much as desired, giving a massive base, thereby increasing the stability of the post. In Fig. 560, a, b, c and d are the sides. The moulding i or j is nailed to the side pieces b and e as shown by the shaded portion. A hole is ct in part c for the connection of the brace. Parts e and g are the sides of the brace mould and part of the bottom, and part h shows clamps for holding together the mould. The line posts are 5 x 5 ins. at the top, 7 x 7 ins. at the ground and 5 ft. high. The moulds are quite simple, being two pieces 5 ft. 6 ins. long, 9 ins. at the bottom and 7 ins. at the top and two pieces 7 ins. at bottom 3 ins. at top, also 5 ft. 6 ins. long, all r-in lumber. Two clamps (h) are used to hold them together. + Fig. 561.—Mould for Line Post. After digging the post holes the forms are set up, the reinforc- ing wire or rods put in place. The concrete is then mixed and tamped into place. Staples may be put in position through holes cut in one side o. the mould. Figures 562 and 563 show two forms of moulds, one for posts with two sides beveled and the other with four sides beveled. With the moulds here shown the moulding is done horizontally. The mould consists of two end pieces having notches to hold in place the longitudinal boards, cross pieces are provided as shown to prevent bulging of the longitudinal pieces. Hooks may be used to hold together the various pieces forming the mould. The post for which mould shown in Fig. 562 is provided is 6 x 6 ins. at the CHIMNEYS, TUNNELS, SUBI'AYS, ETC. 745 base and 3 x 6 ins. at the top and 7 ft. long. If it is desired to chamfer the edges triangular strips of wood may be nailed at the edges of the mould. ~~ The mould is placed on a platform and greased or coated with Fig. 562.—Mould for Fence Posts, with Two Tapering Sides. soft soap. About 1 inch of concrete is deposited and caretully tamped in place, the rods put in place and concrete filled in until about 1 in. from the top yet remains; the top rods are then put in and the concrete finished off. The ends and sides of the mould : Fig. 563.—Mould for Fence Posts, with Four Tapering Sides. may be removed in about 24 hours, but the posts should not be handled for about a week, during which time they should be sprinkled several times daily and protected from the sun and wind. The intermediate strips may be carefully withdrawn at the end of two or three days. If possible the posts should not be set until 740 CONCRETE AND REINFORCED CONCRETE. \ J, ; 98.43— —_— N Sp pede das | a P oa e fs A { it ul a 1 ' | { g ' { ! tr il I It ' i} a Ul ! 1; © ! iy i! i ! {I : 1] \ it { Ha I | 1 ‘ I ie i I it eM \ u POW U \} Vv Vv vo it OV yy y v Transverse Section. Longitudinal Section, Fig. 564.—Sections of Ocean Pier at Southampton, England. they are about 2 months old. A 1: 214: 5 stone or gravel concrete with the stone or gravel under 4 in. has proved satisfactory for this class of work. Mr. Philip L. Wormeley, Jr., Farmers’ Bulle- tin 235, U. S. Dept. of Agriculture, states that a post measuring 6 x6 ins. at the bottom, 6 x 3 ins. at the top, 7 ft. long, should not cost more than 30 cents, the cost items being as follows: One cubic yard of concrete will make 20 posts of the size given abowe and fora 1: 2144: 5 mixture— 1.16 barrels of cement, at $2 ........ cece eee c eee eee eeee $2.32 0.44 cubic yards of sand, at 75 cts. 6... eee eee eee eee 33 , O88sct. yds: Of gravel, at 75. Cts. accowvens nao wvnndeniwessw is 66 Cost of materials for 20 posts = 1 cu. yd. of concrete.. $3.31 Cost of concrete for I post .........ce cece eee eee eee ee $0.17 Cost of 28 ft. of 0.16-in. steel wire, at 3 cts. per pound.... 06 Potal *COSt wess230- easel. een ens eee aes awe gine $0.23 Cost of mrxing concrete, moulding and handiing will not OXCEEM, ocsigushsnaie: o's ba 60k Ob pM SOA ATMEL ELE SS ORES SES .07 otal 4cOSt- OF ToPGSte anonceradaarcceujesc avannaieenn dna $0.30 Of course, the costs of the materials and labor in any given locality will vary and affect the cost accordingly. Piers and Docks.—Reinforced concrete has been used for piers, wharis and docks in Europe, but until recently has been little employed in this country. The usual type of construction con- sisted of reinforced concrete piles braced by longitudinal and transverse struts, carrying beams and girders, supporting the floor slab. The size of the reinforcement used for the various members is essentially the same as that employed for similar mem- bers in other classes of construction. Christophe describes a wharf of Hennebique construction at \ Woolston, Southampton, England. This structure is L-shaped, CHIMNEYS, TUNNELS, SUBWAYS, ETC. 747 having the stems go x 31 and 100 x 47 ft., respectively. It was designed to carry a moving load of 500 lbs. per sq. ft. with a crane to lift 35 tons at the outer end. Figure 564 shows a cross and longitudinal section. The piles were spaced 10 ft. on centers. The details of the reinforcement of the piles and girders are shown in Fig. 565, together with connections of horizontal and diagonal bracing. The most notable piece of pier construction thus far done in the United States is the reconstruction of the Atlantic City Steel Pier at Atlantic City, N. J. This work consists of strengthening the pepe ark} Ld ee § Ged Ep Saye ut aN La" Md Fig. 565.—Details of Southampion Pier. old iron pier, which had become so weakened by rust that it was necessary to either strengthen or rebuild it as a whole, and of adding side bents to increase the width of the pier. The old cross and longitudinal girders were encased in a con- crete beam 13 ins. wide by 27 ins. deep, reinforced at the top and bottom with 1-in. bars, as shown in Fig. 566. The old steel pipe piers, which were 1034 ins. outside diameter, were encased with a, reinforced concrete shell built in place about the pile and sunk as the work progressed. A water jet was used to sink the shells until‘they rested upon the old cast-iron disks 748 CONCRETE AND REINFORCED CONCRETE. supporting the steel pile. The details of these pile reinforcements are shown in Fig. 566. 4,1’ Bars, 16 0"long, (in Overhang only) K/0% ys Section C-D.. Keven en SG hee ce Dt Bottom Plan of Base. Fig. 566.—Section Showing Method of Encasing Steelwork of Atlantic City Pier with Concrete. For the new work two sizes of piles were used, 12 ins. and 25 ins. in diameter, respectively. The transverse girders are 2 ft. 4 ins. deep and 7 ins. wide, while the longitudinal struts are 15 ft. CHIMNEYS, TUNNELS, SUBWAYS, ETC. 749 deep. Details of the girders, bracket and knee brace construction are shown by Fig. 567. As will be seen, the lower end of the pile has a diameter of 2 ft. 6 ins. and together with the pile was built about a 2 in. jet pipe and reinforced with six 34-in. bars. These piles were constructed in advance and sunk with a water jet having a pressure of 65 lbs. per sq. in. When in position the girder moulds were built in place and the girder reinforcement and concrete: forming the girders and struts placed. The piles were sunk from 8 to Iq ft. into the BStirrups.. eee Section C-D Fig. 567.—Details of 12-in. Reinforced Concrete Pile, Atlantic City 3 Steel Pier. sand and had a maximum length of 32 ft. 6 ins. The bearing power of the sand was taken at 5 tons per. sq. ft. The 25-in. piles were carried down to a depth of 16 ft. into the sand. The details are similar to those of the 12-in. piles. The bottom 12 ft. of the 25-in. piles, including the bulb point, was moulded in wooden forms with the jet pipe and reinforcing rods in place. When the concrete had hardened a 75-in. galvanized steel shell was slipped a short distance over the top of the con- crete and the joint made watertight by calking with oakum. The steel shell was constructed watertight and was long enough to reach above the water when the pile was sunk into position. The 750 CONCRETE AND REINFORCED CONCRETE. reinforcing rods were then put in position and hooked to the lower sections and the pile and casing swung into place and jetted down with 85 lbs. water pressure. After being sunk the casing was filled with concrete and the bracketed tops, girders and struts moulded in place. The length of these 25-in. piles was 52 ft. from the top of the girders. A 1: 2: 4 Vuicanite Portland cement concrete was used. The concrete was mixed wet and puddled into the pile forms by means of bamboo fishing poies, which proved very satis- factory in giving a good mortar surface and working the mixture between the reinforcing rods and the face of the former. This construction was designed by the Concrete Stee! Engineering Ca of New York. CHAPTER XXX. CONCRETE IN BRIDGE CONSTRUCTION. Concrete, both reinforced and unreinforced, is extensively used in bridge construction. Without reinforcement it is used in the construction of arches up to quite wide spans; it is also used for abutments, piers, spandrel walls, etc. Reinforced concrete has a still broader use, being empioyed for both girder and arch bridges, spandrel walls, posts, floor slabs and beams, foundations, and for strengthening existing structures. For convenience reinforced concrete bridges may be classified as girder and arch bridges. Girder bridges may consist of a rein- forced slab with or without ‘stiffening ribs. Without stiffening ribs girder bridges are only adapted to short spans, usually not exceeding about 15 ft. For wider spans the ribbed slab is em- ployed, consisting of two or more heavily reinforced concrete girders connected by a reinforced slab, the construction being not unlike that used for wide span floor construction. Bridges of this type have been constructed with spans up to about roo ft. Another type of girder bridge occasionally met with consists of a deep girder having portions of the web removed, the arrangement of the reinforcement being such as to bring about some form of truss action. Girder bridges, especially for the wider spans, are best adapted to the construction of foot bridges and highway bridges. When the span exceeds about 50 ft. the arch bridge will prove the more satisfactory form cf construction. For railroad bridges, on account of the rough usage to which they are subjected, girder bridges are seldom employed for spans exceeding about 25 ft. Arch bridges may consist of a solid or ribbed arch. The solid arch consists of a curved slab, which when reinforced has some one of the arrangements ‘of reinforcement shown in Figs. 145 to 154, pages 257-9. Ribbed arches consist of two or more curved girders connected either by a thin reinforced slab or a framework of beams and girders. The reinforcement for ribbed arches con- sists usually of top ‘and bottom reinforcing bars with or without connecting web members. Sometimes the skeleton consists of a 752 CONCRETE AND REINFORCED CONCRETE. rigidly connected built up truss. The slab or arch rib may be of uniform thickness throughout its whole length, but often is of varying thickness, increasing usually from the crown to the springing points. Sometimes, especially when hinges are used, the arch ring increases in thickness from the crown to the haunches and then decreases again to the springing points. Either solid or skeleton spandrel construction may be used with both the solid and ribbed type of arch bridge. Skeleton spandrel construction, on account of its reduced weight and cost, is, how- ever, most com:aonly used for the ribbed arch bridge and for the wider spans is becoming more popular for the solid arch. The skeleton spandrel construction may consist of either a series of spandrel arches carrying the roadway or of a framework of posts and girders carrying a reinforced slab forming the roadway. Both types of construction will be illustrated. Skeleton post and girder construction greatly reduce the dead weight to be carried and transmits the loads directly to the arch ring, thereby greatly sim- plifying the analysis of strains. Culvert construction is essentially the same as that used for short span bridges, the only material difference being in the addi- tion at times of wing walls to protect the embankment. A culvert may be considered as a short span bridge serving for a water- way through an earth embankment of greater or less height. Floors of steel bridges may often be constructed with economy of reinforced concrete. Such floors replace the various types of metal trough floors used heretofore for highway and_ railroad bridges, and have.in many respects proved much more satisfactory than metal floors. Reinforced concrete may at times be used for strengthening old steel bridges, thereby lengthening their life and enabling increased loads to be carried without the great expense of a new structure. If properly designed and constructed both concrete and rein- forced concrete bridges are practically indestructible and, hence, possess great ultimate economy. Reinforced concrete bridges are considerably lighter than masonry or concrete bridges and do not bring so great weight upon the foundations, often giving a sub- stantial saving in the cost of the latter. Again, on account of their great stiffness, due to the presence of the metal, reinforced concrete bridges possess greater security against danger caused by CONCRETE IN BRIDGE CONSTRUCTION. 753 any slight settlement of the foundations. The steel provides re- sisting power against dangerous tensile strains due to any cause and gives an ample factor of safety against any possible emer- gency. From an aesthetic standpoint reinforced concrete bridges possess all the advantages of masonry bridges. In many cases more slender sections are employed, giving more graceful and pleasing lines, without any loss of strength. The cost of the reinforced concrete bridge in almost all cases will be much less than that of a masonry structure, and in many cases will not greatly, if at all, exceed that of a steel structure. They are free from the excessive vibrations often experienced in metal bridges, and if the foundations are protected against scour will withstand almost any flood and are proof against destruction by fire or tornadoes. The cost of maintenance is practically nothing, in the case of highway bridges being confined to keeping the pavements in repair. The materials and labor used in the construction of this type of bridge are usually obtained in the locality of the bridge site and a large part of the money expended in the construction of ¢he bridge is disbursed among the home people who pay for and use the bridge. The girder bridge, on account of its freedom from corrosion, light weight and low cost, is particularly well adapted to the con- struction of foot bridges, and light highway bridges spanning railroads, canals and small streams. For short spans the flat slab answers all purposes, but for spans from 20 to 60 ft. and even up to 80 or 100 ft. the ribbed slab gives a satisfactory form of con- struction. As a rule for spans greater than 50 feet the arch will prove the more economic form of construction. The longest span reinforced concrete arch thus far built is that of the Gruenwald Bridge, at Munich, Germany. This bridge has two arched spans of 230 ft. This bridge is described on page 789. Mr. Edwin Thacher states that he ‘can see no good reason why reinforced concrete bridges with spans of 500 ft. or more cannot be built with perfect safety, and often with economy ; that he has designed and submitted bids on spans as great as 300 ft., and although the plans and prices were satisfactory, other and weightier considerations from the point of view taken by the officials induced them to prefer steel structures. 754 CONCRETE AND REINFORCED CONCRETE. In this country fixed or monolithic arched bridges have been used almost exclusively, but in Europe both one and three hinged arches of reinforced concrete have been used for wide span bridges. In arched bridges the use of reinforced concrete is not confined to reinforcing the arch ring, but when solid spandrels are not employed it is used for the spandrel arches or posts and girders supporting a reinforced slab carrying the roadway. Again reinforced concrete may be used with economy in the con- struction of piers, abutments and abutment wing walls. It is also used for railroad trestles, the bents and girders being entirely of this material. Cost.—In the construction of highway bridges light metal bridges with wooden floors will usually be found to be cheaper than reinforced concrete, but if heavy steel construction with trough floors be used the reinforced concrete bridge will prove to be the cheaper when no special difficulty is experienced in securing good foundations. When the questions of maintenance and permanency are considered the reinforced concrete bridge, it is believed, will prove the ¢theaper. A reinforced concrete viaduct at Rotterdam was constructed with a saving of 30 per cent. of the cost of a steel viaduct. In addition to this an income is obtained from the rental of shops built in the space under the viaduct. This space could not have been utilized in this way had a steel viaduct been con- structed on account of the great noise due to the traffic on a metal structure. The contract for the Richmond and Chesapeake viaduct, Richmond, Va., described on another page in this chapter, was secured in competition with a steel structure, the question of cost alone determining the award of the contract. For railroad bridges of moderate span reinforced concrete supplies a material of construction which will give a permanent way and practically eliminate from the fixed maintenance charges the expense of a corps of bridge carpenters and inspectors. Again the use of trough floors of reinforced concrete filled with ordinary ballast permits the use of ordinary cross-ties on the bridges, thereby re- ducing maintenance charges, as bridge-ties are much more ex- pensive than ordinary cross-ties. The use of ballast over bridges eliminates the train shocks so unpleasantly experienced when a train passes upon and leaves a metal bridge with framed bridge ties. Of course local conditions will determine whether a steel or CONCRETE IN BRIDGE CONSTRUCTION. 785 reinforced concrete structure should be used. It is probabie that for spans of from 25 to 100 ft. the reinforced concrete arch will prove an economic structure. Many of the reinforced concrete arch bridges used on American railroads have been so designed that the concrete alone has sufficient strength to carry all loads, the steel being put in for additional strength because of ignorance of arch design. These structures cannot be said to be designed as reinforced concrete bridges, and have very high factors of safety. While not advocating the extremely light sections used in some reinforced concrete bridges of European design, the author believes that with careful designing lighter structures of ample strength may be secured and dollars saved for the railroad companies. GIRDER BRIDGES. For short span girder bridges where a reinforced slab without strengthening ribs is used the slab reinforcement may consist of any one of the systems of reinforcement already described for floor slabs. When heavy loads are to be carried care should be taken to see that there is sufficient concreté and metal provided to care for shearing stresses, as with short spans and heavy loads this will be found in many cases to be the determining factor in the design. For ribbed girder bridges any one of the systems of girder reinforcements already described for girder construction may be used. The methods to be used in the computctions are the same as those employed for floor and beam design. In many cases, however, it would seem advisable in the design to treat the beams or ribs as if they acted independently of the slab, so propor- tioning them that they will have sufficient strength. to carry all loads. without assistance from the slab concrete, which in floor de- sign is considered as acting with the rib to form a T-shaped beam. This seems desirable on account of the uncertain character of the load to be brought upon the bridge, the rough usage which it is at times subjected to, as well as being in many cases subjected to the action of ice and drift during time of flood. For culvert and railroad bridges it is often impossible to design the bridge according to hard and fast rules, as the effect of impact from heavy trains is practically an unknown quantity. Under such conditions good judgment serves to fix the sections which should be used. For such bridges the cost of the extra materials 750 CONCRETE AND REINFORCED CONCRETE necessary to give a well proportioned structure is of small moment, especially when it is remembered that the structure will form a permanent one with little or no expense necessary for repairs. ‘ For highway and foot bridges conditions are different and theoretical designs may be more closely followed. Beam Bridges—-Many short bridges of concrete and steel have been constructed for both highway and railroad spans. These mee Bette 80°-——- 7 LY %" Rods tl = |NOraiin Pipe Drain Pipes XN. ~ Longitudinal Section. Half Cross - Section. Fig. 568.—Steel Beam Bridge, B. & O. R. R. consist either of longitudinal I-beams embedded in a concrete slab or longitudinal beams having jack arches of concrete sprung between them. The bridges shown in Figs. 568 and 569 are of this type and are standard bridges used on the Baltimore and Ohio Railroad. Simple slabs of concrete 12 in. thick reinforced with rails, as shown in Fig. 569, are used for spans from 5 to 12 ft. The concrete is made 1: 3: 5 with Portland cement and 1% in. broken stone well rammed. Under each rail is embedded Lgtorke.- Si0t-—-+4---- 5!0%----+ 30"-4 5-Rails : ‘S-Fails * Longitudinal Section Half ‘Cross- Section. Fig. 569.—Steel Rail Bridge, B. & O. R. R. a double line of rails set close together. The top line of rails have their heads turned down and placed between the webs of the lower line and the spaces between the rails filled with a 1:3 cement mortar. The rails are given a bearing of 18 ins. on the tops of the side walls. For spans varying from 12 to 26 ft. steel beams are used in place of rails, as shown in Fig. 568. These beams have a bearing of 2 ft. on the masonry and are embedded in a mass of concrete, CONCRETE IN BRIDGE CONSTRUCTION, 757 extending 2 ins. below and from 4 to 5 ins. above the top flanges. In this case a 1: 2:4 concrete is used with 1-in. broken stone. The bottom sides and upper surfaces are finished with 14-in. of 1:3 mortar carefully rammed in with the concrete. Figure 570 shows cross section of a beam bridge consisting of two 18-in. and three 20-in. I-beams. having concrete arches rein- forced with expanded metal sprung between thei bottom flanges. This bridge has a span of 28-ft. and was designed to carry a 12- ton roller. Hennebique Bridges.—In Europe the Hennebique construction has perhaps been most extensively used for girder bridges This construction usually consists of a flat deck slab supported by longitudinal ribs or girders usually spaced from 3% to 7 ft. on centers, the whole being. built as a monolith The slab is rein- forced in the usual manner with straight and bent rods placed Fig 570.—-Concrete and Steel Beam Highway Bridge. transversely to the direction of the girder and has the usual Hennebique stirrups. The girders are reinforced in the usual manner with straight and bent rods and stirrups. The floor slabs are at times cantilevered from the outside girders to form a side- walk, the reinforcing metal being properly placed to care for -tensile stresses. The Sutton Drain and Milan bridges, described further on, are examples of Hennebique construction. Moller Bridges——In Germany the Moller ribbed slab construc tion is extensively used for girder bridges. The construction is similar in all respects to that used for floor slabs, the ribs ‘being thicker at the center of the span, giving the fish- belly type. The reinforcement is usually a flat bar, having short angles riveted to it at intervals to anchor it in the concrete. (See Fig. 79, page 226). The reinforcement of the deck slab usually consists of small I-beams placed transversely to the ribs or 758 CONCRETE AND REINFORCED CONCRETE. girders. Figure 571 shows the principal features of the Moller construction. Sutton Drain Bridge, Hull, Eng.—This bridge is of Hennebique construction and is the first reinforced concrete highway bridge constructed in England. The bridge is on a slight skew and has a square span of 4o ft. and a width of 60 ft between parapets, the roadway being 4o ft. in width and the two sidewalks each 10 ft. This bridge was designed to carry at the same time four wagons, each carrying 25 tons on two axles 8 ft. apart. The reinforced floor slab is carried by eight Jongitudinal beams 16 ins. wide and 2 ft. 7 ins. deep below the bottom of the slab. Three [ze Ty E i i rt i H i I q I E E Plan. Fig. 571-—Moller Girder Bridge. cross-beams, 8 ins. wide and 10 ins. deep, below the floor slab, span between the main beams under the roadway Three cross- beams, 8 ins. wide and 6 ins. deep connect the bottoms of the’ main beams under the sidewalk slab. These beams are intended to carry water and gas pipes across the bridge. Details of con- struction are shown in Fig. 572. The main beams are reinforced with four straight and four bent rods, 134 ins. diameter near the bottom and with two sets of four straight rods 114 ins. diameter near the top of the beam. Skew Bridge at Milan—The Milan bridge has an 83 ft. 8-in. center span and two 34 ft. g-in. side spans measured on the skew, the skew angle being 65° The piers are 6 ft. 7 ins. thick and are CONCRETE IN BRIDGE CONSTRUCTION. 759 -also of reinforced concrete. The clear width of bridge between parapets is 23 ft., including two sidewalks, 3 ft. 3 ins. wide Two main girders, which also act as parapets, are 2 ft. thick and 6 ft. 7 in. deep and extend 3 ft. 3 ins. above the foct paths. Reinforcement is placed in both the tension and the compression “ye 48 Wood Pavin i paeee a MOO eecesananat spas HE oh = = a bea WG phe fo ncnnnen sane i x ¥ C 20". Ae = 94" phe -80" rhe 80" P- 80" rhe 80" HB re 94" De Terra Cotta Fa “ Fig. 572.—Hennebique Girder Bridge, Sutton Drain, England. flanges of the beams. The compression reinforcement consists of 22 rods, approximately 17 in. in diameter, while the tension reinforcement consists of 12 rods approximately 25% ins. in diameter. A series of small rods is placed transversely between the longitudinal rods to tie them together. Cross-beams, ap- 760 YONCRETE AND REINFORCED CONCRETE. proximately ro ins. wide and 16 ins. deep below the deck slab, spaced 6 ft. centers, span between the main girders and support the deck slab, which is 5% ins. thick. These beams are rein- forced with three $-in. rods at the top and six 13¢-in. rods at the bottom. The deck slab is reinforced with both longitudinal and transverse rods. A partial elevation and cross sections showing details of construction are given in Fig. 573. Center Ling = lags KAS 4-1 tS | |S Be Half Transverse Section. Fig. 573.—Details of Girder Bridge at Milan. Albany, Ind., Bridge—In one or more systems of ribbed slab construction an attempt has been made to secure a beam or rib of uniform strength by varying the depth of the beam—i. e., where the beam is uniformly loaded the cross section will increase from the abutment to the center directly as the bending moment of the beam increases The Moller construction described on page 757 shows one method of applying this principle. This construction has been used both for floor and for girder bridge construction. The Albany, Ind., bridge is another example. This bridge was de- signed to secure a maximum economy of materials in order to meet steel bridge competition and also to secure a girder con- struction of uniform strength. The span is 4o ft. and the width of roadway 14 ft. The construction consists of an arched slab 8 ins. thick at the crown and slightly thicker at the ends and hav- ing a total rise of only 28 ins. The slab is reinforced with five longitudinal ribs, straight on the bottom and 28 ins. deep at mid- span. No dependence is placed on the arched slab for carrying either dead or live loads, it being considered as acting only as a CONCRETE IN BRIDGE CONSTRUCTION. 761 ribbed slab. The slab is reinforced with 5%-in. diameter plain steel rods placed near its lower surface transversely to the axis of the roadway and spaced about 3 ft. centers. The ribs or gir- ders are each reinforced with plain steel rods, having a section of 8 sq. ins. On account of the beam having a section to‘secure uniform strength the r<<.- are equally stressed through- out the whole length of the span. ‘his necessitates a positive anchorage at the ends having sufficient strength to develop the strength of the reinforcement. If the latter-is bent sharply at right angles the concrete will crush under the rods; but by bend- ing the rods with a sufficiently large radius this is avoided, and by gradually reducing the radius of curvature a sufficient length of rod will be embedded in the concrete to develop their strength by means of the adhesion and friction on the rod. .The method of bending the rods to secure a sufficient anchorage is shown in a= Transverse Section. Halt Plan. Fig. 574.—Girder Bridge at Albany, Ind. Fig. 574, which is a half-plan longitudinal and transverse section. This bridge was designed to carry a 20-ton concentrated load, together with 200 lbs. per sq. ft. uniform live load, besides the dead weight of bridge and the filling upon it. Elmwood Bridge, Memphis, Tenn.—The 100-ft. reinforced con- crete girder bridge recently constructed at Memphis, Tenn., is the longest span highway girder bridge thus far constructed. The necessity of providing a clearance of at least 19 ft. over the six railroad tracks spanned by this bridge and the strong objec- tions raised to a graded approach which would have been required in the cemetery ground if an arch span with the required cleararce had been used, made the adoption of a practically flat span im- perative. The bridge as built has a rise of 4 ft.. but was not designed to act as an arch Two longitudinal cirders are used to carrv the reinforced concrete slab. which is suspended from 762 CONCRETE AND REINFORCED CONCRETE. them and forms the roadway and sidewalk. The bridge has a total width of 31 ft., there being a 16-ft. roadway, two 4-ft. sidewalks and the two 3-ft. 6-in girders between the roadway and sidewalks. The girders have a total height of 6 ft. 6 ins., including a 6-in. coping. Massive concrete abutments are pro- vided at both ends and the girders are designed to act as a fixed or restrained beam. Under these conditions the portions of the girders near the abutments act as cantilever beams, while the middle portion acts as a simple beam. The reinforcement of the cantilever portion consists of 30 bars, 14%4-in. diameter, placed in four horizontal rows in the upper or tension portion of the beam. These bars are 4o ft. long, extend 4 ft. beyond the inflection points or, ends of cantilever sections of the girder and cxtend 15 ft. back into the abutment. The middle portion of the girder, which acts as a simple beam, is reinforced near the bottom with 24 bars 1% in. diameter placed in three rows. This rein- forcement is 66 ft. long and extends 4 ft. into the cantilever section at each end, i. e., the two systems of rods lap 4 ft. at each end of the girder. At these points 30 inclined shearing rods, 1¥4-in. diameter, transmit the shear from the lower to the upper rods. Each cantilever is anchored to the abutment by a series of 114-in. diameter rods running from a central point at the top back and downward into the abutment. Several light street railway rails were placed in a vertical position near the end of each girder to bond the girders and abutment together. The abutments were designed to act as anchorages for the cantilever girders, any possible thrust due to arch action being neglected. Between the girders the abutments are hollow, having a retaining wall at the front and a wide flat floor canti- levered back from the rear face of the wall. This floor is rein- iforced near its lower surface with light rails. The front -wall retains the earth, which resting upon the floor provides additional anchorage. The bridge floor is 13 ins. thick and. is reinforced ~ with 10-in. tranverse I-beams. Each beam is attached to the girders on their center lines by two I-in. tie rods extending up into the girder and anchored just below the coping on the latter by means of a 14 x 6-in. steel bar embedded in the concrete. De- tails of construction are shown in Fig. 575. This bridge is designed to sustain a uniform live load of :200 Ibs. per square foot. ‘The dead load is approximately 500 tons. CONCRETE IN BRIDGE CONSTRUCTION. 763 "The false work used in the erection of this bridge consisted of bents built of 12 x 12-in. timbers heavily cross-braced and sup- porting 5 x 16-in. stringers, which carried the lagging. The concrete was a 1: 244: 5 Portland cement broken. stone concrete mixed fairly wet. Corrugated bars were used for the reinforcement. Each girder was built in a single day. The forms were not removed until three months after the concrete had set. = SOS ae a a 1 os 575.—Girder Bridge at Memphis, Tenn. This bridge was designed by and erected under the direc- tion of Mr. J. A. Omberg, City Engineer of Memphis, who states that the total cost of the bridge was $17,500, including the asphalt pavement, iron hand railing and cutstone veneering on posts at the end of the girders. The forms cost $4,000. This large cost was due to difficulties in erection, which was done so as not to interfere with traffic. = Open Web Girder Bridge—The, bridge at Purfleet, England, differs from the usual type of girder bridge in that it is con- 764 CONCRETE AND REINFORCED CONCRETE. structed with open webs. On account of limited head room it’ was necessary to use a through bridge. The bridge rests upon circular piers and forms a part of an approach to an island pier. BARS b4! 9--,, SOARS T ba.y. SRARS O89, x FLOOR. Bana he (teveere) fe yoo roe ame e oS Pe CORW BARS ig . = ee Fig. 576.—Half Elevation, Open Web Girder Bridge, Purfleet, England. It is used to carry a single line of standard gauge railway. The main portion of the pier also consisted of reinforced concrete piles and girders. On account of this bridge being built on a ie 4 BARS 1% L620 5 Sh [STIR 1 — ies ois” Barekr 10) MARES 2BARS 4 LS O - OBARST 46" s »F Ry 3 act fs NecaCk WIRE 13 BWG L9'O ae 3 a ed eA rr at au Ss E28 _ ' 2BARSS S20 a | ears tons +> ‘o ee Kwa 7 ess ta STIR, DrIZAwe. piel 5 ‘ SaARS 1% Usha” (ke, 109 - S e es o! & - 1% U6 eaaRst ba:67 * SUR 288g ai \ ‘Baans x SEGTION P.Q, 7 "012" B.W.C, wea Editi 10) 4 BARS eaRsk @ BARS 14 1-63" BARS 13 L016" BARS L- ak-- 6 ‘2 peas % t-11'9) oF BARS T La’ 6% TKT “18 on ce Fig. 577.—Details of One Panel, Purfleet Bridge. sharp skew, it has an out toeout span of 59 ft. 8 ins. and a square span of 35 ft. Figure 576 shows a half elevation of one truss, while Fig. 577 shows sections and elevation of one CONCRETE IN BRIDGE CONSTRUCTION. 765 panel of the truss. The main portion of the top chord is 9x18 ins. in section, and is reinforced with eight 17%-in. round bars; cross bars 11% in. in diameter, 1 ft. 4 ins. long, are inserted transversely at intervals to prevent the concrete from bulging laterally when under high stress. The reinforcement of the bot- tom or tension chord also consists of eight round rods 17% ins. diameter, bound together by stirrups of No. 12 S.W.G. iron 2 ins. wide, spaced about 10 ‘ins. centers. The vertical members are cruciform in cross-section, each arm of the cross being 7 x 5 ins. in section. They are reinforced with vertical bars hooked over the bottom and top chord bars, and with diagonal bars bent ete See 80°!" Face to Face of Parapets -- ----------—-—--—> : > : ae - j 4 Weenes 160"--- 16*0"-- 16°07- —--re---— Mee O re emp Oars et ay a ey ase are OO EN a aha ee I L|Elevatio K---- 160g" ----a {--=> 16°0%"---~ af -- 1608! oem 1650-16408 Hl He A rye rigs THER He ep HH ae i tt Gebter Line lofi Track itv \ | t ee rea! a Wa 4 ' mip BS VL Plan Py me | SU teeter dire | et Bridge Guy Fig. 578.—Trestle Over Cave Hollow, C., B. & Q. R. R. around the corners of the openings to prevent the concrete from rupturing at these points on account of shearing stresses. The trusses are connected by transverse girders 8 ins. wide and 15 ins. deep, with both top and bottom reinforcing bars. The upper bars have hooked ends reaching to the center of the main truss section, while the lower bars are carried through the chord between the two rows of 17-in. bars forming the reinforcement of the main trusses. The. floor of the bridge consists of a rein- forced slab 5 ins. thick, stiffened with longitudinal ribs placed directly under the track rails. This bridge is of Hennebique construction, and all reinforcing members are anchored in the concrete, and the whole firmly bound together by numerous sheet iron stirrups. It is stated that the structure weighed go tons, 766 CONCRETE AND REINFORCED CONCRETE. of which 15 tons is the weight of the reinforcement. The con- crete was composed of 1 part Portland cement and 4 parts crushed stone, aggregate all passing a 34-in. screen. This bridge when tested by two cars with bogie trucks and 24 ft. wheel base, loaded to 30 tons each, showed a maximum deflection of 0.197 ins. The form given to the main trusses would seem to make a determination of the stresses therein impossible, a state of affairs Gla oo0m 38 vy Slope 2" in 130" " Corr. Bars Li tbenwe ag" 89" 55 Sps. at 3” 13°9" Section through Center Line of Span. Half Transverse Section. Fig. 579.—Details of Floor, Cave Hollow Bridge. which, as far as possible, should be avoided in bridge or structural design. Viaducts—Viaducts of reinforced concrete have been used to a limited extent both in this country and in Europe. Fig. 578 shows a half plan and elevation of a reinforced concrete trestle of heavy construction over Cave Hollow, on the Chicago, Burling- ton & Quincy Railway. Fig. 579 shows longitudinal and trans- Base of Rail ri 6U" A J z + To AE LID —IOL 1y [ : if ie © qf es FPSO re BOOS ae MRS interes 20°" Hay x i : Part Elevation. Pier for Expansion Joints of Bridge. ae Plan. Part Fig. 580.—Viaduct for C., C., C. & St. L. Ry. verse sections, with details of construction. The longitudinal re- inforcement consists of 34-in. corrugated bars spaced 3 ins. centers, while the transverse bars are 14 in. spaced 12 ins. centers. Cleveland, Cincinnati, Chicago & St. Louis R. R. Viaduct.— Several viaducts of reinforced concrete have been recently con- structed by the C.,C., C. & St. L. R. R. Fig. 580 shows an ele- vation and a partial plan of a portion of one of these viaducts. CONCRETE IN BRIDGE CONSTRUCTION. 767 Fig. 581 shows a longitudinal and a transverse section of the piers, floors and girders. These structures consist of a series of piers ‘of reinforced concrete supporting girders of 20 ft. clear span. The longest viaduct constructed has a total length of 1,217 ft. The girders are 5 ft. 4 ins. deep and 2 ft. wide, and are con- nected at mid-depth by a flat floor slab 1 ft. 9 ins. thick. The ar- rangement of the reinforcing bars is clearly shown. For the sake of appearance the faces of the girders and piers are relieved with paneling, as shown on the elevation. A horizontal expansion joint is provided on each abutment and on every fourth pier. Move- es egg cans 7 eee Wf mm ! Aesop ee c fbn ng | | at onerete_| Arrangement of Bars in jirder Ends over Abutment: 23°73 ncaa som “SEB erate over ms ns l2 ete. Use 5.33 Bars, tas a AE Part Section stowing Bass in Girder. Fig. 581.—Details of Viaduct Shown in Fig. 580. ment is provided for by transverse inverted rails embedded in the upper portion, resting upon short lengths of rails embedded in the concrete of the pier itself. To insure clean contact between rails. those of each course project % in. from the face of the concrete, forming a 1%4-in. open joint between the girder and the pier, which is filled with layers of felt. At each fourth pier also there is a vertical expansion joint in the floor and girder. This is filled with two layers of felt reaching to within 2 ins. of the top, the upper portion being filled with asphalt. Fig. 582 shows a partial cross-section of a viaduct approach recently constructed at Oklahoma City, Okla. T. The piers 768 CONCRETE AND REINFORCED CONCRETE. forming the bents were spaced 26 ft. centers. Three longitudinal girders, one 20 x 28 ins. and two 20 x 26 ins. in section, span between bents and carry the roadway slab. The columns are 20 x 20 ins. at the top and increase in size with a batter of 14 in. to the foot downward. The general details, size and amount of reinforcement are shown on the drawing. Guadalquiver River Viaduct.—Two viaducts between 30 and 4o ft. in height were recently constructed for a mineral railway ates Io eae 219" ---1--—----f-----. 6 ‘ Center ‘ . | 3-0" line l Top reinforcing bar inverted over i ' beam, Ve" 14"*6", 4" certters aes, oe ‘ Fe = i aL SL vibe < % ; 2,2" 13 pees 12,14 43% "length of span +4 Wy gt 1-L-J], 2,0" 3 oF es Aue ANON ) 2 14%3%"% 12" in middle hee beSesele Sy 2,1"Kahn bars, 30'long All cols 20" at tap Half Section 'with Watk Fig. 582.—Viaduct Apprcach to Bridge at Oklahoma City, Oklahoma. near Seville, Spain. One viaduct has a length of 371 ft. and the other of 284 ft. The scheme for handling cars to and from a loading pier at the Guadalquiver River, where the ore is loaded in barges by tipping the cars, involves two tracks, the cars being pushed to the loading pier by a locomotive and run back by gravity. The two tracks are carried on separate lines of girders supported by double bents braced together transversely. Figure 583 shows an elevation of the shorter viaduct and loading pier; Fig. 584 shows a transverse section through the CONCRETE IN BRIDGE CONSTRUCTION. 769 4‘ r eneewtea cei length 236" erst Seana eae area ns It Trach. Grade 1% een seee ss 294 Track. Grade 1% 59" Fig, 583.—Elevation of Viaduct and Loading Pier, Guadalquiver River, Spain. a] Sweat SS k-~-3,94- 1 SS = + | ' a Varia ble— ee to” Fig. 584.—Transverse Section, Guadalquiver River Viaduct. 770 CONCRETE AND REINFORCED CONCRETE. bents and Fig. 585 the detail o1 the girder reinforcement. The bents are spaced approximately 294 ft. centers, and are composed of four posts approximately 26 x 9 ins. The girders spanning between the bents are about 48 x 9 ins. in section and carry a slab which supports the track and is cantilevered out to carry the sidewalks. Two or more struts brace the posts forming the bents in a transverse direction. Fig. 584 also shows the foot- ing for the bent posts; this consists of a slab 5 ins. thick, 5 it. 9 ins. wide and 23 ft. long, stiffened by a rib between the posts. This reinforced footing rests upon a bed of concrete about 8 ins. thick. The maximum pressure brought upon the soil is about 1.2 tons. The train loads for which this viaduct was designed consists of a 36-ton locomotive on coupled axles about 9g ft. es 45 Stirrups Jah epee I %e" ee AA 5 | a tt] i | 2, 50> 20126 26-426 420. py 504 28 | -Lattice,6 Rods, 2° q ra? Secondary Reinforcement. 26 Fig. 585.—Girder Reinforcement, Guadalquiver River Viaduct. centers and 12 tons on a bogie truck with axles 5 ft. 3 ins. centers and 20 cars carrying 20 tons each on axles 5 ft. 3 ins. apart. It will be noted that no longitudinal bracing is used between the bents, the only stiffness in this direction being that of a column 26 ins. wide, which for a height of 30 or 4o feet woul. appear to be beyond what is usually considered a safe limit. For the short trestle, which is only 284 ft. long, the braced load- ing pier at one end and the bank at the other will prevent longitudinal movement. For the longer trestle. which is on a curve, it would appear that some form of longitudinal bracing should have been used. Richmond & Chesapeake Bay Ry. Co.'s Viaduct.—A reinforced concrete viaduct having a total length of about 3,000 ft. and a “maximum height of 65 ft. has been recently constructed at CONCRETE IN BRIDGE CONSTRUCTION. 771 Richmond, Va. This Structure is of reinforced concrete throughout, and was designed and the con- struction supervised by the Trussed Concrete Steel Co., of Detroit, Mich. The Kahn bar was used for re- inforcement throughout. The construction consists of reinforced concrete girders from 23 to 49 ft. long, supported by bents and towers of reinforced concrete. Base of Rail The 23-ft. girders are I2 X 30 ins. in section, and are connected and braced by ~ transverse struts 3% x 18 ins. in section. These struts are flared at the ends and divide the floor into three parts, having irregular octagonal openings 5 ft. 9 ins. in width. Details of the standard 23-ft. girder spanning between the single post bents used for heights up to about 21 ft. are shown both in plan and elevation in Fig. 586. The sizes and location of reinforcement for girders, struts and posts are clearly shown in this figure. A transverse section through the girder and bent is shown in Fig. 587, together with general features of construction. The cross-section of the standard post used for this bent is shown in Fig. 588. As will be seen, the post is 16 ins. square and is Elevation Centers an Plan and Elevation of 23-Ft. and 49-Ft. Spans, Richmond Viaduct. crete and 1 2 Rods ie ated ; One rT ixth Tre and Co rough Sleepers and Fig. 586. le EVES! 9 One between Concrete only. Note ; Provide %4" Bolts as here indic throw re 4 BRB 65H 772 CONCRETE AND REINFORCED CONCRFTE. reinforced with four 34-in. Kahn bars tied together every 14 ins. with 34-in.-diameter rods. The detail of the column bases, as should be noted, are also of reinforced concrete. The 12 x 30 in. girders are reinforced with three 1-in. bars ‘23 ft. long and two 34-in. bars 16 ft. long at the middle. Two ¥%-in. bars are also placed near the top of the beam. The cross struts are reinforced with 14-in. round rods. ee Fig. 588.—Section Through Typical Column. Zuo yn 8 /4 Centers Section showing Bents 21010. ss) 5 ia = fo FR Ge Fig. 587.—Details of Bents Nos. 2 to 10. As shown in Figs. 586 and 589, occasional spans have the girders connected with a full top slab. This gives additional stiffness, and when the girders cross a street, as in girders be- tween bents 44-45, and bents 48-49, Fig. 589, protects the street below. Details of a 49 ft. girder span are also shown in Fig. 586. These girders are 20 x 54-in. in section and are connected by 2yn0 2. 773 CONCRETE IN BRIDGE CONSTRUCTION. ‘JONPRIA PUOTIQSIY JO WoOTDNIISUOD Surmoyg ‘Uoreaszq pue uwe[d—'6sgG “210 “UOleunaly eq ens oe = a 25 pen tte pane) eed oP a) ay im 45° SWOLIIM ——___— x 2 q > + ‘e = 8 & FBO Sle SF 9X0! -&||2 : gale "8 Bawe ce SHE al sls Std suogexr2 — 4aquo7.£. Ri® sug axhe'2 WE REE | 4 4 AX 18.2% 2S ~ x af Ree | 8 8X Ls ,8/ £27 og hp ws ae ial APEX! EXD! OXI 49quie),Z = 7 re E See Abie |, 09 X02 Glue Spa? po PH oI. SPIELE a a — f Buos 2 sog Aynuyue), £%, r dog Ayinuypuo7 ¢xf * ‘uvdid "BAIN gL UO BUNYINUS fia] 1 CEd ~~. a soseeneeee 24D Fig. 591.—Typical Trestle Bent, “” Girder. 4 re Fig. 590.—Section of 20 x 5i-In. 774 CONCRETE AND REINFORCED CONCRETE. a continuous 3)4-in. deck slab. The cross-section of this girder is shown in Fig. 590. Two cross ribs, as shown in Fig. 586, brace the girders transversely. The 3%4-in. deck slab is rein- forced by one 34-in. diameter rod running longitudinally along its center line and %4-in. diameter rods spaced 12-in. centers and running transversely. The general arrangement of the towers will be understood Fig 593.—Typical Column Section. Section of Bents, 44,45, 5, 53s v Fig 592.—Details of Tower Bent. from Fig. 589. Two or more separate towers consisting of bents connected by longitudinal struts alternate with two towers connected by longer span girders as shown in the left-hand portion of the figure. Tig. 591 shows a typical bent, while Fig. 592 shows details of the tower bent used for the higher towers. For a height of 49 ft. 18 x 18-in. posts connected by two transverse and two longitudinal struts were used. The rein- CONCRETE IN BRIDGE CONSTRUCTION. 775 Figs. 594 and 595.—Plan and Horizontal Section on Line A-B, Tower No. 43-44. forcement consists of six 34-in. bars as shown in Fig. 593. A 20 x 20-in. post was used at the highest point of the trestle where the base of rail was 65 ft. above the surface of the ground. Fig. 594 shows section A-B through tower 43-44. The trans- | Bent 46 1 l A 7 \ i —i 1 nif S vy rt tt Aus pp Se 3 HL BENT UT Sie | a HM pe I i i 3! Si! jibe Mit el NR Ht iy S nyt! 7 ! Iu 4S Rg IH ji : 1 Wy fiifose LEN aN 4. ies 3s o | tl ro Hy me \ a ! \ cS — N a * a “a mn \ 7 \ 12x18 eam £2 SSS S=S2e Zz 10% 18" = ee Fig. 596,—Plan of Tower No, 45-46. 776 CONCRETE AND REINFORCED CONCRETE. verse and longitudinal bracing of this tower is shown in de- tail in this-figure. Fig. 595 shows a plan of the same tower together with plan of. girders and their bracing. The slender section of longitudinal strut between bents 43 and 44, viz.: 12 x 30-in. for a span of 49 ft., should be noted. The plan of tower 45-46 is shown in Fig. 596. The ened of stiffening this tower in the plane of the top of girders should be noted. ‘ The details of reinforced concrete shoe marked “F” and used for outside post of bent 43 is shown in Fig. 597: The other a > ” G, Fig. 597.—Typical Column Footing. shoes were of similar construction, the amount and arrange- ment of reinforcement varying with the size of shoe needed. Expansion joints were provided at suitable intervals. Fig. 598 shows plan of expansion joint at bent No. 5, and Fig. 599 shows clearly details of construction of expansion joint. This structure was designed to carry a live load of 75 tons on two trucks 33 ft. apart, each truck consisting of two axles 7 ft.’ centers. It was assumed that the structure should carry its dead load, the full live load, and 50 per cent. of the live load for impact. Wind pressure was taken at 30 lbs. per square foot on CONCRETE IN BRIDGE CONSTRUCTION. 777 surface of train and surface of structure. The longitudinal thrust due to braking of trains was taken as 20 per cent. of live load. The loading on towers due to centrifugal force of train on a 7 degree curve was taken as 14 per cent. of live load. As will be noted, the usual diagonal bracing used on all metal towers is replaced by transverse and longitudinal struts, the intention being to so design all joints and all members that they will possess the necessary rigidity to withstand all bending coming upon them, The success or failure of this viaduct will 3 Bar, 76"long, Top and Bottom A A230" RE PERE Si BS wt tt Wet Roe 220 org tt | Sait vei tht tat bt | Dy Hi 1 “3 Rods \76 lang, We enters i ee er here 12°%30" 236" 23'6'on C.Line of Span----- Section AB. Fig. 598.—Plan Showing Expansion Fig. 599.—Details of Expansion Joints. * Joints. be watched with much interest, as it is the largest structure of this kind which has thus far been built of reinforced concrete. ARCH BRIDGES. Arch bridges of concrete are rapidly replacing masonry bridges and in many cases metal structures. Whether it is necessary or not to use steel reinforcement for the arch ring depends upon the conditions governing each bridge and the individual judgment of the designer. A number of railroad bridges have been built during the past few years in which the arch concrete was designed to ‘carry all stresses without rein- forcement and then metal added when the structure was built. While this practice certainly gives a safe bridge, it is a needless 778 CONCRETE AND REINFORCED CONCRETE. waste of materials and hardly conforms to the ethics of good engineering. The principal methods of locating the metal reinforcement in a cross section of the arch formed by a plane cutting the arch ring at right angles to its axis have been shown in Figs. 145 to 154. Arch Design.—The methods employed for the design of a stone masonry arch are usually employed in preparing the design ior a plain concrete arch ring, and may also be employed in the design of reinforced concrete arches. The line of resistance of the arch is determined and located graphically on the profile of the assumed arch. If this line lies within the middle third of the arch ring, no provision for tension will be necessary, and if the assumed safe compressive stresses on the concrete are not ex- ceeded the arch will be safe. It is customary to divide the arch ring by radial planes into sections of convenient length, such that the line of resistance will not depart far from the curve of the lineal arch, 7. ¢., the medial line of the assumed arch ring. - When a reinforced arch is under consideration, if as is usually the case, the reinforcement is symmetrically located, the same method may be followed. If the reinforcement is not symmetrical in the arch rib, con- siderable difficulty will be experienced in locating the neutral axis at any section. Again the position of the neutral axis undoubtedly shifts about under the action of different loads. The presence of steel in a rib will enable it to safely resist tension, but it is the practice of the best designers to so pro- portion the arch’rib that it is seldom subjected to tension under dead and live loads. The maximum stress which can occur at any section of the arch is that due to the thrust of the arch acting along the line of resistance, the bending moment caused by such an arrangement of the loads as to produce the greatest possible stress upon the given plane and the bending moment due to temperature changes. It is usual not to exceed a unit pressure of about 500 lbs. per sq. in. on the concrete for dead and live loads. For temperature stresses, however, these com- pressive stresses are allowed to run up to from 650 to 800 Ibs. per sq. in. These maximum stresses also include dead and live loads and wind stresses. When tension is allowed in the concrete, the unit tensile stress allowed varies from 50 to 75 lbs. per sq. in. When the bending moment at the given sections has been de- CONCRETE IN BRIDGE CONSTRUCTION. 779 termined, the necessary concrete and steel sections may be com- puted. For methods of determining the line of resistance, Baker's Masonry Construction or any well known work on_ graphic statics may be consulted. For determining the true line of re- sistance the external forces must be known or assumed, and the direction, point of application and amount of thrust at the crown shall be known. It is customary to assume, besides the usual dead loads, at least two live loadings: (1) that the arch carries the maximum live load over the entire span: (2) that the arch carries the maximum live load over one-half the span. The first of these loadings gives the maximum thrust and the second the maximum bending moment. Such sections should be chosen as to satisfy both conditions. The elastic theory of the arch is to be preferred over the above method, as it gives a much more satisfactory analysis. A discussion of the elastic arch theory cannot be given in this place. Among the best treatises on this subject are, “Theory of Steel-Concrete Arches,” by Prof. William Cain. “Symmetri- cal Masonry Arches,” by Prof. Malverd A. Howe. “Trusses and Arches, Part III,” by Prof. Charles E. Greene. The author prefers Prof. Greene’s method as giving the most satisfactory solution. Thacher's Formulas.—Having found the thrusts, bending moments and shears at chosen sections in the arch ring, the in- tensities of the stresses in the concrete and the metal and the necessary distribution of the material may be obtained by the use of. Mr. Edwin Thacher’s formulas. The author is indebted to Mr. Thacher for permission to publish these formulas. These formulas apply to any form or variety of reinforced concrete arch or beam within the limits of elasticity of concrete. The following nomenclature will be used: Ee = modulus or coefficient of, elasticity of concrete. Es = modulus or coefficient of elasticity of steel. Es — =e Ee Ac = area of section of concrete one inch wide, square inches. As = area of section of steel in width b, square inches. a = area of steel per inch width = . square inches. Ic == moment of inertia of concrete, Ac, about common neutral axis. Is = moment of inertia of steel, a, about common neutral axis. 780 CONCRETE AND REINFORCED CONCRETE. fe = intensity of stress in the concrete, lbs. per sq. in. fs = intensity of stress in the steel, Ibs. per sq. in. d = depth of concrete in inches. d’ = depth of steel in inches. tu. = distance from neutral axis of combination to outer fibre of concrete, in inches. vy = distance from neutral axis of combination to outer fibre of steel, in inches. = thrust on section of arch, one inch wide, in pounds. = bending moment on section one inch wide in foot pounds. = pressure on line of pressure on section one inch wide. = distance from neutral axis of combination to line of pressure in inches, taken normal to line of pressure. c = distance from center of gravity of steel rib to bottom of con- crete, in inches. b = distance from center to center of steel ribs, measured in the direc- tion of the width of the arch, in inches. For sections in which the steel reinforcement is arranged symmetrically about the center of gravity of the concrete. T 6dM fe = ————— F- ——___.... . . eee eee (1). Actea Te + els eT 6ed'M fs == ———__ | —_____........... cee eee eee (2). Ac tea Ie + els For sections in which the steel reinforcement is not arranged symmetrically about the center of gravity of the concrete. T Pku 8 a tre ute ead Serious (3). Ac tea Ie + els or, . £ 12uM ee ena atch (4). Ac + ea Ic + els eT cPky fs —$$$— ni te ig paid ed ae (5). Ac tea Ie + els or, et IzevM fs = ———_— +t —__ .................... (6). Ace+ea Iet+els The distance of the neutral axis of the combination above the soffit of the arch or the bottom of the concrete will be WwA-dteac d — u = ———___ ................ CZ) Ace tea It is Mr. Thacher's practice, and that of many other engineers, to require that sufficient steel shall be used to take the entire bending moment of the arch without aid from the concrete and not exceed the elastic limit of the steel. The steel can never take the entire bending moment unless. the concrete fails. This CONCRETE IN BRIDGE CONSTRUCTION. 781 cannot occur if the arch ring’ is so designed, as is the usual practice, that the line of pressure will fall within the middle third. To satisfy the condition that the steel within its elastic limit shall be capable of taking the entire bending moment, assuming the elastic limit of steel at 36,000 lbs. per sq. in., we have Mv Is = of > —— oo. eee eee (8). 3,000 For symmetrical sections, i. ¢., when the steel is symmetrically placed about the center of gravity of the concrete, we have M A OF Bm teens (9): ‘1,500 d’ Mb As = Of & ——————. she iiaadicecseoses (10). 1,500 d’ At the crown also make db Aa SS OR Ss Ses ene ye wens: (11). 150 Equation (11) is obtained as a result of Mr. Thacher’s rule that the total cross-section of the steel at the crown shall not be less than 1-150 of the cross-section of the concrete at that point. Usually the area of steel falls within the limits 1-50 and 1-150 of the area of the concrete at the crown. Es The value assumed for the value of e= =20 by many engineers enables the _use of higher stresses in the steel than is possible when a lower value for e is used. The reason for using such a high value for e is that it is believed that the value of the modulus of elasticity E, for concrete in large masses is low2r than for concrete in small sections usually’ used for slabs and beams. Under the conditions obtaining in arches the modulus is taken at 1,500,000 lbs. per sq. in. Austell Bridge——The four-span reinforced concrete arch bridge of the Southern Ry. near Austell, Ga., is composed of four three center arch spans. The clear span is 70 ft. and the rise 20 ft. from spring line to intrados. The radii of the arch are 12 ft. 3 ins., 29 ft. and 56 ft., respectively. This bridge may be taken as an example of a heavy reinforced bridge of the Monier type, corrugated bars being used to form the reinforce- ment. The arches have a thickness of 3 ft. 4 ins. at the crown and have parapet walls 2 ft. 8 ins. high. Near the intrados the 782 CONCRETE AND REINFORCED CONCRETE. arch is reinforced longitudinally for 30 ft. with 34-in. bars, 12 ins. on centers with a depth of cover of 4 ins., thence lapping 6 ft. and placed 5 ins. on centers; the reinforcement continues with 1/4-in. bars to the center of the arch, where the lap is 7 ft. Transverse bars of 14-in. section are placed 3 ft. centers. In the Lx Aone Berks Sort 19 Se & q jf Gors aatong ie toa LCrossBars B4'079 5 SPOCCIEN WOOD SOD 4. H-.—-+ is LH. OD inge Soon 2) PGorselong @iet C \iseswes / p) Srenenor Anan smoron Socmae comsrmgrion Berncen mow rs Aaa jecriaw or Ance snonn® Sioewace CONSTRUCTION BE TWCON PONSA AND Fig. G00.—Southern Railway Bridge, Austell, Ga. extrados the reinforcement consists of 114-in. bars throughout the entire length placed 12 ins. on centers. The lap of the ex- trados bars is 7 ft. The side walls, are reinforced by % and 34-in. bars bent to the desired form. Expansion joints are placed jn the parapet wall over the crown of the arch. A cross- hae a aa a og Longitudinal Saction. ~* Fig. 601.—Details of 79-Ft. Span, Grand River Bridge, Grand Rapids, Mich. section of the bridge showing the reinforcement and centering used, is shown in Fig. 600. Grand River Bridge, Grand Rapids, Mich.—This bridge is a good example of recent reinforced concrete work. It consists of five arch spans, one 87 ft., two 83 ft. and two 79 ft. Figure CONCRETE IN BRIDGE CONSTRUCTION. 783 Section MN Section JK. Fig. 602.—Transverse Sections Grand River Bridge. 601 shows a longitudinal section and part plan of the 79-ft. span. The arch ring is 1 ft. 6 ins. thick at the crown and 3 ft. at the spring. The bridge has solid spandrel walls as shown in Fig. 602. The section of the 83-it. span is shown in Fig. 603, to- gether with centering used to support the forms. The cen- tering consists of posts or piles driven to a firm bearing and braced together by transverse and longitudinal timber. The reinforcement consists of two lines of 14-in. Thacher rods placed 3 ins. from the intra- dosal and extradosal faces of the arch ring. Each pair of rods is connected every 4 ft. by means of a 3%-in. rod with’a hook 7 : c x 3 = a : ° s! : ® : Le % . is A Bal te 8 a.j & © i | = i yo ey as i i oO i d ¢ H x oo i 2. Mes i s get eend meets — ~ eh, i he, ? : a, i Ay | a ! a : te : 3 f j xe fel, al Et sé fF. fA EF | i ==>, gee, b. i ee ; : Hs ral og = RS &s 3 E | 5 SME © 3 : SMe: Ra oye Lak F [Sed [fee et 8. a } "i oe E i eYi 0 S : : : = i 66 Sais = ei gS i Nea + 2 3 = fu s & : ae = ¥ : a : S ey : si] \\e * : = | : to \Ve | : \ —> i dale ; Seals -b i 3 4 i s a“ > pclae at each end. The reinforcing rods are fitted with 3-in. washers and nuts, which give them an anchorage at the abutments, and are made continuous from end to end of span by means of turnbuckles. Fig. 603.—Centering for 83-Ft. Span, Grand River Bridge. 784 CONCRETE AND REINFORCED CONCRETE. The method of constructing the arch rings is as follows: The endmost sections of the reinforcing bars, which had been anchored into the piers and abutments during their construction, were bent down to the curve of the arch ring and connected with the arch rods proper. Scantling placed transversely across the lag- ging of the center served to block up the soffit rods, while the upper rods were held in place by the connecting rods already mentioned. A wet concrete was deposited and worked in under- neath the lower rods. After these were embedded a stiffer contrete was deposited and rammed in 6-in. layers. The arch ring 45°06. | Mottaing: .. Top Firished with Trowel 7" Ged To” Mold for “Ft Strips of ___BxSxI7" rm t t } | ExOx6 wee Mold for “H™ ike 7 Arh Sketch showing: Forming Sockets for Posts. = a Mold for 4%" Saviva it He gore ugg? neg — ., Mold for “B" Mold for “Et KS 8K 127 15 A Fig. 604.—Details of Railing and Forms, Grand River Bridge. was built in transverse sections, and each section was completed in a continuous operation in one day. The crown section was built first and then the two skew back sections, and last the inter- mediate section; the entire ring being completed in five days. Fig. 603 shows the spandrel wall forms and method of bracing same. Expansion joints in spandrel walls were formed by simply laying the concrete against a vertical form and then butting the concrete of the following section against this smooth surface with a sheet of tar paper inserted between. Fig. 604 shows details of railing and forms used in their construction. CONCRETE IN BRIDGE CONSTRUCTION. 785 The loadings assumed in the design of this bridge were as follows: Dead Load. Lbs. per cu. ft. CONERECE:: ccna stave wees Bip iar wR ld oa alae aa aH 150 Barth Alling gievaaagiu nce cranes ae queens paneer at 120 Pavement 12 ims. deep .........0.0 cece cee c cence cues 150 Live Load. Lbs. per sq. ft. Center 20-in. roadway ............ ccc ccc eee cee eens 250 Remainder of roadway ............0cccccee eee eeeeease 150 Sidewalks: i sausuaure v's aiid viaadiunes we ene bon mayeaeoaaans 100 A concentrated load was assumed on roadway consisting of a 15-ton steam roller having axles 11 ft. centers with 6 tons on the forward wheel 4 ft. wide and 4%4 tons on each of the two rear wheels 20 ins. wide and 5 ft. apart on centers. The ratio of the moduli of elasticity between concrete and steel was taken as 20, The maximum compression allowed on the concrete in the arch ring was 500 lbs. per sq. in., not including temperature stresses, and 750 lbs. per sq. in., including temperature stresses, The maximum tension allowed in the concrete in the arches was, including temperature stresses, due to a variation of 40°, 75 lbs. per sq. in. The maximum shear allowed was 75 Ibs. per sq. in. It was required that the ribs reinforcement under a stress not exceeding 18,000 lbs. per sq. in. must be able to take the entire bending moment of the arch without aid from the con- crete. It was also required that the area of steel at the crown of the arch should be at least 2% of the total area of the arch at the crown. The Luten Arch.—A type of arch bridge which has success- fully competed with steel truss bridges is the Luten arch. In this bridge the horizontal thrust is taken up by longitudinal ties extending between the abutments underneath the bed of the stream and buried in concrete. The usual heavy abutments which are necessary when the banks of the stream are not ledge rock are thus dispensed with, only enough material being needed at the abutments to enable the arch ring to be connected to the horizontal ties. A longitudinal and cross section of one of the largest bridges of this type are shown in Fig. 605. This arch was constructed at Yorktown, Ind. The span is 95 ft. and rise of the arch from spring to crown is 11 ft. 1 in., or about one-ninth of the span, the springing being at approximately low water level. The depth of the water at mid-span is about 4 ft. 6 ins., making a 786 CONCRETE AND REINFORCED CONCRETE. total height of opening of 15 ft. 7 ins. The steel tie rods extend from abutment to abutment beneath the bed of the stream and are embedded in a 6-in. concrete pavement. The pavement is provided at both up and down stream edges with aprons pro- jecting downward into the bed of the stream. These prevent e160" 4 Longitudinal Section. Cross Section. Fig. 605.—Lu‘en Arch Bridge, Yorktown, Md. the pavement from being undermined, and make the bridge flood-proof. ¥ The reinforcements of the arch rib consist of 34-in. steel rods, spaced 6 ins. on centers, and arranged in series of single rods >’ K44”1 [ s § Q Av Waterline E1.25.0 \Water El. 20.0. Ky . : xX J Detail of Railing. * 176" k 766". Half Longitudinal Section. Pari Sectloniin, Gopi Gt Pick: Fig. 606.—Details of Melan Arch Bridge at Dayton, 0. passing through the tension region of the arch rib that is near the intrados at the crown and the extrados at the haunches and abutments. Since the limits of the tensile regions are not easily deter- mined, the reinforcing rods are arranged to cross the arch rib CONCRETE IN BRIDGE CONSTRUCTION. 787 from intrados to extrados at points distributed over the area of probable minimum moment. In addition to the 34-in. steel rods, a reinforcement consist- ing of electric welded wire netting was attached to the rods throughout the crown of the arch. This netting was of No. 6 x Wo. 10 wire, spaced 3 ins. and 8 ins. respectively, the heavier wires running longitudinal to the axis of the bridge. The arch rib was built in parallel rings, the middle ring, 12 ft. wide, being placed first, and the two end rings 3 ft. 6 ins. each, with spandrel and rails following. Each ring was started at both footings simultaneously and was advanced continuously to meet at the crown. The separate rings were bonded together with transverse rods across the roadway, and then afterward into the rails with seven over the crown and two at each abut- ment. The wire netting was continuous across the entire width of the roadway. Dayton, Ohio, Melan Arch Bridge.—A seven-span Melan rein- forced concrete bridge having a total length of 588 ft. was con- structed at Dayton, O., in 1903. The lengths of the spans varied from 69 ft. at the ends to 88 ft. at the center. The width of the bridge in the clear is 54 ft. The proportion of rise of arch to length of span adopted increased from 1-13 to 1-10. The bridge was designed to carry a live load of 150 lbs. per sq. ft. and two lines of 4o-ton electric motor cars. The distance be- tween crown of arch and crown of roadway varied from 13 to 15 ins., so that the railway tracks practically rested on the arch ring at the center of the span. Figure 606 shows a half longitudinal section ‘together with partial cross-sections of the 88 ft. span. The size and arrange- ment of the reinforcement are shown on the drawing. A 1:2:4 stone concrete was used for the arch ring. A '%-in. coating of cement mortar covered with a coat of tar was used for water- proofing the arch ring. This bridge was designed by the Con- crete-Steel Engineering Co. of New York City. Melan Hinged Arch.—The reinforced concrete arch bridge at Laibach, Austria, is a good example of the application of the Melan system to the construction of a hinged arch bridge. This bridge was designed by Prof. J. Melan, of Prague, and crosses the Laibach River on a skew of 9° 14’. The clear span ef the arch is 108.2 ft. and the rise is 14.23 ft. center to center CONCRETE AND REINFORCED CONCRETE. 788 BER gp Ta j ¥ ! i 7 i OF Rl i o f oo [| ) £3 = lj Tj 4 sor i “pat oF es" 5 Hinge of Steel Girders. Concrete Hinge Blocks, —Crown Hinge, Laibach Bridge a ; Fig. 608.—Skewback Hinges, Laibach Bridge Fig. 610.—Hangers for Centers, Laibach Bridge Oss. Fig. 609 “elIISNy ‘Woeqiery] 3e osplig Wy pesulH UeTEW—' 109 “31a 262 17, WON $2 PE. “BuaLaW UL Ua B49 SUOLOAITZ i ee ROE EE EL —-— Par TY War alg np sae urea ea i 4aay 40 puesay I i em on wee iol | em ae sre tin pment fea penn nate [BAB] jf ERTL eT AM AL eT et ‘ SUL JOD OLD $60] oreecverervenrrevennnnecerenesesenneanenesstscpennnseene ee xog purs. BK, : aes ae HOY 424 6:60 ene ERE IT BT RR HT Haag ges ! It = i Hs ; Sie H LAT SOT, 6| i |e: “GEL v fer le-- BEZ->f2- $ BEL —— x BEL SCI aok: siete Pe hene z se Ea age agg ag aT a gc CONCRETE IN BRIDGE CONSTRUCTION. 789 of hinges. Fig: 607 shows arch section, together with arrange- ment of the reinforcement. The thickness of the main arch ring varies from 20 ins. at the crown to 27% ins. at the haunches, and 25% ins. at the skewbacks. The arch reinforcement con- sists of 14 arched steel lattice girders whose flanges are every- where about 2 ins. within the concrete and spaced from 3.3 to 3.8 ft. centers. Four sets of steel cross-frames parallel with the axis of the bridge connect and brace these skeleton trusses. Three secondary arches near each end of the main arch assist in carrying the roadway. These secondary arches have spans of 7.4 ft. and their intrados is semi-circular. They have a thickness of 6 ins. in the center, but thicken rapidly toward the haunches. The reinforcement consists. of curved 4 in. I-beams spaced 3 ft. and 3 ft. 10 in. centers. Details of the hinges are shown in Figs. 608 and 609. These hinges are backed by blocks of concrete moulded several months before erection was begun. Full and uniform contact of the curved abutting faces was secured by placing in the joint a strip of hard lead 4 ins. wide and 1-16 in. thick. The center hinge of the steel ribs is a simple abutting pin joint as will be seen from the drawing, but the skewback hinges of the ribs have wedges for accurate adjustment of the span. After the arch was completed and the centering removed, the hinges of the metal ribs were encased in concrete. The character of the falsework is also shown in Fig. 607. Eight centering frames were used, spaced about 7 ft. apart and braced together by diagonal timbers. Each frame rested on 7 supports consisting of single piles. On the top of each support was fixed a sand box. The upper members of the centering frames were not continuous, but were cut in the middle of each panel and here rested on cross timbers hung from the steel reinforcing ribs by means of hangers, as shown in Fig. 610. The Gruenwald Bridge.—The Gruenwald Bridge, at Munich, is the largest reinforced concrete bridge thus far built. This struc- ture consists of two arched spans of 230 ft., and of five 28-ft. girder approach spans. The arched spans, which are three- hinged arches, are of the type with open spandrel construction supporting the beams and slab roadway. The rise of the arches is 42 ft. center to center of hinges. The roadway is 30 ft. wide over all, with a 16.5 'ft. roadway and two 5-ft. sidewalks. The 79° wy TL 7 ; Elevation of TETT_I Main’ Pier. Lawes. a o -— q 3 a ~ a o oo a fa a o = os 2 a a s ro | cd = o ba mi & Section ¢-D % NT x b fa PPh: < 3 Rs Cy go Po NPS ix A t . i H s ye pe8 and arch block against which it abuts. CONCRETE AND REINFORCED CONCRETE. Skewback Hinge. Fig. 612.—Details of Hinges for % Gruenwald Bridge. arches are 26.2 ft. wide, and have a thickness of 30 ins. at the crown, 36 ins. at the springing line, and a maximum thickness of 48 ins. at the quarter points. Figure 611 shows partial eleva- tion, plan and section of the bridge. The hinges are steel castings with a convex-concave rolling surface. Fig. 612 shows detail of hinges. The convex face has a radius of 8 ins. and the con- cave face a radius of 10 ins. A dowel at the center provides security against accident. The hinge castings were made in lengths of 31% ins., and adjoin- ing pairs were spaced 2 ini. apart, giving ten pairs of hinges to each joint. The back face of each casting was planed, and a lead plate about % in. thick was placed between the castings Special blocks of con- crete were necessary on account of the excessive bearing back of the lead plates, 1,400 Ibs. per sq. in. The blocks were CONCRETE IN BRIDGE CONSTRUCTION. 791 moulded in planed cast-iron moulds, and were provided with transverse reinforcing bars to prevent splitting; these bars ex- tend at right angles to the general direction of the hinge joints, and are distributed uniformly through the thickness of the block. One block was placed under each hinge. The reinforcement of the arch ring consists of eighteen 28 mm. (1.1 in.) steel rods, nine each at the top and bottom of the ring. The rods were tied together at 3 ft. intervals with 14 in. stirrups. Round steel rods were used throughout. In addi- tion to this reinforcement, a special reinforcement was placed under each transverse line of posts to aid in the distribution of the post loads on the concrete. | “A Reintorcement ‘of Stringer ” In’ Girder Spans. Greveseehatethenestenenses 70 1797, 2296 Span weeny Reinforcement of Arch-Ring and Posts. Fig. 613.—Main Arch Reinforcement, Gruenwald Bridge. Two 5£-in. diam, transverse rods were placed near the top of the arch rib, and four rods of the same size near the bottom of the rib. The arrangement and size of the reinforcing rods are shown in Fig. 613. The posts supporting the roadway are spaced 3.28 ft. apart transversely, and 6.56 ft. apart longitudinally. All interior posts are approximately 16x16 ins. in section, and vary in height from 5 ft. to 38 ft. Their reinforcement consists of longitudinal rods tied together by 1%4-in. rods spaced 14 ins. on centers. The longitudinal reinforcements vary from about eight rods }%-in. diam., to four rods 7%-in. diam. The posts in the outer rows were widened out at the outer face to a T- section so as to present a face 28 ins. wide in side elevation. Their reinforcement varies from eight rods 4-in. diam. to eight rods ig-in. diam. The reinforcing rods of all posts ex- 792 CONCRETE AND REINFORCED CONCRETE. tend downward from 16 to 20 ins. into the concrete of the arch ring. The roadway consists of a flat plate 7.9 in. thick, and of a 6.56-ft. span resting on five lines of longitudinal stringers of 13.12-ft. span. supported by the posts. Fig. 614 shows cross-section of roadway, also sections of roadway stringer over the arch and section of girder spans. The floor plate is approximately 8 ins. thick, and is reinforced in each 13-ft. panel by twelve top rods, eight of %-in. diam. and four of %4-in. diam., and ten bottom rods, six of %-in. diam. and four of °/,,-in. diam. Six of the bottom rods are bent diagon- ally upwards near the quarter points. The floor stringers over the arches are 10 x 16 ins. in section below floor plate, and are rein- forced with four bottom rods, %-in. diam., and two top. rods, 13/\,-in. diameter, Over the supporting posts half of the bottom 1106 Rods, Av. 22m ite 262 ou Post™ Wéhasi Da sens ‘ Section of Stringer over Arch. Fig. 614.—Cross-Section of Roadway, Gruenwald Bridge. Section of Stringer eo ee eee at Tee ee in Girder Spans. Cross Section in Girder Spans. Gross Sectior overArch. rods are bent upward and lie in the top of the beam over the posts. The approach girders are 16 x 32-in. in section below the floor plate, and are reinforced with 1 rod 48-in. diam. and 5 rods 13@-in. diameter. The arrangement of the rods is shown in Fig. 614. This bridge was designed to carry a uniformly dis- tributed live load of 82 lbs. per sq. ft., and a concentrated load consisting of a 22-ton road’roller. The maximum compression on the concrete was taken at 510 lbs. per sq. ft. (36 kg. per sq. cm.). Parabolic Arch Bridge, Wabash, Ind.—Figure 615 shows eleva- tion and cross sections cf a parabolic arch bridge with a clear span of 75 ft. The reinforcement used was Kahn bars, which gives an unusual arrangement of the steel in-the arch ring. Two spans of 75 ft., together with the approaches, made up a total length of this bridge of 240 ft. The arches carry solid spandrel walls, with earth filling be- tween. The spandrels were designed as vertical cantilever slabs, 793 CONCRETE IN BRIDGE CONSTRUCTION. *uU0149eS $9039 ‘eSplig “pur ‘yseqeM Joy Sul1eqUeD—OT9 ‘31a *u0l49eS pouypn4y:6u01 -puy ‘yseqea\ 3@ e8plag Yory offoquied—eT9 “Std + Uo14928S ourpns{bu0t ef ae oe ! 1 ee Af. Ute by ’, Dog + i °00b tex, 704 CONCRETE AND REINFORCED CONCRETE. The arch ring is 18 ins. thick at the crown, and 3 ft. 4 ins. at the haunches. The size and arrangement of the reinforcing bars are shown in Fig. 615. Figure 616 shows framing of centering used in the construction of this bridge. Ribbed Arches.—Ribbed arches have not thus far been used to any extent in this country, although they are popular in Con- tinental Europe. The saving in materials and reduction in dead weight are items which deserve careful consideration in localities adapted to the use of this type of structure. The cost of forms, however, is higher than for the solid arch. The 75-ft. bridge at Grand Rapids, Michigan, and the Deer Park Gorge Bridge, near La Salle, Ill., may be taken as examples of ribbed arch construc- tion of American design. The Grand Rapids Bridge—The Grand Rapids Bridge is used as an approach to a steel truss bridge across the Grand River, at Grand Rapids, Mich. This bridge has a span of 75 ft., and consists of seven parallel parabolic arch ribs, sup- porting a slab and girder floor by means of columns. Five ribs 2 ft. wide, 50 ins. deep at springing lines, and 32 ins. deep at the crown, support the 21-ft. roadway, while the side- walks are supported by two ribs, each 1 ft. wide, 50 ins. deep at springing and 25 ins. deep at the crown. The soffits are all shaped to the same curve of three centers, approximating very closely a parabola of 14 ft. rise and 75-ft. span. The linear arch of the main ribs has a rise of 12.7 ft. The ribs are connected and braced by 4-in. reinforced concrete slab webs lying near the neutral axis of the ribs. These were deemed necessary to stiffen the ribs to resist the impact of floating ice and drift during floods. The webs extend between the main ribs from each abutment to the second row of columns, and between the outer ribs and those adjacent they extend to the third row of colurmns. The general arrangement of ribs, struts and posts are shown in plan, elevation and section in Figs. 617, 618 and 619. As will be seen, in addition to the webs, the ribs are further stiffened by 8 x 8-in. concrete struts at each of the middle columns. The longer columns are also connected by 4-in. vertical webs of reinforced concrete. The columns under the roadway are 12 x 12 ias., with a I-in. chamfer on the corners. The sidewalk columns are Io x 12 ins. The sidewalk slabs are 9 ft. wide, and overhang the 6 x 12-in. longitudinal beam 3 ft. They are CONCRETE IN BRIDGE CONSTRUCTION. 795 reinforced with 14-in. bars spaced 8 ins. centers. The roadway, which is built in the form of a trough, has an 8-in. reinforced Half Cross-Section’ Half Cross-Section at Postt. at Crown. “aoe Posts 10" l2” ee Posts 4" Vertical Sectional Plan above Arch Rings, Showing Posts, Vertical Webs and Arch Webs. es 187" te 75'0” paige sign" 4 1 | 4"Vertical Webs : ' t J |. Els 23.656 Curb Grade 1.7324 % A + El.422.355 | | {om : et 47 é 3 Herticall ” ‘ ; : Webs- &S s 2 ; 2 ” 4" Horizontal Web | 4'Horizontal Web Ws £ | ‘ re AS 2" Bars pene Ms. \E WS : Wea ® ee BS? 2 ee error a aS : | 7 pase 25 %52" Fig. 617.—Plan and Sections of Grand Rapids, Mich., Bridge. CEH Cees | slab. Sections of arch rings, cantilevered sidewalk, vertical posts and struts are shown in Fig. 618. The arrangement of the shear bars in the arch ribs is shown in Fig. 619. This figure also shows 796 CONCRETE AND REINFORCED CONCRETE. Section of : ; Gounice. ond: Bracke: Sections of Arch Rings. Lee 2" ol yy pee 12M omy Lk 6"> |g Bars. a pty end Sa OO Brot nop) 2S “Og 36x) 3" Bar! Sections of Vertical Posts. Fig. 618.—Details of Arch Rings, Spandrel Posts, etc., Grand Rapids Bridge. construction of centering used for this bridge. As will be seen, it consists of vertical posts braced together to form bents supporting the timbers carrying the lagging, which was only of sufficient length to form bottom of box for the rib. The arch ribs were built com- plete in one operation, usually two ribs being placed in one day. The top of the crowns was roughened to form a bond with. the roadway slab and girders into which the main ribs merged. The reinforce- ment for the columns was placed when the rib concrete was placed and extended nearly to the bottom of the ribs. After the ribs had been concreted, the forms for the post girders -and for slabs were put in posi- tion, and the concreting com- pleted in one operation. Section of Strut. — Ter] > F =e i > Hardwood ~ 2812 %1B* NS BExI0 Hemlock Arches A and A’. Centers for Grand Rapids Bridge. Sectien at Crown Arches B,C,D,C', BY This bridge was constructed without hinges, but expansion joints of tarred felt and tar were made across the bridge at the center and two abutments, the center joint extending through the slabs to the arch ribs and columns. Fig. 619. CONCRETE IN BRIDGE CONSTRUCTION. 797 This bridge was designed to carry a 15-ton road roller, or a 24-ton electric car or a uniform live load of 250 lbs. per sq. ft. on roadway and 100 lbs. per sq. ft. on sidewalks. A factor of safety of two for dead loads and four for live loads was used. It is stated that the cost of forms and concrete in arches, slabs, sidewalks and roadway, etc., 290 cu. yds. being used, was: Cost per cu. yd. of concrete. Forms: Material. cv s.c00.¢xaansesaxenses vanes $3.70 Labor saiyasaaPhacaa yascatpreua i canes hla rae 3.03 — $6.73 Concrete: Materials ...........cec eee eee eee $3.22 Ihabor: \n-nwocanakkkeotelnbornac ee 3.57 — 679 OHA Lebscsis tiaovangnas isvaieelaneeusaehenaeotcaraumhec mas eennossaeED $13.52 Deer Park Gorge Bridge—This bridge may be taken as an example of light construction, as it is intended only for a foot 2 esterase erent + 6G mem ofemens 60 Toor fo Oem x~ ibm - rn : A * _yHard Fall mf = " TONPONIONIZOM |i ; NEON INFOS TINS seo ree" ROAR | INR AKIRA LMPE L re PSE hg | elie Wn, A Half = Plan. Fig, 620.—Deer Park Gorge Bridge. bridge. The clear span is 72 ft., length over all 95 ft., and dis- tance between hand railings 4 ft. 6 ins. The rise of the arch is 7 ft. 6 ins., with a camber of 4 ins. Figure 620 shows half plan elevation and cross-section of the bridge. The arch rings are 16 ins. in thickness, and vary in depth from 20 ins. at the crown to 24 ins. at the haunches. From the arch ring to the floor line there is a 7-in. spandrel wall, on which is carried the 4-in. hori- zontal floor slab. A series of 6-in. diaphragms spaced 5-ft. centers, extending from the floof line to the bottom of the arch ring, were placed between the ribs. Each rib is reinforced with four 1 x I-in. x 0.87-Ib. steel T-bars, located as shown in Fig. 620. The bars are in four lengths, and have wired splices staggered, and are carried entirely through 798 CONCRETE AND REINFORCED CONCRETE. the abutment ends of the ribs. The diaphragms are reinforced with transverse T-bars, as shown. Vertical T-bars are run up from the ribs into the railing posts. The floor slab is reinforced with 1 x 1-in, x 0.87-lb. T-bars running transversely, and spaced Horizontal Section. Side Elevation. Fig. 621.—Details of Hand Railings, Deer Park Gorge Bridge. about 6 ins. apart. Three 1 x '%-in. flats are located in the floor slab, and run longitudinally the full floor length. Figure 621 shows details of reinforced concrete hand railing. Figure 622 shows side elevation and section of centers and forms used for this bridge. The size of timbers and method in which they are placed are shown in the figure. On the top of the A G ! Ressagenay for Teams 8 Section AB. Section c-D Side Elevation. Fig. 622.—Centers for Deer Park Gorge Bridge. 12 x 12-in. longitudinal cross timbers, “which are supported as shown, were erected 2 x 4-in. vertical bracing to support the lagging. The lagging consisted of 2 x 10-in. plank placed length- wise and flat, with staggered joints, and on these a floor of 2 x 10-in. transverse planks were placed, and acted as a working CONCRETE IN BRIDGE CONSTRUCTION. 799 floor as well as bottom for the forms. The ribs were concreted first, then the forms for the remainder of the structure put in position, and the concreting completed. A 1: 2:4 concrete was used. A I-in. mortar finish was applied to the floor for a wearing surface. It is claimed by Mr. J. B. Strauss, who designed this bridge, that a saving of from 25 to 35 per cent. resulted from the use of the ribbed arch type. kalog ne ions £1 58.0 ES kete'g?of ‘ : VS mn one SO sera ararnenne ener nn erent erense meetin Df 1 1 Section K dle of 1250 through Crown. longitudinal Section. Fig. 623.—Three-Hinged Arch, Brookside Park, Cleveland, O. Three-Hinged Concrete Arch Bridge, Brookside Park, Cleve- land, 0.—This concrete bridge over Big Creek, in Brookside Park, Cleveland, O., is one of the few three-hinged arch bridges constructed in this country. The shape of the arch is that of a semi-ellipse, whose major axis is 92 ft. and semi- minor axis g ft. The arch proper, however, stops at the abut- ment hinges, giving a span length between abutment hinges of 86 ft. 414 ins. The rise of the arch, i. e., the vertical distance be- tween center and abutment hinges, is 5 ft. 214 ins., making an LF 3a FS". L,23%2- x2x i? rs q q a SH Me 4 we Ss » ~~ ax Le & | 6%. a 7 Fig. 624.—Hinges for Brookside Park Bridge. extremely flat arch. The width of the arch is 12 ft. 9g ins. Figure 623 shows cross and longitudinal sections of this bridge, while Fig. 624 shows details of a part of one of the hinges. The thickness of the concrete at the crown is 2 ft., and at the abut- ment hinges 3 ft. The abutments rest upon and are buried in firm shale rock. The concrete is entirely unreinforced, with the exception of a few rods used to tie the spandrel walls to the arch CONCRETE AND REINFORCED CONCRETE. 800 ‘9 ‘q ‘WOWUTYsSeM ‘HeerO AOU JOAQ eSplig Wory o[oqered—'ZgO “SL *pabinjug ‘uMoig 4D UOJpOeG-ss01D H-9 UdIg 1NUe149ag ‘y-3 0 UOI¥Dag pa07,ga ay 15,2 uem fay Buy Gy. apy io epising 40 enous uj Biv payiog UMoys $e be CONCRETE IN BRIDGE CONSTRUCTION. 801 proper to prevent any possible failure when the earth filling should be placed on the bridge. A 1:2%4:5 concrete mixture was used, but the outside faces were made of a 2-in. coating of very rich concrete, which was put in at the same time as the body of the concrete. The arch was further waterproofed with a very heavy coating of asphalt gum. The position of the hinges was so chosen as to prevent any el Dian. Pods 46. tol, ii _abternate Rods Bent Meptt Lice hie Sta ‘2 Diam. Frods, @4°C. tol Transverse Wall -2biam. Rods 2'C.106. [ m } aD! Remforcment Details of . Large Colurans. Details of Small Columns. Fig. 626.—Spandrel Wall, Fig. 627.—Interior Spandrel Construction, Piney Creek Bridge. Piney Creek Bridge. tension on the concrete. The hinges were built up of plates and angles, and have cast-iron bearing plates carefully fitted to 214-in. diam. steel shafting, so as to secure a uniform bearing on the shaft. Before being placed in position the hinges were thoroughly greased and the joints all carefully protected against rust. At the joints the concrete was separated % in., and this opening carefully closed by calking it with pure asphalt. The 802 CONCRETE AND REINFORCED CONCRETE. maximum compressive stress coming upon the concrete is 500 Ibs. per square inch. This bridge was designed by A. W. Zesign, Asst. Park Engr., Cleveland, O. Piney Creek Bridge, Washington, D. C.—The parabolic con- crete bridge over Piney Creek at 16th Street, Washington, D. C., is an unusual type of concrete bridge. The arch ring has the curve of a parabola, a clear span of 125 ft., and a rise of 39 ft. The spandrels are hollow, and a framework of reinforced con- crete between curtain walls carries the floor slab. The spandrels and the floor slab are of reinforced concrete, but the arch ring Spring, yor Batter} tol” Batter of Face |) Batter of Face “ial oes at a seeiee t i i { ' Section Section 4 { ' | t through through to Center Center of arch of Pier Fig. 628.—Pennypack Creek Bridge, New York Short Line Railway. is unreinforced, except for a net of face bars to resist surface cracking. I[*igure 625 shows horizontal and vertical sections of the bridge. The spandrel constructions consist of two solid spandrel walls, and between them two rows of columns, al! sup- porting a ribbed floor slab. The longer spandrel columns are stiffened laterally by horizontal braces between columns in both directions ; the transverse braces running with the spandrel walls. Columns, walls and girders are all reinforced, as shown in detail in Figs. 625-627. The spandrel construction is continued over the abutments, with certain modifications. First one row of CONCRETE IN BRIDGE CONSTRUCTION. 803 columns is used instead of two, and the lower portions of these columns are connected by walls to form closed cells, which are filled with earth. The reinforcement of the floor slab is indicated in Fig. 627. The slab is stiffened by transverse ribs over the columns. These ribs or girders vary in section from 24 x 16 to 36 x 18 ins., and are reinforced with from six to nine 114-in. rods spaced 4-ins. centers. Alternate rods are bent up at the ends of span, and carried over the columns. The slab reinforcement consists of 34-in. transverse rods spaced 6-ins. centers and 7é-in. longitudinal rods spaced 12- ins. centers. Pennypack Bridge—An unreinforced concrete bridge 348 ft. long, having an extreme height of about 80 ft., was recently con- Expansion Joint Z “Lead iste eZ Cement. 7 os KestoesBOdd Re ieeion for Expansion Joints 16 Fig. 629.—Expansion Joint, Pennypack Creek Bridge. _structed for the New York Short Line R. R., over the Pennypack Creek, about 12 miles from Philadelphia. This bridge i is a mono- lithic structure, and comprises four full centered arches of 60-ft. span, supported by two abutments and fotir piers, all of concrete. Figure 628 shows plan, elevation and sections of two end spans. The expansion joint at piers is also shown in detail. The arches have a radial thickness of 3 ft. at the crown, increasing over the haunches to a maximum thickness of 11 ft. on the center line of the piers, where the upper surfaces of two arches meet. The upper faces of the arch terminate on the plane of the spandrel walls, which, like the piers, are carried up to the level of the base of rail. Vertical expansion joints are provided in the spandrel walls over each pier, as shown by Fig. 629.