I 
 
 
 
 
 
 
NEW TAY BRIDGE. 
 
 A 
 
 COURSE OF LECTURES 
 
 DELIVERED AT 
 
 THE ROYAL SCHOOL OF MILITARY ENGINEERING, 
 
 AT CHATHAM. 
 

THE 
 
 NEW TAY BRIDGE. 
 
 A 
 
 COURSE OE LECTURES 
 
 DELIVERED AT 
 
 THE ROYAL SCHOOL OF MILITARY ENGINEERING, 
 
 AT CHATHAM, 
 
 NOVEMBER 1888, 
 
 BY 
 
 CRAWFORD BARLOW, B.A., M.I.C.E. 
 
 E. & F. N. SPON, 125, STRAND, LONDON. 
 
 NEW YOKE: 12, CORTLANDT STREET. 
 
 1 8 8 9. 
 
Digitized by the Internet Archive 
 in 2019 with funding from 
 Getty Research Institute 
 
 https://archive.org/details/newtaybridgecourOObarl 
 
TO 
 
 THE MOST HONOURABLE THE MARQUIS OF TWEEDDALE, 
 
 CHAIRMAN OF THE NORTH BRITISH RAILWAY COMPANY, 
 
 THIS WORK IS RESPECTFULLY DEDICATED 
 
 THE AUTHOR. 
 
PEE FACE. 
 
 In presenting these Lectures to the Public I have been chiefly actuated by a desire 
 to give a record of the events connected with the New Tay Bridge which, from 
 the unfortunate disaster to the old one has become of so much general interest, and 
 as numerous erroneous versions of the manner in which the Restoration of this work 
 has been effected, have appeared, it seems due, not only to the Public, but also to the 
 North British Railway Company, and to all those connected with it, that an 
 authenticated record should be given. 
 
 I commenced the Lectures with a short historical sketch of Metal Bridge Design¬ 
 ing, because, being a subject in which both my grandfather, the late Professor Barlow? 
 and my father, have made many investigations, I am able to give information which I 
 thought might be of interest to my audience, and for the same reason I retain it now, 
 as forming a not unfitting introduction to the rest of the work. 
 
 CRAWFORD BARLOW. 
 
 2, Old Palace Yard, Westminster, 
 May 1889. 
 
 b 2 
 
A SHORT HISTORICAL SKETCH OF METAL BRIDGE DESIGNING 
 
 THE COMPARATIVE LENGTH OF THE TAY BRIDGE . 
 
 THE HISTORY OF THE SCHEME OF BRIDGING THE ESTUARY OF THE TAY 
 
 THE HISTORY OF THE OLD BRIDGE . 
 
 THE HISTORY OF THE NEW BRIDGE. 
 
 GENERAL DESCRIPTION OF THE BRIDGE . 
 
 DESIGN OF THE PIERS . 
 
 DESIGN OF THE GIRDERS, FLOORING, ETC. 
 
 PROVISIONS FOR WIND PRESSURE . 
 
 PERMANENT WAY AND SAFETY GUARD. 
 
 ARRANGEMENTS FOR VARIATION OF TEMPERATURE . 
 
 MATERIALS USED IN CONSTRUCTION . 
 
 DESCRIPTION OF CONSTRUCTION. 
 
 TIME OCCUPIED IN CONSTRUCTION . 
 
 * 
 
 ACCIDENTS DURING CONSTRUCTION . 
 
 THE BOARD OF TRADE INSPECTION . 
 
 CONCLUSION. 
 
 SUPPLEMENTARY REMARKS 
 
THE NEW TAY BRIDGE. 
 
 A SHORT HISTORICAL SKETCH OF METAL BRIDGE 
 
 DESIGNING. 
 
 The first metal bridge was constructed 109 years ago, in 1779, and consisted of 
 cast iron, audits design was that of the Arch; from this time to 1820 numerous cast- 
 iron bridges were erected, among which may be mentioned Wilson's bridge over the 
 Wear at Sunderland, with a span of 240 feet; Telford’s at Buildwas, 130 feet span; 
 and Rennie’s at Southwark, 240 feet span. These are examples of what may be said 
 to be the first type of bridge design, in which only one property of metal is utilised, 
 viz. that of resisting compression strains. 
 
 In the meantime experiments were being carried on by Mr. Telford and 
 Professor Barlow, on malleable iron, with a view to its introduction in structural 
 designs, and the result of these was the introduction of the second type , viz. the 
 Suspension bridge, in which the tensile properties of the metal are brought into 
 requisition. The first bridge of this kind was the Union Bridge, over the Tweed, of 
 449 feet span, which was completed in 1820. In 1826 we have Telford’s magnifi¬ 
 cent Menai Bridge, 570 feet span ; followed closely by the Conway, 327 feet span ; 
 and others, amongst which may be mentioned the Freiburg Bridge, erected in 1834, 
 of 870 feet span—the largest span crossed, until quite recently. 
 
 We now come to a period when the construction of railways was commencing, 
 and this led to a great development in bridge designing, not only on account of the 
 demand which arose for bridges, but also because the requirements for these were so 
 different to those that had previously to be dealt with. A bridge for a railway 
 requires a rigid platform, with the greatest accommodation for headway underneath, 
 and in the two types already referred to, both these requirements did not co-exist: in 
 the arch, there is the rigidity of platform at expense of headway, while in the suspen¬ 
 sion type the greatest headway is provided for at a loss of rigidity. (It may be here 
 mentioned that various expedients had been resorted to, to obviate this defect of the 
 suspension bridge, and one well-known railway bridge, that over the Niagara River, 
 just below the Falls, erected in 1854, is an example of this.) To meet this demand the 
 principle of the beam was brought into requisition, and this led to the introduction of 
 die third type of design, viz the Girder bridge, in which the properties of metal, 
 for resisting both tension and compression strains, are utilised. 
 
 About 1843 the first bridge on this principle was completed on the Dublin and 
 
 15 
 
') 
 
 THE NElV TAY BRIDGE. 
 
 Drogheda Railway. It consisted of lattice girders, and is said to have been an 
 imitation, in iron, of the timber bridges which were then being built in the United 
 States. Next we have the celebrated Conway and Britannia Bridges of Mr. Robert 
 Stephenson, the one erected in 1848 and the other in 1850. These were originally 
 intended to be tubes supported by chains, but after a series of experiments, made 
 by Messrs. Stephenson and Fairbairn, the tubes were designed and constructed strong 
 enough to carry themselves and the rolling load. The idea of these tubes, it is said, 
 was suggested by the case of an iron ship which was stranded at the entrance to a 
 dock gate, and at low water was left dry with only her bow and stern ends supported: 
 she, notwithstanding that she had the load of her cargo, proved perfectly capable of 
 carrying it in this novel manner. 
 
 Another bridge—the Torksey Bridge, of similar design, completed in the same 
 year (1850)—may be mentioned, because it was declared, by one of the Inspectors of 
 the Railway Board, to be unfit for public service, as it did not conform to the rules 
 in force for iron structures. At that time, it may be explained, there were no rules 
 with regard to wrought iron. A Royal Commission had investigated the question, 
 and reported, but it was not until 1859 that a rule concerning this material was 
 included amongst the requirements of the Board. 
 
 In the meanwhile girders developed, the tubular into the plate, and the lattice to 
 trellis and “ Warren ” girders, while other forms, such as bowstring and truss girders, 
 appeared; it is needless to mention examples of these, as nine-tenths of railway 
 bridges are of this type. 
 
 Almost simultaneously with the introduction of the girder, the advantages of 
 continuous beams were ascertained, and it is the investigations on this subject which 
 led to the introduction of what may be called the fourth, type of design, viz. 
 continuous girders of varying depth, and cantilevers with intermediate suspended 
 girders. The first step in this direction may be said to have been taken in 1847 
 when Mr. Sadler patented an arrangement by which a span was crossed by two 
 cast-iron cantilever girders, in which there was an increase of depth in the girders at 
 the supporting points. 
 
 In 1855 Mr. W. H. Barlow read a paper before the Royal Society “ On the 
 Resistance of Flexure in Beams, and pursuing this subject afterwards, he wrote 
 in reference to continuous beams:— 
 
 “ It will be seen that an intermediate support, applied to a beam, may be regarded as 
 pressing upwards against the under side of the beam, and this pressure of the support gives 
 to the beam an upward flexure, that is to say it renders it convex on its upper surface and 
 concave on its under. Near the centre of each span of the beam the flexure is downwards, 
 being produced by the weight of the beam itself and of the load upon it. 
 
 Between the centre of each span and the intermediate support there is a point where 
 there is no flexure, and at this point (called the point of contrary flexure) the strain is less than 
 at any other point in the length of the beam. 
 
 “ fhe upper pressure over the pier or intermediate support acts at a point, or nearly so, 
 while the downward pressure occasioned by the weight and load acts over the whole extent of 
 the beam on which such weight and load are distributed: the consequence is, that when a 
 continuous beam is made of equal depth and section throughout, and is loaded uniformly all 
 
THE NEW TAY BRIDGE . 
 
 3 
 
 over, the curvature upwards over the point of support is sharper, that is to say, it is of less 
 radius than the curvature downwards in the centre of the span, and the breaking points of such 
 a beam, so loaded, would be at the places over the intermediate supports.” 
 
 He then ascertained that, by increasing the depth of these beams over the 
 points of support, the points of contrary flexure were moved nearer to the centre of 
 the span, with the result that the sectional area of metal in the flanges of the beams 
 throughout the centre portion of them, between the points of contrary flexure, 
 could be considerably reduced without diminishing the strength of the beam, as 
 compared with one of equal depth throughout. 
 
 Accordingly in 1859 he took out a patent, entitled, “ Improvements in Beams 
 and Girders,” and the following is an extract from the specification :— 
 
 “ According to my invention, in constructing continuous beams or girders I increase the 
 depth of the beam or girder over or near the piers, or intermediate points of support, by 
 which means I not only obtain greater strength over the piers, or intermediate points of 
 support, with the same quantity of material in the flanges, but the radius of curvature of the 
 upward flexure is rendered greater, that is to say, the curve is flatter and the points of contrary 
 flexure are thereby moved nearer to the centre of the span, so that the sectional area of metal 
 in the flanges throughout the centre portion of the beam, between the points of contrary 
 flexure, may be considerably reduced, without diminishing the strength of the beam when 
 compared with a beam of equal section or of equal depth throughout, as heretofore 
 constructed. 
 
 “ And it will be seen that in large girders, when the dead weight of the centre portion 
 of the beam is thus reduced, it also relieves, in a proportionate degree, the strain over 
 the intermediate pier, so that a great economy of material results from this mode of 
 construction. 
 
 “ In constructing beams or girders upon this principle, I continually diminish the depth 
 from the maximum depth over the intermediate pier or support, to a point at or near the mean 
 position of the point of contrary flexure, which will usually be about half-way between the 
 intermediate pier, or support, and the centre of the span. And from this point I continue 
 the depth of the beam equal, or nearly equal, throughout all the centre portion of such beam. 
 
 “ I also make the sectional area of the flanges at and near the piers or intermediate 
 supports, and also at and near the centre of the span, proportional, or as nearly so as may 
 be convenient, to the maximum strain which would arise in such parts from the weight of 
 the structure itself, as well as from the insistant load, or any moving load, which it may be 
 intended to carry. 
 
 “ But to those parts which are at or near the points of contrary flexure, I give a sectional 
 area to the flanges, greater than is required to resist the strains to which such parts are 
 subjected, for the purpose of obtaining greater stiffness and less deflection when the spans are 
 unequally loaded.” 
 
 The increase in the depth of the beams or girders was either made above or 
 below, as best suited the particular circumstances of the case, and on account of 
 this arrangement they were called “ Counterfort Girders.’ 
 
 The patent further describes that when the continuous girder was ot considerable 
 length, joints were to be made at the points of contrary flexure to admit ot the 
 expansion and contraction of the girder. Although called continuous girders, 
 they were not constructed in one continuous piece, the centre portion, between the 
 
 » 2 
 
4 
 
 THE NEIV TAY BRIDGE. 
 
 two points of contrary flexure, being an independent girder, suspended by links (to 
 allow of the expansion of the metal) to the girders on either side. 
 
 Calculations showed that the advantages of the arrangements in this patent 
 were a saving in the weight of metal of about 30 to 50 per cent,, as compared with 
 the best form of continuous girder constructed up to that time. 
 
 This patent has been followed by numerous others, among which may be 
 mentioned Mr. Sedley s in 1804, of a girder supported at its ends by cantilevers, 
 and Mr. Young’s in 1865, where there is an intermediate girder carried at the end of 
 two cantilevers. 
 
 The principle of the cantilever alone has been chiefly employed in the 
 designing of swing bridges; it is a curious fact, however, that the arrangement 
 of continuous and intermediate suspended girders has not been utilised in the 
 construction of fixed bridges until quite recently. The Forth Bridge in this country, 
 the Fraser, Laehine, and the Niagara in Canada, the Hooghly and the Sukkur in 
 India, and the Louisville and Albany and the Poughkeepsie in the United States, are 
 examples of this type of design. 
 
 With regard to the Forth Bridge: at the time the old Tay Bridge fell, a 
 bridge was being commenced over the f orth by Sir Thomas Bouch, of the design 
 of a stiffened suspension bridge of steel. On account of the circumstances of the case, 
 the Directors of the Forth Bridge Company (the Board of which consisted entirely 
 of representatives of the Midland, Great Northern, North-Eastern, and North British 
 Bailway Companies) thought fit to obtain fresh opinion on the bridge, and accordingly 
 they requested Mr. W. H. Barlow, Sir John Fowler, and the late Mr. T. E. Harrison 
 (the representative engineers of three of the Companies) to make a report on the 
 feasibility, cost, and best design ; the result was that they recommended the design 
 which is now being carried out, and which was the one prepared by Sir John Fowler 
 and Mr. Benjamin Baker, with certain modifications. 
 
 With regard to these four typical designs, it is an interesting fact that the 
 principles on which they depend are not new. Examples of each may be found in 
 what we may call the “remote ages”: for instance, the arch dates back nearly to 
 the earliest period of architecture; examples of suspension bridges are even older, 
 they having been found in India and parts of America, where the suspending material 
 was formed of the bark of trees; the beam or girder is represented by the bar of 
 stone put at the top of doors and windows in the most ancient buildings; while 
 instances of the last—the continuous and suspended girder—are recorded in China, 
 where bridges have been built on this principle, and in architecture examples of it 
 occur in the stone architrave of the entablature on the top of the columns in ancient 
 temples, in which a central stone is supported, by being made wedge-shaped, between 
 two stones balanced (as it were) on the top of the columns. 
 
 The relative efficiency of these different types, as measured by the amount of 
 weight of metal necessary, has been computed, and it is found that for large spans 
 the economy of the continuous girder type becomes more and more evident as the 
 span increases. Next in order is the suspension bridge type, then the arch, and 
 lastly the detached girder, and the limiting span of each is in the same order, the con¬ 
 tinuous girder having the greatest and the detached girder the least limiting span ; for 
 
THE NEIV TAY BRIDGE. 
 
 small spans, however, the difference between them being less, other considerations 
 have stronger force in determining which type is the most suitable for the special 
 circumstances of the case. 
 
 The developments of bridge designs already described are those which have 
 resulted from investigations into principles of construction ; the introduction of what 
 may be called a new metal—steel—has been as important a factor in the progress 
 of metal bridge designing as any which had preceded it. 
 
 The commencement of the steel era may be said to date from the year 1856, 
 when Mr. Bessemer exhibited his wonderful process, by which a cauldron of 
 cast iron was converted in a short time by the simple aid of a blast of atmospheric 
 air and the addition of a little manganese to steel ; the production of this metal 
 was next assisted and developed by the regenerative furnace of Sir William 
 (then Dr.) Siemens, and the introduction of the Siemens-Martin process of making 
 steel. 
 
 In 1859 the manufacture of steel had so far advanced that Mr. W. H. Barlow 
 included the use of it in his patent (already referred to). There continued, 
 however, to be a difficulty in applying steel to structures on account of the 
 want of knowledge of its physical properties, and to meet this a committee was 
 appointed by the Institution of Civil Engineers in 186H, which made a number of 
 experiments. These consisted of four series 
 
 The first was to ascertain the relation which existed between the resistance of 
 tension, compression, torsion, and transverse strains. 
 
 The second, to obtain results of tempering in oil and water. 
 
 The third, to investigate the modulus of elasticity ; and 
 
 The fourth consisted of experiments on riveted steel. 
 
 The first scries established that the relation between the several resistances of 
 strains, tension, compression, &c., were practically the same as in wrought iron. 
 
 The second showed that a remarkable decree of strength was gained bv 
 tempering. 
 
 The third series established* the modulus of elasticity as about 30,000,000. 
 
 And the fourth showed that the same rules which applied to riveted iron 
 were applicable also to riveted steel. 
 
 In 1873 Mr. W. H. Barlow, as President of the Mechanical Section of the 
 British Association at Bradford, devoted his address to this subject, saying, “ My 
 object is to draw attention to this material (steel) as to its use and application for 
 structural and engineering purposes,” and giving a history of the progress of the 
 knowledge of steel, he referred to the experiments just mentioned, and said that 
 they exhibited great range of strength commencing as low as that of the best iron 
 and extending to about 53 tons per inch. 
 
 He explained that for structural purposes, mild steel of tensile strength of 
 33-36 tons per square inch, which could be made at a moderate cost, was the most 
 suitable material; that, following the same rule as for wrought iron (namely, that 
 the maximum strain on the metal should not exceed one-fourth of the breaking 
 weight), steel of this quality would be capable of bearing at least 8 tons per 
 square inch. 
 
 \ 
 
THE NEW TAY BRIDGE. 
 
 6 
 
 “ It is not alone in the relative weight,’’ he goes on to say, “ or in the relative 
 eost that the advantage of the stronger material is important, but with steel we shall 
 be enabled to cross openings which are absolutely impracticable in iron.” 
 
 He then discussed the.reasons why it was that steel was not employed, and 
 suggested that they were twofold. First, that there was a want of confidence as to 
 the reliability of steel in regard to its toughness and power to resist fracture from 
 sudden strain; and second, that there was a difficulty in establishing the quality of 
 the material, without elaborate testing, in such a manner that the Board of Trade 
 could recognise it. 
 
 With regard to the first, he showed that the irregularity, in this respect, had 
 been due to the difference in the chemical constituents of the metal or ores 
 employed, or in the process pursued by the makers, and he explained that the 
 manufacture of steel had arrived at a stage when more certainty as to the character 
 of the material was assured, particularly as tests could now be made during the 
 process of manufacture. And as to the second reason, the difficulty, lie explained, 
 was that, in steel, chemical analysis was not (as in the case of most other metals) a 
 sufficient test of quality, and therefore mechanical tests had to be relied on, and as 
 the non-destructive tests on the finished structure afforded no sufficient evidence 
 that the metal possessed that degree of toughness necessary for engineering 
 structures, some other means must be arranged for establishing its quality ; and he 
 suggested that the first step would be to put testing on a systematic and satisfactory 
 basis, and the second, to establish some means whereby metal which had been tested 
 could have its quality indicated upon it in such manner that it can be practically 
 relied upon. 
 
 He concluded his address with the following words :— 
 
 “I consider that the difficulties under which steel is placed are affecting interests of 
 considerable importance. 
 
 “Not only is a large and useful field for the employment of steel practically closed, 
 but the progress of improvement in engineering structures is impeded, both in this country 
 and in other parts of the world where English engineers are engaged. 
 
 “ For in consequence of the impediments to its employment in England very few 
 English engineers turn their attention to the use of steel; they are accustomed to make 
 their designs for iron, and when engaged in works abroad, where the Board of Trade rules 
 do not apply, they continue for the most part to send out the old-fashioned ponderous girders 
 of common iron, in cases where the freight and difficulties of carriage make it extremely 
 desirable that structures of less weight and more easy of transport should be employed. 
 
 “ I would observe that we possess in steel a material which has been proved, by the 
 numerous uses to which it is applied, to be of great capability and value ; we know that 
 it is used for structural purposes in other countries, as, for example, in the Illinois and 
 St. Louis Bridges in America, yet in this country, where modern steel has originated and has 
 been brought to its present state of perfection, we are obstructed by some deficiency in our own 
 arrangements, and by the absence of suitable regulations by the Board of Trade, from making 
 use of it in engineering works.” 
 
 Shortly after this a committee was appointed to discuss what steps should be 
 taken to put the matter into a practical form, and having reported, the Board of 
 
THE NEW TAY BRIDGE. 
 
 Trade inserted among their “ Requirements for Structures " the rules respecting the 
 use of steel which are now in force. 
 
 The first steel girders were erected (sol am informed) on the. Chester and 
 Holyhead section of the London and North-Western Railway about live years ago. 
 The next were on the Chapel Hall branch of the Caledonian Hailway, where seven 
 bridges and a viaduct of three spans were completed in 1887. 
 
 The use of steel has now become much more general, as is evinced by the fact 
 that during and up to October of the present year (1888) twenty-two bridges of this 
 material have been inspected by the Board of Trade. 
 
 This completes the record of events connected with the development of metal 
 bridge designing up to the present time. 
 
 I have dwelt at considerable length on the facts connected with the introduction 
 of steel, as it seems not unlikely that the further progress of this science will be 
 affected bv the progress made in our knowledge of other metals. I allude especially 
 to aluminium and its use as an alloy—but as the object of these lectures is to describe 
 accomplished facts, I will not take up your time by relating what has been and is 
 being done in this direction. 
 
 In designing the new Tay Bridge, the existence of the old work most materially 
 affected the design of the new. It was natural enough that the Company, having 
 spent a considerable sum of money on a bridge, should desire that as much of it as 
 was possible, should be utilised again. The peculiar circumstances of the case had to 
 be considered; and on account of the accident, the bridge (which, under ordinary 
 circumstances, would have been only known to engineers) had become, as it were, 
 public property, and even the House of Commons appointed special Committees for 
 considering the reconstruction of it. All this precluded novel principles of design 
 being adopted; and even steel, the metal which Mr. W. H. Barlow had so long been 
 advocating the use of, had to be abandoned for the better known metal wrought iron. 
 
 THE COMPARATIVE LENGTH OF THE TAY BRIDGE. 
 
 In one respect the Tay Bridge can boast of being distinguished above all other 
 railway bridges at present in existence, and that is in its length and number of 
 spans. 
 
 According to accessible information, forty bridges of length equal to or greater 
 than the Britannia (the first long bridge) have been built, or are in course of erection, 
 in various parts of the world; the distribution of these amongst the various countries 
 is as follows :—the United Kingdom and Colonies is first with fourteen, five of which 
 are in the United Kingdom, four in Canada, four in India, and one in Australia ; the 
 United States is second with eleven bridges ; then follows Russia with five; Holland 
 with four; Germany with three; and France and Austria with only one each. (In 
 the foreign countries, however, it is not unlikely that there are more large bridges 
 
 0/7 v 
 
8 
 
 THE NEW TAY BRIDGE. 
 
 concerning which we have no information.) Seven of the above only are of a mile or 
 more in length, while of these seven the Tay is the only one over two aides long ; the 
 
 lengths of these seven bridges are :— 
 
 The Tay. 10,700 feet. 
 
 The Victoria, Montreal . . . . . . . . 9,500 „ 
 
 The Moerdvk, Holland . . . . . . . . 8,530 „ 
 
 The Forth, Scotland . . . . . . . . 8,300 ,, 
 
 The Poughkeepsie, United States . . . . . . 7,100 ,, 
 
 The Solway, Scotland . . . . . . . . 5,820 „ 
 
 The Cincinnati, United States . . . . . . 5,300 „ 
 
 THE HISTORY OF THE SCHEME OF BRIDGING THE ESTUARY 
 
 OF THE TAY. 
 
 On referring to a map it will be seen that the two long estuaries of the Tay and 
 Forth cut off all direct communication by rail between Edinburgh and the South, 
 and Dundee, Arbroath, Aberdeen, &c., and the North, and almost completely isolate 
 the important towns and coalfields of Fife. 
 
 As long ago as 1849 the scheme for bridging the two estuaries, the Tay and 
 the Forth, dates back. There were then, as now, ferries at Tayport and Burntisland, 
 and a fatal accident occurring that year at the latter place brought before Mr. (after¬ 
 wards Sir Thomas) Bouch, the Engineer and Traffic Manager to the Edinburgh, 
 Perth, and Dundee Railway, the fact of the costliness and clumsiness of the system 
 then in practice; however, it was not until 1854 that he astonished the Directors of 
 the Scottish North-Eastern Railway by propounding a scheme for bridging the Firths 
 of the Tay and the Forth. At this time the Victoria Bridge at Montreal was just 
 commencing, but despite this, his scheme was looked upon with great incredulity, 
 owing most probably to the want of conception in the public mind of the resources of 
 engineers for combating with the forces of nature, which it was evident to all were 
 the requisites in this case. 
 
 The scheme, however, only remained in abeyance. The first tangible form it 
 took was in 1864, when notice was given for a Bill for a bridge across the lay, the 
 site of it being between Newport on the south and Craig Pier on the north. Later 
 on in the same year, in order to conciliate as far as possible local interests, the site 
 was altered considerably to the westward. This bridge was to consist of 80 spans, 
 with a height in the fairway of 100 feet above high water ; owing, however, to a 
 combination of reasons, this Bill was abandoned in 1865. In 1866 another Bill was 
 introduced by the North British Railway Company, in which the site of the bridge 
 was again slightly altered. This too, although it passed through the Committees of 
 both Houses, was withdrawn, on account of the Company’s financial position. Then 
 there was an interval until 1869, when the scheme was again resuscitated, the site 
 
THE NEJV THY BRIDGE. 
 
 q 
 
 then fixed upon being that of the present one, viz. between Wormit on the south 
 and Buckingham Point on the north. The promoters of this consisted of half local 
 men and halt North British Directors, and despite many difficulties, the Bill was 
 passed in 1870. 
 
 Alter obtaining the Act the promoters (as was arranged in the Committee 
 Room) applied to the Board of Trade for leave to reduce the height from 100 feet, 
 with the result that they were permitted to lower the headway at the centre spans to 
 88 feet above high water. 
 
 O 
 
 THE HISTORY OF THE OLD BRIDGE. 
 
 The contract for the construction of the bridge was first let to Messrs, de Berime 
 and Co., but afterwards, owing to the death of the principal partner, it was transferred 
 to Messrs. Hopkins, Gilkes and Co. 
 
 The bridge, as was then designed, consisted of 89 spans, the central ones being 
 fourteen in number, with clear spans of 200 feet, and was for a single line; it was to 
 have solid brick piers for supporting the girders, borings having led to the belief that 
 rock, hard clay, and gravel were accessible for foundations; however, when building 
 the fifteenth pier at the south end, it was found that the underlying material was not 
 hard enough to support a solid pier, so a change in the design was made, and piers 
 having larger bases and less weight w r ere substituted. The larger base was accom¬ 
 plished by various methods, but finally by the use of large caissons, while groups of 
 cast-iron columns above high water in place of brickwork, was the method adopted for 
 diminishing the weight of the piers. It was at this time, too, that a change was made 
 in the number and dimensions of the spans. The spans between the fifteenth pier 
 and the central spans were altered to twelve of 145 feet, and those of the central spans 
 to thirteen of 245 feet. 
 
 This bridge was completed and opened for traffic on May 31st, 1878; but its life 
 was of short duration, for on December 28th, 1879, the great calamity known as “ The 
 Tay Bridge Disaster ” occurred, in which, during a violent gale, the thirteen large 
 central spans (over which a train was passing at the time) collapsed, and fell together 
 with the train, into the river. 
 
 Owing to the very special nature of the disaster, the Board of Trade appointed a 
 Court of Inquiry, consisting of Mr. Rothery, Colonel Yolland, R.E., and Mr. W. H. 
 Barlow, to make a formal investigation into the causes of, and the circumstances 
 attending, the catastrophe. 
 
 This investigation lasted twenty-five days, and searching inquiry was made with 
 reference to the design, workmanship, and materials of the bridge. The Report which 
 was the result of these investigations first describes the construction of the bridge, 
 and then proceeds to state the circumstances attending the accident, which were as 
 follows:— 
 
 The train from Edinburgh, which fell with the bridge, arrived in due course at 
 
10 
 
 THE HE IV TAY BRIDGE. 
 
 St. Fort Station, and there the tickets of the passengers for Dundee were collected. 
 There were, including the men in charge, seventy-four or seventy-five persons in the 
 train. The train left St. Fort Station at 7.8 p.m., and on approaching the cabin winch 
 stands at the southern end of the bridge, the speed was slackened to about three or 
 four miles an hour, to enable the engine-driver to take the baton or train-staff, 
 without which he was not allowed to cross the bridge. On receiving this, the train 
 passed on to the bridge, upon which the signalman signalled to the cabin at the north 
 end of the bridge, the time being 7.13 p.m. It was then blowing a strong gale from 
 about W.S.W., and therefore almost directly across the bridge; there was a full 
 moon, but it was cpiite dark, owing to it being obscured by the clouds. According to 
 a plate-layer Avho was watching the train from the cabin, when it had gone about 
 200 yards he observed sparks flying from the wheels, and after a few minutes there 
 was a sudden bright flash of light, and immediately afterwards total darkness, the 
 tail lamps of the train, the sparks, and the flash of light, all disappearing at the same 
 instant. 
 
 The portion of the bridge which fell consisted of three sets of continuous girders, 
 covering respectively five spans, four spans, and four spans, making thirteen spans 
 altogether. These continuous girders rested on rollers on all their piers except one 
 near the centre of each set, and to these central piers they were fixed. In the 
 accident which took place, the girders turned over and fell on their sides, each girder 
 becoming slightly curved, the centre portion being furthest from the piers, and the 
 ends curving towards them, some irregularity showing itself in the curve at the first 
 fallen pier from the south end. 
 
 The train was found partly in the fourth and fifth spans from the south end, so 
 that, although it had travelled some distance along the first set of continuous girders, 
 it never reached its northern extremity. The engine and tender were found lying on 
 their sides on the eastern girders. The train consisted (counting from the engine) of 
 one third class, one first class, two third class, one second class, and the guard's van. 
 The second class carriage and the guard’s van had their bodies and all their upper 
 portions entirely destroyed; their lower frames were greatly damaged, and the axles 
 of these vehicles as well as those of all the other carriages were bent. The throttle 
 valve of the engine was full open, and the reversing lever standing in the sixth notch 
 from full forward gear, or in the third notch from the centre, and though the train 
 was partly fitted with the Westinghouse brake, there was no appearance of its having 
 been put on, the conclusion to be drawn from these facts being that neither the driver 
 or fireman had any warning of the accident which took place. 
 
 The Court in their report next referred to the scientific evidence, especially that 
 given, concerning wind pressure, by the Astronomer-Royal, Professor Stokes, and 
 Mr. Scott of the Meteorological Department, and then summarised the evidence which 
 bore upon the causes of the disaster, which is briefly as follows :— 
 
 “ There is no absolute knowledge of the mode in which the structure broke down; the 
 evidence of persons who happened to be looking at the bridge at the time agrees in 
 describing lights falling into the river, and that these appearances lasted only a few seconds, 
 but the evidence is not sufficiently clear and definite to determine by it which portion of the 
 bridge fell first.” 
 
THE NEIV TAY BRIDGE . 
 
 11 
 
 “ It is observable in the ruins of the bridge, that the columns have for the most part 
 separated where they had been bolted to the base pieces; in two piers the separation has taken 
 place higher up the pier, one being at the first and the other at the second tier of columns. 
 
 “ The storm which occurred at Dundee on the night of the disaster was recorded on board 
 the Mars training ship, lying near Newport, as being of the force of 10 to 11 of the Beaufort 
 scale, and was especially characterised by strong gusts at intervals. The evidences of wind 
 force in the town of Dundee were not, however, such as to point to extreme wind-pressure, but 
 from the configuration of the land, the main force of the gusts would probably take the line of 
 the river. 
 
 “ The first indication of weakness in the bridge itself was the loosening of a number of the 
 
 ties of the cross bracing. All the evidence, relative to the condition of these ties, states 
 
 that they were, to all appearance, in proper order at the date of the Board of Trade inspection 
 (February, 1878). The loosening which subsequently ensued, must have resulted from lateral 
 action, and was most probably due, as was suggested, to strains on the cross-bracing produced 
 by storms of wind. 
 
 “ Sir Thomas Bouch, in his evidence, considers 4 that the loosening arose from the bending 
 of the pins in the holes which had been left conical in casting the lugs.’ 
 
 “ Within a few months of the disaster it was ascertained that four of the columns were 
 cracked with vertical cracks, two of them being in the northern part of the bridge, and 
 one in one of the piers under the fallen girders. The columns of the whole bridge were 
 
 filled after their erection with Portland cement concrete, put in from the top; and concrete 
 
 of this material, unless carefully managed, is liable to swell in setting. From this circum¬ 
 stance, and from the unequal contraction of cast iron and concrete by cold, internal strains 
 might have arisen sufficient to produce such cracks. Cracks of a like character have occurred 
 in other viaducts; and when the fracture is vertical it is capable of remedy, to a consider¬ 
 able extent, by hooping with wrought-iron bands. (Precautions were taken with regard to 
 these damaged columns.) 
 
 “The storm of the 28th December, 1879, would necessarily produce great tension on the 
 ties, varying as the heavy gusts bore upon different parts of the bridge; and when under these 
 strains the train came on the viaduct, bringing a larger surface of wind-pressure to bear, as 
 well as increased weight on the piers, and accompanied by the jarring action, due to its motion 
 along the rails, the final catastrophe occurred. 
 
 “ The distance at which the girders were found from the piers, and the position of the 
 wreckage on the piers, is such as would result from a fracture and separation taking place in 
 the piers somewhere above the base of the columns; and such a fracture might have arisen 
 from two causes: firstly, by the yielding of the cross-bracing, and the consequent distortion of 
 the form of the piers, which would throw unequal strains on the flanges and connecting bolts; 
 or secondly, fracture might have taken place in one of the outer leeward columns from causes 
 similar to those which produced the fractures found in other columns shortly before the accident. 
 
 “ Sir T. Bouch states it to be his opinion that the accident was occasioned by the over¬ 
 turning of the second-class carriage and the van behind it by the force of the wind, that they 
 were canted over against the girder, and that the force of the blow given by these vehicles, at 
 the speed at which they were travelling, was sufficient to destroy portions of the girders, and so 
 occasioned the fall. But in this opinion the Court did not concur, nor did they consider it 
 supported by the evidence of the engineers, who were called on the part of the railway 
 company, Sir T. Bouch, and the contractors.” 
 
 The Report then gives the conclusions arrived at by the Court, which are briefly 
 
 as follows:— 
 
THE NEIV TAY BRIDGE. 
 
 12 
 
 “ There was nothing; to indicate any movement or settlement as having taken place in the 
 foundations of the piers which fell. 
 
 “The wrought iron employed was of fair strength, though not of high quality as regards 
 toughness; and the cast iron was also fairly good in strength, but sluggish when melted, and 
 presented difficulty in obtaining sound castings. 
 
 “The girders which have fallen were of sufficient strength, and had been carefully studied 
 in proportioning the several parts to the duty they had to perform. In these girders some 
 imperfections of workmanship were found, but they were not of a character which contributed to 
 the accident, and the fractures found in these girders were, we think, all caused by the fall from 
 the tops of the piers. 
 
 “The iron piers used in place of the brick piers originally contemplated were strong 
 enough for supporting the vertical weight, but were not of a sufficiently substantial character to 
 sustain, at so great a height, girders of such magnitude as those which fell. That the cross¬ 
 bracing and its fastenings were too weak to resist the lateral action of heavy gales of wind.” 
 
 The Report then referred to the workmanship of the several parts, comprising 
 the piers, and the supervision during construction and after completion, stating that 
 these were not of a satisfactory character. 
 
 The Report then concludes as follows :— 
 
 “That the fall of the bridge was occasioned by the insufficiency of the cross-bracings, and 
 their fastenings, to sustain the foi’ce of the gale on the night of December 28th, 1879, and that 
 the bridge had been previously strained by other gales. 
 
 “ That although the general bearing of the evidence indicates the cross-bracing as being 
 the first part to yield, yet it is possible that the fall of the bridge may have been occasioned by 
 a fracture, or partial fracture, in one of the outward leeward columns, produced by causes 
 analogous to those which fractured other columns shortly before the accident. 
 
 ****** 
 
 “ That the first or southern set of continuous girders, covering five spans, was the first 
 that fell after the engine and part of the train had passed over the fourth pier, and that the 
 two consecutive sets of continuous girders, each covering four spans, were in succession pulled 
 off the piers on which their northern ends rested, by the action of the first set of continuous 
 girders falling over, and probably breaking some of the supporting columns. 
 
 “ That the extent of the work which fell must be attributed to the employment of long 
 continuous girders, supported by piers, built up of a series of cast-iron columns of the 
 dimensions used. 
 
 ****** 
 
 “ In conclusion, we have to state that there is no requirement issued by the Board of 
 Trade respecting wind-pressure, and there does not appear to be any understood rule in the 
 engineering profession regarding wind-pressure in railway structures; and we therefore re¬ 
 commend that the Board of Trade should take such steps as may be necessary for the 
 establishment of rules for that purpose. 
 
 “ We also recommend, before any steps are taken for the reconstruction of the Tay Bridge, 
 that a careful examination should be made of those parts of the structure left standing, espe¬ 
 cially as regards the piers, with a view to ensuring such alterations and amendments as may be 
 necessary to give to these portions of the work complete stability.” 
 
THE NEW TAY BRIDGE. 
 
 THE HISTORY OF THE NEW BRIDGE. 
 
 Although the old bridge had been only in existence for so short a time, yet it 
 proved the necessity to the company and the public of railway communication across 
 the Tay. Accordingly the North British Railway Company determined to restore 
 this communication as soon as possible, and accordingly made application to bring in 
 a Bill in the Session of 1880 to enable them to restore the old bridge, a scheme for 
 this having been prepared by Sir James Brunlees; for this purpose the Standing- 
 Orders of the House had to be suspended, and this having been allowed, the Bill 
 was remitted to a Select Committee of seven members, with the following special 
 instructions from the House of Commons:— 
 
 “ That they have the power to inquire and report as to whether the Tay Bridge should be 
 rebuilt in its present position, or whether there is any situation more suitable, having due 
 regard to the safety of the travelling public and the convenience of the locality. 
 
 “ That their special attention be directed to the interests of the navigation, and that the 
 height of the bridge shall be so fixed as not injuriously to interfere with the river navigation. 
 
 “ That they shall consider generally in what way the bridge that may be authorised 
 should be constructed so as to secure its permanent safety.” 
 
 Th is Committee after a long inquiry agreed to the following Report 
 
 “ 1. The Committee have been placed in an unusual and difficult position by the withdrawal 
 
 of all independent opposition to the Bill. 
 
 *#■*-*#* 
 
 “ 2. Having carefully considered the details of the scheme proposed by the Bill, as well as 
 the evidence which has been adduced by the promoters, they have arrived at the following 
 conclusions on the points referred to them :— 
 
 “(1) That the bridge over the river Tay should in the interests of the public and the 
 railway company be reconstructed. 
 
 “ (2) That the present site ol the bridge is on the whole the most suitable. 
 
 “(3) That the reconstruction of the bridge at the lower elevation of 77 feet over four- 
 spans of 245 feet from centre to centre of piers, instead of 88 feet above high 
 water spring tides, will occasion no undue interference with the navigation of 
 the river. 
 
 . ■* . * * * ■* * 
 
 “ -3. The fourth point referred to them, viz., ‘ In what way any bridge that may be 
 authorised should be constructed so as to secure its permanent safety’ has occupied the chief 
 time and attention of the Committee, inasmuch as it involved very serious responsibility ; and 
 after careful consideration they have unanimously come to the decision that they should not he 
 justified in sanctioning the scheme presented to them by the Bill. 
 
 “4. One of the main features of the scheme submitted to the Committee was to secure a 
 wider base for the superstructure by sinking new caissons parallel with those already existing 
 and uniting these foundations by a brick arch, upon which brick piers supporting wrought 
 iron were to be raised. 
 
 “ On considering this scheme, distinct elements of uncertainty immediately suggested 
 
 themselves, viz.: 
 
 “(1) That to raise piers on these foundations was to return to the original design of Sir 
 Thomas Boucli, which he had abandoned as soon as he discovered the real 
 
 * 
 
14 
 
 THE NEIV TAY BRIDGE. 
 
 nature of the strata with which he had to deal, when he substituted iron 
 for brick in order to lighten the weight upon the caissons. 
 
 “ (2) That beyond a general inspection and a concurrence of opinion in their favour, 
 there was no certain evidence that the caissons still occupied their original 
 positions. 
 
 “ (3) That no test had been applied to any of them in order to ascertain whether 
 they would bear the much larger weight per foot of bearing surface that it 
 was proposed by the brick piers to place upon them. 
 
 “It also appeared to the Committee that such a combination of old and new work, 
 especially in such a locality and with such a foundation, was one which essentially required 
 not only most careful consideration, but actual preliminary tests, before it could be with 
 safety decided upon by the railway company, or sanctioned by Parliament. 
 
 “ 5. It clearly appeared from the evidence that some of the existing caissons were not sunk 
 to a sufficient depth, and that a very considerable scour had already taken place in the vicinity 
 of some of them. It had become and still continues necessary from time to time to place large 
 quantities of rubble round them to prevent their being undermined. 
 
 “ G. The Committee are of opinion that the safety of the public might best be consulted by 
 the bridge being rebuilt upon entirely new foundations ; but evidence having been adduced 
 that, subject to certain conditions, by sheet piling or otherwise, the existing caissons might be 
 secured and utilised, this opinion might be open to re-consideration, if hereafter it should be 
 proved that the existing caissons had been thoroughly tested and found trustworthy, or a 
 carefully considered plan brought forward for rendering them secure. 
 
 “ 7. The Committee have no doubt that a bridge properly constructed would resist the 
 lateral pressure of any wind; but they have not taken direct evidence as to wind pressure, as 
 this subject was fully considered before the Court of Inquiry on the Tay Bridge disaster, and is 
 under the consideration of a Committee of the Board of Trade. 
 
 “ 8. No provision for giving any shelter to the train from the wind during its passage 
 over the bridge was included in the scheme before the Committee. This subject they consider 
 most important, and it will no doubt receive the attention of the company’s engineer, in pre¬ 
 paring plans for the reconstruction of the bridge. 
 
 “ 9. The Committee are of opinion that the undertaking given by the promoters to remove 
 the existing railway junction from off the bridge should be embodied in any future scheme, and 
 that the gradient on the north side should be reduced from 1 in 74 to 1 in 101. 
 
 ****** 
 
 On receipt of this decision, the Directors of the North British Bailway 
 Company referred the entire question of reconstruction to Mr. W. H. Barlow, who 
 was requested to report as to the best course to be pursued to effect the restoration 
 of the bridge in such a way as to secure absolute and permanent stability of the 
 structure. It was also decided by the Directors to make the new work for a double 
 line of railway, 
 
 f or this purpose the first step we deemed advisable was to ascertain by careful 
 examination and tests to what extent the old bridge could be utilised in the 
 reconstruction, and for this purpose a series of soundings and sections of the river-bed 
 were taken to learn what had been the effects of the scouring action of the tides in 
 the vicinity of the bridge, and two of the old piers were loaded with weights. 
 
 AVe also considered it necessary to obtain fresh information about the character 
 of the materials composing the river-bed, and for this purpose borings were made at 
 
THE NEW TAY BRIDGE. 
 
 15 
 
 intervals of about every 500 feet in a line parallel to the centre line of the old bridge, and 
 a trial cylinder was sunk in the worst material found by the borings, and then loaded. 
 
 The result of these investigations was as follows:—The soundings and sections 
 of the river-bed showed that the construction of the old Tay Bridge had caused a 
 deepening of the river in the vicinity of the bridge, more especially at those parts 
 where the current of the ebb-tide was strongest. The total area of waterway occupied 
 by the piers amounted to about one-tenth of the total waterway of the river, and it 
 was found that the extent of scour was such as to restore to the river about the same 
 area as that occupied by the piers. 
 
 With regard to the loading two of the old piers, they were loaded with 1500 tons 
 of rails, so that the weight applied, together with the weight of the cutwater and 
 foundations amounted to 3'G tons per square foot gross, or, deducting the weight of 
 sand and water displaced, was equal to a net increase of pressure of 2'87 tons per 
 square foot. One of these piers was in clean sand, and the settlement was only 
 quarter inch; the other was in tine micaceous sand, and the settlement was a little 
 over two inches 
 
 The borings showed that on and near the shores on the north and south sides of 
 the river, the material was whinstone, while from the south shore for 900 feet it was 
 sandstone rock. Beyond the rock on both sides, very tough boulder clay extended 
 for about another 900 feet, and between these points the material was mainly 
 micaceous sand mixed in some parts with a small quantity of clay, forming what was 
 termed “ silty sand,” which exceeded 70 feet in thickness. 
 
 The trial cylinder was sunk (by means of the pneumatic process) in that part of 
 the river-bed where the borings showed the worst material, “ the silty sand,” to a 
 depth of 20 feet. A bottom of concrete having been put in, it was loaded until a 
 gross weight of 7 tons per square foot (equal to 5f tons net weight) was reached. 
 This produced a settlement of 5i inches, which did not increase, although the weight 
 was kept on for three and a half months. 
 
 In the meantime comparative designs and estimates were prepared for the 
 following ways of dealing with the reconstruction. 
 
 1. By Avideniiig* the bridge on one side : 
 
 J O O 
 
 2. By widening it on both sides; 
 
 3. By constructing a new single-line bridge parallel to the old, and bracing the 
 two structures together ; and 
 
 4. By constructing an independent bridge. 
 
 The results of these investigations and preliminary tests were, that it was 
 ascertained that if the piers of the old bridge were to be utilised, protection works 
 would have to be constructed in connection with the old foundations, and that owing 
 to their various forms, these works would be of great difficulty and complexity ; that 
 their upper parts (the cast-iron columns) would have to be replaced by structures of 
 different materials, and finally that it was not advisable to increase the weight on the 
 old foundations. 
 
 Taking all these facts into consideration, we advised the directors to adopt the 
 fourth alternative, viz. to construct an independent bridge, and utilise in it only the 
 girders of the standing portions of the old bridge, which, after careful examination, 
 
lf> 
 
 THE NEIV TAY BRIDGE. 
 
 had been found to be in good condition. We also recommended that the new work 
 should be close to the old, so that the old girders might the more easily be transferred, 
 and the old bridge be used as a means of communication for men and material during 
 the construction of the new bridge. 
 
 The directors having concurred in this view, the necessary plans were deposited 
 in November, 1880. 
 
 After the depositing of these plans, and before this Bill was considered in 
 committee, a strong representation was made to the company that the public feeling, 
 as regards the safety of the new bridge, would not be satisfied unless it was rebuilt at 
 a lower level. The company, anxious to do all in its power to restore public 
 confidence, acceded to this expression of opinion, and accordingly plans were 
 prepared for constructing the new bridge at a considerably reduced elevation, and 
 application was made to Parliament that the Standing Orders might be dispensed 
 with in order to allow these to be deposited ; this, however, was refused; thereupon 
 the company decided to proceed with the Bill which they had deposited. This Bill 
 was considered in Committee, when Mr. W. H. Barlow explained how he had met 
 the various points raised in the Report of the Select Committee on the first 
 restoration scheme. Sir J. Hawkshaw, Sir C. H. Gregory, and Mr. Galbraith gave 
 evidence in approval of the design, and after hearing the opposition of the Perth 
 traders, the Committee decided that the preamble was proved, and the Bill obtained 
 the Royal assent in July, 1881. 
 
 This Act, which was called “ The New Tay Viaduct Act,” contains two clauses 
 concerning which it is necessary to say a few words. 
 
 'fhe first is as follows :— 
 
 “ Every cylinder foundation of the piers of the viaduct shall be properly tested 
 to at least 33 per centum above the maximum weight to which it will be subjected 
 and to the satisfaction of the Board of Trade.” 
 
 This provision was inserted on account of Mr. Barlow having stated in his 
 evidence that he proposed to test every cylinder foundation. The Committee 
 considered it advisable to make this testing compulsory, and to make the Board of 
 Trade responsible for carrying it out. 
 
 T he other clause relates to the disposal of the old bridge, and is as follows :— 
 
 “The company shall remove the ruins and debris of the old bridge and all 
 obstructions interfering with the navigation caused by the old bridge, to the 
 satisfaction of the Board of Trade. 
 
 fhe peculiar wording of this clause led to considerable delay in the commence¬ 
 ment of the work. In preparing the contract for the new bridge, the arrangements 
 (in consequence of a correspondence with the Board of Trade) were based on the 
 assumption that they would permit the old bridge to remain up during the 
 construction of the new. This was a special feature in the design, because by so 
 doing the old bridge could be used as a staging during construction, and afterwards 
 the girders would be in a position to be transferred over to the new bridge when the 
 piers of it were ready. 
 
 When however the arrangements with regard to the contract were almost 
 
 O CJ 
 
 complete, the Board of Trade stated to the company that they were not at liberty (by 
 
THE NEIV TAY BRIDGE. 
 
 17 
 
 their reading of the clause) to dispense with the removal of the old bridge entirely, 
 and intimated that they could not consent to the commencing of the works until the 
 old bridge was removed. This unexpected decision stopped all proceedings for a 
 time. At length, after much correspondence and many discussions, the Board of 
 Trade gave permission for the works to proceed, on the company giving an 
 undertaking that they would apply to Parliament as soon as possible for an Act to 
 give the board the discretionary powers requisite with regard to the old bridge. The 
 contract was then finally completed and the works proceeded with. 
 
 It may as well be mentioned here that, in 1885, in pursuance of the undertaking 
 given, the company went for and after much difficulty obtained powers to leave in 
 the cutwaters of all the piers of the old bridge in the navigable channel except 
 five, which were to be removed to 15 feet below low water. 
 
 However, at the inspection by the Board of Trade in 1887, previous to the 
 opening of the new bridge, the inspectors reported that it was very undesirable that 
 these five piers should be removed; so the company this year (1888) again, after 
 some difficulty, obtained powers to enable them to leave them in. So, as the matter 
 now stands, the cutwaters of all the piers of the old bridge, along the straight portion 
 of it, are left in. 
 
 GENERAL DESCRIPTION OF THE BRIDGE. 
 
 The new Tay Bridge is 10,711 feet in length; ot‘ this 839(3 feet is in a straight 
 line, in a nearly north and south direction, and parallel to the old bridge, the centre 
 line of the new being 60 feet distant from that of the old. 
 
 At its northern end, the direction of the centre line is brought by means of a 
 curve of 21 chains radius in an easterly direction, into a line nearly parallel to the 
 river; and at the extreme north end of the curve the centre line of the new bridge is 
 thus made identical with that of the old. The object of the straight portion is to 
 make the crossing of the river as short as possible, whilst that of the curve is to bring 
 the line of railway into a direction suitable for the arrangements at the station at 
 Dundee (see Photo. I.). 
 
 The bridge consists of an abutment at the south end and 85 piers, and for 
 convenience of reference the piers are numbered consecutively 1 to 85, commencing 
 at the south end. 
 
 The height above high water and the gradients of the railway on the bridge are 
 as follows:—From the south abutment to pier 4 the rails are level, and 83 feet 
 6 inches above high water; between pier 4 and pier 28 there is a slight down 
 gradient of 1 in 762; from pier 28 to pier 32 the rails are 79 feet above high water, 
 and are level; and from this pier to the north end, where the rails are 26 feet 
 6 inches above high water, there is a down gradient of 1 in 113 * 75. (See Plate I. 
 Fig. 1.) 
 
THE NEIV TAY BRIDGE. 
 
 18 
 
 The two ends of the bridge on the south and north foreshores, called respec¬ 
 tively the “ Wormit Arching ” and the “ Esplanade Spans,” being different in their 
 design and manner of construction and erection from the main portion, in conse¬ 
 quence of their being partly on land, will be first briefly described. 
 
 The “ Wormit Arching ” consists of the south abutment and the first four piers. 
 The abutment and first, pier are founded on land, and the remaining three piers on 
 the south foreshore of the river. They are built entirely of brickwork, and on them 
 are four arches, also of brickwork, of 50 feet clear span. The last pier (No. 4) is 
 constructed of greater thickness than the others, as it acts as an abutment at the 
 north end of the arches. 
 
 It will be remembered that the Select Committee on the first restoration scheme 
 recommended that the junction should be removed from off the bridge, but as the 
 configuration of the adjoining country did not permit of this being done, it was 
 decided to construct this part of the bridge of arching on solid brick piers, so that 
 the junction could be made on it (see Photo. II.). On account of this, this arching 
 is constructed wider at its southern than northern end, the width between the para¬ 
 pets at the south end being 114 feet, and at the north 24 feet, the normal width of 
 the bridge; the first two arches consequently are considerably wider on their 
 southern than on their northern sides, and in order to equalise the pressure on the 
 two sides, hollow spaces with small relieving arches are built on the south side of 
 each arch. 
 
 The “Esplanade Spans” are so called because three of them cross an existing 
 esplanade and proposed extension of the same, which is situated along the north 
 shore of the River Tay at Dundee. They consist of eight spans, six of the piers of 
 which are founded on the foreshore of the river between high and low water marks, 
 
 o 
 
 and the last two on land. The first two spans consist of wrought-iron skew arches 
 on three oblique piers, so made to suit the direction of the proposed esplanade—the 
 two outer ones acting: as abutments to the arches. The next four consist of girders 
 of fib feet lengths, carried on groups of cast-iron columns, founded on granite and 
 brickwork pedestals. This part of the bridge was constructed in this manner to 
 provide accommodation for recreation ground in connection with the esplanade there. 
 The next span consists of a curved top girder of 108 feet in length, on brick piers ; 
 and finally there is a small brick arch, to connect the new work with the brick 
 arching (previously constructed) which carries the railway down to the station yard. 
 
 The main portion of the bridge, over the tidal water, consists of seventy-four 
 spans. The piers of these are founded in the river-bed, and may be said to be 
 entirely sub-aqueous, for although a few of them at the north side are in that 
 part of the river-bed which is dry at low water, yet it was found to be most con¬ 
 venient to deal with them as if they were entirely sub-aqueous, owing to their 
 being so for a greater part of the tides. 
 
 The character of the design is similar throughout, to the extent that it consists of 
 girders supported by piers. At the twenty-four spans at the south end and thirty- 
 seven spans at the north end the girders are underneath the railway, while at the 
 remaining thirteen spans at the centre of the river the girders are above, so as to 
 give the maximum headway for shipping (see Photo. III.)- The bridge maybe said, 
 
THE NEIV TAY BRIDGE . 
 
 19 
 
 therefore, to be divided into three parts— the south, the central, and the north 
 spans. 
 
 As has been already stated, it was decided to utilise the uninjured girders of the 
 old bridge, and consequently the dimensions of the spans of the new bridge are the 
 same as those in the old, and are as follows:— 
 
 At Piers Nos. 
 
 4- 
 
 -5, 
 
 1 
 
 span 
 
 of 
 
 118 
 
 feet. 
 
 99 
 
 99 
 
 5- 
 
 -15, 
 
 10 
 
 spans 
 
 9? 
 
 129 
 
 99 
 
 99 
 
 99 
 
 15- 
 
 -28, 
 
 13 
 
 it 
 
 99 
 
 145 
 
 99 
 
 
 
 28- 
 
 -41, 
 
 (11 
 
 99 
 
 99 
 
 245 
 
 99 
 
 99 
 
 99 
 
 1 9 
 
 99 
 
 99 
 
 227 
 
 99 
 
 99 
 
 99 
 
 41- 
 
 -42, 
 
 1 
 
 span 
 
 99 
 
 1G2 
 
 99 
 
 99 
 
 99 
 
 42- 
 
 -53, 
 
 11 
 
 spans 
 
 99 
 
 129 
 
 99 
 
 99 
 
 99 
 
 53- 
 
 -77, 
 
 24 
 
 ii 
 
 99 
 
 71 
 
 9 9 
 
 99 
 
 99 
 
 77- 
 
 -78, 
 
 1 
 
 span 
 
 99 
 
 56 
 
 99 
 
 It may be here explained that the dimensions of the spans are the distances from 
 centre to centre of the piers. 
 
 DESIGN OF THE PIERS. 
 
 The piers consist of a pair of cylinders, joined together above high water by a 
 horizontal member or connecting piece ; upon these are shafts of octagonal form, 
 united near the top by a semicircular arch, forming what is called the superstructure 
 of the piers see (Photo. IV.). The height and dimensions of the piers vary consider¬ 
 ably, in consequence of the variety of the dimensions of the spans, the gradients, the 
 arrangements of the girders above or below the rails, and the different depths of the 
 girders, and to meet this the piers are divided into three different types. 
 
 Type I. for the piers at the south and north spans, where the girders are 
 below the rails (see Photo. V.). 
 
 Type II. for the piers at the central spans (Nos. 28-41), where the girders are 
 above the rails (see Photo. VI.). 
 
 Type III. for the piers of the small north spans (Nos. 54-77) at the curve. 
 
 At the last twelve of the piers of the third type (Nos. 65-77), the shafts and 
 connecting arches are dispensed with, on account of the smallness of their heights, and 
 their upper part is one rectangular structure supported by the pair of cylinders, thus 
 forming a connecting piece to them, and the horizontal member to the cylinders is 
 omitted. 
 
 Piers 28 and 41, at the junction of the south, central, and north spans, require 
 special arrangements to suit the difference of level of the girders. Also pier 53, on 
 account of the difference of the depth of the girders. These special piers are called 
 junction piers, 
 
20 
 
 THE NEIV TAY BRIDGE. 
 
 The cylinders of the piers, Types I. and IT, consist of brick shafts filled with 
 concrete, founded on wrought iron caissons lined with brickwork and also filled with 
 concrete. These caissons or cylinder foundations are made of larger diameter than 
 the shafts above, to allow of adjustment in case the foundation went out of position, 
 as sometimes occurred during sinking. The cylinders for the piers, Type III. (being 
 of smaller diameter), are constructed of cast iron, lined with brickwork and filled with 
 concrete. 
 
 The bottom part of all the cylinder foundations tapers out, and so makes a larger 
 base to increase their bearing areas. The diameters of the bases of the cylinders vary 
 according to the dimensions of the spans. 
 
 At the spans of 245 and 227 feet the diameters are 23 feet. 
 
 ] | r 
 
 51 15 i O ,, l-i.J ,, ,, ,, 
 
 129 
 
 • • • «| • « • . 
 
 ,i If ,1 
 
 71 
 
 15 
 
 10 
 
 These diameters are arranged so as to give areas of foundations which will not 
 involve a greater pressure than 3| tons to the square foot on the underlying material, 
 this pressure being considered the maximum that should be put upon the silty sand, 
 on which many of the piers are founded. With reference to this, it will be 
 remembered that the trial cylinder was tested to a pressure of 7 tons per square foot; 
 but in that case the load was entirely a dead load, whereas in these one-third (or a 
 little over 1 ton to the foot) is due to the live load, and therefore the less pressure of 
 3^- tons was decided upon. 
 
 Except in a few cases where rock was met with, the foundations are carried down 
 to at least a depth of 20 feet below the lowest part of the river-bed in their proximity, 
 this depth being considered necessary, owing to the scour action which has been 
 referred to. In Types I. and III., the distance apart of the pair of cylinders which 
 constitute each pier is 2(> feet, and in Type II. 32 feet. 
 
 At a level ol 1 loot 6 inches above high water is the horizontal member or 
 connecting piece, of width nearly the same as that of the cylinders, and of a depth of 
 8 feet. The object ot this member is to give strength to the cylinders at a part where 
 they are liable to receive blows from floating masses, such as ice, wreckage, &c. This 
 connecting piece is constructed of cast-iron girders, wrought-iron ties, and brick¬ 
 work, filled with concrete, and the top of it is covered over with a thick layer of 
 cement. 
 
 Above the connecting piece is the superstructure of the pier; this consists of two 
 shafts (one on each cylinder) of octagonal form, constructed of wrought-iron plates 
 riveted on to a framework also of wrought iron. This framework is built up of angle 
 irons at the inside, and channels at the outside of the corners, and tee irons both 
 inside and out at the vertical joints of the plates; in the interior of these shafts, at 
 intervals of from 10 to 13 feet, there are wrought-iron diaphragms and horizontal cross 
 bracings. The bases of the shafts consist of strong frames of channel irons to 
 distribute the weights uniformly over the brick shafts ; these frames are secured by 
 eight wrought-iron holding-down bolts of 2| inches diameter and 20 feet in length, 
 the bottoms of which are anchored down in the brickwork and concrete by cast-iron 
 
THE NEIV FAY BRIDGE. 
 
 21 
 
 plates. The connecting arch at the top of the shafts is constructed of plates, channel, 
 angle, and tee irons in a similar manner as the shafts themselves. 
 
 fhe arrangement for carrying the girders at the top of these superstructures 
 differs considerably at the central spans (Type II.) from that at the spans south and 
 north (Types I. and III.) 
 
 At the central spans, where the girders are above the rails, there arc only two 
 girders, and each is supported directly by one shaft of the superstructure; their 
 weight and that of the rolling load is thus transmitted directly down to the cylinders 
 and foundations. To enable this to be effected, at the top of each shaft are four box 
 girders, two placed in the direction of the girders and nearly under them, and two at 
 right angles ; these carry a steel plate which supports the bearings of the girders; the 
 connecting arch at these piers simply acts as a tie to the shafts at their tops (see 
 
 Plate VI.). 
 
 At the south and north spans (Types I. and IIP), where there are four girders, 
 and where the two intermediate ones, which carry the chief part of the weight, are 
 situated over the connecting arch, the arch acts, to a certain extent, as a girder as 
 well as a tie to the shafts. To effect this, there are at the top of these superstructures 
 four box girders, one under each main girder, and under these, are frameworks of 
 angle irons riveted to the bottom of the box girders, and to the plates of the super¬ 
 structures (see Plate V.). By this means, and by horizontal and vertical cross 
 bracings, and gussets, in the soffit of the arch, the weight of the girders and rolling- 
 load, is transmitted to the shafts, and so to the cylinders and foundations. 
 
 In the case of the piers (Nos. G5-77) where their height is not sufficient to 
 permit of shafts with connecting arches, the superstructure is constructed in the same 
 manner as the upper part of those already described, above the connecting arch, and 
 forms a rectangular structure, similar to a hollow girder, resting on the two cylinders. 
 
 In these superstructures of the piers the plates not only act as bracings to the 
 vertical members of the frameworks, bur also assist in carrying the vertical pressures. 
 Although this arrangement may have the objection of presenting a larger surface to 
 the wind, it is to be borne in mind that the wind can only act on the outside surface, 
 and that there is no second surface for it to act on, as would be the case if they were 
 constructed of open framework. 
 
 The strain on the ironwork of these superstructures, due to vertical pressures, 
 produces no greater stress, on any part of the metal, than 2 2 tons per square inch. 
 
22 
 
 THE NEW TAY BRIDGE. 
 
 DESIGN OF THE GIRDERS, FLOORING, &c. 
 
 The design of the girders for the south and north spans is materially affected by 
 the fact of utilising the girders of the old bridge. A pair of the old girders was 
 available for all these spans except the two extreme end ones (Piers 4-5, and 77-78), 
 but as they were only designed for a single line, and as the new bridge is for double, 
 it was arranged to have two new intermediate girders, to carry the greater part of the 
 weight of each span, so that the old girders should not be loaded fully to their 
 calculated capabilities. 
 
 The new girders for these spans are similar in appearance to the old. They are 
 rectangular, and their top and bottom members are in the form of troughs; the 
 bracing consists of ties formed of flat plates, and struts, built up of plates and angle 
 irons, and between the intersection of the bracings, and the top member, there are 
 also vertical struts. These girders are lb feet in depth, except those for the 71 feet 
 spans, which are only 9 feet deep. 
 
 Another point with regard to the use of the old girders was, that as they were 
 designed as continuous girders for five, and in one case six spans; and as in the new 
 design, it was not considered advisable to have more than four spans continuous, it 
 was necessary to arrange these systems of continuity, so that the new girders would 
 best fit in with the old girders as built, to avoid having to shift (except laterally from 
 one bridge to the other) their positions. 
 
 'file general elevation (see Plate I., fig. 1) shows these systems as arranged, 
 they are as follows : — 
 
 At the 
 
 South 
 
 spans 
 
 between 
 
 Pier> 
 
 4-5 
 
 is a detached span. 
 
 11 
 
 11 
 
 ii 
 
 11 
 
 11 
 
 5-9 
 
 four spans continuous. 
 
 11 
 
 11 
 
 u 
 
 ii 
 
 11 
 
 9-13 
 
 11 
 
 11 
 
 11 
 
 ii 
 
 11 
 
 11 
 
 13-15 
 
 two spans continuous. 
 
 11 
 
 11 
 
 * i 
 
 V 
 
 11 
 
 15-18 
 
 
 11 
 
 11 
 
 11 
 
 11 
 
 ii 
 
 ii 
 
 «• 
 
 11 
 
 11 
 
 18-21 
 
 21-24 
 
 1 4 sets of three spans continuous. 
 
 11 
 
 11 
 
 ii 
 
 
 11 
 
 24-27 ) 
 
 
 11 
 
 11 
 
 ii 
 
 Ii 
 
 11 
 
 27-28 
 
 a detached span. 
 
 11 
 
 North 
 
 ii 
 
 11 
 
 11 
 
 41-42 
 
 11 11 
 
 11 
 
 11 
 
 ii 
 
 11 
 
 11 
 
 42-45 
 
 three spans continuous. 
 
 11 
 
 11 
 
 11 
 
 11 
 
 ii 
 
 ii 
 
 11 
 
 11 
 
 11 
 
 11 
 
 45-49) 
 
 49-53) 
 
 2 sets of four spans continuous. 
 
 1i 
 
 11 
 
 ii 
 
 11 
 
 11 
 
 53-57 
 
 12 sets of two spans continuous. 
 
 11 
 
 11 
 
 ii 
 
 11 
 
 11 
 
 77-78 
 
 a detached span. 
 
 I he four girders, of each of these spans, are connected at their top members by 
 the flooring (described afterwards), and at the bottom, by horizontal bracings, and 
 between them there are also, at intervals, vertical cross bracings. 
 
 At the central spans, where the girders are above the rails, the design is as 
 follows:—• 
 
THE NEIV TAY BRIDGE. 
 
 on 
 
 w * ) 
 
 The bottom members are straight (with the exception of a slight camber), and 
 the top is curved; they are 20 feet high at their ends, and 29 feet at their centres. 
 The top and bottom members are constructed of plates and angle irons in the form of 
 troughs 18 inches deep. The system of bracing is that known as the single triangula¬ 
 tion system, in which the ties consist of flat iron plates, and the vertical struts are 
 each built up of a plate and four channel irons, and the end posts are 4 feet wide. 
 
 Each of these spans is arranged to act as a detached span, although, for purposes 
 of expansion, they are united together in pairs at their bottom members. The 
 girders of each span are transversely connected together at their bottom booms by 
 the flooring, and at their top, by horizontal bracing made of large Tee-irons, and 
 strong frameworks at each end, and by deep vertical frames extending from the top 
 of the girders to 16 feet above the rails at every third strut, and smaller vertical 
 frames in between them. 
 
 The flooring is corrugated in form throughout. At the spans, where there are 
 four girders, it is constructed by plates formed into ridges and hollows, riveted 
 together with a cover plate at their ridges. The distance apart of these ridges and 
 hollows is 2 feet, and the depth of the troughs is 8 inches. At the central spans, 
 where the girders are 25 feet 9 inches apart, the flooring consists of two channel irons, 
 one for the top of the ridge, and the other for the bottom of the trough, and the sides 
 of the troughs are formed by plates riveted to them. The distance apart of the 
 centres of the ridges or troughs is 2 feet 6 inches, and the depth of the troughs is 
 16 inches. 
 
 Th is form of flooring is a very strong one, and has the advantage of distributing 
 the pressure along the top or bottom member of the girders, as the case may be, 
 and besides that it forms a very strong connecting member to the girders. 
 
 With regard to the calculations for the girders it would be going beyond the 
 scope of these lectures to enter into the details by which they were arrived at, more 
 especially as they are girders of the ordinary type and therefore did not require any 
 particular mode of investigation. 
 
 For the purposes of illustration, the calculated stresses in tons produced by the 
 dead and live loads, the sectional area in square inches, and the strains in tons per 
 square inch, in each particular member of the girders are given in two typical 
 cases, viz. a detached 245 foot girder, and a girder and a half of a set of three 
 continuous girders of 145 feet lengths (see pp. 24 and 25). 
 
 The strains in tons per square inch indicate the economic arrangement of the 
 metal; if the metal was only required for the strains produced in the girder by 
 the weight of dead and live loads, its arrangement would be simple. But other 
 questions have to be taken into consideration; one of these is, that the different 
 members of the girders have other functions besides that of weight carrying to 
 perform; for instance, one boom (the bottom in one case and the top in the other) 
 has to carry the flooring, and for this purpose it has to act as a girder between the 
 points where it is connected to the struts and ties, while the other boom has to act 
 as a connecting member between the heavier part of it at the centre and the ends, 
 and also has to connect together the vertical frameworks between the girders. 
 Again, in the ties, the element of vibration from the moving loads, and in the struts, 
 
24 
 
 THE NEW TAY BRIDGE. 
 
 No. in 
 Diagram. 
 
 Strain in 
 Tons. 
 
 Sectional Area. 
 Square Inches. 
 Gross. 
 
 Strain in 
 Tons per 
 Square Inch. 
 
 No. in 
 Diagram. 
 
 Strain in 
 Tons. 
 
 Sectional Area. 
 Square Inches. 
 Net. 
 
 Strain in 
 Tons per 
 Square Inch. 
 
 
 
 Top Boom. 
 
 
 
 
 Bottom Boom. 
 
 
 1 
 
 694 
 
 160-00 
 
 4-34 
 
 1 
 
 694 
 
 142-24 
 
 4-88 
 
 2 
 
 694 
 
 160-00 
 
 4-34 
 
 2 
 
 673 
 
 135-24 
 
 4-97 
 
 3 
 
 690 
 
 160-00 
 
 4-31 
 
 3 
 
 647 
 
 137-74 
 
 4-70 
 
 4 
 
 673 
 
 160-00 
 
 4-20 
 
 4 
 
 608 
 
 130-40 
 
 4-66 
 
 5 
 
 648 
 
 151-60 
 
 4-27 
 
 5 
 
 554 
 
 112-40 
 
 4-93 
 
 6 
 
 610 
 
 154-35 
 
 3-96 
 
 6 
 
 483 
 
 112-40 
 
 4-30 
 
 7 
 
 556 
 
 133-35 
 
 417 
 
 7 
 
 387 
 
 96-67 
 
 4-00 
 
 8 
 
 486 
 
 112-35 
 
 4-32 
 
 8 
 
 261 
 
 59-40 
 
 4-40 
 
 9 
 
 390 
 
 91-35 
 
 4-27 
 
 9 
 
 94 
 
 59-40 
 
 1-58 
 
 10 
 
 265 
 
 70-35 
 
 3-76 
 
 10 
 
 0 
 
 59-40 
 
 •00 
 
 
 
 Struts. 
 
 
 
 
 Ties. 
 
 
 1 
 
 119 
 
 39-00 
 
 3-05 
 
 1 
 
 180 
 
 36-76 
 
 4-89 
 
 2 
 
 91 
 
 39-00 
 
 2-33 
 
 2 
 
 209 
 
 42-00 
 
 4-98 
 
 3 
 
 70 
 
 30-60 
 
 2 • 29 
 
 3 
 
 164 
 
 33-24 
 
 4-93 
 
 4 
 
 51 
 
 30-60 
 
 1-67 
 
 4 
 
 128 
 
 25-50 
 
 5-00 
 
 5 
 
 35 
 
 24-60 
 
 1-42 
 
 5 
 
 100 
 
 21-25 
 
 4-70 
 
 0 
 
 21 
 
 24-60 
 
 •85 
 
 6 
 
 78 
 
 18-75 
 
 4-16 
 
 7 
 
 8 
 
 24-60 
 
 •33 
 
 7 
 
 58 
 
 17-50 
 
 3-31 
 
 8 
 
 5 
 
 22-20 
 
 • 22 
 
 8 
 
 40 
 
 16-25 
 
 2-46 
 
 9 
 
 0 
 
 22-20 
 
 •00 
 
 9 
 
 25 
 
 16-25 
 
 1-54 
 
 
 
 
 
 10 
 
 6 
 
 16-25 
 
 •36 
 
 
 
 
 
 11 
 
 0 
 
 16-25 
 
 •00 
 
 that ot buckling, have to be allowed for, with the result that in all these cases more 
 metal has to be put in them than is required as members of the girders, hence the 
 strains in them per square inch are less. 
 
 Another and very important consideration, and one which has occupied the 
 attention ot engineers since the introduction of wrought iron girders is that as 
 
THE NEIV TAY BRIDGE. 
 
 9 
 
 5 
 
 END SPAN. INTERMEDIATE SPAN. 
 
 1 
 
 2 
 
 3 
 
 4- 
 
 6 
 
 e 
 
 7 
 
 8 
 
 8 
 
 
 ro 
 
 II 
 
 12 
 
 13 
 
 14- 
 
 \ 
 
 
 
 X / 
 
 \9 / 
 
 x. Z* 2 
 
 
 X /' 6 
 
 \ /> 8 
 
 
 I9\/ 
 
 2l\>' 
 
 /\ / 
 
 23\X 
 
 zt\A 
 
 
 
 
 
 
 
 
 
 
 
 UJ 
 
 
 
 X 
 
 
 
 A2 \ 
 
 \ \ 
 
 Ao \ 
 
 A \ 
 
 Ao \ 
 
 
 / '3\ / 
 
 ' 16\ ,/ 
 
 / ,7 \ 
 
 CL 
 
 y/20 \ 
 
 722 ' 
 
 \ 724 \ 
 
 726 \ 
 
 727 \ / 
 
 1 
 
 2 
 
 3 
 
 4- 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 
 10 
 
 II 
 
 12 
 
 13 
 
 14- 
 
 The thick lines show the members in Compression; the thin lines those in Tension. 
 
 No. in 
 Diagram. 
 
 Strain in 
 Tons. 
 
 Sectional Area. 
 Square Inches. 
 
 Strain in 
 Tons per 
 Square Inch. 
 
 No. in 
 Diagram. 
 
 Strain in 
 Tons. 
 
 Sectional Area. 
 Square Inches. 
 
 Strain in 
 Tons per 
 Square Inch. 
 
 
 
 Top Boom. 
 
 
 
 
 Bottom Boom. 
 
 
 1 
 
 40 
 
 32-89 
 
 1-21 
 
 1 
 
 54 
 
 32-89 
 
 1-64 
 
 2 
 
 122 
 
 32 ■ 89 
 
 3-71 
 
 2 
 
 136 
 
 32-89 
 
 4-13 
 
 3 
 
 178 
 
 42-11 
 
 4-23 
 
 3 
 
 192 
 
 42-11 
 
 4-56 
 
 4 
 
 206 
 
 44-28 
 
 4-65 
 
 4 
 
 192 
 
 44-28 
 
 4-33 
 
 5 
 
 208 
 
 44-28 
 
 4-69 
 
 5 
 
 196 
 
 44-28 
 
 4-43 
 
 6 
 
 180 
 
 42-11 
 
 4-27 
 
 6 
 
 196 
 
 42-11 
 
 4 • 65 
 
 7 
 
 124 
 
 32-89 
 
 3-77 
 
 7 
 
 140 
 
 32-89 
 
 4-26 
 
 8 
 
 56 
 
 32-89 
 
 1-70 
 
 8 
 
 56 
 
 32-89 
 
 1-70 
 
 9 
 
 131 
 
 34-59 
 
 3-79 
 
 9 
 
 165 
 
 34-59 
 
 4-77 
 
 Pier 
 
 219 
 
 49-34 
 
 4-44 
 
 Pier 
 
 219 
 
 49-34 
 
 4-44 
 
 10 
 
 138 
 
 32-89 
 
 4-19 
 
 10 
 
 137 
 
 32-89 
 
 4-17 
 
 11 
 
 56 
 
 32-89 
 
 1-70 
 
 11 
 
 56 
 
 32-89 
 
 1-70 
 
 12 
 
 112 
 
 32-89 
 
 3-41 
 
 12 
 
 112 
 
 32-89 
 
 3-41 
 
 13 
 
 140 
 
 32-89 
 
 4-26 
 
 13 
 
 126 
 
 32-89 
 
 3-83 
 
 14 
 
 168 
 
 41-48 
 
 4-50 
 
 14 
 
 168 
 
 41-48 
 
 4-50 
 
 
 
 Struts. 
 
 
 
 
 Ties. 
 
 
 2 
 
 76-7 
 
 21-25 
 
 3-61 
 
 1 
 
 59-4 
 
 12-44 
 
 4-77 
 
 4 
 
 59-4 
 
 16-58 
 
 3-58 
 
 3 
 
 39-6 
 
 9-06 
 
 4-37 
 
 G 
 
 39-2 
 
 13-37 
 
 2-93 
 
 5 
 
 19-8 
 
 7-06 
 
 2-80 
 
 7 
 
 24-0 
 
 13-37 
 
 1-80 
 
 12 
 
 19-8 
 
 8-06 
 
 2-45 
 
 8 
 
 19-8 
 
 13-37 
 
 1-48 
 
 14 
 
 39-6 
 
 11-32 
 
 3-50 
 
 9 
 
 19-8 
 
 13-37 
 
 1-48 
 
 16 
 
 59-4 
 
 13-70 
 
 4-33 
 
 10 
 
 24-0 
 
 13-37 
 
 1-80 
 
 18 
 
 76-0 
 
 17-96 
 
 4-23 
 
 11 
 
 39-6 
 
 13-37 
 
 2-96 
 
 19 
 
 76-0 
 
 15-76 
 
 4-82 
 
 13 
 
 79-2 
 
 16-59 
 
 4-77 
 
 21 
 
 39-6 
 
 12-44 
 
 3-18 
 
 15 
 
 79-2 
 
 24-19 
 
 3-27 
 
 23 
 
 39-6 
 
 9-06 
 
 4-37 
 
 17 
 
 116-3 
 
 24-78 
 
 4-69 
 
 25 
 
 28-0 
 
 7-06 
 
 3-97 
 
 20 
 
 76-7 
 
 24-25 
 
 3-16 
 
 
 
 
 
 22 
 
 79-2 
 
 21-25 
 
 3-72 
 
 
 
 
 
 24 
 
 39-6 
 
 16-58 
 
 LO 
 
 CO 
 
 GO 
 
 
 
 
 
 26 
 
 39-6 
 
 13-42 
 
 2-95 
 
 
 
 
 
 27 
 
 28-0 
 
 13-42 
 
 2-09 
 
 
 
 
 
 II 
 
THE NEJV TAY BRIDGE. 
 
 2(> 
 
 experiments show that a permanent change occurs in iron, on the application of 
 weights, dependent on the amount and rapidity of the application, it is deemed 
 advisable to put less than the maximum Board of Trade strain on those members, or 
 parts of girders, where either the range of stresses is great or alternating, or where 
 they are of rapid application as those due directly to the live load. The central ties 
 in the detached girders, and central ties and struts and parts of the booms of the 
 continuous girders are the parts where the range of the stresses is great or alternating, 
 while the flooring is the part where the strains are due chiefly to the live load, and 
 where impulsive action exists ; accordingly in all these the metal is arranged so that 
 the strains per square inch shall not exceed 4 tons. 
 
 With reference to this question, since Mr. Eaton Hodgkinson, in a report to the 
 British Association in 1837, expressed an opinion that “there is no weight, however 
 small, that will not injure the elasticity of iron,” this subject has been more or less 
 under consideration, bnt, to relate all the investigations that have been made would 
 take much longer than the time at my disposal. I will therefore only mention that 
 a Committee appointed by the British Association in 1885—of which 1 was a 
 member—reported last year (1887) that the attention of the Board of Trade should 
 be called to the effects of the fatigue of metal, from range of stress under repeated 
 loads, also to the dynamic effect and consequent vibratory action caused by the live 
 load, when moving at a considerable velocity, and suggested that the Board should 
 appoint a Commission for the purpose of inquiring into and revising the present 
 “Buies and Recommendations” as applied to iron and steel used in Engineering 
 structures. 
 
 A very ingenious instrument for measuring the actual strain in any member of a 
 structure has been invented by Mr. Strohmeyer ; it consists of two clamps which are 
 fixed at each end of the member whose strain is to be ascertained. A steel wire 
 extends from one clamp to the other, so that its direction is parallel to the member to 
 be investigated ; this wire is fixed rigidly to one clamp, and by a spring to the other; 
 between and near one of the clamps the wire is caused to pass over a roller of small 
 diameter; thus any movement in the longitudinal wire causes this to revolve, and an 
 index attached to it indicates the amount of motion. This instrument measures the 
 relative extension or compression of the member, but, by comparing this measurement 
 with observations taken under circumstances when the strains are known, actual 
 results can be obtained. 
 
 PROVISIONS FOR WIND PRESSURE. 
 
 file provisions for wind pressure naturally were among the chief considerations 
 in preparing the design for this work. Before, however, describing these, I propose 
 to refer to the investigations and Report made by the Committee which was 
 appointed by the Board of Trade immediately after the decision of the Court of 
 
THE NEJF TAY BRIDGE. 
 
 27 
 
 Inquiry was given, and in consequence of the paragraph in it relating to the absence 
 of any rule with regard to wind pressure, on railway structures. 
 
 The gentlemen composing this Committee were, Sir William Armstrong, Mr. 
 W. H. Barlow, Sir John Hawkshaw, Professor Stokes, and Colonel Yolland, R.E. 
 
 Besides considering the question generally they were asked to include, in the 
 scope of their inquiry, the point raised by the 8th paragraph in the Report of the 
 Select Committee of the House of Commons, on the First Restoration Scheme, viz. : 
 that “ No provision for giving any shelter to the train from the wind during its passage 
 over the bridge was included in that scheme.” 
 
 The first step taken was to ascertain from the various observatories in the United 
 Kingdom the greatest pressure of wind recorded since registering instruments had 
 been instituted. It was found that the pressures were measured only at some of them 
 by Osier’s Self-registering Anemometers (the pressure plates being either 2 feet or 
 4 feet square). At others the actual run of the wind in miles was recorded by 
 Robinson’s Self-registering Anemometer, and in these cases, in order to deduce the 
 pressure from the runs of the wind, in any one hour, it was necessary to have recourse 
 to an observatory where both of these sets of quantities had been measured. The 
 Bidston Observatory, near Liverpool, was selected for this purpose, it being very 
 suitable both from the wide range of the velocities and pressures experienced, and 
 from the care and order with which the observations were recorded and published. 
 The results obtained from the records of this observatory showed that for winds of 
 high velocities the pressures are very nearly proportional to the squares of the 
 velocities in every case, and the Committee stated in their Report that, “ in the 
 case of high winds, with which alone we have to deal . . .the empirical formula 
 
 y 2 
 
 = P (where V = maximum run in miles of the wind in any one hour, and 
 100 v J 
 
 P = maximum pressure in pounds on the square foot at any time during the storms 
 to which V refers), represented very fairly the greatest pressure as deduced from 
 the mean velocity for an hour.” 
 
 Using this formula for those stations where the pressure of the wind was not 
 measured direct, the following greatest pressures were obtained at each of the 
 observatories in the United Kingdom ;— 
 
 
 
 Lbs. per 
 
 
 Lbs. per 
 
 
 
 sq. foot. 
 
 
 sq. foot. 
 
 Aberdeen 
 
 
 41* 
 
 Holyhead 
 
 G4* 
 
 Alnwick 
 
 
 62*4* 
 
 Ivew 
 
 27* 
 
 Armagh 
 
 
 27* 
 
 Liverpool (Bidston) 
 
 90 
 
 Birmingham 
 
 
 27 
 
 London . . 
 
 20-2 
 
 Edinburgh 
 
 
 25 
 
 Sandwick 
 
 G5 ’ 6* 
 
 Falmouth 
 
 
 53-3* 
 
 Seaham . . 
 
 4G* 2* 
 
 Glasgow 
 
 
 47 
 
 Stony hurst 
 
 3L4* 
 
 Greenwich 
 
 
 42 
 
 Valentia 
 
 65 • G* 
 
 Halifax . . 
 
 
 30-2* 
 
 Yarmouth 
 
 42'2* 
 
 
 
 * Calculated pressure. 
 
 
THE NEW TAY BRIDGE. 
 
 •_>s 
 
 Inquiries were also made at observatories on the Continent with the following 
 results:— 
 
 Brussels . 
 Flushing . 
 
 Lbs. per 
 sq. foot. 
 
 21-8 
 
 20 
 
 Utrecht . . 
 Paris 
 
 Lbs. per 
 sq. foot 
 
 31 
 
 17 
 
 And lastly, similar information was obtained from India, which was as follows 
 
 Bombay . . 
 Calcutta . . 
 
 Lbs. per 
 sq. foot. 
 
 38 
 
 40 
 
 Dodabetta 
 
 Madras 
 
 Lbs. per 
 sq. foot. 
 
 40 
 
 O Q . Q 
 dd o 
 
 With reference to this information the Committee say that “it will be seen 
 that the wind pressures vary greatly at different stations. This, no doubt, mainly 
 arises from difference of exposure of the stations to the action of the wind, in conse¬ 
 quence of the geographical and local circumstances of their position, but may in 
 some cases be partly caused by differences in the instruments used for measurement. 
 Thus at Glasgow, the highest recorded pressure per square foot is 47 lbs., while 
 at Bidston, near Liverpool, the indicated pressure on one occasion amounted to 
 1)0 lbs., and on another occasion to 80 lbs. The pressures at Bidston seem very 
 abnormal, being much beyond what have been noticed at any of the other stations. 
 The conformation of the ground on which the Bidston Observatory is situated, is 
 such that the velocity of the wind there might be greatly intensified.” 
 
 On account of the great variations in the pressures thus obtained, the Committee 
 thought it expedient to learn from the Railway Companies their experience of wind 
 effect on rolling stock, bearing in mind that “ a wind pressure varying from 30 to 
 40 lbs. per square foot is sufficient to overturn the ordinary carriages that have been 
 in use during the last twenty-five or thirty years.’ 
 
 In reply to these inquiries the Railway Companies reported that in the United 
 Kingdom there had been three cases of portions of trains being overturned by the 
 wind, in India two cases, in New Zealand one, and in France four cases. 
 
 The Committee, after having fully considered the foregoing and other infor¬ 
 mation, drew up a lengthy report; the conclusion of which is as follows :— 
 
 “ We are of opinion that the following rules will sufficientlv meet the cases referred to 
 
 us 
 
 “ (1) That for railway bridges and viaducts a maximum wind pressure of 56 lbs. per 
 square foot should be assumed for the purpose of calculation. 
 
 “ (2) That where the bridge or viaduct is formed of close girders and the tops of such 
 girders are as high or higher than the top of the train passing over the bridge, the total wind 
 pressure upon such bridge or viaduct should be ascertained by applying the full pressure of 
 56 lbs. per square foot to the entire vertical surface of one main girder only. But if the top 
 of a train passing over the bridge is higher than the tops of the main girders, the total wind 
 pressure upon such bridge or viaduct should be ascertained by applying the full pressure of 
 
THE NEW TAY BRIDGE. 
 
 29 
 
 56 lbs. per square foot to the entire vertical surface from the bottom of the main girders to the 
 top of tbe train passing over the bridge. 
 
 “ (3) That where the bridge or viaduct is of the lattice form or of open construction, the 
 wind pressure upon the outer or windward girder should be ascertained by applying the full 
 pressure of 56 lbs. per square foot as if the girder were a close girder, from the level of the 
 rails to the top of the train passing over such bridge or viaduct, and by applying in addition 
 the full pressure of 56 lbs. per square foot to the ascertained vertical area of surface of the iron 
 work of the same girder situated below the level of the rails or above the top of a train 
 passing over such bridge or viaduct. The wind pressure upon the inner or leeward girder or 
 girders should be ascertained by applying a pressure per square foot, to the ascertained vertical 
 area of surface of the iron work of one girder only situated below the level of the rails or 
 above the top of a train passing over the said bridge or viaduct, according to the following- 
 scale, viz.:— 
 
 “(a) If the surface area of the open spaces does not exceed two-thirds of the whole 
 area included within the outline of the girder, the pressure should be taken at 
 28 lbs. per square foot. 
 
 “ ( b) If the surface area of the open spaces lie between two-thirds and three-fourths of 
 the whole area included within the outline of the girder, the pressure should be 
 taken at 42 lbs. per square foot. 
 
 “ ic) If the surface area of the open spaces be greater than three-fourths of the whole 
 area included within the outline of the girder, the pressure should be taken at 
 the full pressure of 56 lbs. per square foot. 
 
 “ (4) That the pressure upon arches and the piers of bridges and viaducts should be 
 ascertained as nearly as possible in conformity with the rules above stated. 
 
 “(5) That in order to ensure a proper margin of safety for bridges and viaducts in 
 respect of the strains caused by wind pressure they should be made of sufficient strength to 
 withstand a strain of four times the amount due to the pressure calculated by the foregoing- 
 rules. And that for cases where the tendency of the wind to overturn structures is counter¬ 
 acted by gravity alone, a factor of safety of 2 will be sufficient. 
 
 “ With regard to the eighth paragraph of the report of the Select Committee on the North 
 British Railway (Tay Bridge) Bill, to which our attention has been drawn, we beg to observe 
 that where trains run between girders they will generally be sufficiently protected from the 
 wind, the degree of protection afforded by the girders depending upon the extent to which the 
 girders are open or close ; where the girders are so open as to afford insufficient protection, or 
 where trains run as in some cases they may do, on the tops of girders, we assume that the 
 engineer will provide a sufficient parapet, but wo are indisposed to go further into details 
 on this subject, as it might tend to stereotype modes of construction, which we think is 
 undesirable.” 
 
 As a sequence to this report the Board of Trade inserted in the Requirements 
 for railway structures the following rule :— 
 
 “ In all large structures the stability of the work must be such as will provide for a wind 
 pressure of 56 lbs. on the square foot.” 
 
 In providing for wind pressure in the New Bridge the widths of the piers were 
 arranged so that the overturning point should be sufficiently distant from their centres 
 and line of action of gravity, in order that the lateral action of the wind should be 
 more than counterbalanced. 
 
 i 
 
30 
 
 THE NEIV TAY BRIDGE. 
 
 To show this two diagrams are given, one showing the wind and gravity effects 
 at the central spans, and the other at the south spans, where the rails are at their 
 highest point above high water, and where, therefore, the wind action is the greatest. 
 In each case, the worst condition is considered, viz: when a train consisting of 
 empty passenger carriages is on the leeward line of rails. 
 
 i 
 
 Foot-tons. Foot-tons. 
 
 Of Girders, &c. . . . . . . . . . . 13,794 
 
 Of Train. 1,047 
 
 -15,441 
 
 Wind effect. 
 
 On Train, &c. 
 
 4,050 
 
 
 On Girder 
 
 0,517 
 
 
 On Superstructure of Pier 
 
 018 
 
 11,185 
 
 Balance in favour of Gravity effect 
 
 
 4,250 
 
 Add resistance of Holding-down Bolts . . 
 
 
 6,800 
 
 Total margin of Safety . . 
 
 
 11,110 
 
THE NEIV TAY BRIDGE. 
 
 31 
 
 Of Girders . 5,048 
 
 Of Train . . . . . . . . . . . . 750 
 
 - 0,404 
 
 Wind effect. 
 
 On Train . . *. 3,344 
 
 On Girder . 2,453 
 
 On Superstructure of Pier . . . . . . 342 
 
 -0,130 
 
 Balance in favour of Gravity effect . . . . 205 
 
 Add resistance of Holding-down Bolts . . 4,770 
 
 Total margin of Safety . . . . . . . . 5,035 
 
 It will be seen that these calculations are made on the basis of a .5(5 lb. pressure 
 and in the case of the part of the girders which is above the train at the central 
 spans, and below at the south spans, an extra allowance is made of 28 lbs. for the 
 inner, or leeward, surface, also in estimating the vertical area of the superstructure of 
 the piers, the side of the octagonal shaft is assumed to be a square surface. These 
 
32 
 
 THE NElV TA Y BRIDGE. 
 
 calculations show that in the first case there is a balance in favour of gravity of 4,256 
 foot-tons; besides this there are the holding-down bolts which give an additional 
 amount of 6860 foot-tons, the total result therefore being that there is 11,116 foot-tons 
 as margin of safety against overturning with a wind pressure of 56 lbs. per square foot. 
 
 In the second case, at the south spans, the result is that the balance in favour of 
 gravity effect, is 265 foot-tons; and the total margin of safety, when including the 
 resistance of the holding down bolts, is 5035 foot-tons. 
 
 With regard to providing shelter for the train, the trains which pass over the bridge 
 have also to travel on the top of high embankments, where they are exposed to the 
 full force of the wind, and after considering the information, obtained by the Wind 
 Committee, the conclusion arrived at was, that if the upward action of the wind was 
 checked, the train would be as secure on the bridge as on any other part of the 
 railway, and for this purpose, the parapet is designed. It is 5 feet high above the 
 rail level, this height being so fixed to prevent the wind from impinging against the 
 bottom of the carriages. It is constructed of lattice bars of wrought iron, 3 inches 
 broad and 11 inches apart, and is supported at intervals by standards riveted on to 
 the top members of the girders. At the central spans, this same parapet is fixed 
 between the vertical struts of the girders. 
 
 This open lattice work completely checks the action of the wind by breaking it 
 up. There have been recently erected in New Zealand, wind screens on a similar 
 principle on the very exposed railway over the Rimutaka Range in the North Island, 
 the one on which an accident (referred to by the Wind Committee) happened. It is 
 7 feet high, and consists of strong strips of wood with spaces between, and it is said 
 to act very effectuallv. 
 
 PERMANENT WAY AND SAFETY GUARDS. 
 
 The Permanent Way consists of rails, chairs and cross sleepers, bedded in 
 ballast composed of broken slag and cinders. 
 
 There are many advantages in this character of road ; the ballast distributes the 
 weight of the rolling load over a larger surface and to a great extent deadens the 
 impulsive action. It also enables the permanent way to be easier adjusted for line 
 and level, and, compared to a permanent way which is fixed to the flooring itself it 
 is far preferable, because it allows of the expansion and contraction of the road to be 
 dealt with independently to that of the girders. 
 
 l'he corrugated form of the flooring is especially favourable to this kind of 
 roadway, for the sleepers are bedded in ballast in each of the troughs, and the ridges 
 prevent a needless amount of ballast, which would be extra weight to be carried by 
 the girders. 
 
 Between the outer rails and the parapets are fixed Safety Guards; these are 
 considered necessary on long bridges or viaducts, to prevent a vehicle or even a train 
 (should it leave the rails), from either wrecking itself by running over the side of the 
 
THE NEW THY BRIDGE . 
 
 ») ‘> 
 DO 
 
 bridge, or wrecking the structure (as was suggested to have happened by Sir T. 
 Bouch on the old l ay Bridge) by impinging against, and so destroying the girders 
 on which it is passing. Guard rails which have hitherto been used are objected 
 to, because there have been cases where pieces of iron have fallen from a train, and 
 by lying across the rail and guard, have thrown the train off, and so caused the 
 very mischief which they are intended to prevent. The idea of the safety guards 
 (it is supposed) has been obtained from the wooden trellis bridges in the United 
 States, where wooden baulks of timber were laid just outside the permanent way 
 rails, to prevent a “ de-railed ” train or vehicle coming in contact with the trellis work. 
 
 The safety guard on this bridge consists of baulks of timber 18 inches by b 
 inches which are bolted on to the corrugated flooring between the outer rail and 
 the parapet, or the girder, as the case may be. The upper corner of this baulk, 
 next to the permanent way, is protected by an angle iron, and between the baulks 
 and the parapet or girder, are struts at intervals of about 9 feet. 
 
 It may be here mentioned that behind this baulk on one side, is a steel water 
 pipe 9 inches in diameter, and on the other an iron pipe for telegraph wires. 
 These are boarded over by 3-inch planks, and this arrangement affords a convenient 
 footpath on each side of the bridge from end to end. 
 
 ARRANGEMENTS FOR VARIATION OF TEMPERATURE. 
 
 In a metallic structure of so great a length, it is necessary that efficient provision 
 should be made for alteration of length due to variations of temperature. 
 
 Such provision is made at about every 500 feet in length. The girders are 
 fixed to two or three piers, dependent on the number of continuous spans, and 
 are supported at the other pier or piers by rocker bearings. 
 
 At the south and north spans the rocker bearings are at each end of the sets 
 of continuous spans, while at the central spans, where the girders are arranged 
 in pairs as already described, the rocker bearings are at one end of the pair. The 
 position of the rocker bearings is shown on the General Elevation by the letter R 
 (see Plate I., fig. 1). 
 
 The fixed bearings consist of a substantial steel casting, and at those places 
 where provision has to be made for alteration of length, a bearing of cast steel of less 
 height than the fixed bearing is placed, and between this and the underside of the 
 girders are a set of rockers of hardened cast steel, the curved surfaces of which are 
 turned. At the end of each of these rockers there are two pins, which fit into two 
 wrought iron frames, the object of this arrangement being, that all the rockers should 
 turn together, when they are in action. At the central spans these bearings are 
 4 feet 2 inches long and 3 feet 9 inches wide, the rockers being 3 feet 6 inches long, 
 8 inches deep, and eight in number. At the end spans the bearings and rockers are 
 constructed in a similar manner, but their dimensions arc smaller, to suit the lesser 
 dimensions of the spans. 
 
THE NEW THY BRIDGE. 
 
 54 
 
 The variations in length and temperature have been observed since the completion 
 of the bridge for a period of twelve months by Mr. Kelsey, the Resident Engineer, 
 at one of the rocker bearings, and the result was, that in a length of 516 feet 
 of the structure, the variation was 1*65 inches during a range of temperature 
 of 55 degrees. 
 
 In the permanent way, also, provision was made for the variation of length, and 
 this was effected by means of fished expansion joints. These joints are placed ill 
 the permanent way over the expansion joints in the girders. 
 
 The choice of the colour of the bridge was a subject of some consideration 
 also, on account of its known effect on the temperature of the structure. General 
 Hutchinson, in his report after the inspection of the old Tay Bridge, recommended 
 that the girders should be painted white, to reduce as much as possible the variation 
 of length due to difference of temperature. In the old bridge, the longitudinal part 
 of the flooring was of timber, whereas in the new structure, the flooring is entirely of 
 metal; hence variation of length is chiefly due to it, and as this could not be white, 
 or even of a light colour, it was deemed advisable to have the girders of a dark 
 colour, so that equality of action of temperature should take place in the lower and 
 upper portions of the girders, so as to avoid, as far as possible, the setting up of 
 vertical deflections. 
 
 The colour selected was a red brown, approaching to a chocolate. The exterior 
 surface of the superstructure of the piers is painted also with the same shade of 
 colour, for the sake of uniformity, but their interiors are painted white to facilitate 
 their inspection. 
 
 MATERIALS USED IN CONSTRUCTION. 
 
 The quality of the chief materials used in the construction of the bridge was 
 defined in the Specification to be as follows:— 
 
 The Wrought Iron to be capable of bearing a tensile strain of 22 tons per square 
 inch, and of extending 6-j per cent, of its length without fracture. 
 
 The Steel to bear not less than 27 tons to the inch, and to have an elongation 
 of not less than 15 per cent, without fracture. 
 
 The Cement to be Portland cement of the best quality, ground so fine that the 
 residue on a sieve of 5800 meshes to the square inch (equal to about 76 per lineal 
 inch) shall not exceed 10 per cent, by weight. The cement for testing is to be 
 gauged with three times its weight of dry sand, which has been passed through a 
 sieve of 400, and has been retained upon one of 900 meshes to the square inch. The 
 cement and sand having been well mixed dry, about 10 per cent, of their weight of 
 water is to be added, and briquettes formed in moulds approved by the engineers. 
 The briquettes, having in the meantime been kept in a damp atmosphere, are to be 
 put into water 24 hours after they have been made, and remain in water 28 days ; 
 they must then bear without breaking, a weight of 170 lbs. per square inch. 
 
THE NEIV TAY BRIDGE. 
 
 35 
 
 A special staff also was appointed, whose sole duty was to see that the require¬ 
 ments of the Specification with regard to quality of materials were rigorously carried 
 out. 
 
 The quantities of the more important materials utilised in the construction of the 
 whole of the bridge were as follows:— 
 
 Cement concrete 
 Brickwork 
 
 Cast iron in cylinders, &c. 
 
 W rought ironwork in cylinders and superstruc¬ 
 tures of piers 
 
 Wrought ironwork in girders, parapets, &c. 
 
 Steel work in flooring, &c. 
 
 37,024 cubic yards. 
 20,419 
 2,705 tons 
 
 7,626 tons. 
 13,452 „ 
 
 3,588 „ 
 
 With regard to the use of steel, this material was used chiefly in the flooring, 
 where, on account of its corrugated form, better results were produced by its 
 adoption. 
 
 DESCRIPTION OF CONSTRUCTION. 
 
 The contract of the construction and erection of the whole bridge was let to 
 Messrs. Wm, Arrol & Co., of Glasgow. 
 
 In the following description of the mode of carrying out the works. I am in¬ 
 debted to Mr. Inglis (Messrs. Arrol’s Resident Engineer) for the details of the plant 
 uesd. 
 
 The sinking of the cylinders was accomplished by means of pontoons (four in 
 number), each of which were composed of five watertight tanks (see Photo. VII.), 
 two long lateral tanks being connected by three short ones, the intervening spaces 
 being left open. Through the open spaces, or wells, the cylinders were sunk. For 
 supporting these pontoons, columns or legs were passed through the apertures at their 
 corners, the extremities of which rested on the river bed, and the shafts of which were 
 fitted with pin-holes, by which the height of the platform could be regulated. The 
 apparatus on each pontoon was an engine and boiler for actuating the hydraulic and 
 other pumps, workshops for the repair of tools, three cranes, a concrete-mixer, and a 
 centrifugal pump. The platform was raised or lowered by hydraulic apparatus. 
 When the pontoon was to be floated from one pier to another, it was lowered to 
 catch the tide two hours before high-water. Ropes were carried from one side of the 
 pontoon to the piers of the old bridge, and to three heavy anchors on the other. 
 The steam-crane was used as a winch, and when the pontoon had been brought to its 
 new position, the legs were lowered down and fixed. 
 
 d'lie foundation cylinders were riveted together on shore, and conveyed in 
 convenient lengths by cargo-boats to the pontoons. The various lengths were lifted 
 
THE NEJV TAY BRIDGE. 
 
 *>() 
 
 from the boats on to the pontoon, and placed inside the well-holes. Each added 
 length, as it was placed in the well-hole by the crane, was bolted through an internal 
 flange to the preceding one. These were finally lined with brickwork in the upper 
 portion, and gradually lowered to the bed of the river by hydraulic jacks. 
 
 The excavation within the cylinder foundations was accomplished for the most 
 part by steel diggers of the Milroy pattern. This implement, however, was found 
 ineffectual where silty sand had to be lifted, and another process was successfully 
 adopted. Two flexible hose pipes, each 6 inches in diameter and 20 feet in length, 
 were placed in the bottom of the cylinder, the ends being brought together and joined 
 into one 12-inch pipe leading to the pump on the pontoon. A diver was then sent 
 down, who manipulated the suction-pipes, so that, whilst the one threw up sand, the 
 other kept the pump free, by drawing clean water only. In this way as much as 
 40 cubic yards were pumped up in an hour, causing a subsidence of over 2 feet in 
 the cylinder. 
 
 The cylinders having reached the proper depth, and the interior having been 
 cleaned out to the cutting-edge, the concrete was then put in. Tipping measure- 
 boxes, filled with gravel and the necessary proportion of cement, were lifted to a 
 staging erected above the concrete-mixer. The revolving casing of the mixer was 
 
 O o o o 
 
 square in section, thus ensuring more thorough mixing. The receiving-boxes were 
 fitted with hinged hopper bottoms, so that, when lowered into the cylinder, the 
 concrete was deposited on touching the material already in position. When the 
 concrete was level with the flange carrying the brickwork, the diver packed it care¬ 
 fully underneath. 
 
 After the cylinders were completed to low-water level, they were tested in 
 accordance with the clause of the Act (which has been already referred to), and levels 
 were taken and recorded previous to this load being applied, and afterwards, until 
 all subsidence had ceased, and these levels being checked personally by Major 
 Marindin, R.E., for the Board of Trade. 
 
 The test weighting of the cylinder foundations was effected by means of cast- 
 iron blocks, each weighing half-a-ton, which were piled upon the tops of the cylinders. 
 The weight on the cylinders varied according to the spans and the consequent load 
 which would be brought upon them ; but each was subjected to a weight 33 per cent, 
 above that which it was eventually required to carry, assuming each line of rails to 
 be covered with engines. 
 
 The average weight gross imposed per square foot of foundation was 5 * 3 tons, 
 the greatest weight of 6 • 8 tons being in the case of Pier No. 20, and the least of 
 3'8 tons being in the case of Pier No. 53, which was upon the most northern of the 
 15 feet cylinders, which carried one end of the first of the 71 feet girders, so that it 
 was the least heavily weighted pier in the Viaduct. 
 
 The average amount of subsidence measured was 1 ' 37 inch, being the same 
 for both the east and west set of cylinders. The greatest amount of subsidence was 
 in the case of the west cylinder of Pier No. 62, in which it was 7'02 inches, the 
 amount for the east cylinder of the same pier being only 6 * 84 inches. The least 
 amount of subsidence was in the case of Pier No. 6, the 15 feet cylinders of which 
 were sunk to the red sandstone, and which, under a weight of 5 • 4 tons per square 
 
THE NEIV TAY BRIDGE. 
 
 37 
 
 foot, did not subside at all. As a rule the greatest subsidences were in the 10 feet 
 cylinders for the Piers Type III; in the whole bridge there were only 17 cylinders 
 (out of the 146 which were tested) which subsided as much as 3 inches. 
 
 It may be mentioned that after the weights were taken off, there was a rebound 
 in most cases, which seemed to vary with the nature of the strata. The amount of 
 this varied from g- to g- of an inch. 
 
 The labour of carrying out these testing operations was very considerable, each 
 of the 14 largest piers having to carry a test weight of from 2,201 tons to 2,438 tons, 
 the total amount of weights, which had to be shifted for the whole of the foundations, 
 being no less than 94,122 tons. 
 
 When the cylinder-foundations of the piers had been tested, temporary wrought 
 iron caissons were attached to them, and the bottom framework of the wrought iron 
 superstructures of the piers, with the holding-down bolts being temporarily put in 
 position, the brickwork of the shafts of the cylinders and connecting-piece, and the 
 concrete filling, was built up to its level, the last part of the work being executed by 
 the process known as underpinning (see Photo. VIII.). 
 
 The superstructures of the piers were constructed at Glasgow in sections, so that 
 they might be taken apart, and conveyed easily to the Tay. Each pair of shafts 
 with the connecting arch was temporarily erected at the works at Glasgow, partially 
 riveted, and the various parts marked, to facilitate re-erection at the bridge. By 
 this process the operations at the bridge were greatly simplified, as each part was 
 merely taken to its position and riveted in its appointed place. 
 
 The superstructures of the piers at the south spans were erected from one of 
 the movable pontoons just described, but from which all the heavy cranes had been 
 removed, and a 5-ton steam derrick substituted (see Photo. IX.). This crane had a 
 jib sufficient in height to allow of the erection of the whole pier. The pontoon was 
 floated alongside the new pier, and the different sections of the superstructure were 
 conveyed out by cargo boats. 
 
 On the north side of the river the superstructures were not so high owing to 
 the gradient of the bridge. These were brought out and erected from boats having- 
 special derrick-cranes on board (see Photo. X.). Owing to the shallowness of the 
 water on the sandbanks, this operation had to be executed very expeditiously, the 
 greater part of the superstructure of a pier being erected during portions of three 
 tides, or a total of 12 working hours. The riveting was done afterwards, and was 
 accomplished on a staging consisting of two light lattice girders, one on each side 
 of the pier, on which planks were laid. This platform was suspended with chains 
 from two special winches resting on the top of the superstructure. The power for 
 lowering or raising these was obtained by a ratchet and worm wheel attached to 
 drums. This staging was also used for painting the superstructure. Communication 
 to these platforms was obtained from the roadway on the old bridge by means of 
 a light gangway between it and the new bridge. 
 
 At the central spans the superstructures were erected in a similar manner, but 
 after the girders were floated out and placed on the cylinders of the piers, and will 
 be described later on. 
 
 The method of constructing and erecting the girders of the south and north 
 
 L 
 
THE NEW TAY BRIDGE. 
 
 :>s 
 
 spans differed materially from that employed at the central spans, on account of the 
 utilisation of the old girders. 
 
 At the former, as soon as the superstructures of the piers were ready for the 
 girders, the girders of the old bridge (which up to this time had served to take out 
 men and materials to the various parts of the work) were shifted over laterally from 
 the old to the new piers. Each pair of girders with its cross bracing was moved over 
 complete, and on them rails were laid, so that the two new girders could be brought 
 out, and lowered in between them. 
 
 The old girders were transferred to the new piers, by floating them upon two large 
 iron pontoons, stiffened laterally by lattice girders and watertight bulkheads. These 
 were bound together by girders, upon which lattice columns were erected, fitted with 
 telescopic portions, that could be adjusted to any required height (see Photo. XI.). 
 The pontoons were floated at low water underneath the girders to be removed, and 
 as the tide rose the telescopic portions were pushed up and securely pinned to the 
 main column. As soon as the girders were free from the old bed-plates, and were 
 afloat, which was in about 15 minutes, the pontoon was moved, by manipulating 
 mooring ropes, to the site of the new bridge, a distance of 60 feet (see Photo. XII.). 
 On reaching its intended position, the span was allowed to drop into its place on the 
 new structure by the hydraulic rams. 
 
 The curve of the bridge at the north side of the river, prevented this method 
 from being adopted there, and the girders in this case were transferred from the old 
 to the new piers by means of steam travelling cranes, each girder being lifted indi¬ 
 vidually (see Photo. XIII.). 
 
 r fhe new girders for the south and north spans were constructed as follows:— 
 the plates forming the booms of the girders were planed and built in the contractor’s 
 yard in Glasgow, on longitudinal and transverse supports. They were set at a 
 convenient distance from and parallel to rails on which a drilling machine travelled. 
 The supports were so arranged as to give the required camber, whilst the web-plates 
 were kept in their true positions by wrought-iron distance pieces, thus allowing the 
 machine to drill everything through the solid. Any number of drills could be 
 attached, as found necessary, both for the horizontal and vertical holes of the booms 
 of the girders. The driving power was communicated by an endless rope fixed over¬ 
 head. 
 
 The ties and struts were planed and drilled by templates and their ends were 
 cut cold by steel circular saws, thus ensuring perfect fitting. 
 
 When the preparation of the different parts of the girders was completed, they 
 were transferred to the site of the bridge and the girders were built in groups in the 
 contractors’ yard on ground adjacent, and parallel to, the railway sidings on either 
 side of the river. The riveting was done by hydraulic machines, the pressure being 
 obtained from an accumulator placed in the vicinity. The riveting machines were 
 hung from light hand cranes, mounted on railway waggons running on a temporary line 
 of rails within an easy range of the entire girder. Being of the continuous type, in 
 sets of four for the 129 foot spans, and three for the 145 foot spans, they were so 
 placed in relation to each other, that no difficulty would be experienced in their 
 removal to the bridge. 
 
 O 
 
THE NEW TAY BRIDGE. 
 
 39 
 
 For the purpose of transferring the new girders when built, to their positions in 
 the bridge, two traversers were constructed for bringing the girders out sideways 
 to the main lines (see Photo. XIV.). These traversers consisted of iron trolleys 
 which were placed about 20 feet from the end posts, and the girder was raised 
 by screws from the ground : the whole was then drawn out and deposited ready for 
 the next operation, viz.: of running the girder out on to the bridge: for this 
 purpose two travellers were constructed, these consisted of a heavy framework 
 having a base of box girders on which were fastened eight wheels, four of them 
 for running on the ordinary gauge, and the other four for a gauge of 9 feet to fit the 
 temporary rails placed on the top booms of the girders of the old bridge. The 
 travellers had a wheel base of 11 feet 6 inches, and were constructed high enough 
 to allow of the new girders (16 feet in depth) being hung between the frames, and 
 sufficient to clear the rails (see Photo. XV.) Surmounting the travellers were 
 hydraulic cylinders, and a locomotive engine being attached behind, pushed the 
 whole forward, and as the travellers neared their destination, the rails were so laid, that 
 the wheels of the 9 feet gauge came into operation shortly before the old girders were 
 reached, and when the girder arrived at its proper span, it was lowered down 
 between the pair of old girders by the hydraulic cylinders and steel rods (see Photo. 
 XVI.). The second new girder having being transferred in the same way, the old 
 girders were separated, and all the four girders were placed in their proper positions, 
 the vertical and horizontal bracing between them put in, and finally the flooring was 
 fixed on the top. 
 
 The corrugated form of the flooring was effected by heating the plates of which 
 it is constructed and pressing them by hydraulic rams between steel blocks (of suitable 
 form) to the required shape. These corrugated plates were then connected together 
 by cover plates riveted to them at the top of the ridges and the whole was riveted 
 to the four girders composing each of the spans. At the same time the standards 
 and lattice work of the parapets were also fixed to the top members of the two outer 
 irders, and thus the whole was completed ready for ballast and permanent way. 
 
 The shaping and drilling of the ironwork of the various members of the girders 
 of the central spans were carried out at Glasgow in the same manner as has already 
 been described for the other new girders. 
 
 Their erection was effected on the south shore of the river, where each span 
 was constructed complete (with the exception of a small portion of the connecting 
 members at their ends), and whence they were eventually floated out to their 
 destinations, and lifted to the top of the piers. For this purpose a large timber 
 jetty was constructed at the east of the two bridges, 400 feet long with an 
 average width of 100 feet from east to west. It was provided with two docks or 
 openings, 30 feet wide, capable of admitting the pontoons for floating out the spans. 
 These docks were floored during the erection of the spans by planking, supported on 
 light temporary girders and logs, all of which could easily be removed. Sidings were 
 laid so as to enable travelling steam cranes to run between the main girders of each 
 span, and assist at the erection and riveting of the different portions of the structure. 
 On the outsides of the two spans light service roadways were laid for carrying hand 
 cranes mounted on railway waggons for handling the hydraulic riveting machines. 
 
 O v 
 
40 
 
 THE NEIV TAY BRIDGE. 
 
 All the material was delivered, by being lowered by steam cranes from the old 
 bridge on to small waggons running on the sidings already mentioned, and conveyed 
 to the travelling steam cranes for erection. The girders were built on timber blocks 
 raised 2 feet 0 inches above the level of the jetty; which were supplemented by large 
 tapered wedges, so that the camber of the girders could be properly adjusted from 
 time to time. The bottom booms were first laid down and riveted; the struts, ties, 
 and parapets were next dealt with; then the top booms were placed and riveted, 
 and afterwards the top cross bracings and wind ties. The steam cranes were then 
 withdrawn from between the girders, and the flooring was erected and riveted by 
 portable hand cranes. When this was completed the span was ready for floating out. 
 The jetty was capable of accommodating two spans, and it was always aimed at having 
 the two ready at the same time, so that the second or inside span might be removed 
 the following tide. The riveting was done by hydraulic power, supplied by a steam 
 accumulator placed at the south-west corner of the jetty. Pipes were laid to different 
 points, and stop-valves and branches placed for making the necessary connections 
 by flexible rubber pipes, capable of resisting a pressure of over one ton to the square 
 inch. The hydraulic riveting machines were made of steel, and varied in weight 
 from 2 to 12 cwt. They were portable, being suspended from either the steam— 
 or hand—cranes, as required. The building of the girders was carried on day and 
 night. Light being obtained at night from the “ Lucigen ” produced by burning 
 heavy hydro-carbon oils, with the aid of compressed air in a special burner. The 
 air compressor, with a 6-inch cylinder, proved sufficient to work five lights. Rivet- 
 furnaces were also heated by a similar process. 
 
 When the spans were completed, the flooring covering the docks Avas removed, 
 and pontoons were placed underneath the first span at low-water. These pontoons 
 were the same as were used for transferring the old girders to the new piers. On 
 their decks were two strong framings of stools, and preparatory to commencing the 
 operation of floating, pitch pine logs were placed across the stools to give additional 
 height to the girder, before landing on the new piers. During the rising of the tide 
 the pontoons were adjusted, after the weight of the span (about 514 tons) had been 
 transferred from the jetty to the pontoons, heavy chains were lashed round the stools 
 and the struts of the girders to prevent shifting. About an hour and a half before 
 high-water the steam winches were set in motion, and by means of snatch ropes 
 the floating girder was cleared from the docks, and four steam tugs took the pontoons 
 in tow (see Photo. XVII., and Plate I., fig. 2). Owing to the near proximity of the 
 jetty to the bridge, the tugs had to be kept well down the stream till opposite the 
 piers where the girder was to be landed. Then the ropes attached to the tugs were 
 slackened, allowing the whole to float into position with the tide. Iron buoys were 
 placed advantageously during the previous tide, and by moorings to them, as well as 
 to the old and the new piers, the structure was finally secured. Chains with union- 
 screws were then fixed from the end posts of the girders to the tops of the piers, and 
 the span was accurately adjusted (see Photo. XVIII.). Beech blocks were placed 
 underneath the ends of the girders, which were generally about 5 feet above the brick¬ 
 work of the piers. At high-water, the valves of the pontoons were opened, and water 
 was allowed to flow inside to the extent of from 12 to 15 inches, thus hastening the 
 
THE NEIV THY BRIDGE. 
 
 41 
 
 settlement of the weight of the span on the beech blocks. The pontoons were free 
 of the span generally about two and a half hours after high-water, and were towed 
 back to the jetty, there to bring out the next span with the following tide. 
 
 The process of erecting the superstructure of the piers (as already mentioned) 
 was now commenced ; for this purpose derrick cranes were employed, which were 
 placed on timber trestles, resting on the flooring of the girders near the piers, and 
 high enough to admit of the building of all the plates (see Photo. XIX.). Cargo 
 boats brought out the material, and landed it on the open end of the span. A 
 steam-winch set in the middle of the span, supplied the necessary lifting power by 
 means of chains and snatch-blocks. As the end-posts of the girders passed through 
 the sides of the superstructure, several plates were there left out, and others above the 
 end-posts were only temporarily bolted, whilst the rest of the structure was riveted 
 up complete. 
 
 For the purpose of raising the girders eight steel angles (each 8 inches by 
 4^ inches by 1 inch) were fixed in pairs round the end-posts, and attached to a sole- 
 plate bedded on top of the cylinder. These angles were placed rectangularly, and 
 the greatest care was taken to have them exactly vertical. They had diagonal 
 bracing-bars attached, which formed a framework 5 feet by 3 feet 9 inches, by the 
 height of the pier where the girder was being lifted (that height varying in the 
 13 spans from (18 feet (> inches to 47 feet 6 inches). This framework was attached 
 with stiffeners and ties to the permanent ironwork of the superstructure of the pier. 
 Holes, 2 inches in diameter with 7| inches pitch, were drilled in the 8-inch member 
 of the angle-irons for receiving the steel pins of the lifting girder. The 4|-inch 
 members of the angles were placed on the outside, so as to allow of the fixing of the 
 bracing-bars which bound the two sets of angles running parallel with the girder ; 
 these were never disturbed in the raising of the span, whereas the cross-bracing 
 running* at right-angles, which was fixed to the 8-inch member of the angles, 
 had to be re-adjusted, as the elevation progressed. Underneath each end-post 
 at 3 feet from the end of the girder, inverted hydraulic rams were bolted to the 
 bottom of each girder (see Photo. XX., and Plate I., fig. 3) ; attached to these 
 rams, and sliding between the members of these same lifting columns, were cross 
 girders 5 feet deep, from which, when secured to the columns, the rams could 
 take their thrust. At the other side of the column were two cross girders, upon 
 which the weight of the span could be rested, whilst the rams were being prepared for 
 another lift. The upper of these was fixed to the main girder; and while being 
 raised, the lower one acted as a safety girder, and was fixed to the column. 
 
 The lifting power for elevating the girders, was obtained thus : a steam boiler 
 and set of pumps were placed on the centre of the span, having pipes leading to the 
 four hydraulic rams. By an arrangement of stopcocks the full force of the pumps 
 could be directed to the two rams at one end of the girders and shut off from the 
 others, and thus raise that end, and when the process was reversed, the opposite end 
 was treated in the same fashion. When everything was ready, the pressure was 
 turned on to two of the rams at one end of the span, which allowed the back pins to 
 be relieved and taken out; the girder was then pushed upwards by the rams till the 
 2-inch holes of the cross-girders were opposite the holes drilled in the broad members 
 
42 
 
 THE NEW TAY BRIDGE. 
 
 of the* angle's of the lifting columns. Pins were then inserted in each column, and the 
 span was allowed to rest thereon. Whilst the girder was in course of being lifted 
 hardwood wedges were inserted between the safety girders and the cross-girders 
 which were attached to the end-posts of the girder, to prevent any drop, in the event 
 of a pipe bursting, or anything going wrong with the rams. The span being secured 
 on the back cross-girders, the safety girders were pushed up and re-fixed. This 
 enabled the pins of the front cross-girders attached to the rams to be withdrawn; 
 pressure being applied, the cylinder and cross-girder were drawn up, and pinned ready 
 for another lift. In this manner the span was lifted at one end, 15 inches in two lifts, 
 (see Photo. XXI.). The same operation was repeated at the other end, and so on 
 till the top of the superstructure was reached, where one of the permanent cross¬ 
 girders at the top of the shafts of the superstructures was inserted, and riveted 
 in its proper position. The girders were then temporarily rested on blocks on 
 these permanent cross-girders, thus enabling the lifting columns and bracings to be 
 removed to another pier, and again erected ready for lifting another span. After the 
 spans were lifted to the required height, arrangements were made for inserting under 
 the girders the remaining cross girders, bedplates and rockers. 
 
 When this operation was completed the cast steel bearings with or without the 
 rockers, were inserted, and the girders were lowered down finally to their proper 
 positions, and made secure to the fixed bearings, or adjusted to the rocker bearings as 
 the case might be. 
 
 Lastly, the frameworks at the top of the end-posts, and the ends of the flooring 
 (which had been left out until the girders were in position) were inserted, and thus 
 the whole was completed, ready for the ballast and permanent way. 
 
 The rest of the works necessary for the completion of the bridge ready for traffic 
 were of ordinary character, and require no special description. 
 
 TIME OCCUPIED IN CONSTRUCTION. 
 
 The date of the commencement of the work was June 22, 1882, that of the 
 opening for goods traffic, June 12, 1887, the interval between these two dates being 
 almost five years. Of this period, the first year was practically taken up in preparing 
 the plant for the work, the actual date for commencing the foundations in the river 
 being July (>, 1883. 
 
 The average time involved in carrying out the various parts of the work was as 
 follows: In sinking cylinder foundations, 30 days for the pair; in testing cylinders, 
 49 days for the pair ; and for erecting the superstructures of the piers 17 days. 
 
 With regard to the construction of the new girders of the south and north spans, 
 this work being on shore, was executed at times when the weather did not permit of 
 the men working on the water, and therefore no time can be given. 
 
 The transferring of the girders from the old bridge to the new was generally 
 
THE NEIV TAY BRIDGE. 
 
 43 
 
 accomplished in a few hours, and on some occasions, as many as three spans were 
 shifted in one day. 
 
 The transferring of the new girders to those spans, and lowering them to their 
 positions was also a short operation; weather permitting, it was possible to run out 
 two per day and lower them between the old girders. 
 
 The time occupied in erecting the central spans complete on the jetty was on an 
 average 72 days, and the whole of the operation of floating them out and placing 
 them on the piers took only about 4 hours, and the final process of raising them to 
 the top of the piers occupied about 21 days. 
 
 ACCIDENTS DURING CONSTRUCTION. 
 
 It is satisfactory to be able to state that although the works were carried on by 
 night as Avell as by day, comparatively few fatal accidents occurred considering the 
 number of men employed and the stormy character of the estuary. 
 
 The number of men in the shops at Glasgow was about 300, and those employed 
 at the site of the bridge varied, at different times, from 100 to 900. 
 
 The number of fatal accidents was 13. These were almost entirely confined to 
 men falling from the pontoons or wharves into the river, or from their over-balancing 
 themselves on the high parts of the structure ; in fact they were not occasioned by 
 negligence or carelessness in the manner of carrying out the works, but were due 
 in almost every case to the individual recklessness of the men themselves. 
 
 THE BOARD OF TRADE INSPECTION. 
 
 The bridge was inspected on behalf of the Board of Trade on the 16th, 17th, and 
 18th of June, 18S7, by Colonel Rich, R.E., Chief Inspector, and Major-General 
 Hutchinson, R.E. For this purpose the Company supplied, at the request of the 
 inspectors, 16 engines, 8 on each line, the gross weight of which amounted to 955 
 tons. With these the compression of a certain number of the piers, and the deflec¬ 
 tions of all the girders, were observed. The measurements were taken by levels or 
 by stretched steel wires, the latter process giving the best results. 
 
 The piers were first tested with the view of ascertaining, if loading produced any 
 compression in them. Those tested were piers Nos. 7, 16, 22, 43,50, 51 and 53 of 
 the south and north spans, and Nos. 28, 29, 31, 33, 35, 37, 39, and 41 of the central 
 spans. The observations indicated a slight compression, when the load was on, from 
 *001 to • 005 of a foot, owing no doubt, to the compression of the materials of which 
 
44 
 
 THE NEW TAY BRIDGE. 
 
 the piers were composed, but on the load being removed no permanent effect was 
 observed. 
 
 With regard to the testing of the girders, the average of all the readings of all 
 the spans was as follows 
 
 At the 245 feet girders the deflection was 
 
 145 
 
 129 
 
 71 
 
 •115 of a foot. 
 
 •048 
 
 •041 
 
 •020 
 
 V> 
 
 And the permanent set may be said to have been “ nil ”•—the only observation which 
 
 gave a permanent set of t 4q foot deflection, was at the 245 ft span, Pier Nos. 30-31, 
 
 and that was only observed on the west side. 
 
 */ 
 
 Tests also were made to ascertain the amount of lateral vibration from the rolling 
 load; for this purpose plumb bolts were suspended by steel wires from the top of the 
 bracing between the girders of the central spans, with the result that the amount of 
 lateral movement at the centre of a span during the passage of 4 engines was, 4 inch 
 towards the road on which they ran,* but at the pier, the lateral movement was “ nil.' 
 Lastly a plumb-bob was hung from the top to the bottom of the highest junction 
 pier, viz. Pier 28, and in this case again, no lateral deviation was observed at all 
 during the passage of the engines at about 30 miles an hour, on either road. 
 
 The results of these tests may be said to be most satisfactory to everyone 
 concerned in the work, and, as a consequence, the Board of Trade gave the Company 
 permission to open the bridge for passenger traffic, which was done on the following 
 Monday, June 20th, 1887. 
 
 * It is interesting to note that these results are confirmed by Professor Ewing, F.R.S., Professor of 
 Engineering in University College, Dundee, who, in a Paper read before the Royal Society on June 20, 1888, 
 entitled “ Seismometric Measurements of the Vibration of the New Tav Bridge during the passing of 
 Railway Trains,” describes his experiments as follows :— 
 
 “The Seismograph (which was a Duplex Pendulum one, designed for and applied in the measurement of 
 earthquakes in Japan) was set upon the ground in the six-foot way between the two pairs of rails at the 
 middle of the length of the southernmost high girder, at a distance of about 11 mile from the Dundee end of 
 the bridge, and mile from the Fife end. The girders are there 245 feet long, and stand at a height of 
 about 110 feet above the bottom of the river and 135 feet above the foundations of the piers. 
 
 “ Observations were made while eight trains crossed the bridge. There was no wind, and, until a train 
 came on, the recording index of the seismograph stood perfectly at rest. As soon, however, as a train entered 
 the bridge, from either end, the index began to move The movements were at first so minute that it was 
 difficult to estimate their range with any accuracy ; allowing for the multiplication given by the lever, the 
 movement began with longitudinal shaking something like g^ of an inch. In the case of trains coming from 
 Dundee this was transmitted round the curve of the bridge, and was noticed long before the train had reached 
 the straight part. At first the movement was wholly longitudinal, and it was not until the train had come 
 much nearer that lateral oscillation began to be felt. The interval by which longitudinal vibrations 
 preceded transverse vibrations was much greater than could be explained by difference in their velocity of 
 transmission. Near the source of disturbance (as one learnt later when the train was passing the seismograph) 
 the lateral movement was actually greater than the longitudinal; it appeared, therefore, that longitudinal 
 disturbance reached the instrument from greater distances than lateral disturbance, because it was transmitted 
 along the bridge with less loss. As the train came nearer, lateral movements became superposed on the 
 longitudinal ones, and the index of the seismograph described an immense series of irregular loops, the range 
 of which increased at first slowly and then quickly to a maximum as the train passed the instrument. Along 
 with this progressive increase there was a periodic rise and fall in amplitude, the beat of which apparently 
 agreed with the interval taken by the train to pass from pier to pier over successive spans. The last faint 
 movements terminated abruptly when the train cleared the structure. Thr greatest lateral movement appears to 
 have been about one-tentli, certainly not more than one-eighth of an inch ; the greatest longitudinal movement 
 about one-fourth of this. There were about three complete vibrations per second.” 
 
THE NEIV TAY BRIDGE. 
 
 4.') 
 
 CONCLUSION. 
 
 I have not said anything about the cost of these works, as it seems to me that 
 the details of this will not be of much interest to such an audience as I am here 
 addressing; but I may mention, to give an idea of the value of the bridge to the North 
 British Kailway Company, that previous to its opening they were paying, per annum, 
 to the Caledonian Railway Company, a sum almost equal to 5 per cent, on the cost 
 of the new bridge, for conveying their traffic round by Perth. 
 
 f he number of trains crossing the Bridge daily (notcounting “ Specials”) is 104. 
 
 I his brings my description of the new Tay Bridge and its manner of construction 
 and erection to a close, and in conclusion I have to thank you for the kind and 
 appreciative manner in which you have listened to my lectures, and I trust that I have 
 put before you some information which will be of use—though perhaps in an indirect 
 way—to the noble profession which is being developed here, and which has produced 
 so many eminent men distinguished both in the Military and Civil world. 
 
 SUPPLEMENTARY REMARKS. 
 
 The foregoing description is presented almost in the shape it was given in the 
 Lectures—a few more details perhaps may be with advantage added especially as 
 regards the cost of the work. 
 
 The total cost of the undertaking was 670,000/., being at the rate of a little 
 under 64/. per lineal foot. In considering these figures it must be borne in mind that 
 a certain amount of economy was effected by the use of the girders of the old 
 bridge, which were applicable for two-thirds of the length. The girder work of the 
 thirteen central spans cost about 47/. per lineal foot, while that of the remainder 
 (where the saving above mentioned occurred) was about 26/. per lineal foot. The 
 average cost of the river piers was 4000/. per pier, the foundation work being rather 
 under half that amount. The cost of testing the cylinder foundations, in accordance 
 with the clause in the Act, came to 9,200/., or on an average 126/. per pier. 
 
 The Staff* employed consisted of Mr. Fletcher E. S. Kelsey, the resident 
 engineer, whose constant and strict supervision of the works produced the very 
 satisfactory results which have been described. Connected with him was Mr. E. C. 
 Caffin, the Assistant Resident Engineer, who, on occasions when Mr. Kelsey was 
 unavoidably absent from the works, undertook the whole responsibility of superin¬ 
 tendence ; added to his engineering knowledge was his experience in photography, 
 and it is to this we are indebted for a very valuable series of photographs taken 
 during the progress of the works—a selection of which appear in this book. 
 The work of supervising the testing of all the ironwork for the bridge was 
 first entrusted to the late Mr. A. C. Boothby, but owing to the press of other 
 
 N 
 
THE NILIV THY BRIDGE. 
 
 46 
 
 engagements he retired, and the post was given to Mr. H. Congreve, who carried it 
 out most efficiently to the end. The details of the calculations of the strains, &c., 
 and of the ironwork drawings were worked ont by Mr. W. H. Bidder and a staff of 
 assistants, who carried this part of the work ont very satisfactorily. 
 
 With regard to the Contractors, Messrs. William Arrol and Company, it may be 
 said that the work itself speaks for them. Mr. William Arrol designed the 
 plant and appliances used in the construction and erection of the various parts of the 
 Bridge, and wherever it was possible he arranged that machinery should take the 
 place of hand labour, and so insured that great accuracy which is so essential in such 
 a large work. 
 
 In conclusion it should be mentioned that the Directors of the North British 
 Railway Company showed by their numerous visits to the works during progress, 
 their lively interest in the undertaking. The works were commenced during the 
 chairmanship of Mr. James Stirling of Kippendale. On his death Sir James Falshaw, 
 Bart., became chairman until 1886, when the Marquis of Tweeddale undertook that 
 position. 
 
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