//a 
 
 • 
 
 
 
 
 
 PROPER NAILING Of CAP BRACING 
 
 January 1936 
 
 Nc. LQ1C88 
 
 i of mm 
 
 OF 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wisconsin 
 
props?. :taili::c- or car 3EACi::g 
 
 By 
 
 L.J. MARKWABDT, Senior Engineer 
 
 and 
 J.M. GAKAGAH, Assistant Engineer 
 
 The ease with \tfhich wood can he cut, fitted, and fastened, in addition 
 to its light weight and availability, has made it an efficient and practical 
 material for car bracing. Yet the very ease and simplicity of using wood often 
 causes some of the basic principles of nailing to be overlooked, with the re- 
 sult that the bracing may not measure up to its full possibilities for strength 
 and effectiveness. 
 
 The nailing of car bracing frequently requires the exercise of judgment 
 as to best practice, especially when in some particular instance it is impossi- 
 ble to meet ideal conditions. Jor example, what is the best detail for nail- 
 ing a. 2-inch cleat to the 2-inch car floor when it is known that, in general, 
 the penetration in the piece receiving the point of the nail should be at least 
 twice that through which the nail passes? Again, is there any advantage in 
 having the nail pass entirely through both pieces being joined? 
 
 3efore discussing nailing in detail, it is well to recount the several 
 ways nails may be called on to function. Hails may be subjected to direct with- 
 drawal, to lateral displacement, or to a combination of both. Resistance to 
 withdrawal, as the name implies, is the reaction to forces tending to pull the 
 nail out in the direction of its length, whereas, lateral resistance is the re- 
 action to forces tending to bend the nail or push it sidevise. 
 
 It is known that resistance to withdrawal is related to the density or 
 hardness of the wood. The dense woods hold nails much better than do the light 
 weight woods. In fact, resistance to direct withdrawal (as opposed to lateral 
 resistance) varies about as the second power of the specific gravity of the 
 wood. This does not imply that light or low density species are not entirely 
 suitable for car bracing. To get the same nail strength with the softer woods, 
 however, requires more, larger, or improved nails. The resistance to withdrawal 
 also depends on the area of contact of the nail with the wood, and hence in- 
 creases directly with the diameter of nail and with depth of penetration as 
 long as no splitting of the wood occurs. 
 
 Lateral resistance for a nail of given size increases with the density 
 of the wood, but not quite so rapidly. It also increases about as the 3/2 
 power of the nail diameter. Thus, the safe lateral load for a 20d nail in 
 white pine is nearly twice that on an 8d. ?or white oak the ratio is about the 
 same but, because of its higher density, the loads are about 50 percent higher 
 than for the pine. 
 
 R1036 
 
r >me Important Details i n C ar 3 racin g 
 'o obtain food nailing the following general details should be ob- 
 
 served : 
 
 Use nails of proper length. 7<herever possible the nails should be 
 long enough so that in softwoods approximately two-thirds of the length goes 
 into the member rec*- iving the point* This means that the length of the nail 
 should be at least three times the thickness of the outer piece (fig. 1). 
 There the thickness of the members does not permit this suggested depth of 
 
 lefcration a sufficient number of shorter nails should be used to provide 
 equivalent area of contact in the wood member receiving the point. 
 
 Drive nails so that the points do not come out of the side of the 
 piece. These "shiners" as they are called not only result in weakened joints 
 but are also a cause of injury. 
 
 Be sure the nails you use do not split the wood. Splitting greatly 
 weakens the joint. If the wood tends to split badly use a bhinner nail, 
 blunt the points, or, better still, purchase nonsplitting nails. "'Then prac- 
 tical, boring lead holes slightly smaller in diameter than the diameter of 
 the shank of the nail is excellent practice. 
 
 Use plenty of nails. The strength increases directly as the number 
 of nails used, 
 
 enever possible, do not use nails in direct tension, but use them 
 preferably in lateral resistance, "'Vhen nails in direct tension give way 
 they usually fail suddenly and may cause injury or !« The resistance 
 to withdrawal is influenced greatly by the surface condition of the nail. For 
 temporary service, cement-coated nails may ^e expected materially to increase 
 the holding power but a more permanent and greater increase may be obtained 
 with special nails having s minutely pitted or etched surface. 
 
 Do not expect ?ood nailed joints when using green wood that will later 
 dry out. Nails driven in green wood that later dries out quite commonly lose 
 most of their holding power* Hence, use dry lumber. 
 
 Resistance to Lateral Stress 
 
 .Jails are more efficient when driven into side grain of dry wood than 
 when driven into the end grain. 
 
 3/2 
 
 The lateral resistance of nails is expressed by the formula P = Kd ' 
 
 VJhere P represe bs he ultimate load on the nail in pounds; K repre- 
 sents a constant depei Ln til e species of wood (oak 8,500, northern white 
 pine 4,500, s yellow pine 7,000), and d represents the diameter of 
 the nail in inches. 
 
 R10 88 -2- 
 
The accompanying table "based on this formula gives recommended 
 values of safe lateral resistance, expressed in pounds per nail, for common 
 wire nails, driven perpendicular to the grain of wood at 15 percent moisture. 
 
 The "bracing material should "be free of knots and cross grain at the 
 places where it is to be nailed. Wood splits easily when nailed near a knot 
 or when cross-grained at the nailing ends, with the result that the effective- 
 ness of the nailing is either seriously impaired or perhaps entirely lost. 
 
 Table 1. — Safe lateral resistance- of nails 
 
 Species Pounds per nail size of 
 
 4d 6d 8d lOd 13d 16d 30d 30d 40d 
 
 Northern white pine, pon- 
 derosa pine, and 3pruce ..28 34 43 51 51 59 76 85 96 
 
 Southern yellow pine, Doug- 
 las-fir, and western 
 larch 43 52 65 78 78 90 116 130 147 
 
 Oak, sugar maple, birch, 
 beech, and ash 53 65 81 97 97 111 143 160 181 
 
 •=These safe loads are recommended for permanent nailed construction, 
 and consequently for temporary nailing such as in car bracing, higher values 
 may be used. When ultimate loads are required for design, they may be con- 
 servatively considered as five times the safe loads given in the table. The 
 actual ultimates are from six to eleven times the safe loads. 
 
 Some Special Problems in Car Bracing 
 
 Let us consider some of the special problems of bracing carload 
 shipments, assuming nominal 2 by 4 inch to 2 by 10 inch bracing lumber, 
 sheathing, or car lining ranging from l-l/4 to 1-3/4 inches, and car floors 
 1-1/4 to 2-1/2 inches thick. 
 
 Nail Sizes . — What size of nail should be used? First, we must se- 
 lect a size and type of point that does not split the wood, and when used with 
 sheathing or flooring, a length sufficient to completely penetrate the piece 
 holding the point. With stanchions and very thick material two-thirds of the 
 length should be in the member holding the point. With these conditions ful- 
 filled, the size of nail makes little difference as long as the same total 
 weight of nails is used and provided the nails do not bend in driving. The 
 slight advantage in this instance is in favor of the smaller diameter nail 
 used in greater quantity. 
 
 Nails Penetrating Through Members . — When nails penetrate through a 
 piece of wood they frequently tear off a sliver when the point emerges. High- 
 est resistance to withdrawal results with nails just short enough so that they 
 do not come through the member receiving the point. On the other hand, the 
 shock, Or repetition of shock required to tear the bracing entirely off is 
 greatest for a long nail that protrudes some distance through the piece. 
 
 R1088 -3- 
 
Figure 2— Diagrammatic sketch of "K" 
 car shipment. 
 
 brace commonly used In 
 
 Figure 1 — Nail Joint sawed open to expose lengths of nail. Above: 
 
 Good practice. Nail of proper length, about two-thirds of the length 
 
 being in the block receiving the point. Below: Poor practice. Nail 
 
 too short, giving Insufficient length in block. 
 
 Z M 28312 F 
 
Direction of Nail . — Slant driving of nails does not give any advantage 
 over straight driving. In fact, when the points doe not pass entirely through 
 all members, the straight driving is preferable because a greater portion of the 
 length will be in the place receiving the points. When the nail extends through 
 the member receiving the point but little difference is evident. 
 
 go sit ion of Cleat . — It is important to place wall cleats so that the 
 nails go into the stanchions rather than into the sheathing or siding alone, A 
 nail may then be chosen which will more nearly meet the desired condition of 
 having about two-thirds of its length in the members to which the cleat is 
 fastened. 
 
 Number of Fails . — A dry 2 by 6 placed with its edge against a load will 
 require three to six 20d nails in the cleat at each end to develop the full 
 strength of the 2 by 6, depending upon the arrangement of the cleat and the 
 quality of the 2 by 6. 
 
 Let us assume that one of the diagonals of a K brace (fig. 2) is a 2 by 
 6 of Douglas-fir, 6 feet long. This brace acts as a long column and the 
 crippling load it should take is about 6,000 pounds. Part of the load is taken 
 by thrust against the side of the car, part by friction, and the ba.lance by 
 thrust against the cleats. If it is estimated that 3,000 pounds of the total 
 thrust is taken by the cleat, and that the ultimate lateral resistance load 
 for a 20d nail is 580 pounds (safe load 116 x 5) , it is evident that at least 
 five 20d nails should be used to develop the strength of the car brace. If 
 this brace were only 4 feet long, and of good grade and quality of material, 
 double the above number of nails in the cleat would be required to hold it # 
 
 Quality of the Wood . — The effective nailing scheme to fit any problem 
 in car bracing cannot be applied if the lumber to be used consists of indis- 
 criminately mixed species and mixed grades. However, the use of mixed material 
 is not objectionable provided it is first segregated into groups of species 
 having the same nailing properties. Furthermore, if low-grade material is other- 
 wise permissible, none of the defects, as previously pointed out, should be 
 allowed at the point of nailing. 
 
 UNIVERSITY OF FLORIDA 
 
 3 1262 08929 0703 
 
 £1088 -4-