42 STANDARD SPECIFICATIONS 



have a single system of stringer bracing and a lateral, double- 

 intersection system of bracing in the plane of the bottom chord. 

 All bracing shall be composed of rigid members. (Par 131.) 



169. Minimum Size of Material. The minimum thickness 

 of metal, except for fillers, shall be for girders in building or 

 highway bridges ^ in. with f-in. rivets, and for girders in railroad 

 bridges f- in. with -J-in. rivets. 



170. Rivets. In proportioning rivets their nominal diameter 

 shall be used. The diameter of the rivets in any angle carrying 

 a calculated stress shall not exceed one-quarter (J) the width 

 of the leg through which they are driven. Rivets carrying a 

 calculated stress and whose grip exceeds four diameters shall 

 be increased in number, at least one per cent for each additional 

 & in. of grip. 



171. Rivet Spacing. The minimum distance between cen- 

 ters of rivet holes shall be three diameters of the rivet and, if 

 possible, not less than 3 in. for J-in. rivets and 2 in. for f-in. 

 rivets. In the flanges the maximum pitch, in the direction of the 

 stress, shall be 6 in. for J-in. rivets and 5 in. for j-in. rivets. 

 For angles with tw r o gauge lines and rivets staggered the maxi- 

 mum shall be twice the above in each line. Cover plates more 

 than 16 in. wide shall have four lines of rivets. (Pars. 161 

 and 164.) 



The maximum pitch at ends of cover plates shall not exceed 

 four diameters of the rivet for a length equal to two times the 

 width of the plate. 



The maximum pich in stiffeners shall be determined by the 

 loading, if any, but shall in no case exceed 4J in. The vertical 

 web splice shall, where no horizontal plates are used, have at 

 least two rows of rivets on each side of the joint with the above 

 maximum pitch. 



172. Edge Distance. (See Par. 140.) 



173. Bearings. (See Par. 151.) 



174. Temperature. (See Par. 152.) 



