38 STANDARD SPECIFICATIONS 



(e) Bearing on: Turned bolts and field rivets when 



hand driven 18,000 Ibs. 



Field rivets when power driven 22,000 " 



Shop-driven rivets and pins 24,000 " 



Expansion rollers, per lin. inch 600d 



where d= diameter of roller in inches. 



(/) For girders in buildings the above unit stresses for 

 rivets and pins shall be reduced 16 per cent. 

 (0) For combined stresses see Par. 124. 



For allowable unit stresses in cast steel see Par. 



70. 

 For allowable pressures on walls and masonry 



foundations see Pars. 18 and 66. 

 For allowable pressures on soils see Par. 20. 



156. General Proportions. The width between centers of 

 girders in deck bridges, carrying a single straight electric railway 

 or railroad track, shall generally be as follows: 



For spans up to 60 feet inclusive 6' 6" 



" " from 60 feet to 80 " 7' 0" 



" " " 80 " and over 7' 6" 



In through bridges the girders shall generally bo spaced so- 

 as to give a clear width of 10 ft. at the top of rails increasing to 

 14 ft. at a height of 4 ft. above same. 



For additional clearance on curves see Pars. .V_> and 106. 



The depth of plate girders in buildings shall preferably not 

 be less than one-sixteenth (fg) of the span, or in bridges less- 

 than one-twelfth ( T y of the span and, if shallower girders be 

 used, the section be increased so that the deflection will not be 

 greater than if the above limiting ratios had not been exceeded. 



For general dimensions see Par. 75. 



157. Through Bridges. Through plate girders shall have 

 their top flanges stayed at each end of every floor beam, or in 

 case of solid floors, at distances not exceeding 12 ft., by knee 

 braces or gusset plates stiffened by angles. 



Where flooring or ties are supported 0n shelf angles riveted 

 to the webs of the girders these angles shall have a minimum 



