HIGHWAY BRIDGES 19 



member itself and do not exceed 1600 Ibs. per sq.in., the effect 

 may be neglected, otherwise the maximum unit stresses (Pars. 

 65 and 73) may be increased 10 per cent. 



The bending moment in chord segments of riveted structures, 

 or in pin-connected members when continuous over joints, shall 

 be computed from the compromise formula, 



M=^1.2 wL 2 , 



where M = positive moment at center or negative moment at 



the joint, 



w = total transverse load in Ibs. per lin. ft., 

 L = length of member in feet. 



72. Eccentric Stresses. Whenever angles, used as web 

 members or bracing, are connected up by one leg only the above 

 unit stresses (Par. 65) shall be decreased 25 per cent. 



73. Maximum Stresses. When combining the stresses due 

 to vertical forces with those due to lateral forces, including the 

 direct and indirect wind stresses, centrifugal forces, and bend- 

 ing stresses in the end posts due to wind, the specified unit stresses 

 (Pars. 65 and 71) may be increased 25 per cent, provided that 

 this combination gives a greater sectional area. 



74. Reversal of Stresses. Where the stresses due to wind 

 and centrifugal forces reverse the stresses in a member due to 

 vertical forces proper provisions must be made for the piece to 

 resist compression. 



Members and connections subject to reversal of stresses 

 shall be proportioned for an equivalent stress equal to that stress 

 which, when added to 50 per cent of the other, will give the 

 greater section, both impacts included. 



DESIGN OF STRUCTURE 



75. General Dimensions. The following dimensions shall 

 first be calculated or assumed: 



Span of girders, center to center of bearings. 

 Span of trusses, center to center of pedestals or end pins. 

 Span of floor-beams, center to center of girders or trusses. 

 Span of joists or stringers, center to center of floor-beams 

 or one panel length. 



