10 



tioned to resist each kind of strain. Both of the strains 

 shall, however, be considered as increased by an amount 

 equal to T 8 T of the least of the two strains, for determining 

 the sectional areas of the members by the above-allowed 

 unit strains. ( 31, 35.) The connections of such 

 members must have the rivets and bearing areas on pins 

 increased 50 per cent, over the usual requirements ( 40, 



40. 

 Effect of Lateral 39. The strains in the truss members or trestle posts from 



Forces on Chord J ~ 



the assumed lateral forces need not be considered except as 

 follows : 



ist. When the strains on any member from the lateral 

 forces exceed 30 per cent, of the maximum strains due to 

 the dead and live loads upon the same member. The sec- 

 tion shall then be increased until the total strain per square 

 inch will not exceed by more than 30 per cent, the maxi- 

 mum fixed for dead and live loads only. 



2d. When the lateral forces, alone or in combination with 

 other forces, can neutralize or reverse the strains in any 

 member. ( 27, 28, 29.) 



r Rivets, Bohs 40. The rivets in all members, other than those of the 

 floor and lateral systems, must be so spaced that the shear- 

 ing strain per square inch shall not exceed 9,000 pounds ; 

 nor the pressure on the bearing surface (diameter X thick- 

 ness of the piece) of the rivet-hole exceed 15,000 pounds per 

 square inch. 



The rivets in all members of the floor system, including 

 all connections, must be so spaced that the shearing strains 

 and bearing pressures shall not exceed 80 per cent, of the 

 above limits. 



The rivets in the lateral and sway bracing will be allowed 

 50 per cent, increase upon the above limits for lateral forces 

 as per 24, 25, but not per 27, 29. Each connection of the 

 bracing must have at least three rivets in plate girder spans 

 and four rivets in truss spans and trestles. 



Rivets countersunk in material of less thickness than the 

 diameter of the rivet, shall only be given a value compared 

 to that of a regular rivet equal to the proportion of the 



