320 



DECK BRIDGE LATERAL SYSTEM. 



Art. 162. 



In addition to the stress here shown in aa' it is assumed to 

 get 1 of the total wind load on the bottom lateral system. The 

 horizontal reactions at a and a' are likewise increased. 



It is seen that a stress equal to (R+P)- is added to the 



b 



vertical load stress in the end post A'a'. 



If the support is at the top chord as shown in Fig. 214, the 

 end sway frame is inclined and carries the wind load from the 



lower lateral system to A . The 

 stresses are obtained in exactly 

 the same manner as given above 

 for the vertical end frame. The 

 horizontal components of the 

 reactions at A and A' produce 

 a uniform stress in the top 

 chords, compression on one side 

 or truss and tension on the 

 other truss. These stresses increase the wind chord stresses. If 

 the bridge in Fig. 212 was made with an inclined end post aB, 

 the end sway frame, carrying the top lateral wind load, should 

 be in its plane. In this case, as in that of Fig. 214, the hori- 

 zontal components of the reactions would be taken up by a uni- 

 form stress in the chord. 



The wind on the train tends to overturn it as shown in 

 Fig. 20, page 35. This increases the vertical load on the lee- 

 ward truss and decreases it on the windward truss. The center 



Fig. 214. 



