Art. 162. 



DECK BRIDGE LATERAL SYSTEMS. 



319 



d e* 



Fig. 212. 



ing at the panel points. The bottom lateral system carries its 

 part of the wind load directly to the supports. The reactions at 

 the four shoes "a" are assumed to be equal. The top lateral 

 system carries its load to the end sway frames at A, and these 

 take it to the supports. In this case of an eight panel bridge, if 

 there is no end floor beam at A and the stringers rest directly on 

 the abutments, we shall have 4 panel loads of dead load and 3% 

 panel loads of live load wind going to the supports through the 

 end sway frames. If there are end floor beams at A we will have 4 

 panel loads of each, dead and live wind load, going to the sup- 

 ports through the end sway frames. No stresses are calculated 

 for the intermediate sivay bracing, but it serves to prevent distor- 

 tion of the cross section of the bridge due to loads on the bridge, 

 rot symmetrical with the center line between trusses and to the 

 excess wind load at the top chord over that at the bottom chord. 1 



The lateral systems are simple Pratt trusses and the chord 

 stresses must be taken into account if they exceed 25% to 50% 

 of the total live and dead load stresses due to vertical load. There 

 is no stress in ab from vertical loads, but it will be in compression 

 from wind loads. There may be a reversal of stress in some of 

 the other panels of the lower chord, especially if the span is 

 long and the dead load comparatively small. 



The stresses in the end sway frame are shown in Fig. 213. 



P=one panel of wind load, 



.K=transverse component of end diagonal A'B". (Fig. 

 212.) 



^ee Johnson's 'Modern Framed Structures," Part I, Art. 191. 



