282 



SKEW BRIDGES. 



Art. 139- 



wise the portal would lie in a warped surface. Warped portals 

 are expensive to construct, difficult to connect and are not as 

 efficient as bracing in a plane. 



The weight of the trusses and bracing is usually assumed 

 to be equally divided among the panel points, but the weight 

 of the floor system is proportional to the area of the floor trib- 

 utary to the panel points. This will not make a great deal of 



Equal Pauels along Center Liue 



Fig. 197. 



difference in the dead load panel loads of single track railroad 

 bridges, but in highway bridges where the entire floor is covered 

 with a heavy flooring there may be a considerable difference 

 in the panel loads. 



In single track railroad bridges the live load is usually as- 

 sumed to be applied on the center line of the bridge. This makes 

 the live load panel loads all equal, if the panels are equal on the 

 center line. In double track bridges, and in highway bridges 

 where the live load is usually specified in pounds per square 

 foot of roadway, the end panel loads will be unequal. The 



