222 



FRAMEWORK 



where M = bending moment in inch-pounds, and h = the distance 

 between centers of gravity of the flange areas (effective depth), (a) 

 Fig. 108. 



The net flange area, A, will be A = F -=- f where / = the allow- 

 able unit stress. The tension flanges of plate girders are designed as 

 above, and the compression flanges are made with the same gross area. 



(cO 



(b) 



5 (O 



fe) 



Web. The web plate should not be less than 5-16 of an inch in 

 thickness although >4-inch plates may be used if provided with suf- 

 ficient stiffeners. The shear in the web is commonly assumed as uni- 

 formly distributed over the entire cross-section of the plate. 



Stiffeners. There is no rational method for the design of stif- 

 feners. If they are placed at distances apart not exceeding the depth 

 of the girder, nor more than 5 feet, where the shearing stress is greater 



