RECTANGULAR BEAMS 



121 



Where web reinforcement is used, it is a good plan to require the rods to 

 be made up into frames and have them placed in the forms as such. If loose 

 rods must be used, the reinforcing elements should be wired together to 

 insure their being in place. A good plan is to have the main bars held in 

 place by metal spacers. 



Illustrative Problem. Design a beam to span 15 ft. and to support the 

 loads shown in Fig. 58. The reactions are readily found and are given in the 

 sketch. The maximum moment occurs at the center load since the shear 



-- 34!4 >\ 



pp ''-'"" r 



passes through the value zero at this point. We shall assume the weight 

 of beam included in the uniform load of 1000 Ib. per foot % 



M =(25,500) (8) (12) -(23,000) (4) (12) = 1,344,000 in. Ib. 



1,344,000 

 (0.0077) (16,000) (0.874) 



Assume 6 = 16 in. 



d'-^-782,orrf-28in. 



We shall take 6 = 16 in., and d = 28 in. 



V 25,500 



57 Ib. per square inch. 



