RECTANGULAR BEAMS 



131 



loading is usually indefinite, and is generally considered uniformly 

 distributed except where the exact conditions of panel loading 

 or concentrated loads are known in advance. Fig. 64 shows 

 the variation in shear and moment along a continuous beam due 

 to a uniformly distributed load. The diagram shows that if a 

 beam is built continuously, pull or tension is bound to occur over 

 each intermediate support, with compression at these points at 

 the bottom of the beam. This is shown by the bending moment 



t 



t 



t 



Moment 



Shear 



FIG. 64. 



being negative at these supports. The same is also true at the 

 ends of such beams when fixed. 



Many of the foremost authorities have reached the conclusion 

 that for a continuous beam of any number of spans, the maximum 

 positive moment in the middle of all but the end spans and the 

 negative bending moment over the supports (with the exception 

 of the second support from each end) may be taken as numeric- 

 ally equal to each other and represented by the formula 



wl 2 



The center of the end span and the adjoining support between 

 this and the next span should be designed for a moment 



