RECTANGULAR BEAMS 



63 



makes some investigation necessary in the design of short deep 

 beams to prevent crippling of the web due to column action. 



In reinforced concrete beams, on the other hand, the concrete is 

 strong in compression but exceedingly weak in tension and 

 usually the diagonal tensile stresses become fully as important as 

 the maximum fiber stresses. An investigation will now be made 

 of the distribution of tension and shear in the concrete to deter- 

 mine what effect such stresses have on the diagonal tensile 

 stresses, and then we can decide on the method of providing for 

 these stresses. The variation of the bond stress between the 

 concrete and steel will also be considered.] 



35. Shearing Stresses. As previously mentioned, the intro- 



duction of steel into a concrete beam affects the direction of the 

 diagonal tension lines to a certain extent, by reason of the large 

 shearing stresses which are brought into existence immediately 

 above the steel. First of all, however, let us see the method 

 employed in determining this shear. 



In Fig. 30 is represented a short portion of a beam which we 

 will assume so short that no part of the load need be directly 

 considered. The total vertical shear will be denoted by V. The 

 student has already learned that the horizontal and vertical 

 shearing stresses per unit area at any point in a beam are the 

 same. Let v = intensity of either stress at the neutral axis. 

 The tension area of the concrete may be neglected. Then, 

 C" = T' and C=T. The total shearing stress on any horizontal 

 plane between the steel and the neutral plane will be equal to 



