72 REINFORCED CONCRETE CONSTRUCTION 



lower surface of a reinforced concrete beam is a maximum near 

 the center of beam and decreases each way toward the end. 

 The difference in the tension between any two points is trans- 

 mitted to the concrete by the bond between the steel and the 

 concrete. This increment (or decrement) of the tension in 

 the steel is finally transferred to the compression area of the 



U U I U i i i ! I i i 1 I 



stirrup--' 



B 



t 



steel ' 



FIG. 38. 



concrete, and becomes an increment (or decrement) to the com- 

 pressive stress in the concrete above the neutral axis. The 

 formula for bond will now be derived for beams in which the 

 reinforcement is horizontal or straight throughout. 



1 1 1 11 j j I j j i 1 1 4 i 4 



inclined rod-'' 



t 



steel 



FIG. 39. 



The total shearing stress per linear inch between the steel 

 and the concrete, considering a length of beam equal to x, is 



T'-T 



x 

 From Fig. 30 



Vx=(T'-T)jd, 



T'T V 



or = -7-^(bond stress per linear inch) 



x yd 



and the bond stress per square inch of the surface of the steel 



