USEFUL DATA 



reinforcement of the beam should be considered. The stresses in stirrups and inclined 

 members when combined with bent up bars are to be determined by finding the amount 

 of the total shear which may be allowed by reason of the bent up bars, and subtracting 

 this shear from the total external vertical shear. Two-thirds of the remainder will be 

 the shear to be carried by the stirrups, using Formulas 24 or 25 (see page 9). 



Wliere punching shear occurs, provided the diagonal tension requirements are met, 

 a shearing stress of 6 per cent of the compressive strength may be allowed. 



Bond. The bond stress between concrete and plain reinforcing bars may be 

 assumed at 4 per cent of the compressive strength, or 2 per cent in the case of drawn 

 wire. In the best types of deformed bar the bond stress may be increased, but not to 

 exceed 5 per cent of the compressive strength of the concrete. 



Reinforcement. The tensile or compressive stress in steel should not exceed 

 16,000 pounds per square inch. 



In structural steel members the working stresses adopted by the American Railway 

 Engineering Association are recommended. 



Modulus of Elasticity. The value of the modulus of elasticity of concrete has 

 a wide range, depending on the materials used, the age, the range of stresses between 

 which it is considered, as well as other conditions. It is recommended that in compu- 

 tations for the position of the neutral axis, and for the resisting moment of beams 

 and for compression of concrete in colunms, it be assumed as: 



(a) — One-fortieth that of steel, when the strength of the concrete is taken as not 

 more than 800 pounds per square inch. 



(6) — One-fifteenth that of steel, when the strength of the concrete is taken as greater 

 than 800 pounds per square inch. 



(c) — One-twelfth that of steel, when the strength of the concrete is taken as greater 

 than 2,200 pounds per square inch, and less than 2,900 pounds per square inch, and 



{d) — One-tenth that of steel, when the strength of the concrete is taken as greater 

 than 2,900 pounds per square inch. 



Although not rigorously accurate, these assumptions will give safe results. For the 

 deflection of beams which are free to move longitudinally at the supports, in using 

 formulas for deflection which do not take into account the tensile strength developed 

 in the concrete, a modulus of one-eighth of that of steel is recommended. 



211 



