86 REINFORCED CONCRETE CONSTRUCTION 



and not more than 4 per cent of longitudinal bars and with 

 bands or hoops, stresses 45 per cent higher than given for 

 (b) , or 650 Ib. per square inch on 2000 Ib. concrete. 



" (e) Columns reinforced with structural steel column 

 units which thoroughly encase the concrete core, stresses 45 

 per cent higher than given for (b) , or 650 Ib. per square inch 

 on 2000 Ib. concrete. 



"Compression on Extreme Fiber. The extreme fiber 

 stress of a beam, calculated on the assumption of a constant 

 modulus of elasticity for concrete under working stresses, 

 may be allowed to reach 32.5 per cent of the compressive 

 strength at 28 days, or 650 Ib. per square inch for 2000 Ib. 

 concrete. Adjacent to the support of continuous beams, 

 stresses 15 per cent higher may be used. 



" Shear and Diagonal Tension. Where pure shearing 

 stress occurs, that is, uncombined with compression normal 

 to the shearing surface, and with all tension normal to the 

 shearing plane provided for by reinforcement, a shearing 

 stress of 6 per cent of the compressive strength at 28 days, 

 or 120 Ib. per square inch on 2000 Ib. concrete, may be 

 allowed. Where the shear is combined with an equal 

 compression, as on a section of a column at 45 degrees with 

 the axis, the stress may equal one-half the compressive 

 stress allowed. For ratios of compressive stress to shear 

 intermediate between and 1, proportionate shearing 

 stresses shall be used. 



"In calculations on beams in which diagonal tension is 

 considered to be taken by the concrete, the vertical shearing 

 stresses should not exceed 2 per cent of the compressive 

 strength at 28 days, or 40 Ib. per square inch for 2000 Ib. 

 concrete. 



"Bond. The bonding stress between concrete and plain 

 reinforcing bars may be assumed at 4 per cent of the com- 

 pressive strength at 28 days, or 80 Ib. per square inch for 

 2000 Ib. concrete; in the case of drawn wire, 2 per cent or 

 40 Ib. on 2000 Ib. concrete. 



"Reinforcement. The tensile stress in steel should not ex- 

 ceed 16,000 Ib. per square inch. The compressive stress in 

 reinforcing steel should not exceed 16,000 Ib. per square inch, 

 or 15 times the working compressive stress in the concrete. 



"Modulus of Elasticity. The value of the modulus of 



