362 BUILDING LAWS 



LB. PER SQ. IN. 



Iron 12,000 



Steel 16,000 



"The allowable unit shearing strength upon concrete: 



LB. PER SQ. IN. 



Stone or gravel concrete 75 



Slag concrete 50 



Cinder concrete 25 



"The allowable unit adhesive strength of concrete: 



LB. PER SQ. IN. 



Stone or gravel concrete 50 



Slag concrete 40 



Cinder concrete 15 



"The allowable unit stresses upon concrete in direct com- 

 pression in columns: 



LB. PER Sy. Ix. 



Stone or gravel concrete 500 



Slag concrete 300 



Cinder concrete. ..'..... 150 



"The allowable unit stress upon hoop columns composed of 

 stone or gravel concrete shall not be over 1,000 Ib. per sq. in., 

 figuring the net area of the circle within the hooping. The 

 percentage of longitudinal rods and the spacing of the hoops 

 to be such as to permit the concrete to safely develop the 

 above unit stress with a factor of safety of 4. 



"When steel or iron is in the compression sides of beams, 

 the proportion of unit stress taken by the steel or iron shall 

 be in the ratio of the modulus of elasticity of the steel or iron 

 to the modulus of elasticity of the concrete; provided that 

 the rods are well tied with stirrups connecting with the lower 

 rods of the beams; provided, further, that when rods are used 

 in compression, the approval of the Chief of the Bureau of 

 Building Inspection must be obtained. 



"In the design of structures involving reinforced-concrete 

 beams and girders, as well as slabs, the beams and girders 

 shall be treated as T beams, with a portion of the slab acting 

 as flange in each case. The portion of the slab that may be 

 used to take compression shall be dependent upon the hori- 

 zontal shearing stress that may exist in the beam, and in no 



