BUILDING LAWS 361 



"Walls. Reinforced concrete may be used in place of brick 

 and stone walls, in which cases the thickness may be two- 

 thirds of that required for brick walls, as shown in the 

 Schedule, Section 18 of the Act of Assembly, No. 123, of the 

 Commonwealth of Pennsylvania, approved June 5, 1901, 

 provided the unit stresses as set forth in these regulations 

 are not exceeded. 



"Concrete walls in such cases must be reinforced in both 

 directions in a manner to meet the approval of the Chief of 

 the Bureau of Building Inspection. 



"Steel. All reinforcements used in reinforced concrete 

 shall be of standard grade of structural steel or iron of either 

 grade to meet the Manufacturers' Standard Specifications, 

 revised February 3, 1903. 



"Reinforced-concrete slabs, beams, and girders shall be 

 designed in accordance with the following assumptions and 

 requirements : 



"(a) The common theory of flexure to be applied to all 

 beams and members resisting bending. 



"(b) The adhesion between the concrete and the steel 

 is sufficient to make the two materials act together. 



"(c) The design shall be based on the assumption of a 

 load four times as great as the total load (ordinary dead load 

 plus ordinary live load). 



"(<f) The steel to take all the tensile stresses. 



"(<?) The stress-strain curve of concrete in compression 

 is a straight line. 



"(/) The ratio of the moduli of elasticity of concrete to 

 steel: 



Stone or gravel concrete 1 to 12 



Slag concrete 1 to 15 



Cinder concrete 1 to 30 



"The allowable unit transverse stress upon concrete in 

 compression : 



LB. PER SQ. IN. 



Stone or gravel concrete 600 



Slag concrete 400 



Cinder concrete 250 



"The allowable unit stress in tension: 



