73 



Prom experience we would assume the weight of the 

 floor to be about 50 Ib. per sq. ft., making the total load 

 per sq. ft. equal to 200 Ib. We would also have to es- 

 tablish the spacing of the beams, which in most cases 

 would preferably be from 36 in. to 48 in. between centers. 



For 36 in. between centers the total load on each beam 



T 20X36X1'00 



: 6 tons 



12X2000 



and the total stress 



If we use a 1 in. bar having a safe tensile strength of 

 10 tons, the depth D would equal 20.6 in. The minimum 

 thickness for the slab to give the required compressive 



strength would be 



5X10 

 36 



= 1.4 in. 



an amount less than it would be advisable to use, prac- 

 tical considerations suggesting a minimum thickness of 

 2 or 2Vfe in. 



The slab should be figured as a flat floor spanning from 

 beam to beam. 



The width of beam W and total height // depend upon 

 the size of the bar and are given in table below. 



Size 

 of 

 Bar 



H 

 W 



Kin. 



in. 

 + 

 VA 



in. 



in. 



D+1H 



lin. 



in. 



l&in 



in. 



in. 

 D+2% 



2 in. 



in. 



D+3 



6 



If, Instead of a 1 In. bar we should use a 1*4 in. bar 

 having a safe tensile strength of 15.625 tons, the least 

 depth /> would be i.'l.U in., the minimum thickness 7' would be 



15.625X5 



-36 = 



and the other dimensions would be obtained from the 1% 

 in. bar column in the table. 



Where the length ,,f span warrnnts It. one or more 

 stiffening ribs should be formed, at right angles to the 



