STKENGTH AND ELASTICITY OF REINFORCED CONCRETE. 167 



have approximately 



% ( h — a) n f s + \bd 2 



b d + n f a 



d . d 2 



= * - o + 



2 6(2x-d) 

 The maximum stress in the steel is : — 

 _ M 



f s (/t - a - # + y) 

 The maximum stress in the concrete is : — 



x 



c=p s 



n(h — a-x) 



Here n = — - = 12, say f s = the total area of tbe rods 



-Be 



equal say 7*5 square inches. 



Let h = 36 inches, b = 57 inches, a = 3 inches, d = 5*5 

 inches, b = 12 inches. 



Applying the foregoing equations we obtain : — 

 x = 9*5 and y = 7. 



If M = 2008000 inch-pounds corresponding with a dis- 

 tributed load of 35700 pounds on a span of 37*5 feet we 

 should have : — 



P s — 9000 pounds per square inch, 

 c 3= 303 pounds per square inch. 



A beam similar to Fig. 18 and having approximately the 

 dimensions assumed, was made by the Ferro-concrete 

 Company of Cincinnati, U.S.A., and tested by Mr. Gustave 

 W. Dracli, 1 witli a load of 35,700 lbs. distributed over a span 

 of 37*5 feet, and gave a central deflection of only one- 

 eighth of an inch. The load was allowed to remain on 

 the beam for 21 hours. 



The author wishes to thank Messrs. Gummow and 

 Forrest, Steel Concrete Engineers, for their kindness in 

 making all the concrete specimens referred to in the tests 

 given in this paper. He also wishes to acknowledge the 



1 The Engineering K. cord, Vol. l., No. 3, page 90. 



