May 8, 1916 



Tests of Reinjorced-Concrete Slabs 



207 



moment of the slab. The area BDGI, obtained by dividing the area 

 AJHFE by its maximum ordinate CH, has the same total concrete- 

 resisting moment with the stress uniformly distributed as the whole slab, 

 and its width BD is that which may be effective in furnishing sufficient 

 resistance under these conditions to carry the load. The width BD, 

 obtained in this manner, is the "effective width." 



DESCRIPTION OF APPARATUS 



Load-applying apparatus. — The slabs tested were 32 feet. wide, with 

 a span length of 16 feet, and in order to accommodate such extraordinarily 

 large test specimens it was necessary to build special apparatus. Two 

 supports 32 feet long were constructed of reinforced concrete, and em- 

 bedded in each of them at the center were two loop-welded eyes car- 

 rying four 24-inch 80-pound I beams 6 feet above the level of the supports 



Fig. I . — Diagram illustrating the method of obtaining ' ' effective width ' ' in reinforced-concrete slab tests. 



(PI. XXVI). Loads were applied by means of a hand-operated hydraulic 

 jack mounted between the slab and the overhead I beams. 



For weighing the loads a specially calibrated chrome-nickel beam 

 (PI. XXVI) was mounted between the jack and the load-applying I beams, 

 and its deflection at the center was a measure of the load applied. This 

 chrome-nickel beam was 7 inches wide, 5 inches deep, and 27 inches in 

 span, and its deflection was measured with an Ames dial reading to o.oooi 

 inch. The dial was fastened to the beam and its plunger rested on a 

 _J/^-inch square steel rod mounted on the side of the beam at the neutral 

 axis. It was found that by fastening an electric buzzer on this rod 

 more consistent readings could be obtained with the dial. The entire 

 load-applying device was calibrated in a 200,000-pound universal testing 

 machine, and the beam deflections corresponding to known loads were 

 obtained. A deflection of approximately 0.0001 inch occurred for each 

 500 pounds of load applied. A number of calibrations were made and a 

 calibration curve was plotted. When used for measuring loads, it was 

 only necessary to read the central deflection on the Ames dial and the 

 corresponding load could be read from the curve. ' 



