May 8, 1916 



Tests of Reinjorced-Concrete Slabs 



209 



directed to secure work thoroughly representative of that obtained 

 under field conditions. The sand was a good grade for use in concrete, 

 and the gravel was clean, well graded, and free from weak pebbles. 



The steel reinforcing consisted of ^-inch plain square bars in slabs 835 

 and 930, and the bars in slab 934 were ^-inch square. The yield point of 

 this material is. about 39,000 pounds, and the ultimate strength 60,000 

 pounds per square inch. 



The slabs were necessarily built in place on their supports, and the 

 forms were struck at the end of about two weeks. The concrete was 

 sprinkled daily for several weeks during the earlier stages of hardening 

 and was allowed to cure protected from the weather until the destruc- 

 tion of the slab. 



Table I contains the essential data concerning the slabs tested. 



Table I. — Description of reinforced-concrete slabs used in tests^ 



' The slabs were not reinforced transversely. 



At the time the slab specimens were made, 8 by 16 inch concrete 

 cylinders were molded from the same mixture and were allowed to cure 

 under the same conditions as the slabs. These were tested later for their 

 crushing strength and modulus of elasticity. 



METHOD OF TESTING SLABS 



At the age of 28 days the initial strain-gauge and deflection readings 

 were taken with no load on the slab. The first load was then applied 

 through an 8-inch cylindrical bearing block set in plaster of Paris at the 

 center of the slab. Strain-gauge and deflection observations were made 

 again over the entire slab. Due account was taken of the air and concrete 

 temperatures in order to make corrections for any appreciable change 

 occurring during the progress of the tests. The increments of load 

 applied to the difi"erent specimens were varied in the diff"erent slabs, 

 depending on their thickness, and the aim was to stress neither the steel 

 nor the concrete beyond working limits, also to obtain about five incre- 

 ments of load within the working load. 



