Ultimate Strength of Reinforced Concrete Flat Slabs

A study was undertaken to investigate the ultimate strength of flat slab floors with regard to ultimate flexural strength and other design factors, such as shear strength and deflection. Three reinforced concrete slab models were built and tested. All models were 10 ft square, 2 in. thick, and supported by four interior columns producing an interior panel 5-1/2 ft square. Column supports were designed to rotate and translate freely, thus minimizing the influence of column restraint and membrane stresses. Variables included percentage of reinforcement and size of column capital. Uniform loads were applied by means of air pressure, and the models were loaded to failure, which was assumed to occur when large increments of deflection were produced by negligible increases in load. The results of the test program indicate close agreement between the predicted and the measured ultimate capacities of the three model slabs. The actual yield patterns that resulted from the tests conformed, in general, to the predicted patterns.