Comparative Study on Slab Deflections

Abstract

Slabs are one of the most common structural components in RC-framed structures, usually analysed under transverse loading. In the analysis, the thickness of the slab generally governs the serviceability requirement for deflection. The thickness of the slab controls the weight of the building since its contribution is nearly 50% of the total weight of the building. In order to minimize the weight of the building, proper analysis of the slab ensures minimum thickness satisfying deflection criteria. For a given loading, span, and assumed thickness of the slab, analysis will be performed using the material properties such as modulus of elasticity and Poisson’s ratio. Several theories, including the Rankine-Grashoff theory, Timoshenko’s plate theory, Marcus, and other methods have been proposed over the years using the same concept. These methods do not consider the participation of reinforcement in deflection estimation. IS code 456 – 2016 specifies limiting span to depth ratios with suitable modification factors based on percentage of tension reinforcement and stress level in steel for satisfactory serviceability criteria of deflection. In the present study, an attempt was made to compare the slab deflections analytically and experimentally with and without reinforcement contribution for the exactness of proposed theories. It concludes that, in one-way simply supported slabs, theoretical values differ by 45% from experimental values in reinforced concrete (RC) slabs. In two-way simply supported plain concrete (PC) slabs, the Rankine-Grashoff theory is in good agreement with the experimental values. Theoretical values of the two-way slabs when compared with experimental (RC slab) values are in good agreement with plate theory.