Behavior of Shallow-Beam Supported Reinforced Concrete Rectangular Slabs: Analytical and Experimental Investigations

Abstract

A design equation useful for proportioning the rectangular reinforced concrete slab cast monolithic with the equally spaced shallow in-built beams and resting over the simple supports on its outer boundaries is presented herein. The use of these beams becomes mandatory in buildings due to some architectural constraints. Full-scale slabs designed using the proposed design equations are experimentally validated. The actual crack pattern at the collapse load, for the two and three-panel slabs tested in the laboratory, was found to be in good agreement with the analytical results. A non-dimensional parameter, λ (= moment of resistance of beam/moment of resistance of beam required for the simultaneous formation of global and local collapse mechanism) has been proposed to distinguish the nature of shallow beams. Test slabs designed using the λ-value less than unity failed following a global-collapse mechanism with a load factor of more than 1.40. However, these slabs show more deflection at the design load than the permissible values but selecting a highest possible value of the beam depth satisfying both the serviceability criterion as well as the span/depth ratio of the shallow beam can reduce the actual deflection of the slab system under the design load. It is suggested that the actual slab-beam system with shallow beams should never be proportioned with λ-value more than unity as it leads to failure of the slab in a local-collapse mechanism with a reduced load factor.