STUDIES IN STRUCTURAL INTERACTION BETWEEN BAND BEAM AND WAFFLE SLAB

Abstract

Waffle slab consists of thin ribs along the two orthogonal directions with a thin top slab. These ribs have to be connected to a solid slab component at their edges to provide connectivity with the columns. This solid slab component is referred to as a wide beam or a Band Beam. This slab has higher width than depth since the depth is equal to the thickness of the Waffle Slab and structurally behaves like edge beams. As a result, there is interaction between this slab and the Waffle Slab depending upon their relative stiffness. The solid slab is referred to as Band Beam for being wide and forming a band around the Waffle Slab. This Band Beam may be used to play its role as a structural member and try to control the deflection of the slab apart from providing an interface between the discrete ribs and the isolated columns. The Band Beam has its own limited flexural and torsional stiffness and hence possesses limited capacity to structurally influence the behaviour of the slab. However, it is possible to reasonably enhance its flexural stiffness by providing reinforcement both in the tension as well as compression zones and also make it torsionally stiff through closely spaced stirrups. In the present studies, attempts have been made to see the impact of enhanced flexural and torsional stiffness on the maximum deflection of the slab. Reduction in self-weight moment while satisfying all the other design requirements is the primary aim to be achieved for various floor-plans and live load intensities. Also, it is possible to substantially increase the torsional stiffness of the Band beam by increasing its depths beyond the floor depths. Attempts in this regard have been made to study the impact of the enhanced torsional stiffness on the floor deflection keeping in view the available headroom in mind.