Earthquake Behaviour of Flat Slab Buildings – An Elastic Study

Abstract: Buildings are provided with flat slabs due to their versatility in interior design, architectural needs, rapidity in construction, and reduced storey height. But such buildings evidenced poor performance from past earthquakes sustaining brittle damages. Therefore, IS 1893-1 places restrictions on the design of a flat slab building with a response reduction factor of R = 3 considering (i) RC structural walls designed to resist entire lateral loads; (ii) perimeter RC special moment resisting frames designed to resist 25% lateral loads; and (if possible) an outrigger and belt truss system that connects the core structural wall and perimeter frames. Therefore, a set of RC buildings with different flat slab buildings is considered, and responses from equivalent static analysis (ESA) and model analyses are compared with conventional slab buildings. Response parameters considered include (i) the distribution of hogging and sagging moments in the slab under gravity and lateral loads; (ii) diaphragm flexibility; (iii) maximum interstorey drift; (iv) storey shear; (v) the modal mass participation ratio and natural period; and (vi) base shear. The bending moment in slabs increases in flat slab buildings under gravity loads and is reduced under lateral loads with the provision of structural walls. It is necessary to design flat slab buildings for huge forces, considering diaphragm action, and checking for diaphragm flexibility without including rigid diaphragms. The provision of perimeter beams with structural walls may increase the structural performance under inelastic actions, but it requires a detailed study.