Seismic Performance of Flat Slab Buildings

Abstract

Flat slab system is becoming widely popular for multistorey buildings due to its several advantages. But performance of flat slab buildings under earthquake loading is unsatisfactory due to its vulnerability to punching shear failure. Several codes provide the guidelines for deigning flat slab system under gravity load only. However flat slab buildings are also being constructed in high seismicity region which can cause collapse of the buildings under seismic loading. In this paper, performance of flat slab buildings designed as per existing code guidelines have been evaluated under earthquake loading. This study is carried out on a five and a ten storied buildings with identical plan. These buildings have been designed as per guidelines of Indian code, ACI code, Eurocode and New Zealand code. Nonlinear static analysis has been carried out to evaluate the performance of these buildings with and without considering the continuity of slab bottom reinforcement through column cages. Equivalent frame approach with transverse torsional members has been used to model these flat slab buildings. From the results of nonlinear analysis it is clear that most of the buildings are not ensuring CP performance for MCE level of hazard in high seismicity areas. Continuity of slab bottom reinforcement has an influence on performance of flat slab buildings. It improves the performance of the buildings. Maximum inter-storey drifts of the buildings at collapse have been compared with the limiting value of maximum inter-storey drifts corresponding to gravity shear ratio, given in literature. It is found that most of the buildings analyzed here are collapsing at an inter-storey drifts lower than that prescribed in literature.