Performance Based Seismic Design of Tall R.C Buildings With and Without In-Plane Flexibility of Slabs

Earthquakes are unpredictable catastrophic events leading to loss of life and property. After the Northridge earthquake, the need to shift from the conventional codal design was felt necessary. In this context, performance based design is the new emerging technique, wherein the performance of the structure under a seismic event is predicted using non-linear analysis techniques and designed accordingly to surpass certain performance levels. In contextto performance based design, pushover analysis is gaining popularity as a simple and convenient tool to evaluate the true performance structures. Also, the floors in a building are usually modelled with a rigid floor assumption considering the deformation of the slab in its plane to be negligible. However, this assumption leads to discrepancy especially when a dynamic analysis is carried out. In the present work, a 10 story building model has been generated with three types of slab systems, viz. flat slab, grid slab and beam slab systems. Initially the in-plane stiffness of slabs is highlighted by carrying out a free vibration as well as response spectrum analysis, using two methods to model slabs. Four different types of beam sections are also used. The number of stories is varied to 20 and 30, and its effect on in-plane stiffness is highlighted. Lastly a pushover analysis for a few models is carried out to demonstrate the effect of in-plane stiffness of slabs on the inelastic behaviour of the structure. The performance points obtained from the pushover curves are used to suggest a performance based seismic design.