Seismic Vulnerability of flat Slab Structures

Abstract

The effectiveness of flat slab construction is very well known, however itsvulnerability when subjected to seismic excitation also needs to be studied owing toits flexibility. Flat slab buildings though prove to take gravity loads effectively, theirperformance under earthquake excitation has always been in question. For the studypurpose, a 5-storey regular building has been taken. For the modeling of flat slab, aneffective beam width concept hasbeen incorporated where the portion of the slab thatparticipates in stiffness sharing is formulated. The analytical procedure to be followedfor the analysis procedure has been linear static method. Here the vertical distributionof base shear to different floor levels has been done in accordance with the IndianStandard IS 1893 (Part 1) : 2002. The seismic performance of the given buildingmodel for flat slab system as well as for the corresponding conventional slab-beam-column system has been studied. The check for limit states for inter-storey drifts aswell as punching shear has been done. Comparison has been for the exceedence of theabove mentioned limits states for the two systems. Flat slab buildings are found toshow higher inter-storey drift values as compared to those shown by conventionalframed system. Cost analysis has been performed for the two systems taking intoconsideration the different parameters: quantity of concrete volume, reinforcement,formwork, total volume of building and the timescale factor. The total cost involvedin construction for the two systems is compared for different configurations ofbuilding to state the effectiveness of flat slab building over the conventional beam-slab-column system. Flat slab system is found to be cost effective for panel sizeranging upto 6m x 6m and not so much effective afterwards.