Analysis of Flat Slab Connection System for Seismic Loads

Abstract

Flat slab structural systems have a large applicability due to their functional and economic advantages. As such, a good number of commercial and office buildings around many Indian metro cities, in India, have been observed to adopt flat-slab system. Initially, the reinforced concrete flat slabs had drops, and columns with capitals, and were considered to be the structures of choice for warehouse construction and heavy loads because shear was not a problem. Flat plates were subsequently developed, with no drops and no column capitals, and due to the much cheaper shuttering required, they became popular for residential and office buildings. But, till date the analysis of flat-slab systems has been a problem due to its complex load transfer mechanism and failure patterns. Flat plate slabs exhibit higher stress at the column connection and are most likely to fail due to punching shear rather than flexural failure. Thus, the vulnerability to punching shear failure has caused structural engineers to rethink the design of slab-column connections in new flat-plate frames constructed in areas of high seismicity. To avoid shear failure, parameters influencing the punching strength should be clearly investigated by realistic analytical or experimental studies. The present analytical study investigates the influence of some of the parameters governing the behavior of connections under punching shear which are concrete strength, column aspect ratio, slab thickness, gravity loading. Firstly, modelling of the whole building is carried out using the computer program SAP 2000 V [14] with columns and slabs modeled as frame and shell elements respectively. Parametric Studies on aspect ratio and depth-to-span ratio have been carried out using displacement control nonlinear static pushover analysis to investigate the influence of these parameters on punching shear capacity of the intermediate and corner column connection which proved to be the governing criteria to prescribe drift limits for flat plate systems in seismic zones.