Comparative Study of Seismic Response of RC Frame Soft-Storey Buildings

Abstract

The use of brick masonry as infill walls in reinforced concrete (RC) framed buildings is inevitable even in highly earthquake prone areas. Due to increase in demands for architectural features in the framed buildings, the provision of soft storey is a common practice in many multi storeyed structures throughout the world, for parking. In the past earthquakes, surveys of buildings failed show that these types of structures are found to be the most vulnerable. After the Bhuj earthquake in 2001, the revision of code IS:1893 was done in 2002, introducing certain new design recommendations especially for stilt framed buildings. As per the clause 7.10.3(a) of the same code: “The columns and beams of the soft-storey are to be designed for the multiplication factor of 2.5 times the storey shears and moments calculated under seismic loads of bare frame”. The given multiplication factor (MF) of 2.5, applicable for all the stilt framed buildings, is proved to be quite high and suggests that all existing stilt framed buildings (whose design was based on the earlier codes) are considered to be highly vulnerable under seismic loading. However, this value of MF does not account for the types and numbers of infill walls, number of bays and storeys, etc. The present study is an attempt to study the variation in different structural properties such as lateral strength, stiffness, ductility, etc., for the considered frame when designed for zone III and redesigned as per the clause 7.10.3(a) of IS:1893-2002.