PUSHOVER ANALYSIS OF 20 STOREY RCC SETBACK BUILDINGS OF DIFFERENT CONFIGURATION USING SAP2000

Abstract

Behaviour of multi-storey framed buildings throughout strong earthquake motion depend on the stiffness, strength and mass distribution in horizontal as well as vertical planes of the buildings. Damage occurring due to earthquake ground motion mainly starts at locations where structural weakness is present in the frames of multi-storey buildings. This weakness further increases and concentrates on the damage of structures by plastification resulting in complete collapse of building. In many cases weakness occurs due to discontinuities in stiffness, mass or strength between two successive storeys. The storey discontinuities are often due to immediate variations in the geometry of frames along with height. In past earthquakes, there are many examples of building failure due to such type of discontinuity in vertical direction. Irregularity in configuration either in elevation or plan was sometimes recognised as one of the main causes building failure during earthquakes. A common type of vertical irregularity (geometrical) in building develops due to sudden reduction in the lateral dimension at specific levels of the building. This type of building is known as setback building. Many investigations has been performed to understand the behaviour of setback buildings and to visualise method for further improvement in performance. Pushover analysis is a non-linear static analysis mainly used for evaluation of seismic properties of framed buildings conventional pushover analysis outlined in ATC 40:1996 and FEMA 356:2000 is limited for buildings having regular geometry. Using conventional non- linear static pushover analysis, it may not be possible to measure the seismic performance of setback buildings because of the limitation for higher modes effects in irregular structures. There is less research found in the literature for the use of non-linear static (pushover) analysis of setback buildings. The study of conventional method of pushover analysis is instructive. In the present study a comparative study of non-linear static (pushover) analysis is carried out on different vertically irregular buildings having equal plan area and equal setbacks with different shapes using displacement method.