Seismic Behavior Of Irregular RC Building Subjected To Multiple Earthquake Excitation

Abstract

An earthquake is the most vulnerable natural disaster, which causes intensive shaking of ground and structure over it. In the past two decades, India has experienced six major earthquakes, which has caused huge damage to buildings and other infrastructure; also, more than 23,000 lives were lost. Many case studies and researchers have identified that Buildings having irregularity of either plan or vertical irregularity suffer more damage as compared to symmetric and regular buildings. Building having plan irregularity causes torsion in the building which results in twisting of building with respect to vertical axis. Such buildings when subjected to high intensity earthquakes may undergo large deformation. In the majority of the strong ground motions, the structures are likely to be pushed into an inelastic zone, so to predict the collapse mechanism and inelastic response of the structure it is necessary to perform nonlinear analysis. Nonlinear analysis procedures are time consuming but more realistic than linear analysis. In this project nonlinear static procedures are studied from standards like FEMA 273, ATC 40, ASCE 41 and FEMA 440. From these standards, two such Procedures namely, Displacement Coefficient Method and Capacity Spectrum Method are performed for nonlinear static analysis. Nonlinear time history analysis and incremental dynamic analysis are performed for nonlinear dynamic analysis. Present study is an attempt to understand inelastic behavior of irregular RC building. Usually, earthquakes occur as a series of shocks but in seismic design it is mostly assumed as a single shock. Strong earthquakes have more and larger foreshocks, as well as aftershocks, and the sequences can last for months or years or even longer. Generally, Aftershocks can be of large magnitude and are unpredictable, which may collapse buildings damaged from the main shock. Thus, the structural behavior of buildings subjected to multiple earthquakes is different compared to single earthquakes. In this work, verification of pushover analysis is carried out to understand nonlinear static methods. Also, IDA on G+2 plan irregular building (hypothetical building) and G+7 realistic building is carried out considering unidirectional and bidirectional earthquake excitation. Torsional irregularity indices are calculated according to different country's seismic codes to find out whether a building is torsionally irregular or not. Based on results of IDA, regression analysis is carried out between interstorey drift ratio and indices, which shows better correlation of indices mentioned in IS 1893:2016 with interstorey drift ratio.