Seismic response of setback building in hilly region with effect of lift well

Abstract. Setback irregular buildings are common in hilly urban regions, including Indian sub-continent, where seismic safety is critical. Significant research has focused on plan irregularities; fewer studies performed with vertically irregularities, such as setback buildings. Vertical irregularities arise from uneven mass and stiffness distributions or changing geometric configurations along the height. Codes of various countries provide some information on plan and vertical irregularities. Limited guidelines are available in the codes such as IS 1893 (Part-I): 2016, Eurocode-8 (Part-I): 2004, and FEMA-450 (Part-1): 2003 [1-3]. Existing literature [4-5] offers two empirical expressions for the fundamental periods of irregular structures. The present study try to focus on North-East part of India, which is seismically highly sensitive (Seismic Zone - V). This study deals with setback building made of reinforced concrete and brick masonry, incorporating the effect of a reinforced concrete lift well. The lift well is acting as a shear wall. The models are performed using finite element analysis (FEA). The fundamental periods, base shear and mode shapes [6] of the building are found out with the help of response spectrum method. Fundamental periods calculated with formulae provided by various codes, existing literatures and FEA are compared for the building considering and without considering lift well. Base shears calculated with Complete Quadratic Combination (CQC) method, are also compared. It is found that initial mode shapes are indicates the more stability of the setback building with considering lift well as compared to without lift well. The variation in moments of the member basically surrounding the location of lift well plays a vital role reducing the critical stress concentration as compared to the building considering without lift well. Overall, this paper tries to contribute for improving the understanding and development of design guidelines for setback structures, including the influence of lift wells.