Suman Verma, Manish Sakhlecha, Alok Kumar Jain
Base isolation is regarded as a promising solution of earthquake resistant design, which results in significantly low floor accelerations, and inters storey drifts. This ensures the safety of structural as well as non structural elements, thereby keeping the building operational even after a severe earthquake. The effectiveness of a base isolation system is governed by the bilinear characteristics offered by the isolators. The present work attempts to study the effectiveness of base isolation using friction pendulum bearings (FPB) over conventional construction, using a hypothetical case study of identical conventional and isolated buildings constructed in the most seismically active region in India (Zone V). It is seen that the base isolated building exhibits excellent performance compared to the conventional ductile building. The modeling procedure for both fixed base and base isolated building in ETABS software is carried out for a regular (G+8) storied MRF building. Linear analysis using Time History Analysis (THA) for the records of Kobe earthquake, 1995 and Nonlinear analysis using Incremental Dynamic Analysis (IDA) was carried out. For IDA, incremental intensities of 0.2g, 0.4g, 0.6g, 0.8g, 1.0g and 1.2g for the previously considered Kobe earthquake were taken as input.The results of various parameters such as the variation in maximum storey displacement, maximum storey drift, lateral loads to stories, storey overturning and torsional moments and storey shear of both the buildings are studied. Using base isolation system for a (G+8) storied frame, it was found that the base isolation technique although enhanced the original performance of the building, would not be better suited for structures more than 10 storey which may exhibit time periods around 1s. It was observed that the variation in maximum storey displacement in isolated model is very low while compared with fixed base model, with the isolated frame exhibiting higher displacements. However, the interstorey displacements and drift were comparatively reduced leading to a safe design. It was also observed that storey overturning moment & storey shear exhibit a similar trend in base isolated building. The radius of proposed FPB are calculated using a suggested by Naeim, 1999 and comments were made on the overall feasibility of the proposed isolation system.
ETABS