Analysis And Design of Base Isolated Asymmetric Structure

Abstract

In order to control the vibration of building during seismic events, base isolators is most commonly used for energy absorption. It dissipates the energy by its own char- acteristics and also changes the dynamic behavior of the building. Today there are number of types of isolators available in the market, which uses a variety of materials and designs to obtain various levels of sti ness and damping. Some of this includes Lead rubber bearings, High damping rubber bearings and Friction pendulum system. These isolators can be installed at various location of the building, but are usually provided at the bottom of the building.In present study an attempt is made to un- derstand the Seismic behavior of base isolated asymmetric structures. Finite element models were employed in the analysis using the computer program SAP 2000 version 14.1. A fast nonlinear Kobe Response spectrum analysis were car- ried out to obtain the response of the structure. A strategy for protecting building from earthquake is to limit the base shear, which provides an overall assessment of the seismic response of the structure. In this study 0%, 5%, 10% and 15% of mass and sti ness eccentricities are in- corporated in super structure. Mass eccentricity in super structure is incorporated by shifting the center of mass by 5%, 10% and 15% to one side of building, while sti ness eccentricity is incorporated by shifting the center of sti ness by 5%, 10% and 15% to one side of building, and to study the in uence of base isolated buildings with mass and sti ness eccentricity in super structure on the seismic response for 3 and 6 storey buildings. The results of analysis are compiled in form of time period, base shear, displacement, and storey drift. Comparison of results of base isolated buildings of 0%, 5%, 10% and 15% of mass and sti ness eccentricities with the xed base building. Also comparison is done for mass and sti ness eccentricities in base isolated buildings is carried out. vi Results form this study conclude that a higher base shear, displacement and story drift exits in base isolated buildings with mass eccentricities in the superstructure than in base isolated buildings with sti ness eccentricity in the building. Second to study the best location of isolators when 5%, 10% and 15% of mass eccentricities in super structure and various distribution of isolators in base isolation system such that CI = CM, CI = - CM, CI = 0.5 CM, CI = - 0.5 CM. This includes the sti ness eccentricities in base isolation system for 3 storey building. Where CI means the center of isolator and CM means the center of mass. The results of analysis are compiled in form of time period, base shear, displacement, storey drift and ampli- cation factor. Comparison of results of base isolated buildings of 5%, 10% and 15% of mass eccentricities in super structure and sti ness eccentricities in base isolation system for models CI = CM, CI = - CM, CI = 0.5 CM, CI = - 0.5 CM with the xed base building. Results form this study conclude that the minimum rotation for the base isolated buildings were obtained for the case of CI = CM isolator distribution.