Analyses of the Base Isolated Buildings; Nonlinear Model Time History Versus Codes' Methods

Abstract

Multi-story hypothetical reinforced concrete buildings of variable geometric configurations (symmetrical, vertically irregular, horizontally irregular, with and without shear walls); with the isolated bases via high damping rubber bearing and friction pendulum systems, are analyzed using finite element method under seismic load function (North-South component of the ground motion that recorded at a site in El Centro, California in 1940) via SAP2000-V16 software. Four methods of analysis are adopted. The accuracy of the nonlinear model time history is compared with that recommended by the international codes, namely; nonlinear direct integration, equivalent lateral force, and response spectrum methods. The bilinear hysteretic model of base isolation system and the Rayleigh damping framework for superstructure are adopted. The results support the powerful nonlinear model time history analysis, due to the negligible deviations from those predicted by the robust nonlinear direct integration method. The response spectrum method is proved to be more reliable than the equivalent lateral force method which over predicts the displacement and rotation profiles for the isolated buildings.