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

Multi-story hypothetical reinforced concrete buildings of variable geometric configurations (symmetrical, vertically irregular, horizontally irregular, with and without shear walls); with isolated bases via high damping rubber bearing and friction pendulum systems, are analyzed by using finite element method under seismic load function (North-South component of the ground motion recorded at a site in El Centro, California in 1940) via SAP2000-V16 software. Four methods of analysis are adopted. The accuracy of nonlinear modal time history is compared to that of methods recommended by 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 powerfulness of the nonlinear modal time history analysis, due to the negligible deviations from those predicted by the robust nonlinear direct integration method. The response spectrum method proved to be more reliable than the equivalent lateral force method which over predicts the displacement and rotation profiles for the isolated buildings. DOI: http://dx.doi.org/10.25130/tjes.24.2017.32