Study of the combination rules to estimate the inelastic response of in-plan asymmetry multi-story buildings subjected to bi-directional seismic motions

Time history response (THR) analysis on three-dimensional parametric models of five story asymmetric-plan buildings considering bi-directional earthquake action and nonlinear behavior are carried out. The buildings have six resisting plane frames connected at each floor by a rigid diaphragm (flat slab with aspect ratio 2:1) so that in the center of mass three degrees of freedom (two horizontal displacements and in plan rotation) and lumped masses are considered. The earthquake action is defined by the two horizontal components of twenty artificial records matching the average response spectrum of a set of real earthquakes. The design strengths determined as per the Chilean design practice are compared with the results of the THR considering bi-directional input motions. The ground motion components are applied changing the angle of incidence in 15° increments to find the angle of incidence where the local and global response quantities are maximized. The results have shown that it is possible to estimate the maximum values of the response under bi-directional excitation and considering nonlinear behavior using the appropriate combination rules and the elastic responses for uni-directional excitation represented by the average response spectrum. The amplification of the elastic response is similar in magnitude to the response reduction factor R*.