A single-run 3D modal pushover analysis of asymmetric-plan buildings under simultaneous bi-directional seismic excitation

In recent years, by developing the performance-based design methodology the application of the pushover analysis as a practical procedure has been widely developed for the design and seismic assessment of structures. Nevertheless, the conventional pushover procedures, such as the suggested procedures by the guidelines, are restricted to a single-mode and cannot consider the effects of the higher and torsional modes as well as the effects of the simultaneous bi-directional excitation. In this paper, a new single-run pushover procedure is proposed for pushover analysis of asymmetric-plan buildings under the simultaneous bi-directional excitation, in which, the applied load pattern is calculated based on the combined modal story shear and torque profiles under the simultaneous excitation in x and y directions so that the obtained story shears and torques responses be equal to the combined modal story shears and torques from the linear response spectrum analysis. In the proposed load pattern, the contribution of the higher and torsional modes and their interaction as well as the effects of the frequency content of a design spectrum and also the effects of the simultaneous bi-directional excitation in the inelastic behavior of the structures are considered. Furthermore, in order to consider the instantaneous changes in the nonlinear characteristics of the structure during the pushover analysis, the capacity curve of the structure is obtained based on the adaptive capacity spectrum method. In order to verify the accuracy and the efficiency of the mentioned method, using the OpenSees software, the proposed method is evaluated through two asymmetric-plan buildings under seven horizontal pairs of ground motion records and the resulted responses from the proposed procedure and the other studied pushover methods are compared with the responses of the nonlinear time history analysis as the accurate responses. The results establish the high accuracy of the proposed method in the estimation of the structural responses.