A Pushover Procedure Based on the Modal Story Shear and Torsional Moment for Asymmetric-Plan Buildings under Simultaneous Bi-Directional Seismic Excitation

In this paper, a modal pushover method is introduced for the assessment of the asymmetric-plan buildings in which, a load pattern is derived based on the story shears and story torque of building due to the simultaneous excitation in x and y directions. The proposed method is a single-run procedure and its significant advantage is its capability in consideration of the structural yielding in one direction on the total responses of the structure due to the simultaneous excitation in two orthogonal directions. In this method, in order to consider the instantaneous changes during the pushover analysis, two capacity curves of the structure are established based on the adaptive capacity spectrum method and the target displacement corresponding to each capacity curve is determined. Then, the structural responses at two pushover steps corresponding to the obtained target displacements are obtained. Eventually, the total responses of the structure are computed by combining the responses corresponding to the x and y directions. In order to evaluate the proposed method, this method has been applied to an irregular 20-story building subjected to the seven pairs of ground motion records and the obtained results are compared with the responses of nonlinear dynamic analysis as the exact responses. The results show the high accuracy of the proposed method in estimating the inter-story drifts of the studied building.