Developing a method for multi-modal shear-based pushover analysis

Abstract

The nonlinear static seismic analysis has become the focus of many research works because of its simplicity compared with dynamic time history analysis. Procedures have been proposed to include the effect of higher modes in pushover analysis. In this study, a combinatory procedure of two independent modal pushover analyses is presented. The proposed method uses the story shear force. Essentially, the elastic relative stiffness of each story along with the story drifts are used to calculate the story shear force. Two different ways are utilized to estimate the contributions of higher modes to the story shear force. As confirmed by representative examples, it is shown that a combinatory approach of picking up the maximum values of responses between the two presented pushover procedures results in minimum RMS errors in comparison to the exact nonlinear dynamic analysis. In other words, always the maximum response between the two methods is nearest to the exact value calculated as the average of nonlinear time history analysis with earthquakes. Moreover, the combinatory method is shown to be considerably more accurate than previous methods including the modal pushover (MPA) and a recent method of pushover analysis (SSAP) on the basis of story shear force. This is true while the proposed method is much easier to carry out than both MPA and SSAP approaches.