Adaptive Force-Based Multimode Pushover Analysis for Seismic Evaluation of Midrise Buildings

To consider the effect of higher modes in predicting the seismic responses of midrise buildings, as well as the progressive changes in the dynamic characteristics during the nonlinear analysis, an adaptive force-based multimode pushover (AFMP) procedure is presented. This procedure is an adaptive version of the single-run multimode pushover (SMP) procedure that it is envisaged to be an enhancement of the previously proposed procedure. The procedure encompasses some adaptive pushover analyses. First, an adaptive single-mode pushover analysis using the first mode shape is performed. Moreover, one or two adaptive multimode pushover analyses are implemented by means of the enhanced lateral load distributions calculated by algebraically adding the instantaneous modal story forces. Therefore, the sign reversals of load vectors in the higher modes are considered. The results obtained through the adaptive single-mode and multimode pushover analyses are enveloped to compute the final seismic responses. It is demonstrated that the AFMP procedure can estimate with acceptable accuracy the seismic responses of midrise building frames.