Prediction of the peak seismic response of asymmetric buildings under bidirectional horizontal ground motion using equivalent SDOF model

The applicability of a simplified procedure, namely mode‐adaptive bidirectional pushover analysis ( MABPA ), to the prediction of the non‐linear peak response of a multistory asymmetric building subjected to bidirectional excitation is discussed. The first part of the paper summarizes the formulation of 2 independent equivalent single‐degree‐of‐freedom models representing the first and second modal responses. The relationship between the critical assumptions of MABPA and the torsional index defined based on mode shape is then discussed. In the latter part of the paper, non‐linear time‐history analyses of 4‐story torsionally stiff ( TS ) or torsionally flexible asymmetric buildings are described, and the results are compared with the predictions. The results show that MABPA predicts the peak response displacement of only the TS asymmetric buildings satisfactorily. Therefore, MABPA should be considered applicable only to TS buildings. The applicability of MABPA to a given asymmetric building may be evaluated by using the torsional indices of the first 3 modes.