Prediction of the peak seismic response of asymmetric buildings under bidirectional horizontal ground motion using equivalentSDOFmodel

Abstract

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.

Pushover-Based Seismic Capacity Evaluation of Uto City Hall Damaged by the 2016 Kumamoto Earthquake

“…The second assumption is that the principal directions of the first and second modal responses are almost orthogonal. The limitation of the current version of MABPA has been discussed in a previous report [29].…”

“…">Brief Review of Related StudiesThe author has determined that there are four possible approaches toward predicting the peak response of an asymmetric building with consideration given to the torsional effects. The first one is the extended N2 method [10][11][12][13][14]; the second one is a modal pushover analysis [15][16][17][18][19][20][21][22]; the third one consists of combining two pushover analyses and the envelope of the results, as proposed by Bosco et al [23,24]; the fourth one consists of combining the analyses of two independently equivalent SDOF models (representing the first and second modes) with the envelope of four pushover analyses (including the effect of bidirectional excitation) [25][26][27][28][29].The first approach, namely, the extended N2 method, is an extended version of the simplified procedure proposed by Fajfar and Fischinger [4]. This approach involves the estimation of the peak response for each frame in the pushover analysis results multiplied by a correction factor, which is defined using the linear dynamic analysis and pushover analysis results [10][11][12][13].The second approach, namely, modal pushover analysis (MPA), was proposed by Chopra and Goel for regular buildings and considers the effect of higher modes.…”

“…Bosco et al [24] investigated the applicability of this procedure to multistory building models with the same geometry on each floor. In this procedure, corrective eccentricity is a key parameter in the pushover analyses.The fourth approach has been proposed by the author [25][26][27][28][29]. In this paper, this simplified procedure is called mode-adaptive bidirectional pushover analysis (MABPA), and it involves the evaluation of the first and second mode peak responses independently from the equivalent SDOF models formulated with consideration given to the principal direction of the first modal response.…”

“…The second assumption is that the principal directions of the first and second modal responses are almost orthogonal. The limitation of the current version of MABPA has been discussed in a previous report [29].These studies mentioned above were mainly focused on the prediction of the peak response (mainly displacement) under given ground motions (mostly by the response spectrum). Some of these procedures may be used for the prediction of the seismic intensity, or scaling factor, corresponding to a certain (given) displacement limit.…”

“…Buildings 2019, 9, 140 2 of 37 the nonlinear seismic behavior of buildings. In recent years, the author and other researchers have worked to extend these simplified procedures and improve the seismic performance estimates of buildings with plan and/or elevation irregularities [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”