Performance Evaluation of a New NSP for Estimation of Seismic Demands of Nonlinear Irregular BRB Frames
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RESEARCH PAPER
Performance Evaluation of a New NSP for Estimation of Seismic Demands of Nonlinear Irregular BRB Frames Hosein Sangtarash1,2 · Mohammad Reza Banan1 · Mahmoud Reza Banan1 Received: 26 May 2018 / Accepted: 31 May 2019 © Shiraz University 2019
Abstract Nonlinear static procedures are commonly used to compute seismic demands of structural systems. This paper combines the modified capacity spectrum method (MCSM) and modal pushover analysis (MPA) and proposes a new nonlinear static method called MPA–MCSM. To evaluate the accuracy of the proposed method, 30 different buckling-restrained braced (BRB) structures which consist of 3-, 9- and 20-story BRB frames with irregularities in plan and in elevation are selected. Each structure was analyzed subjected to seven pairs of ground motions. As a measure for the performance assessment of the proposed method, four structural seismic demands: (1) peak roof displacement, (2) story drift, (3) story shear and (4) base shear, are computed for each considered structure. The accuracy of MPA–MCSM responses is checked against the results obtained from nonlinear time-history analysis (NL-THA). The results reveal that MPA–MCSM provides conservative seismic demands for BRB frames. Keywords Buckling-restrained braced frames · BRB · Equivalent nonlinear static procedure · Modal pushover analysis · Capacity spectrum method · 3D steel structure
1 Introduction In order to consider inelastic behavior of a structural system, the current civil engineering practice prefers to use a nonlinear static procedure (NSP) for computing seismic demands of a structure. ATC-40 (1996) recommended capacity spectrum method (CSM), and FEMA 440 (2005) employed modified capacity spectrum method (MCSM) for evaluating structural seismic demands. Modal pushover analysis (MPA) introduced by Chopra and Goel (2002) is a nonlinear static method. In this method, the applied lateral force pattern depends on the mode shape of the structure and remains constant during analysis. Chopra and Goel * Mohammad Reza Banan [email protected] Hosein Sangtarash [email protected] Mahmoud Reza Banan [email protected] 1
Department of Civil and Environmental Engineering, Shiraz University, Shiraz, Fars 71348‑51156, Iran
Present Address: Sistan and Baluchestan University, Zahedan, Iran
2
(2004) extended MPA method for unsymmetric buildings. This method was improved by Jianmeng et al. (2008) by considering the redistribution of lateral load pattern after the structure yields. Goel and Chopra (2004) conducted a comparison between MPA and FEMA pushover analysis. Karavasilis et al. (2008) studied the effect of mass and setback for steel moment-resisting frames. Dutta et al. (2009) studied various pushover analysis methods over a variety of problems. A comparison between the results from FEMA 356 (2000) pushover analysis and MPA method was conducted by Khoshnoudi and Marsono (2012). Kashkooli and Banan (2012) evaluated the accuracy of MPA–MCM procedure for irregular moment-resisting frames. Ghahari et
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