APPLICATION OF THE PUSHOVER-BASED PROCEDURE TO PREDICT THE LARGEST PEAK RESPONSE OF ASYMMETRIC BUILDINGS WITH BUCKLING-RESTRAINED BRACES

Abstract eng:
Asymmetric buildings are known to be vulnerable to earthquakes. This is because excessive deformation may occur at the frame of the flexible and/or weak side owing to an unfavourable torsional effect. Such deformation may lead to premature failure of the brittle members and finally to the collapse of whole buildings. To reduce the unfavourable torsional effect, one promising method is to install dampers to the frame in which excessive deformation is expected. The buckling-restrained brace (BRB) is widely used as a hysteresis damper in new buildings and for the seismic upgrading of existing buildings. For the evaluation of the peak seismic response of buildings, a pushover-based simplified procedure, which is often referred to as the nonlinear static procedure (NSP), has been developed and adopted to seismic design codes. In the case of reinforced concrete asymmetric buildings with BRBs, the first mode shape may notably change in the nonlinear range. This change may be critical in the accurate prediction of the peak response employing the NSP. However, there have been few studies on the applicability of NSPs to asymmetric buildings with BRBs. In this paper, the applicability of the simplified procedure proposed by the author to four-storey reinforcedconcrete asymmetric buildings with BRBs is numerically investigated. In the simplified procedure presented in the previous study, the largest peak response is predicted from (a) the response of two independent equivalent single-degree-of-freedom models representing the first and second modes, considering the change in the first mode shape in each nonlinear stage, and (b) the envelope obtained from the combination of four pushover analyses considering the effect of bidirectional excitation. The predicted largest peak response is compared with the nonlinear time-history analysis results considering various directions of incidence of seismic input. The results show that the largest peak response of asymmetric buildings with BRBs is satisfactorily predicted by the procedure presented in the previous study. The effect of the change in mode shape on the accuracy of the NSP is also investigated and shown to be important in the accurate prediction of the peak response.

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