| Buckling-restrained brace (BRB), which is one of the metallic yielding braces with high ductility and stable energy-dissipation capacity, is increasingly used in new structures and seismic retrofit of existing structures. Previous analytical results have demonstrated that the beneficial effect of the BRBs cannot be fully controlled under a traditional seismic design approach, and a performance-based seismic design approach (PBSD) which explicitly controlls the structural performance is more suitable for seismic design of BRB structures. However, most current PBSD approaches, which employ the "design-validation-redesign" manner to complete structure design, require cumbersome and time-consuming iterative assessment process by using nonlinear time history analysis till the desired performance objectives are achieved. In this study, a direct seismic design approach has been developed for buckling-restrained braced frames, based on research results of the numerical simulation technology and earthquake-resistant capacity of BRB structures. The main work and conclusions are as follows:(1) The numerical simulation technology of buckling-restrained braced frames is introduced, then verified through previous component and shaking table tests. The results show that:the fiber beam element is applicable in simulating the hysteretic behavior of steel columns, steel beams and composite beams; the modified Menegotto-Pinto model (Steel MPF model) is applicable in simulating the hysteretic behavior of BRBs, including kinematic hardening, isotropic hardening, hysteretic curve shape, asymmetric tension and compression strength, asymmetric tension and compression stiffness after yielding; the proposed numerical simulation technology is applicable in predicting earthquake response of the shaking table test structure.(2) The seismic performance of buckling-restrained braced frames is compared with that of the concentrically braced frames. Based on an incremental dynamic analysis (IDA), the collapse-resistant capacity of buckling-restrained braced frames is quantitatively evaluated with a collapse fragility analysis. The results show that:the bearing capacity of concentrically braced frames is lower than that of buckling-restrained braced frames; the deformation and acceleration responses of concentrically braced frames are larger duo to buckling of concentrical braces at some stories; considering fracture of BRBs, the collapse-resistant capacity of buckling-restrained braced frames is proved to reduce; BRBs are suggested to have good low cycle fatigue performance and large strain capacity to ensure the braces do not damage before structural collapse causing by other factors.(3) By reference to the rules stipulated in "General rule for performance-based seismic design of buildings", the structural influencing coefficients (C) of two kinds of buckling-restrained braced frames are suggested, including buckling-restrained braced frames with pinned beam-column connections (BRBF), steel dual systems with buckling-restrained braces and moment-resisting frames (BRBF-MRF). The results show that:the inter-story drifts, residual drifts and BRB maximum ductility demands control the C values of the two structures, rather than the BRB cumulative ductility demands; the C values of BRBF and BRBF-MRF are suggested to be 0.35 and 0.3, respectively.(4) A performance based seismic design approach with no iterations is developed for moment-resisting frames incorporating BRBs (BMRF), based on desirable yield mechanism, equivalent elastic-plastic SDOF system and inelastic displacement spectra. The results show that:the BMRFs designed following the proposed approach can successfully achieve the desired yield mechanism; the inter-story drifts are smaller than the target drifts under three level ground motions; the residual drifts are within the economically replaceable range; the BRB maximum ductility and cumulative ductility demands are within the ductility limit states reported by previous specimen tests. |
PDF Full Text Request