Performance-based Seismic Design Method Of Multi-story Self-centering Steel Frames With Shape Memory Alloy Braces

Steel frames are widely-used building types.Installing damping devices is an effective means to improve the seismic performance of steel frames.However.conventional damping devices cannot effectively eliminate the residual deformation of the frame,and excessive residual deformation may lead to huge social and economic losses.Shape memory alloys(SMAs)are attracting more and more attention in the field of earthquake engineering because of its superelasticity.They can recover large inelastic deformations while dissipating energy under earthquakes.Therefore,SMA braced frames(SMABFs)have broad application prospect.However,the design methods of SMA braced frames are still to be developedFor steel frames,the interstory drift ratio(IDR)is directly related to the damage degree of structural and non-structural components.For SMABFs,which is not clearly defined in the current seismic codes,their interstory drift ratios under earthquakes needs to be effectively and reliably estimated.This paper proposes an estimation method based on the inelastic displacement ratios(CR)to estimate the interstory displacement of SMABF.Based on the single-degree-of-freedom self-centering systems representing the typical flag-type hysteretic behavior of SMABFs,the effects of different parameters on CR are studied,and a simplified equation is proposed through nonlinear regression analysis.Then,a six-story frame is used to validate the proposed estimation method.The results show that the estimated IDR is in good agreement with the nonlinear response history analysis.The proposed method can accurately estimate the interstory displacement of SMA braced frameConsidering that many moment-resisting frames already have a certain seismic resistance,in order to improve the seismic resistance of the structure and reduce the residual deformation,this paper proposes a design method to improve the seismic performance of steel frames by installing SMA braces.The maximum interstory drift ratios and residual interstory drift ratios are selected as performance targets,and two three-or six-story frames are used to verify the method.The results of seismic analysis show that the seismic response of steel frames with reasonably designed SMA braces can meet the design targets well.In order to quantify the performance improvement effect,peak interstory drift ratios,residual interstory drift ratios and peak acceleration are selected as the key parameters for establishing single-parameter indices and multi-parameter indicators.The results show that the overall seismic performance of the steel frame is significantly improved after installation of SMA braces.Finally,this paper examines the robustness of the performance-based plastic design method for SMABF proposed by Qiu and Zhu.The examination is performed by defining different performance objectives and using different seismic design response spectra.The analysis results show that the frames designed according to the method can always meet the performance goals.Therefore,this paper proves the robustness of the method for SMA braced frames.