Study On The Cyclic Behavior Of The Buckling Restrained SMA Damper And Seismic Analysis Of Braced Frames

Shape Memory Alloy(SMA)is one type of metal alloy with nearly ideal superelasticity and good damping behavior.Differ from conventional materials in civil engineering,superelastic SMAs show typical loading plateau whereas recover deformation along a lower stress path,generating salient property of partially or fully recovering large deformation,in both forms of wires and bars,when the temperature is above the austenite finish temperature.As such,the favorable properties of superelastic SMAs attract increasing attention in the community of earthquake engineering,and have been developed and applied in many fields such as self-centering braces and dampers for buildings or bridges.But in the current development of SMA dampers,only the tensile properties of SMA materials are used,which requires some special measures.If SMA's tensile and compressive properties can be directly used,the damper design can be simplified and the utilization rate of the SMA material can be improved.In this paper,SMA's tensile and compressive properties are used to design a buckling-restrained SMA damper,and the damper's hysteretic behaviors are tested with cyclic loading.Different cross-section shapes and areas,loading rates,with or without initial damages,with or without "training"in pre-treatment,behavior changing after the pseudo-dynamic load were tested via experiments.Then the optimal group of SMA dampers was selected to carry out the experiment and research.In this paper,Wilde's constitutive model is used to match the tensile and compressive model parameters of SMA bars,and its mechanical properties are simulated numerically.SMA-based self-centering concentrically braced frames(SCCBF)perform excellently with controlling peak drift and elimating residual drift upon earthquakes.SMAs show variability in the hysteretic parameters due to the difference in metal types,crystallographic structures,component ratios,and heating treatments in producing process.In this paper,the OpenSees is used to conduct seismic analysis on SCCBF with different SMA materials on the basis of performance-based plastic design(PBPD)proposed by Qiu and Zhu.The seismic analysis results prove that despite the noticeable variety in the hysteretic properties,the SCCBF with different SMAs can successfully achieve the same performance targets prescribed in advance.Because the PBSD didn't verify its generality in different levels of SCCBF,this study aims to extend the ad hoc design approach to low-to-high rise multi-story SCCBF using SMABs and examine its generality.As such,the seismic performance of four SCCBF with various stories were intensively analyzed by subjecting them to ground motion records corresponding to the design-basis earthquake.The analysis results show that all the resulting were coinciding well with the prescribed targets of peak interstory drift ratios and ductility demands.Inaddition,the structures returned to at-rest positions without producing residual deformation after earthquakeevents.Therefore,this study successfully validates the applicability of the ad hoc design approach in SCCBF with various stories.