Research On Hysteretic Performance Of Self-centring And Energy Dissipation Connections With Shape Memory Alloy Plates

Shape memory alloy(SMA)shows great potential in seismic application because of its excellent superelasticity.In order to promote the application of SMA in seismic applications,the material properties of SMA and the hysteretic performance of SMA selfcentering energy dissipation connections(SSEC)were systematically studied supported by the major project of the National Natural Science Foundation of China(51890902)in this paper.The main work and research conclusions are as follows:Firstly,the thermodynamic properties of SMA plate were tested,and the transition temperature was determined.Then,the monotonic tension,cyclic tension-release and cyclic tension-compression tests of SMA plates were carried out.The test parameters were plate thickness,test temperature,training program and loading system.The hysteretic performance of SMA plate was analyzed,such as strength,self-centering capacity and energy dissipation capacity.The maximum difference of ultimate strength and residual strain of SMA plates with three thicknesses was 16.6% and 68%,respectively.The test results showed that the test temperature has an effect on the strength and selfcentering capacity of SMA plate.The ultimate strength of SMA plate at 25℃ was 64.3%higher than that at 0℃.However,the residual strain of SMA plate at 0℃ was 7.11 times higher than that at 25℃.The most suitable training program is 4% tension training,which reduced the residual strain of SMA plate by 35.5%,and increased the ultimate strength by 8.6%.Moreover,SMA plate does not need tension-compression training when bearing cyclic tension-compression load.The stress-strain curve of SMA plate under cyclic tension-compression load shows obvious asymmetric characteristics.At the same strain,the compression stress is higher than the tension stress,and the recoverable strain of compression response is smaller.Under cyclic tension-compression load,the residual strain of SMA plate decreased from 0.64% to 0.19%,because the reverse compression load can effectively inhibit the martensitic slip/dislocation deformation in SMA plate.A SMA constitutive model considering residual strain and tension-compression asymmetry was proposed,which can accurately predict the stress-strain behavior of superelastic SMA.Based on the seismic concept of damage control,a new type of SSEC was proposed.Firstly,the quasi-static test of 15 SSEC were carried out.The test parameters included the material of connecting plate,the layers of connecting plate,the stiffness ratio of SMAQ160/aluminum alloy(ALA),the preload of flange bolts and loading system.The flexural strength,stiffness,ductility,self-centering capacity and energy dissipation capacity of SSEC were analyzed.The flexural strength and stiffness of connection with two layer SMA was 1.96 and 1.79 times that of connection with one layer SMA,respectively.The rotation capacity of SSEC was greater than 4% drift angle.The SSEC with superelastic SMA showed excellent self-centering response.When unloading from 4% drift angle,the residual drift angle was only 0.35%.SMA-Q160/ALA system can significantly improve the energy dissipation capacity of SSEC.The total energy consumption and equivalent viscous damping coefficient of SMA-Q160/ALA connections were 2.96 and 3.73 times that of SMA connections,respectively.Moreover,SMA-Q160/ALA connections can restore the loading angle of 79.2% at most.Compared with bolt sliding friction energy dissipation,SMA-Q160/ALA system is a better method to improve the energy dissipation capacity of SSEC.The energy dissipation capacity of connection with SMA-Q160/ALA were three times that of connection with bolt sliding,and the residual drift angle were only 66.9% of that of connection with bolt sliding.The finite element(FE)model of SSEC was established by using ABAQUS.The detailed FE parameter analysis was carried out,and the effects of SMA-Q160 stiffness ratio and SMA-ALA stiffness ratio on the hysteretic performance of SSEC were systematically studied.The numerical results showed that the stiffness ratio of SMAQ160/ALA had a coupling effect on the flexural strength,self-centering capacity and energy dissipation capacity of SSEC.When the thickness ratio of SMA and Q160/ALA increased from 0.08 to 0.58 and 0.33 respectively,the dimensionless bending strength increased from 0.13 to 0.74,the residual angle decreases by 86.8% when the thickness of SMA increased from 2 mm to 20 mm,and the total energy consumption increases by 6times when the thickness ratio of Q160/ALA increased from 2 mm to 20 mm.Based on the comprehensive analysis of the hysteretic performance of SSEC,the hysteretic design method of SSEC was proposed through the comprehensive analysis of the hysteretic behavior of SSEC.The calculation formulas of skeleton curve and flexural strength were deduced.According to the results of FE analysis,the calculation formula of residual drift angle was fitted by genetic algorithm.The theoretical values were compared with the test and FE values.The theoretical analysis results showed that the skeleton curve obtained by the theoretical formula can accurately reflect the variation trend of the moment-angle,and the theoretical formula can accurately calculate the flexural strength and residual drift angle of the connection.