Development Of Constitutive Model And Seismic Reduction Effect Of Shape Memory Alloy

As a new type material of dissipating energy and reducing seismic responses,SMA material has been applied in civil engineering to a certain degree.Its good self-centering property can reduce the residual deformation of the structure while consuming energy.Based on previous work,this paper proposes a multi-segment linear mathematical model based on Aabqus that can describe the mechanical behavior of the reinforced section of SMA material.The model realizes the separation of the loading path and unloading path of the martensite strengthening segment.Compared with the SMA model proposed by other scholars,the constitutive relationship model of the path separation is closer to the actual mechanical behavior of the SMA,the constitutive relationship model after path separation is closer to the actual mechanical behavior of SMA.With a 6-story of steel frame structure as the research object,using the method of numerical simulation and quantitative contrast the different constitutive model of SMA braced frame structure seismic response differences,The results show that the sub-cyclic unloading mode of the SMA constitutive model affects the peak displacement and residual strain of the structure.According to the results of the choice of different SMA constitutive model is given.Compared with the steel frame structure,the SMA braced structure can effectively control the inter-storey drift ratio of the structure,so that the deformation of the structure is more evenly distributed in each floor,which greatly reduces the residual displacement of the top floor after large deformation,and shows a good self-centering performance.The following works have been completed in the thesis:Superelastic SMA performance test,the mechanical properties of SMA under different temperatures,strain amplitude and rate were completed,and the stress-strain relationship,residual deformation evolution,energy dissipation attenuation law and equivalent damping ratio change of the hyperelastic SMA material under 24℃,18℃and 12℃ were studied.According to the experimental results,the exponential evolution equation was used to simulate the change process of residual strain with the cycle,and the mechanical behavior of SMA under the loading frequencies of 0.4Hz,0.2Hz and 0.1Hz was studied.The SMA residual strain-free constitutive model was developed.Based on the performance test phenomenon of hyperelastic SMA and the experimental results of other scholars,the mechanical behavior of SMA in transition section was improved,the SMA cycle constitutive model was developed,the exponential evolution equation was proposed,and the simulation of residual strain,stress and strain was realized.The model can accurately simulate the mechanical properties of materials under different temperatures,amplituresand loading rates,and can capture the phase change ratcheting effect of SMA.In order to study the shock absorption effect of SMA materials,the improved constitutive model and three common SMA constitutive models were redeveloped.Taking a 6-story steel frame structure as an example,the influence of the model differences on the seismic performance of the structure is compared,and the selection of different SMA constitutive models is proposed.The disadvantages of braces large-strain seismic structures and the advantages of braces small-strain seismic structures are studied.Taking a 4-story frame structure as an example,the effects of six different SMA bracing arrangements on the damping effect of the structure are compared.