Numerical Simulation And Structural Seismic Isolation Performance Of Shape Memory Alloy Spring-Double Concave Friction Pendulum Bearing(SMA-DCFPB)

Foundation seismic isolation is a measure to isolate the transfer of seismic energy from the seismic isolation layer to the superstructure by adding seismic isolation devices to the base of the building to avoid the building being damaged.Seismic isolators need to have some specific conditions,such as:having a certain strength and initial stiffness;having sufficient deformation capacity;being able to provide large damping and having good energy dissipation capacity,etc.Among them,slip friction isolators are widely used in building and bridge structures because of their good seismic isolation performance.Double Concave Friction Pendulum Bearing(DCFPB)has the advantages of high bearing capacity,high energy consumption and high stability.There are also some disadvantages,such as:in the case of the radius of curvature is determined,its seismic isolation period will not change,under the action of long-period earthquake,easy to cause low-frequency resonance problems;self-resetting performance is not good;under the action of large earthquake,the seismic isolation bearing will produce excessive displacement,resulting in the risk of bearing overturning,etc.Shape Memory Alloys(SMA)materials have a variety of excellent characteristics such as shape memory effect,super elasticity effect,and high damping effect.Therefore,this paper combines SMA spring and DCFPB effectively to design a composite support,namely SMA-DCFPB,in a reasonable way.On the one hand,the hyperelasticity effect of SMA springs can be used to extend the period of the seismic isolation structure and avoid the occurrence of low-frequency resonance;on the other hand,the shape memory effect of SMA springs can be used to make the bearing better selfresetting and reduce the residual displacement of the bearing;SMA springs can also increase the horizontal stiffness of DCFPB,which can effectively control the horizontal displacement of DCFPB under the action of large earthquake and prevent the instability of the bearing due to excessive displacement;finally,the high damping effect of SMA springs can be used to consume seismic energy and reduce the seismic response of the seismic isolation structure.In order to study the mechanical properties and seismic isolation efficiency of SMA-DCFPB,the following work was carried out in this paper:(1)The basic structure and working principle of DCFPB are introduced,the hysteresis model,residual displacement,stiffness and self-oscillation period equations of DCFPB are derived,and SMA-DCFPB is proposed on this basis.the basic structure,working principle and design points of SMADCFPB are described,theoretical analysis of SMA-DCFPB is carried out,and the stiffness,self-oscillation period and self-reset characteristics of DCFPB and SMA-DCFPB are compared.The results show that the stiffness,selfoscillation period and self-resetting characteristics of the SMA-DCFPB are better than those of the DCFPB.The results show that the SMA spring can provide nonlinear restoring force compared with DCFPB,and the increased stiffness of SMA-DCFPB can change its self-oscillation period and reduce the residual displacement.The equivalent linearization parameter calculation method of SMA-DCFPB is presented.(2)The solid models of DCFPB and SMA-DCFPB were established by using ABAQUS finite element software,and the energy dissipation,equivalent stiffness,equivalent damping ratio and self-resetting performance of the two supports were compared by simulating low circumferential reciprocation tests.And the finite element solution results are compared with the theoretical analysis results.The effects of vertical pressure,displacement amplitude,friction coefficient,radius of curvature and number of SMA spring turns on the mechanical properties(hysteretic energy dissipation,equivalent stiffness and equivalent damping ratio)of SMA-DCFPB were further investigated.The results show that the error between the numerical simulation and the theoretical analysis is within 10%,which proves that the theoretical derivation is reasonable,and the hysteretic energy dissipation of SMA-DCFPB increases with the increase of vertical pressure,design displacement and friction coefficient,and decreases with the increase of radius of curvature and number of SMA spring turns;the equivalent stiff ness increases with the increase of vertical pressure and friction coefficient,and decreases with the increase of design displacement,radius of curvature and number of SMA spring turns.The equivalent damping ratio increases with increasing vertical pressure,friction coefficient,and radius of curvature,and decreases with increasing design displacement and number of coils of SMA springs.(3)The finite element models of three structures(non-seismic isolated structure,DCFPB isolated structure and SMA-DCFPB isolated structure)were developed separately using the finite element software ETABS.Five natural waves and two artificial waves were selected to carry out the modal analysis and dynamic time analysis of the three structures under multiple and rare earthquakes.The seismic isolation effects of DCFPB and SMA-DCFPB were further investigated by comparing the interstory shear force,interstory displacement,relative acceleration and seismic isolation bearing displacement responses of the above three structures.The results show that the seismic isolation performance of the DCFPB isolation structure and SMADCFPB isolation structure can be better under the action of rare earthquakes,and the seismic isolation efficiency of the SMA-DCFPB isolation structure is more significant than that of the DCFPB isolation structure.