Experimental Study And Optimization Of SMA-based Negative Stiffness Isolation Device For Bridges

Seismic tests have shown that under near-fault seismic action,even when a bridge is designed with seismic isolation,its superstructure may produce a large displacement response,causing damage such as girder collisions,mainly due to the inadequate limiting capacity of conventional vibration isolation devices.Shape Memory Alloys(SMAs)are a good solution to these problems due to their super elasticity and damping properties.However,with the introduction of SMA,the overall stiffness of the vibration isolation device increases,resulting in a large internal force response of the bridge substructure and posing a new safety hazard to the structure.In order to solve the above problems and balance the contradictory relationship between "force and displacement",this paper designs and fabricates an SMA negative stiffness isolation device,using a combination of theoretical analysis,numerical simulation and model tests,the specific research content is as follows:(1)Based on the theoretical analysis,the design principle and device construction of SMA negative stiffness isolators are explained,and the restoring force model of SMA negative stiffness isolators is revealed.(2)The specimens of the SMA negative stiffness isolators were designed and fabricated,and static tests were carried out to verify the restoring force model of the devices.The test results show that the design of the inverse surface can effectively generate negative stiffness in the device,weakening the overall stiffness of the device;while the arrangement of SMA cables in a ring around the bearing may lead to premature fracture due to insufficient sliding at the corner of the bearing,reducing the maximum displacement of the device.(3)Based on the Abaqus 2021 software,numerical simulations were carried out for the SMA negative stiffness isolation device,and the finite element model of the device was calibrated according to the test results.The finite element analysis showed that there was indeed a problem of finite sliding between the SMA cable and the support in the specimen,resulting in a reduction in the effective length of the SMA cable.Following this,an optimisation scheme for the SMA negative stiffness isolation device was proposed and the optimised device was subjected to static parameter analysis and comparative analysis by means of Abaqus 2021 software.The results show that the optimised device can effectively avoid the problem of reduced effective length of SMA cords,and the SMA negative stiffness device has a smaller force compared with the SMA positive stiffness device and SMA zero stiffness device.(4)Based on SAP 2000 software,a finite element model of an actual continuous girder bridge was established to analyse the dynamic parameters of the optimised SMA negative stiffness seismic isolators,revealing the effects of radius of curvature,friction coefficient and the amount of SMA cables on the seismic performance of the device.Afterwards,the seismic isolation performance of the optimised SMA negative stiffness isolator was compared and analysed by inputting several seismic waves.The results show that the SMA negative stiffness isolation device has better seismic isolation performance than the SMA positive stiffness device and the SMA zero stiffness device,and significantly reduces the internal force response of the bridge substructure while ensuring little or no increase in the displacement of the superstructure.