Based On Analysis Of Seismic Isolation Performance To Research Design Method Of Multi-level Performance SMA-LRB

Under near-fault earthquakes,the bridge will have large displacement and residual deformation.The limit displacement of the traditional isolation device is insufficient,which leads to the serious earthquake damage such as falling beam.The traditional mechanical model of bearing is simple,and increasing the stiffness can improve the capacity of limit displacement,but the effect of isolation will be worse.On the contrary,the isolation effect can be improved by reducing the stiffness of the bearing,but the capability of limit displacement will be weakened.According to the concept of multi-level performance,a new type of bearing is designed,which has good isolation effect under small and medium earthquakes and the excellent limit displacement capability under strong earthquakes.The new bearing adopts a special material,shape memory alloy(SMA),which has shape memory effect(SME),super-elasticity effect(SE)and high damping effect.A multi-performance levels SMA-LRB composite bearing is designed by combining multiple batches of SMA cables with LRB.On the one hand,different idle stroke and length of SMA cable is designed to achieve the purpose of multi-level performance;On the other hand,the super elastic and high damping properties of SMA cable are used to consume the seismic energy,so as to achieve seismic isolation.In order to study the mechanical properties and design method of multi-level performance SMA-LRB,the main works and conclusions are as follows:(1)The design requirements and key points and concrete design scheme of multi-level performance SMA-LRB composite bearing are introduced emphatically.The mechanism of multi-level performance SMA-LRB is introduced.And then the restoring force model of SMA in the bearing is presented according to the mechanism of each batch of SMA cables.(2)The finite element model of multi-level performance SMA-LRB is established by using OpenSees.Through pseudo-static test,its constitutive model is numerically simulated and analyzed.The result shows that the damping effect of SMA-LRB is better than LRB.The constitutive model of numerical simulation is consistent with the presupposition,which lays a foundation for studying the designing method of multi-level performance SMA-LRB.(3)Taking a four-span continuous bridge as an example,the designing method of multilevel performance SMA-LRB is studied.According to the diameter,the design batches and idle stroke of SMA,22 kinds of working condition are setted.Time history analysis was carried out on the working condition of each bridge with three different seismic waves.Through analysis and comparison of the bearing displacement and pier base bending moment of the structural response,the influences of bearing design parameters on the seismic performance are studied,the designing method of multi-level performance SMA-LRB is summarized.The results show that the multi-level performance SMA-LRB has better limit displacement effect and seismic isolation performance in the application of bridge seismic resistance by setting reasonable design parameters.(4)Optimization of continuous bridge seismic system based on multi-stage performance SMA-LRB.In order to apply the bearing to the bridge with piers of different heights,it is necessary to optimize it by making a reasonable optimization plan,carrying out time history analysis and analyzing the optimization results.The results show that the new bearing is well suited for the bridge with piers of different heights by increasing the stiffness of bearing on high piers and decreasing the stiffness of bearing on low pier simultaneously.Bearing on lower pier may not have a third batch of SMA cables.