Studies On Isolation Bridges System Of Multi-Level Seismic Fortification

Previous earthquake events show that the internal force of bridge substructure can be significantly reduced by the application of seismic isolation design.However,for bridges built near seismic faults,the action of velocity pulse ground motion always causes excessive deformation,which results in residual deformation of the bearings,beam collision,and beam falling.In order to satisfy the different performance requirements of bridges under different seismic levels,a multi-level seismic fortification and isolation bridge structure system is proposed.Combined with shape memory alloys(SMA),a multi-level SMA lead rubber bearing(MSLRB)is studied in this paper.Through the pseudo-static test and numerical simulation of the device,the restoring force model is revealed.And the seismic performance of multi-level seismic fortification and isolation bridge systems is further studied base on the revealed restoring force model.Here are the specific works that have been done and conclusions:(1)According to the design principle of a multistage fortification device,an MSLRB is designed and manufactured.The layout and working principle of three batches of SMA cables are discussed in detail,as well as the calculation formula of the length of each batch of cables.(2)Tensile test of SMA cable and quasi-static test of MLLRB were carried out.The tensile property and restoring force model of SMA cable were verified.The difference of hysteretic performance between ordinary lead rubber bearing and MSLRB device is compared.The test results show that the hysteretic performance of MSLRB device fully conforms to the multilevel fortification concept: the isolation efficiency is high under small displacement,and the displacement limit capacity is strong while there is a large displacement;compared with LRB,MSLRB has better energy dissipation capacity and self recovery performance.(3)Numerical simulation of the device was run by Open SEES software,and the numerical model was corrected by the test results.The parameters of MSLRB were analyzed with the parameters of SMA diameter and free travel of three batches of SMA cables.The results show that the energy consumption and equivalent stiffness of the bearings increase with the increase of SMA diameter.Meanwhile,the different design of the free travel of three batches of cables has a great influence on the mechanical properties of the bearings under different displacement conditions.(4)The numerical model of a medium and small span continuous beam bridge is established based on SAP2000 finite element software.With three near-fault seismic records as time history excitation,the difference of seismic isolation performance between LRB and MSLRB under different seismic levels is studied and compared.The seismic performance of the bridge is evaluated by the displacement of the bearings and the moment at the bottom of the pier.The results show that the isolation efficiency of MSLRB is similar to that of LRB under medium and small earthquakes,and the relative displacement between piers and beams is well controlled under strong earthquakes.