Seismic Reduction And Isolation Analysis Of Near Fault High Speed Railway Bridge With Mr Bearing Based On Hysteretic Energy Analysis

With the rapid development and scale increase of high-speed railway technology in China,the train speed is getting faster,and the response value of each part of the structure of high-speed railway bridge is getting bigger when it is subjected to earthquake.Therefore,the requirements for seismic performance of high-speed railway bridge design are getting higher.High-speed railway bridge is an important transportation infrastructure.How to improve its seismic capacity and reduce the safety of bridge structure in earthquake epicenter and after earthquake is still an important subject worthy of continuous research and test.Most of the traditional bridge bearings are ordinary rubber bearings,and the stiffness and damping properties of the bearings are fixed.When the ground motion period is similar to the natural vibration period of the bridge,the damping and isolation device is difficult to play a role,and it is easy to cause severe damage to the bridge.Magnetorheological vibration isolation bearing is due to its controllable stiffness,the bridge structure can play a good effect of vibration isolation,which can control each part of the bridge response value.Existing for magnetorheological bearing research mainly focused on the performance of magnetic current variation test,the design of research and support on the analysis of the magnetorheological bearing also focused on the seismic response analysis,From the perspective of energy,there are still few studies on the seismic effect and stability of magnetorheological bearings under the influence of near-fault ground motion.In this paper,a prestressed concrete continuous girder bridge（32×5m）of the First section of Beijing-Shanghai high-speed railway was used as the prototype to conduct a simulation study.Based on hysteretic energy analysis,the seismic isolation effect of the m agnetorheological（Mr）seismic isolation bearing in the face of near and far faults under the influence of different applied excitation currents was compared with the lead rubber bearing under the same conditions.The main content of this paper is divided into the following four points:（1）According to the bearing force-displacement bilinear model and its quantified parameters in the American AASHTO LRFD Bridge Design Specifications,the bearing parameters of the MRF bearing in this paper were analyzed and determined,and the finite element full-bridge model was established.Assuming that the equivalent horizontal stiffness is close to the average value of secant stiffness of hysteretic curve simulated by finite element method,the secant stiffness time history curve of hysteretic curve is drawn for comparative analysis.It is found that the value of the stiffness ratio（K1/K2）before and after yielding under different currents ranges from 5.5 to 8,which conforms to the value range of K1/K2 provided by AASHTO specification ranging from 5 to 15.（2）The finite element model is modeled and optimized.Different types of seismic waves are selected and only horizontal and transverse seismic wave data are input to verify the hysteretic performance of the magnetorheological bearing.By analyzing the hysteretic energy dissipation curves of the MAGnetorheological bearings under the influence of different excitation currents,it is found that the hysteretic area increases rapidly to about 70%of the total hysteretic area of the magnetorheological bearings and decreases rapidly after a short period of time when the amplitude of ground motion is obviously higher.The energy dissipation capacity and displacement control ability of the magnetorheological bearing are better than those of rubber bearings by comparing and analyzing the energy dissipation curves of rubber bearings.（3）Select and input ground motion for magnetorheological bearing isolation Bridges and rubber bearing isolation bridge,lead model for seismic response reduction analysis,by comparing the different plus the exciting current before and after the bridge under the influence of vibration isolation of the response data before and after the bridge and the lead rubber bearing isolation response data,the results showed that magnetorheological support played an obvious isolation effect.The results showed that the overall damping rate is about 37.5%,the maximum damping rate is 66.52%.In the same case,the damping rate of the lead rubber bearing is about 25%,the maximum damping rate is 46.64%.（4）The dual-parameter control method is adopted to control the magnetorheological bearing,and the damping and stiffness of the magnetorheological bearing are controlled by applying 0～3A excitation current,so that the bridge structure itself has 7 stages of adjustable damping and stiffness to avoid resonance in the face of earthquake.Through the analysis of earthquake response,we found that using double parameters control will lead to magnetorheological bearing transverse displacement of the effect of vibration isolation,with the strong current is added,the acceleration response of the effect of vibration isolation changed little,the bottom of the pier shear force and bending moment response reduction frame-shear wall pier effect gradually weakened,but does not affect the vibration isolation performance of magnetorheological bearing itself is good.The stiffness and damping of magnetorheological bearings increase with current,which is the reason why the magnetorheological bearings are better than lead-core rubber bearings.