Seismic Performance And Seismic Isolation Analysis Of Railway Long-span Cable-stayed Bridges In Near Fault Environment

Cable-stayed bridges are increasingly valued by the bridge community due to their unique advantages such as novel structure and large span.Although the domestic cable-stayed bridge started relatively late,in recent years,as domestic bridge construction has reached new highs,people gradually began to attach importance to the performance and seismic design of the cable-stayed bridge.However,the long-span cable-stayed bridge serves as an important transportation hub.Once it is damaged by a strong earthquake,it will cause significant losses to people's lives and property.Therefore,it has become increasingly urgent to systematically study the seismic performance of long-span cable-stayed bridges.In this paper,the cable-stayed bridge is taken as the research object,the seismic response and seismic isolation design of the long-span cable-stayed bridge under near-fault seismic environment are studied,and the changing law of the dynamic response of the bridge structure under the traveling wave effect is discussed.The details are as follows:(1)This study takes the Yujiang double-line super large cable-stayed bridge as the engineering background and used the APDL language programming in the finite element analysis software ANSYS to establish a three-dimensional finite element model.Taking a certain seismic wave as a benchmark,this paper with a non-linear time-history analysis method studies the influence law of the down wave effect of different apparent wave velocities on the seismic response of bridge structures based on the mass method.The results show that:when the apparent wave velocity is less than 1500m/s,the displacement response of the key parts of the bridge is oscillating,and after reaching a peak around 200m/s,it gradually approaches the displacement response under consistent excitation;when the apparent wave velocity is less than 4000m/s,the internal force response of the key parts of the bridge shows an oscillating change,and then gradually approaches the internal force response under consistent excitation as the apparent wave velocity increases.(2)The consistent excitation and multi-point excitation motion equations of long-span cable-stayed bridges are established,and the numerical solution method of the motion equations is preliminarily analyzed.According to the requirements of seismic design specifications,eighteen ground motions are selected,and the near-fault ground motions are taken as the main research objects.The vibration of the rail structure of the bridge structure is considered,and the consistent and inconsistent excitation inputs are inputs to the long-span cable-stayed bridge.What's more,this paper studies the impact of wave effect on the dynamic response of bridge structure with the mass method.The results show that:after considering the traveling wave effect,the displacement and inward response of each key part of the bridge are significantly reduced,but the vertical displacement of the mid-span will increase,which is not conducive to the seismic design of the bridge(3)This paper analyzes the peak change law of earthquake response which is caused by different Ap/Vp(the ratio of peak acceleration to peak velocity)and V/H(the ratio of vertical acceleration peak to horizontal acceleration peak)under the three types of ground motion.The results show that:the overall dynamic response of the bridge structure increases with the increase of V/H,and decreases with the increase of Ap/Vp,and especially the seismic response under the near-fault pulsed ground motion changes most obviously,which indicates that The pulsatility in the near-fault ground motion cannot be ignored(4)The parameters of lead rubber bearing and viscous damper are optimized.By calculating the dynamic response of the bridge structure after arranging seven different lead core diameter lead rubber bearings,the optimal lead core diameter is determined to be 213mm;the paper uses the orthogonal design method to analyze the parameter of the viscous damper,and finds the best parameters of the viscous damper after calculating seismic response:the damping coefficient is 7000 kN·s/m and the damping index is 0.3;and then the research arranges the longitudinal viscous damper and the lead rubber bearing between the tower and the beam according to this parameter and compares it with the model using two seismic isolation measures at the same time.Through the seismic response time history analysis of the structure,the seismic reduction rates under the three models are calculated,and the respective reduction effects on the peak displacement and internal force response of the key parts of the bridge are compared and analyzed.The results show that:when only one type of vibration isolation device is used,the lead rubber bearing has better control effect on the displacement of the main structure and the internal force at the upper and lower beams,and the viscous damper has better control effect on the internal force at the bottom of the tower.When these two types of seismic isolation devices are used at the same time,the seismic performance of the bridge reaches its best.The seismic isolation scheme discussed through the above analysis can be used as a reference for the research and analysis of seismic isolation of other long-span cable-stayed bridges.