Research On Seismic Mitigation And Isolation Control Of Near Fault High Speed Railway Cable-Stayed Bridges Based On Energy Analysis

The seismic problem of large span cable-stayed bridges in strong seismic areas is prominent,and the bearing uplift damage is a common damage feature,which may induce serious damage to the bearings,piers and superstructure,and the adverse effect of bearing uplift requires the use of seismic isolation technology in the design and transformation process of cable-stayed bridges;at present,the domestic research on seismic isolation technology using viscous dampers and magnetorheological bearings on large span cable-stayed bridges for high speed railways is relatively weak,and the actual application in Therefore,the seismic isolation technology of large span cable-stayed bridges needs further research.In this paper,the bridge model is established by using the finite element software ANSYS to study the structural response of a large-span cable-stayed bridge under different ground vibrations.The main research contents of this paper are as follows:(1)Three different types of seismic waves,namely near-fault pulsed earthquake,near-fault non-pulsed earthquake and far-fault seismic wave,were selected as seismic excitation inputs.The analysis of seismic wave time curve,phase spectrum,Fourier spectrum and semantic map(time-frequency diagram)revealed that the damage effect of pulsed near-fault seismic wave is the strongest,and thus the bridge has the highest seismic design requirement under pulsed near-fault earthquake.The simulation of the bridge model using the large mass method concluded that the self-oscillation period of the cable-stayed bridge is relatively large and the structure is flexible.After the arrangement of magnetorheological bearings,the structural self-oscillation frequency of the large-span cable-stayed bridge is reduced and the structural self-oscillation period is prolonged,which is consistent with the idea of prolonging the self-oscillation period as the focus of seismic design in the American AASHTO code.(2)Referring to the American AASHTO code,the mechanical model of the magnetorheological bearings is designed,the parameters of the bearings are solved,and the finite element software is used to simulate them,and it is found that the force-displacement curves of the four bearings of the cable-stayed bridge are all flat "elliptical-like" nonlinear curves,which is consistent with the experimental conclusions of domestic and foreign researchers and verifies the reasonableness of referring to the American AASHTO code.It is found that the force-displacement curves of all four bearings are flat "elliptic-like" nonlinear curves,which are consistent with the test results of domestic and foreign researchers.The analysis of the hysteresis characteristics of the magnetorheological bearings shows that the maximum hysteresis loop occurs at the high amplitude stage of the seismic wave,and the accumulated hysteresis area increases rapidly to more than 60%during the high amplitude stage of the seismic wave,and reaches 80%of the total area of the hysteresis curve,then the seismic wave is in the gradual decay stage,and the hysteresis loop area increases slowly.(3)Comparing the ground shaking response of bridge structures with and without magnetorheological bearings,it is concluded that for near-fault pulsed-type earthquake,near-fault non-pulsed-type earthquake,and far-fault earthquake,the overall average seismic reduction rates of bridge structures under the three types of ground shaking are 17%,32.5%,and 30%,respectively,after applying excitation currents;indicating that the setting of magnetorheological bearings has a certain degree of seismic reduction effect on cable-stayed bridges,and the bridge The seismic design is more complicated under the action of near-fault impulse-type ground shaking.(4)By simulating the arrangement of viscous dampers for a large-span cable-stayed bridge,a damping index of 0.3 and a damping coefficient of 5000 kN-s/m viscous dampers were selected.The overall damping effect of the bridge with only transverse viscous dampers or longitudinal viscous dampers was found to be slight,considering the response of the uplift of the cable-stayed bridge bearings and comparing the response peaks and damping rates of the main influencing structures.Both the transverse viscous dampers with magnetorheological bearings(A=3.0)and the longitudinal viscous dampers with magnetorheological bearings(A=3.0)produce bearing uplift response,but the bearing uplift displacement is small and does not pose a threat to the cable-stayed bridges studied in this paper.The average damping rate of the longitudinal displacement response of the bridge structure with transverse viscous dampers and magnetorheological bearings is more than 40%,and the overall seismic isolation capacity of the bridge is good.The deployment of longitudinal viscous dampers plus magnetorheological bearings has the best effect on the control of the longitudinal displacement response of the bridge structure,with an average damping rate of 44.65%;the maximum damping rate of the upper crossbeam shear force reaches 54.92%.However,the control of the internal force response such as the bottom bending moment of the tower and the shear force of the lower crossbeam was not as effective as the arrangement of transverse dampers plus magnetorheological bearings.(5)After the simultaneous arrangement of transverse and longitudinal viscous dampers plus magnetorheological bearings,the longitudinal displacement damping rate of the bridge structure is lower than that with transverse viscous dampers plus magnetorheological bearings or longitudinal viscous dampers plus magnetorheological bearings,but higher than that with only transverse viscous dampers or longitudinal viscous dampers.For the internal force response of the bridge structure,the damping effect of simultaneously arranging transverse and longitudinal viscous dampers plus magnetorheological bearings is much greater than that of other damping measures.For the large-span cable-stayed bridge studied in this paper,viscous dampers and magnetorheological bearings are effective in controlling the longitudinal displacement and internal force response of the bridge deck by introducing a large amount of damping ratio and consuming seismic energy,and although they cannot prevent the occurrence of bearing lift,they can reduce change the internal force of the bridge and the displacement response of the girder end,and provide some relief to the uplift response of the deck end with bearing pressure demand and bridge deck.Therefore,in the case of reducing the longitudinal displacement response of the bridge only,the arrangement of longitudinal viscous dampers plus magnetorheological bearings can be given priority as a seismic isolation measure;from the point of view of the overall structural damping of the bridge,the simultaneous arrangement of transverse and longitudinal viscous dampers plus magnetorheological bearings is more effective.