Study On Seismic Control And Driving Safety Of Rigid-Frame Continuous Beam Bridges Considering Hydraulics From Ground Motion

With the continuous densification of high-speed railway lines in my country,it is inevitable for high-speed railway bridges to cross water areas such as mountain streams,rivers,and reservoirs.Among them,the high-speed railway rigid frame-continuous girder bridge inherits the characteristics of continuous girder bridge deck and smooth driving,and has the advantages of strong spanning capacity and large horizontal and vertical stiffness of continuous rigid frame bridge.widely used.However,when an earthquake occurs,the substructure of the rigid frame-continuous girder bridge will interact with the water,resulting in the hydraulic force of the earthquake.Especially when the rigid frame-continuous girder bridge is in deep water and high piers,it is more likely to have adverse effects on the bridge.Therefore,this paper focuses on the shock absorption control and driving safety of high-speed railway rigid-frame-continuous girder bridges in areas with water,using Midas Civil 2020 and the train-track-bridge-seismic analysis program TTBSAS compiled by the research group to analyze a rigid-frame-continuous girder bridge.The girder bridge is simulated and calculated,and the influence of seismic vibration hydraulics on the seismic response,shock absorption control and train safety of the rigid frame-continuous girder bridge is systematically studied after the seismic wave is selected.The main research conclusions are as follows:(1)Considering the seismic hydrodynamic effect,the natural frequency of a rigid-continuous beam bridge will decrease,and the impact of seismic hydrodynamic on the lower structure of the bridge is greater than that on the upper structure.For the rigid-continuous beam bridge in this paper,the frequency range with the greatest impact of seismic hydrodynamic is 0.799Hz-1.909 Hz,6.431Hz-10.660 Hz,and above 16.715 Hz,with maximum relative errors of 18.5%,11.4%,and 16.0% respectively,with or without hydrodynamic effect.(2)Seismic hydrodynamic will increase the longitudinal and transverse internal forces and displacement responses of the main pier and pile foundation of the rigid-continuous beam bridge.Under the calculation conditions of this paper,after considering seismic hydrodynamic,the internal force and displacement response curves of the main pier and pile foundation of the rigid-continuous beam are consistent with those without considering seismic hydrodynamic in terms of the trend along the height of the pier and pile,and the increase ranges from 10.39% to 40.88%,and from 15.88% to 40.95%.Meanwhile,through calculation,the maximum internal force and displacement response amplification occur at the upper boundary section,lower boundary section,and bottom section of the 20 m high main pier;the maximum internal force response amplification occurs at the section 2m below the lower boundary of the seismic hydrodynamic for the main bridge pile foundation,and at the section 6m below the lower boundary for the main bridge pile foundation,which requires additional attention to the material and reinforcement construction.(3)For the seismic isolation bearing model,the seismic isolation bearing has a good damping control effect on the longitudinal and transverse bending moments,transverse shear forces,and longitudinal displacements of the main pier and pile foundation of the rigid-continuous beam bridge(considering seismic hydrodynamic).Under the calculation conditions of this paper,after the seismic isolation bearings are arranged,the trend of the internal force and displacement response curves of the bridge as a whole remains unchanged,and the damping ratio of the internal force and longitudinal displacement of the main pier ranges from 14.41% to 38.83%,and from 15.24% to 38.88%,respectively.However,arranging seismic isolation bearings will increase the maximum internal force of the pile foundation by nearly 10%,which poses a threat to the pile foundation.(4)For the model of a liquid viscous damper,the seismic control effect of the damper on the longitudinal and transverse bending moments,transverse and longitudinal shear forces,and longitudinal displacement of the main bridge piers and pile foundations of the rigid-continuous beam bridge(considering seismic and hydraulic effects)is good.For the calculation conditions in this paper,after the arrangement of liquid viscous dampers,the overall trend of the internal force and displacement response curve of the bridge did not change,and the damping ratios of the main pier’s internal force and longitudinal displacement were between 11.99% and 55.15%,and 14.72% to 39.73%,respectively.However,the arrangement of liquid viscous dampers will increase the maximum internal force of the pile foundation by nearly 10%,which threatens the pile foundation.In addition,the damping effect of liquid viscous dampers is not as smooth and stable as isolation bearings.Therefore,in the actual engineering of rigid-continuous beam bridges,it is recommended to prioritize the use of isolation bearings for seismic control design.(5)When the train crosses the bridge at different speeds,the bridge’s dynamic response caused by the train-bridge coupling vibration is mainly contributed by low-order modes,and the influence of high-order modes is very limited.The effect of seismic and hydraulic forces on the acceleration and displacement of the main beam span of the rigid-continuous beam bridge is only manifested as a difference in amplitude,with almost no impact on the waveform and peak occurrence time.In addition,seismic and hydraulic forces have an impact on the safety performance indicators of the train on the bridge,but their effect on the safety speed threshold is very limited.For the calculation conditions in this paper,under the action of earthquake waves 1 to 3,the safety speed thresholds for trains on the bridge are 250km/h,200km/h,and 225km/h,respectively,when considering seismic and hydraulic effects.