Research On Dynamic Response Of Geological Bodies And Bridges Considering Fault Effects Under Earthquake Action

On January 8,2022,a magnitude Ms6.9 earthquake occurred in Menyuan County,Haibei Tibetan Autonomous Prefecture,Qinghai Province.The Menyuan earthquake caused severe deformation of the Liuhuanggou Bridge,rendering it unusable,and produced a large number of ground fissures above the underground fault near the Liuhuanggou Bridge.In this paper,based on the Liuhuanggou Bridge Menyuan earthquake damage accident,the bridge and its underlying geological body were studied,combined with regional geological structures and ground fissure distribution,and the seismic response of the Liuhuanggou Bridge and geological body was analyzed using the COMSOL numerical simulation software based on the earthquake excitation attenuation model.The dynamic response characteristics of the Liuhuanggou Bridge and geological body under three-directional seismic forces were analyzed,and the fault effects during the bridge vibration destruction process were compared with the measured Liuhuanggou Bridge deformation.The main achievements obtained are as follows:(1)Based on the statistical analysis of strong earthquake records,the attenuation relationship of earthquake acceleration response spectrum and the relationship between epicentral distance and peak acceleration of earthquake acceleration response spectrum were determined to obtain the earthquake excitation attenuation function and the excitation at the boundary of the model formed by the three-directional incident seismic waves of the Menyuan earthquake.The attenuation of earthquake acceleration response spectrum is related to seismic parameters and epicentral distance.Through the statistical analysis of strong earthquake records,the regression coefficient and nearfield saturation factor were obtained as constants under the same site type and response spectrum characteristic period conditions.However,the near-field saturation factor in the attenuation function is not fixed,but changes with the epicentral distance.This paper provides a method to solve the near-fault attenuation function and uses it to obtain the boundary excitation of the geological body and bridge models.(2)The finite element model of geological body considering fault was established.The movement of fault was simulated by setting the movement velocity of hangingwall,and the slippage of fault was simulated by setting Stribeck friction surface,so as to analyze the seismic dynamic response of geological body model.It is found that in the X and Y directions of the model,there will be two acceleration cloud circles with roughly equal accelerations and opposite symbols between the two faults.In the Z direction,there is only a circle of accelerating clouds growing towards the middle.(3)The finite element model of Sulfangou Bridge is established and the seismic dynamic response of the bridge model is analyzed.In the geological body with faults,the three-way time-history acceleration extracted from the bridge observation point is selected as the seismic force input,and then the seismic dynamic response of the bridge structure is analyzed.It is found that under the influence of fault,SH wave propagates faster and reaches the bridge at the same time as the first peak of SV wave.At the same time,the SV wave changes from a single peak state to a double peak state,and the second peak area reaches the bridge at the same time as the P-wave acceleration peak.The former leads to the intensification and advance of horizontal seismic effect,while the latter leads to the increase of vertical seismic destructive power.(4)The seismic dynamic response of Bridges with or without fault is compared,and the influence of fault on the seismic dynamic response of Bridges is analyzed.The results show that the acceleration response of Bridges with faults increases significantly in the three directions compared with that of Bridges without faults.In terms of stress,the stress values at both ends of the bridge surge,and the intermediate stress is lower,but the stress in the middle of the former is greater.In terms of displacement,there is little change in each position in the X direction,while the middle position in the Y direction is consistent,and the gap between the two sides is obvious.In the Z direction,the former is negative overall,while the latter is positive.The seismic dynamic response of Bridges with or without faults is compared with the measured deformation of Bridges.The seismic dynamic response of Bridges with faults is consistent with the actual deformation trend in all aspects.