| Affected by permanent ground displacement caused by fault dislocation,under the action of cross-fault ground motions,the seismic response of the structure will increase significantly.In previous studies,scholars at home and abroad have carried out in-depth studies on the seismic response and anti-seismic measures of bridges under conventional far-field and near-fault through a large number of theoretical analyses,numerical simulations and related experiments,and have achieved fruitful results.However,there are few studies on bridge crossing faults,and the research content mainly focuses on the seismic response of conventional small and medium-span simply supported beams and continuous beams and structural seismic damage under the action of forward,reverse and strike-slip faults.As we all know,long-span cable-stayed bridge,as a control project in the line,has a complex structure and a large span and oblique-slip faults include the ground motion characteristics of both normal and reverse faults and strike-slip faults,namely hanging wall and vertical effects,slip thrust effects and rupture directional effects.Based on the actual engineering as the background of the long-span mixed-girder railway cable-stayed bridge(main span 448m)as the research object,this paper comprehensively studies the bridge’s ground motion response under the crossing of an oblique-slip fault.First,according to the ground motions recorded by TCU052 in the Chi-Chi earthquake,a time history record of permanent ground displacement of the bridge across the fault is synthesized.The synthetic ground motions of equal magnitude and opposite directions are input in the transverse direction to simulate the fault movement.Based on the bridge design parameters,the full bridge finite element model(elastic state)was established by the software of CSB and Midas Civil.As a prerequisite for structural dynamic analysis,first analyze the linearity,internal force and stress changes of the structure during the critical construction phase to ensure that the structure is reasonably stressed and in a safe state under static load.Then the accuracy of the model was verified by the comparison of the static calculation results,and the natural vibration characteristics of the seismic isolation and non-isolation system bridges were analyzed.By selecting different fault crossing positions(from the main span to the side span,a total of 3 working conditions),different crossing angles(15 to90°,a total of 6 working conditions),two ground motion input modes(multi-point displacement input and multiple Point acceleration input),seismic isolation and non-seismic system bridges,and the seismic response of bridge under the far field and near and span faults,a numerical simulation was carried out on the impact of bridge seismic response.However,these studies did not systematically analyze the ground motion response of long-span bridges crossing oblique-slip faults.The research results show that:(1)The Mavroeidis method can better simulate the time history of cross-fault pulse-type earthquakes;(2)In each key construction stage,the bridge is always in a safe state under the action of static load and meets the design requirements.The static calculation results of the two software are relatively close,which verifies the correctness of the built model;(3)The basic period of the seismic isolation system and non-seismic isolation system bridges are both larger,but the period of each step of the seismic isolation system bridge is larger than that of the non-seismic isolation system;(4)When the fault traverses the main span of the bridge vertically,the structural internal force and displacement response are optimal;(5)Multi-point displacement is more reasonable than the multi-point acceleration input result;(6)Under the crossing fault,the internal force response of the seismic isolation system bridge is reduced compared with the non-seismic isolation system bridge,but the displacement is increased,which is caused by the yielding of the seismic isolation support;(7)The seismic response of the cable-stayed bridge across the fault is much larger than that of the far field and near fault. |
