Seismic Response Analysis Of Fault-crossing Simply-supported Girder Bridges Based On Viscous-spring Boundary

Earthquakes on both sides of active faults have strong rupture directional effects and slip thrust effects.Therefore,bridges spanning faults are more severely damaged than bridges that do not span faults.Seismic codes of various countries prohibit the construction of bridges in or near active fault areas.my country’s active faults are widely distributed and earthquakes occur frequently,and the fault movement in the Sichuan-Tibet region is particularly intense.The bridges of the newly built Sichuan-Tibet Railway are as long as 114.22 kilometers and cross multiple active faults.In the foreseeable future,the number of bridges across faults will increase.Dramatic increase.In addition,the geological conditions and soil characteristics of the Sichuan-Tibet region are complex and changeable,and the soil-pile dynamic interaction has a great influence on the dynamic response of the bridge under the action of high-intensity ground motion.Seismic research of bridges across faults is of great significance.In this thesis,based on the research background of a simple-supported girder bridge spanning a strike-slip fault in the Sichuan-Tibet region,a systematic study on the seismic response of the simply-supported girder bridge spanning the fault under different simplified models of soil-pile dynamic interaction is carried out.The main research work and conclusions are as follows :(1)The current research status of cross-fault bridges and viscoelastic boundaries is systematically reviewed,with emphasis on the acquisition of cross-fault ground motions,nonuniform excitation input models,viscoelastic artificial boundaries and equivalent load input methods.Correct and scale the original fault ground motion data to generate fault ground motion data suitable for the analysis of simply supported girder bridges;(2)Based on the finite element software ANSYS,the pier bottom consolidation model,the linear soil spring model considering the soil-pile dynamic interaction,and the viscoelastic boundary-soil-pile-bridge model are established respectively,and the modal analysis of each model is carried out.The results show that: after considering the soil-pile dynamic interaction,the simply supported girder bridge structure softens,the natural vibration frequency decreases,the natural vibration period increases,and the order of some mode shapes changes.The viscoelastic boundary-soil-pile-bridge model before The tenth-order natural frequency has a maximum decrease of 20%,and a new mode of vibration of the foundation soil appears;(3)The influence of soil-pile dynamic interaction on the seismic response of a simply supported beam bridge across a fault is investigated.The results show that: after considering the soil-pile dynamic interaction,the internal force of the pier in the linear soil-spring model and the viscoelastic boundary-soil-pile-bridge model decreases significantly,and the displacement demand increases.The seismic response of girder bridges has a significant impact;in addition,compared with the linear soil-spring model,since the viscoelastic boundary-soil-pile-bridge model takes into account factors such as soil material damping,soil plastic deformation,and far-field radiation damping,its internal force requirements The maximum decrease is 77%,and the maximum increase in displacement demand is 4%;it is more reasonable to use the viscoelastic boundary-soil-pile-bridge model to consider the soil-pile dynamic interaction;(4)Under the premise of considering soil-pile dynamic interaction,the influence of fault spanning position,soil properties and lead-core rubber isolation bearings on the seismic response of a simply supported beam bridge spanning the fault was systematically explored.The results show that: the fault is most unfavorable to the bridge structure when it crosses the side span;when the site soil is weak,the dynamic response of the bridge structure will be increased;the seismic isolation bearing has obvious seismic isolation effect for the simply supported beam bridge spanning the fault,and the fault span The torque demand of the pier bottom and the longitudinal shear force demand of the bearing dropped by 50% and 53%,respectively.