Research On Running Safety Of Fault-crossing Simply-supported Girder Bridge Of High-speed Railway Under Earthquakes With Different Intensities

In recent years,more than 20 bridges have been seriously damaged due to active faults crossing,resulting in heavy losses.However,with the rapid development of transportation infrastructure,highway and railway bridges across active faults are emerging.At present,the seismic research of bridges across faults at home and abroad is still in its infancy.The structural safety and running safety of bridges across faults,especially high-speed railway bridges under earthquakes,need to be studied urgently.In this paper,the eight-span simply supported girder bridge of high-speed railway in China was taken as the research object.The response characteristics of bridge structure and track structure under different intensities of fault-crossing earthquakes were studied in depth,and the structural safety was evaluated.Based on the horizontal deformation index of track,the running safety at different speeds was evaluated.The main work of this paper is as follows:(1)An integrated model of the eight-span high-speed railway simply-supported girder bridge was established based on OpenSees platform.Abaqus software was also used to verify the rationality of the model from the level of structural natural vibration characteristics.Effects of track constraints on the natural vibration characteristics of bridge structures were compared and analyzed in this paper.The research shows that the track structure improves the overall stiffness of the high-speed railway simply-supported girder bridge.(2)A new method of fault-crossing ground motion synthesis was introduced to decompose the high-frequency components,main and secondary impulses of near-fault impulsive ground motion.The main impulses were generated by artificial velocity impulse simulation model,and the fault-crossing fling-step effect ground motions at different intensities were synthesized.(3)Damage states of different components of bridge structure and track structure were defined,and the non-linear time history analysis method was used to calculate and analyze the response laws and safety of support,pier,sliding layer,lateral chock blocks,CA mortar layer,shear reinforcement and fastener under frequent,design and major earthquakes.The results show that the seismic response of fault-crossing spans and their adjacent spans is the largest,and they face great risk of damage.At the same time,a considerable proportion of residual deformation still exists after the earthquake.(4)Horizontal deformation laws of track under the action of frequent,design and major earthquakes were studied.Based on the three indicators of track dislocation,horizontal angle and turning angle,the running safety of vehicles with different driving speeds was quantitatively determined.The results show that under frequent earthquake,the horizontal deformation of track meets the running safety requirements under various speed condi,tions;under design earthquake,the safety requirement can be guaranteed only when the train speed is 100 km/h;under major earthquake,the fault span and its adjacent spans can not meet the requirement of running safety.(5)Effects of the number of lateral chock blocks and shear reinforcements on the transverse deformation of sliding layer and CA mortar layer were studied,and their effects on improving the horizontal deformation of track were discussed.The results show that increasing the number of lateral chock blocks can avoid excessive deformation of the sliding layer and improve the safety of the track.The influence of lateral chock block on the deformation of the CA mortar layer is more complex and tends to decrease in general.Increasing the number of shear reinforcements can reduce the deformation of the CA mortar layer,but it has little effect on the horizontal deformation of the track.