Study On Dynamic Response Characteristics Of Bridge Superstructure Under Rockfall Impact

Because most of the bridges and highways in western mountainous areas are built on hills and are located in earthquake areas,the rockfall disaster caused by earthquakes has become an important disaster-causing factor in traffic engineering.Stone rolling often occurs on the main traffic trunk lines,and the accidents of bridges impacted by rockfall occur from time to time.Rockfall and rolling stones caused by rock collapse of mountain bodies are very easy to cause the impact damage of bridges,seriously affects the normal use of bridges.At present,the research on rockfall impact bridges at home and abroad mainly focuses on impacting piers.There are few studies on the superstructure of bridges.The superstructure of bridge deck will produce obvious dynamic response in local range under rockfall impact,which is quite different from the research on the lower structure of the former and deserves further study.In this paper,numerical simulation is used to analyze and study the above problems.The concrete contents and conclusions are as follows:The finite element model of continuous girder bridge is established by Midas/Civil.Simulating the process of bridge deck under rockfall impact load.The dynamic and static responses of bridge superstructure under different load conditions are obtained.Based on the concept of impact dynamic response amplification coefficient.The variation law of dynamic response amplification coefficient is summarized.(1)Dynamic Response Analysis of Undamaged StructuresBy studying the law of dynamic response amplification coefficient of three-span continuous girder bridge under different load conditions,it can be seen that the factors affecting the dynamic response amplification coefficient of components in local scope are the magnitude of impact force under loading and the location of loading nodes,and the dynamic response amplification coefficient of local elements and the length of loading nodes from element distance L can be obtained by curve fitting method.The dynamic magnification factor of vertical displacement response is less affected by the impact force.(2)Dynamic Response Analysis of Damaged Structures.Combined with the results of dynamic response analysis of non-damaged structure,the basis of local concrete slab failure judgment is introduced.Considering the damage of the bridge deck in the local area under the action of rockfall impact,the dynamic amplification factor of the member studied in the non-damage structure is affected,and two structures are obtained.The difference between the dynamic amplification factors of the components and the size of the damage area have a certain influence on the dynamic response.(3)Analysis of Dynamic Response of the Overall Structural FormBased on the different damage-free continuous girder bridge structure,a twodimensional bar system model is introduced.The dynamic response of each section and the static response of the corresponding section bar system model are obtained by simulation.Influencing factors of dynamic amplification coefficient of internal forceresponse of different sections of bridge superstructure are obtained...