Numerical Simulation And Analysis On Dynamic Response Of A High-speed Railway’s Multi-span Simply Supported Bridge In Liquefying Soils Subjected To Strong Earthquake

China’s high-speed railway bridges pass a vast zone with liquefiable soil region, which lies in highly seismic region of 7, 8 or 9. Liquefaction induced by earthquake may cause severe damage to high-speed railway bridges, and immeasurable losses to national economy,and the study on dynamic pile-soil-bridge structure interaction is the key to solve this problem. The substructure method and the integral method are principal methods to investigate dynamic pile-soil-bridge structure interaction. In the substructure method, the dynamic Winkler foundation beam method to simulate pile-soil interaction is an effective approach. However, more attention is paid to the destruction of pile foundation of bridges induced by liquefaction, and the size effect of superstructure is ignored. For this purpose, based on a high-speed railway bridge engineering, using the substructure method, a numerical simulation method to investigate seismic response of multi-span simply supported bridge system in liquefying soils was established, and the seismic response and its influencing factors of multi-span simply supported bridge system were analyzed. The main obtained research is as follows:Firstly, a numerical simulation method to investigate seismic response of the multispan simply supported bridge system in liquefying soils was established. Based on the substructure method, a multi-span simply supported bridge system was divided into foundation substructure and superstructure-pile group substructure, and a onedimensional free-field liquefying soil column model was established by using the CYCLIC 1D finite element program. And a three-dimensional pile-soil-bridge structure system numerical model was established by OpenSees finite element computing platform, at the same time, the dynamic Winkler foundation beam model was used to simulate pilesoil interaction.Then, using the numerical models, and seismic response analysis of the multi-span simply supported bridge system under three typical earthquake waves was performed,and analysis of effect of soil structure interaction(including liquefaction effect) on seismic response of multi-span simply supported Bridge System was made. The results showed that the soil structure interaction had significant influence on natural vibration characteristics, displacement at the pier’s top, bending moment and shear force at the pier’s bottom of the multi-span simply supported bridge system.Finally, discussing the effect of influence factors, such as the height of pier, the pier reinforcement ratio, PGA and the pile’s diameter, on seismic response of multi-span simply supported bridge system. The tendency and peak value of displacement at the pier’s top, bending moment at the pier’s bottom, the deck’s acceleration and the pile’s bending moment was focused on. In addition, soil-structure interaction effect was discussed. Finally,preliminary recommendations for seismic design of bridge system in liquefying soils were made.