Study On Several Key Problems About The Dynamic Response Of Train-Bridge System Subjected To Earthquake Action

Recently,the high-speed railway(HSR)has developed a lot in China,which solved the traffic problems between big cities to a great extent and improved the travel efficiency.To ensure the safety and stability of running trains as well as to reduce the influence of railway lines on the existing built environment,extensive elevated bridges are built on the HSR line,which definitely increases the possibility of trains running on bridges when an earthquake occurs.As a result,it is of important significance to study the dynamic response of the train-bridge system during earthquakes.In seismic analysis of train-bridge coupled system,the variations of ground motions and the interaction between the piles and the soil are two important factors which cannot be neglected.As one of the important aspects of spatial variation,the influence of local topography on the seismic response of a train-bridge system should be considered.In order to study the effects of the above two factors on the dynamic response of the train-bridge system during an earthquake,based on the existing research results in China and abroad,the frameworks for dynamic analysis of train-bridge system considering soil-structure interaction and for seismic analysis of train-bridge system considering topographic effects are established respectively.The main contents and contributions of this dissertation are as follows:(1)Analytical method for calculating dynamic response of coupled train-bridge system based on Duhamel integralBased on the theory of Duhamel integral,the analytical solution of a single-degree-of-freedom system under linear load is deduced.On the base of this analytical solution,with the assumption that the train-bridge interaction forces change linearly within each time step,the dynamic response of the system during this period is obtained by iteration computation.A moving unit with a wheel(unsprung-mass),a spring,a damper and a sprung-mass passing through a simply-supported beam and a 4-axle vehicle passing through a 32 m simply-supported beam are taken as case studies.The calculation results are compared with those obtained by the traditional Newmark ? method and so are the computational efficiencies.The results show that the dynamic response obtained by these two methods are very close,and compared with the Newmark-? method,the method based on Duhamel integral can increase the time interval of integration as well as the computational efficiency.The proposal of this new method laid the foundation for the following analysis and calculation.(2)Analytical model for seismic analysis of train-bridge system based on seismic displacement inputThe influence of the quasi-static item on the seismic response of the train-bridge system is analyzed by taking a moving unit with a wheel(unsprung-mass),a spring,a damper and a sprung-mass passing through a simply-supported beam as case study.The modal superposition method for dynamic analysis of structures excited by prescribed support displacement is verified,and based on this method,the analytical framework for seismic analysis of train-bridge system based on seismic displacement input is established.In this framework,the influence of the quasi-static item is taken into account without complex analysis and calculation.Meanwhile,compared with the traditional acceleration input pattern,the displacement input pattern is suitable for various kinds of wheel-track relationships,which can be applied in more kinds of situations.(3)Dynamic analysis of train-bridge system considering soil-structure interactionAn analytical framework for the dynamic analysis of train-bridge system considering the soil-structure interaction(SSI)is proposed,in which the frequency dependency of the impedance functions is considered.Based on the substructure method,the whole train-bridge-pile foundation-soil system is divided into the train-bridge interaction subsystem and the pile-soil interaction subsystem,the motion equations of which are established separately.By iterative solution method,the dynamic response of the two subsystems can then be obtained.A train with 8 vehicles passing over 5-span simply-supported beam is taken as a case study.The influence of SSI on the dynamic response of the train-bridge system and the threshold values of soil shear velocity for neglecting the effect of SSI are studied.(4)Dynamic analysis of train-bridge system subjected to earthquake considering topographic effectThe influence of the local topography on the seismic response of a train-bridge system is considered for the first time.Based on the viscous-spring artificial boundary,a finite element model of the local site where the bridge is located is established.The process of wave input is realized by transforming the seismic time history into equivalent loads acting on the artificial boundary,by means of which the seismic time history at each support of bridge can be obtained.The dynamic analysis of a train-bridge system subjected to multi-support seismic excitations is carried out,in which the displacement time histories of seismic excitations are exerted on the bridge supports,and finally,the seismic response of train-bridge system considering the topographic effect can be obtained.Based on the above framework,the effects of the local topography,the type and the incident angle of the seismic wave as well as the train speed are analyzed and some useful conclusions are drawn.