Coupling Vibration And Running Safety Of Train-Track-Bridge System Under Non-Uniform Seismic Excitations

Earthquake will affect the safety of bridge itself and threaten the running safety of the train on bridge as well. As to high-speed railway bridges, the requirements of the bridge seismic design must be met. But beyond that, the running safety of the train under seismic excitations must be ensued. Both theoretical research and earthquake damage analysis indicate that earthquake ground motion has spatial variability. It includes four aspects: traveling wave effect, incoherence effect, local site effect and attenuation effect. So, it is significant to research the coupling vibration and running safety of train-track-bridge system under non-uniform seismic excitations, that is one of the key subjects to ensure the safety operation of high-speed railway. In this paper, a series of studies around this subject are carried out, and the main works and achievements are listed as follows:(1) A method to generate the multi-support and multi-dimension earthquake ground motion is proposed. In this method, the random field of earthquake ground motion is described as the matrix of power spectral density function, and the correlations of earthquake wave components in different point and different direction are considered. But beyond that, the stationary auto-power spectrum and cross-power spectrum are described as Clough-Penzien model and Qutiequn-Wangqunjie coherent model respectively.(2) A dynamic model of train-track-bridge system under non-uniform seismic excitations is set up. Based on the theory of train-track-bridge dynamic interaction, a dynamic model of train-track-bridge system under non-uniform seismic excitations through considering the seismic force boundary of subgrade and bridge is set up, which is consist of a vehicle model with 35 degrees of freedom, a ballast track model with three layer elastic point-support, a slab track model and an FEM bridge model. In this model, four methods are used to deal with the seismic force boundary, direct solving method, relative movement method, large mass method and large stiffness method. Meanwhile, a new wheel/rail contact relationship model is established through introducing the new assumption of wheel/rail contact relationship, and the bridge/track relationship models of ballast track and slab track are established through considering the static equilibrium and displacement coordination on the bridge/track contact interface.(3) A simulated analysis program of train-track-bridge-seismic system is compiled. The coupling vibration equation of train-track-bridge system under non-uniform seismic excitations are solved by explicit-implicit it mixed integral method, and the program of Train-Track-Bridge-Seismic Analytical System (TTBSAS) is compiled and verified based on Compaq Visual Fortran 6.5. Through this program, the coupling vibration of vehicle-track-bridge system under seismic action and aseismic action can be analyzed, and the input methods of seismic wave, including direct solving method, relative movement method, large mass method and large stiffness method, can be chosen as needed. Beyond that, the input modes of seismic wave, including uniform excitation, traveling wave excitation and multiple-support excitation, can be chosen as well.(4) The influence of several key factors on the seismic responses of train-track-bridge coupling system are discussed. Aiming at a rigid-continuous combination beam bridge with spans of 48+5×80+48 m, the influence of three key factors on the seismic responses of train-track-bridge coupling system are discussed, including the damping term of direct solving method and relative movement method, the quasi-static components of structure and the input method of non-uniform seismic excitations. The results show that the dynamic responses of bridge and rail have a little change without thinking the damping term, but the centroid acceleration of car body is larger; The longitudinal quasi-static component is almost no effect on the seismic responses of coupling system, but the transversal quasi-static component will significantly increase the amplitudes of derail coefficient, reduction ratio of wheel load and wheel rail lateral force; Large stiffness method and direct solving method are completely equivalent, but the seismic responses of vehicle solved by large mass method and relative movement method are separately overestimated and underestimated.(5) The coupling vibration characteristic of train-track-bridge system under non-uniform seismic excitations are analyzed. Aiming at the deck arch bridge of Beipanjiang with a span of 445m, the influence of traveling wave effect and full spatial variability on the dynamic responses of train-track-bridge coupling system under non-uniform seismic excitations is analyzed by TTBSAS program, and the multi-support and multi-dimension earthquake ground motion is inputted by large stiffness method. The results show that the spatial variability of earthquake ground motion has a huge impact on the dynamic response amplitudes of coupling system. If the spatial variability of earthquake ground motion considers only the traveling wave effect, the dynamic responses of vehicle on bridge may be underestimated.(6) The running safety of high-speed train running over a bridge under non-uniform seismic excitations is researched. Four judging indexes, continuous overrun time of derail coefficient, continuous overrun time of reduction ratio of wheel load, lateral displacement of contact point, lifting displacement of wheel, are used. Then, the running safety of high-speed train running over the bridge of Beipanjiang under non-uniform seismic excitations is researched. The results show that the spatial variability of earthquake ground motion has some influence on the amplitudes of running safety judging index, but it has a little influence on the threshold value of safety speed. If the tradition judging indexes of derail coefficient and reduction ratio of wheel load are used to judge the running safety of a train on bridge under seismic action, the threshold value of safety speed may be underestimated.