The Research Of Dynamic Character Of The Rail System Under Express Trains

The subject of the track system's dynamic response to express trains has its significant theoretical meanings and great reference values for projects. With the increasing development of China's track construction and the improvement of trains' running speed,the resulting dynamic effects on track structure have been apparently increased,the effects on the environment caused by running vibration have reached such an extent that great attention has to be paid. But current domestic evaluation of along railways' environment vibration and forecasts' method still focuses on the site experiments and empirical formula,lacking systematic study and quantitative analysis,therefore we cannot conduct design and execution effectively before construction. In order to properly evaluate vibration of the environment along railway,it is quite necessary to penetrate into the research of dynamic response of express railway to track structure.The track system consists of rails,sleepers and filling layers of crushed stones. The mechanism for vibration for trains' running is the mutual effects between wheels and the track system. The mutual effects cause tracks and grounds to be deformed,and engender crooked waves in the tracks. The deforming effects of grounds lead to vibration which spreads outwardly through soil layers. By changing the tracks' deforming effects into load on the ground,we can calculate the engendering and spreading of waves in the ground.Based on the mechanism to engender and spread vibration,this paper mainly studies the subject of power response in the case of vertical load. We consider each sleeper as an abutment of opposite forces,rails on horizontal sleepers as a mock dispersed elastic ground beam model and trains as moving load on beams. Geometric roughness and damping are not taken into consideration. The paper tests tracks' dynamic responses by using Euler beam model with no accounts of shear and rotary inertia effects and Timoshenko model with consideration of shear and rotary inertia effects respectively. The paper takes integral calculus equation of time domain to express rails' dynamic response,then obtains the answers to time domain.In accordance with the dominant equations of the two models,this paper uses Green function method to calculate vibration caused by effects among wheels,tracks,and sleepers. Because of continuity of load effects in time and space,displacement effects of previous time period in the latter time period and effects in various places have been taken into accounts. It is on these basis that the paper puts forward the dispersed counting way discrete algorithm based on such relationship,takes time-stepping integration to calculate rails' dynamic response,uses Fortran language to write counting program,and conducts computer mock tests about rails' power response. The paper then compares the calculation results of the two beam models and reaches a beneficial conclusion.In the end,the paper summarizes the contents and raises a few questions for this subject which need to be deeply studied.