Research On Fatigue Damage And Fatigue Reliability Of High-Speed Railway Ballastless Track

High-speed railway is well-known by its large capacity for passengers,short departure interval,and strong effectiveness,which make it the primary option in modern railway transportation.At present,ballastless track is the main laying form for high-speed railway line in our country.Of all the newly built railway lines,ballastless track is also adopted in a large proportion.The main structure of ballastless track of high-speed railway is required to have a service life of 60 years.With the increase of the service years of ballastless track,the frequency of vehicle load will increase year by year,which is likely to cause fatigue damage of track structure.The existence of these fatigue damage will seriously affect the safety performance of the train and the service life of ballastless track structure.This paper aims at studying the fatigue damage and reliability of high-speed railway ballastless track under train load.A multi-scale fatigue analysis model of ballastless track is established by self-made program and finite element software,and the dynamic response of ballastless track structure under train load is simulated.Using P-M linear cumulative damage theory and S-N curve method to analyze the fatigue damage and service life of concrete and reinforcement in each layer of ballastless track structure.The limit state equation for fatigue reliability analysis is established.The fatigue reliability of ballastless track is figured out.The main research contents and achievements of this paper are as follows:(1)A multi-scale fatigue analysis model considering the macro and micro mechanical characteristics is established.The FORTRAN language and ABAQUS finite element software are used to establish the sub models of high-speed railway train and track respectively.The stiffness,mass and damping matrices of the train and track subsystem are extracted respectively,and the vehicle track coupling is realized by self-made program.The differential equation of motion of the coupling system is formed.The differential equation of motion is solved by Newmark numerical method.According to the actual size of ballastless track,a refined finite element model is established,which includes track slab,self-compacting concrete,base slab and its internal reinforcing mesh.(2)The fatigue damage and service life of each layer of ballastless track structure considering the coupling vibration effect within vehicle and track are studied.The dynamic responses of ballastless track obtained from the macro model are loaded into the micro model,and the stress time history results of concrete and steel bars in the track slab,self-compacting concrete and base slab with and without track irregularity are analyzed and extracted.The maximum stress distribution diagram of three-layer structure is drawn.According to the linear cumulative damage theory and S-N curve method,the damage and lifetime at the most disadvantageous position of fatigue in the three-layer structure of ballastless track are studied.The influence of fastener rigidity,driving speed and vehicle axle load on the fatigue damage and service life of ballastless track structure are analyzed.(3)A set of fatigue reliability analysis method basing on vehicle rail coupling random vibration analysis is proposed.The reliability theory and fatigue equation are used to establish the fatigue limit state analysis equation of track structure.Using Python program to realize the fatigue analysis and calculation under random parameters,then obtaining the probability distribution characteristics of ballastless track load under random parameters,which is aimed to obtain the distribution of equivalent stress parameters of track structure in the equation.According to the principle of damage equivalence,the fatigue equivalent stress of track structure is extracted,and the probability distribution characteristics of equivalent stress are obtained.Using Monte-Carlo method to solve the fatigue state equation,the time-varying fatigue reliability curve of ballastless track under different driving intervals is obtained.This research contents and methods can contribute to the existing service performance and safety assessment of ballastless track in China.Meanwhile,it has theoretical research importance and engineering application value for the design,maintenance and other technologies of ballastless track.