Research On The Damage Characteristics Of CRTS ? Slab Ballastless Track Under Temperature And Vehicle Loads

With the development of Chinese High-speed railway(HSR),the study interests in slab track no longer merely focus on the design and construction process,and it is quite an inevitable trend for researchers to turn to the operation and maintenance issues.The diversity of formations and materials,uncertainty and randomness of incipient deficiencies,complexity and variety of loading conditions,which characterize the slab track,make the occurrence and accumulation of damages during service inevitable,leading to the macroscopic diseases in future.Investigation shows that many kinds of diseases emerge during the service of the slab track in HSR,especially the CRTS II slab track,such as breakage at the wide-narrow juncture,delamination between layers and warping of the slab.This situation affects the operation safe of vehicles and increases the cost of maintenance and repair.It is of great significance to explore the mechanism of the occurrence and accumulation of slab track damages and provide theoretical reference for the work of maintenance and repair.Based on the constitutive theory of the plastic damage of concrete and splitting and tensile tests of CA mortar,the author first establishes a non-linear random damage model taking a full account for the elastic-plastic constitutive features of the components of CRTS ? slab track,with which the damage characteristics under temperature and loading conditions are studied.The main contents are as follows:1.Based on the statistical damage constitutive theory of concrete microscopic dynamics,this paper chooses the damage evaluation index characterizing how severe the damages of slab track are.On the basis of existing codes,literatures and strength tests,the key parameters representing the elastic-plastic damage constitutive relation of the components are obtained.Also,the accuracy of the plastic damage parameters is verified by exerting compressing force on the simulation model.Furthermore,the result demonstrates that the simulated breakage forms corresponds well to those under practical circumstances and the simulated and formulated curves accord with each other quite well.2.Based on FEM,this paper unprecedentedly develops a non-linear statics/dynamics model for slab track using ABAQUS,taking full consideration of the damages.The model is verified by comparing the results of existing literatures and field tests with the simulated ones.The author also analyzes the influences of the created non-linear damage model and linear-elastic model on the simulation results under different conditions,such as temperature and vehicle loads.The study shows that the choice of different model has a negligible effect on the analysis results while the force and deformation state of the structure is within linear-elastic phase.However,when damages emerge inside the concrete,the analysis results differ in an increasing trend,making the linear-elastic model not applicable any longer.3.A comprehensive study on the force,deformation and damage features of the slab track under conditions of global temperature rising or dropping,positive or negative temperature gradients and cyclic temperature loads is conducted.The results indicate that the ballastless track is damaged by tension when the dropping in temperature is 10 degrees centigrade.Compared with the rising of temperature,the dropping has more severe effects on breakage of the slab track.The tensile damage occurred for the first time in the mortar layer and the wide-narrow juncture when the positive temperature gradients is 80?/m.Early cyclic temperature loads predominantly influence the force,deformation and damage features of the slab track.While the cycles rise,the damage and deformation state of the slab track accumulates constantly and tend to hit a plateau.However,the stresses are relieving and prone to be stable at mean time.Poor contact conditions of the wide-narrow juncture between slabs may make the once uniform and continuous damage distribution dispersive.In addition,poor contact conditions may lead to the discontinuity of force and deformation of slab track,deteriorating the service state of the slab structure.4.The damage properties of ballastless track under integral temperature rising or dropping load of slab and train load,positive or negative temperature gradient load of slab and train load are systematically studied.The results show that when the speed of the train changes between 200km/h-350km/h,the vertical acceleration of the rail is between the 90g?160g and the vertical displacement between the 0.7mm?1.0mm;the wide-narrow juncture and the mortar layer are damaged under the coupling load of temperature and vehicle.The damage is mainly caused by the temperature load.When the temperature load is constant,the choices of different speed classes or axial loads have negligible effects on the increase of damage degree of the slab track.While under single train load,the damage tends to increase slightly,but the effect of the increase is not obvious.However,the damage of ballastless track accumulates continuously under long-term cyclic load of train,possibly leading to macroscopic diseases in the end.