| With the rapid development of high-speed railway in China,ballastless track has a wide laying range and a long mileage.Under the influence of environmental factors such as temperature difference in different areas,extreme high and low temperature,complex temperature cycle and long-term train load,ballastless track is prone to produce a variety of structural diseases,which not only increases the maintenance workload of the line,but also endangers the operation safety of high-speed trains.Therefore,it is urgent to study the temperature field change of ballastless track under different regional climate conditions,as well as the mechanical characteristics and disease mechanism of ballastless track under the coupling effect of temperature and train.However,there are many difficulties in the actual test of ballastless track temperature field and the climate change in different regions cannot be considered.The existing ballastless track test platform also lacks the consideration of temperature-train coupling test for the overall structure of ballastless track.Based on the urgent needs of the experimental research of high-speed railway ballastless track in China and the shortcomings of the existing research,this paper makes a series of prospective basic research on the design and test function of the comprehensive test platform of high-speed railway ballastless track.The main research work and achievements are as follows:(1)Based on the test research requirements of ballastless track,the basic functions of the high-speed railway ballastless track comprehensive test platform are positioned,and the functional module compositions,structures and basic test parameters of the test platform are preliminarily designed.In consideration of the basic functions of high-speed railway ballastless track test platform and the requirements of test operation space,the functional module compositions are preliminarily designed including temperature and humidity control system,fatigue load control system,test ballastless track system,sensor monitoring and detection system and auxiliary devices,as well as the external structure characteristics and space dimensions of the test platform;The basic test parameters of the test platform are designed,in which the temperature control range is-60℃～+70℃,the maximum dynamic amplitude of the fatigue loader is 1000 k N,and the standard loading frequency is 50 Hz.(2)Based on the finite element method and heat transfer theory,the design and analysis model of the test platform is established,including the external structure model,indoor air temperature field analysis model,mechanical analysis and heat transfer analysis model of ballastless track for test.Combined with the preliminary design of the structure and size of the comprehensive test platform for ballastless track,the design and analysis model of the test platform is established based on the finite element method and heat transfer theory,in which the air temperature field analysis model combines the CFD analysis function of the finite element,and the CRTSⅡ slab ballastless track analysis model with the length of three plates is established according to the laying conditions in the test platform.By comparing with the existing literature and theoretical results,the reliability of ballastless track analysis model and the results of finite element heat transfer analysis are verified.(3)For the consideration of function guarantee and structural stability of highspeed railway ballastless track comprehensive test platform,on the basis of the preliminary design of the test platform,the design optimization of its structure,temperature rise and fall rate control and ballastless track constraint mode is studied,and the structural design scheme of the test platform is determined,and the structural design diagram is drawn.In order to ensure the stable and balanced temperature control and regulation function of the test platform,the heat preservation and insulation performance of the test platform box,the uniformity of air temperature field and the influencing factors of air temperature rise and fall rate are analyzed respectively.It is determined that the insulation layer of the test platform box should be made of rigid polyurethane with a thickness of 100 mm,the upper air inlet and the lower return should be used when the air temperature rises In order to ensure the stability of the structure of the test platform under gravity and fatigue loading,the design thickness of the side box plate of the test platform is 150 mm,the thickness of the top plate should be increased to 180 mm,and the foundation of the test platform should be adopted In order to ensure the accuracy of the test results,it is determined to use the jack pushing restraint mode and the longitudinal bar anchoring + planting bar restraint mode to constrain the free end of the track plate.The structural design diagram of the high-speed railway ballastless track comprehensive test platform is drawn,which is detailed in the appendix A.(4)Combined with the basic functions of temperature control and regulation of the test platform,the simulation control test function of ballastless track temperature field of the test platform is studied based on the finite element method,and the test control method is summarized to provide theoretical support and guidance for the actual test function realization and test operation.When simulating the temperature field of ballastless track,the air temperature rise and fall load should be taken as the main control method,and the heat source radiation load should be taken as the auxiliary method;according to the summarized temperature field simulation control method of ballastless track,the temperature gradient change of track plate obtained by simulation and the measured temperature gradient change agree well;the temperature field simulation of ballastless track based on the test platform The control test function and test control method can realize the test simulation and research on the temperature field of ballastless track under different regional climate conditions,and solve many research difficulties in the railway line monitoring test.(5)Based on the basic function of fatigue loading of the test platform,the mechanical characteristics and damage characteristics of the ballastless track under the action of temperature and dynamic coupling are analyzed based on the finite element method.The loading frequency and time curve of the train load test under the dynamic loading mode of the test platform are studied which provides theoretical support and guidance for the actual test function realization and test operation.The change of temperature has little effect on the vibration acceleration of the rail under the dynamic load.The change of stress amplitude of ballastless track is mainly affected by the temperature load,while the vertical dynamic load only causes the small fluctuation change of stress;the coupling effect of temperature and dynamic load will accelerate the initiation of the interface damage of ballastless track and aggravate the development of the damage degree.Through the research and analysis of the train load frequency,the test load curve under the dynamic load mode suitable for the test platform is obtained,which can simulate the train load effect truly and realize the temperature train coupling test function of the test platform for ballastless track.The greater the temperature load on the track slab,the greater the influence of the train load on the stress change of the track slab;the influence of the temperature load on the initiation and development of the damage between layers of ballastless track is more significant than that of the train load.Under the long-term temperature train coupling effect,the damage between layers is likely to occur earlier than the position of the slab edge. |
