| The rolled steel sleeper is a semi-closed groove structure which is formed by rolling and forging the U steel and then bending both ends.When installing,the steel sleeper is directly embedded in the track bed,and the contact between the ballast of inner cavity and the spade structure guarantees the stability of the track.Up to now,the history of steel sleepers development and application has exceeded more than 100 years,forming a complete steel sleeper-fastening structure system with long life,light weight,large carrying capacity,simple and reliable structure,strong applicability,etc.It is widely used in Australia,UK,North America,South America,Africa,Southeast Asia,etc.Among them,Australia is the main application area of steel sleepers.Its domestic consumption accounts for about 13%of the total rail sleeper,and it is expected to reach 25%by 2020 which has formed a complete design processing,testing and application technology system.In addition to the standard gauge universal speed and heavy-duty lines,the steel sleepers are also suitable for complex line sections including wide/narrow gauges,deserts,jungles,and mountains.In addition,the lateral resistance of the track is an important parameter to ensure the lateral stability of the CWR line which mainly affected by factors such as sleeper type,weight,type and condition of ballast,maintenance operations.However,at present,due to the limitations of its own structural characteristics such as light weight,low friction coefficient and shallow depth of embedded track bed,the lateral resistance of the steel sleeper is lower than that of concrete sleepers,and the current research and corresponding structural optimization methods in this area are still insufficient which results in the application speed grade of steel sleeper is limited to speeds of up to 160km/h,and which is an important reason that it cannot be applied to higher speed and larger axle weight grade lines.In this paper,four kinds of lateral resistance optimization scheme for steel sleeper are proposed:optimized end spade steel sleeper,ribbed steel sleeper,under-sleeper-pad(USP)steel sleeper and nailed steel sleeper,which based on the current research status of the low lateral resistance of steel sleeper,the deficiency of related structural optimization research,and the subsequent comprehensive analysis and summary of the research status of the ballast lateral resistance and the existing concrete sleeper lateral resistance reinforcement scheme.Then the full-scale ballast test model is laid,and the single sleeper push test is used to test the lateral stability of the U steel sleeper and the above-mentioned partially optimized steel sleepers.Finally,the three-dimensional steel sleeper-ballast lateral resistance test model corresponding to the above test track ballast condition is modeling based on the existing 3D laser scanning technology and discrete element method(DEM).After the model is verified based on the above test results,the lateral resistance of each type of steel sleeper is simulated and the micromechanical characteristics of each type of steel sleeper are analyzed.The specific main work and research results of this paper are as follows:1.Comparison of lateral resistance of U steel sleepers and ?c concrete sleepers with single sleeper push testAs mentioned above,the research on the lateral resistance of steel sleepers is relatively insufficient at home and abroad,and the application of steel sleepers in China is very rare.Therefore,under the standard of ballasted track in China,the lateral stability of steel sleepers is not known.In addition,the width and height of the ballast shoulder are two important parameters that affect the lateral resistance of the sleeper.The influence of the two on the lateral resistance of the steel sleeper is also unclear.Therefore,based on the full-scale test method of lateral resistance of ballast bed,the U steel sleeper produced in China is tested.The influence of ballast shoulder width and height on the lateral resistance of U steel sleeper in China is analyzed and compared with ?c sleeper.The test results of the sleepers under the same conditions are compared to analyze the difference between resistance improvement effects.The experimental results show that the lateral resistance of the steel sleeper is lower than that of the ?c sleeper,and the improvement effect of the shoulder width and height of the ballast is greatly reduced for the lateral resistance of the U steel sleeper compared with the ?c sleeper,and the lateral resistance is mainly caused by the interaction between the steel sleeper and ballast in the cavity by the research on the steel sleeper resistance distribution.2.Optimize the lateral resistance of the existing U steel sleepers,and process the ribbed steel sleepers and the USP steel sleepers,and conduct the lateral resistance test for them.Based on the summary of the reinforcement stability scheme of the sleeper in the first chapter of the paper,the existing reinforcement schemes are mostly:increasing the shear band between the ballast and the sleeper(boosting the shearing effect)and increasing the friction coefficient of the bottom of the sleeper.Therefore,based on the groove structure characteristics of steel sleepers,a variety of ribbed steel sleepers are designed and manufactured,and USP is added to increase the friction coefficient of the sleeper bottom,in order to increase the lateral resistance of the steel sleepers and reduce the stiffness of the contact surface between the bottom and ballast to slow down the steel sleeper vibration and noise and the ballast deterioration under sleepers.Then,the lateral resistance test was carried out to determine the improvement effect of the two steel sleepers,and the results of the ?c sleeper test were compared.The test results show that both the ribbed steel sleeper and the USP steel sleeper can improve the lateral resistance,and the ribbed steel sleeper improvement is better,and can be comparable to the ?c sleeper in some conditions.3.Establish a three-dimensional steel sleeper-ballast lateral resistance test model,study the resistance improvement of each type steel sleeper through parameter analysis,and analyze the micromechanical characteristics of the interaction between the steel sleeper and the ballast.Due to the U steel sleeper system and test conditions,it is impossible to study the optimized spade and the nailed steel sleeper.At the same time,due to the particularity of the steel sleeper structure,according to the general definition,the ballast thickness under the sleeper is different from that of the traditional single block sleeper.Therefore,the optimum ballast thickness of the steel sleeper is also analyzed from the aspect of lateral resistance.Based on the above conditions,the paper establishes a three-dimensional steel sleeper-ballast lateral resistance test numerical model to analyze the effect on the lateral resistance of the ballast thickness,the optimized spade inclination angle/the depth,the number of vertical ribs,and the length of the mail.Analysis of the formation and improvement mechanism of lateral resistance of various steel sleeper are conducted form microscopic level,such as ballast displacement cloud diagram and ballast-sleeper contact state.The specific research results are as follows:optimized spade,ribbed and mailed steel sleeper can increase the lateral resistance to the same or even better level than the ?c sleeper.The structure optimization design is simple and efficient. |
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