Mechanism of the Sleeper-Ballast Dynamic Impact in Void Zones

To investigate the influences of through-transverse mortar disengagement with different lengths and heights on the dynamic responses of vehicle and track systems under the high frequency train loads, a coupled rigid vehicle–flexible track multi-body dynamics (MBD) model with mortar disengagement was established in SIMPACK platforms with the help of ANSYS software. The results indicate that when the mortar disengagement length is no more than 1 m, the responses of vehicle and track systems are hardly influenced by mortar disengagement with an increase rate of no more than 10% except for the slab displacement. When LMD reaches 1.5 m, the maximum slab displacement exceeds the safety limit of 0.5 mm. The vertical wheel–rail contact force and the rail displacement exceed the safety limit with the mortar disengagement length of 2 m and the mortar disengagement height of 1.5 mm. The most increase rates induced by mortar disengagement are 190% and 272% with regards to the slab displacement and the longitudinal tension stress of slab, respectively, which is significantly detrimental to the service life of slab. The proposed approach has the potential to preliminarily determine the critical mortar disengagement size, which is conductive to relieving the pressure of track maintenance while ensuring the service life of track structures and the operation safety and riding comfort of the vehicle.

The Effect of Interface Damage between Slab and Mortar Layer on the Dynamic Performances of Vehicle and Track Systems under the High Frequency Train Loads

Xin

Ren

2022

Study on Representative Parameters of Reverse Engineering for Maintenance of Ballasted Tracks

Park

Kim

Seo³

2022

Reverse engineering (RE) is a technology used to create three-dimensional (3D) models by scanning structures and can be used to examine the current condition of structures. Applying RE to the maintenance of railroad facilities with a high proportion of safety accidents can be an alternative to increase the efficiency of railroad facilities. However, most tasks while constructing Building Information Modeling (BIM) after 3D scanning and extracting two-dimensional (2D) drawings are still performed manually. In particular, denoising, registration, and 3D modeling based on point clouds are labor-intensive and time-consuming tasks, and their efficiency needs to be enhanced by introducing automation technology. In this study, we selected point clouds-based representative parameters for ballasted tracks of a straight single-line section for automating railroad maintenance. Scan data and a BIM of a ballasted track were compared using the selected representative parameters. In addition, the types of damage to ballasted track requiring maintenance were examined. And a testbed was consisted of ballasted a track was selected, and 3D scanning was performed to obtain point cloud data of a testbed. Then, a BIM model was created by measuring the numerical values corresponding to the representative parameters on the scan data. The feasibility of constructing a railroad maintenance BIM based on representative 3D object detection parameters during RE work on the ballasted track was evaluated.

Experimental Research on the Load Transfer Mechanism of Tie Plates for 400 km/h High-Speed Turnouts

Wang

Sun²,

Mu³

et al. 2022

Based on the research and development demand of the 400 km/h high-speed turnout, a new type of elastic iron tie plate based on stiffness optimization is proposed. The new elastic iron tie plate is expected to reduce the stiffness unevenness and effectively solve the problems in the use of existing elastic iron tie plates. However, the new plate uses rubber bosses instead of rubber washers. There are certain differences in the force transmission mechanism from the original tie plate because of the change in structure of the new tie plate. In this paper, a series of experiments are designed to quantitatively compare and analyze the overall stiffness characteristics of different tie-plate structures and the differences in bolt force transmission and distribution laws. The main conclusions are as follows. The laws of vertical load transfer and distribution in the new tie plate are remarkably different from those for the original tie plate because of the differences in their structures. Under the rated bolt torque, the force transferred to the upper surface of the tie plate through the rubber boss in the new tie plate is less than that in the original tie-plate structure by 5.18 kN in the assembled state. Further, the new structure also has lower tie plate precompression; hence, the influence on the stiffness characteristics of the tie plate is less than that in the original structure. However, the steel sleeve deflection in the new tie plate is greater than that in the original tie plate; that is, a larger proportion of the bolt preload force is borne by the steel sleeve, thus making the vulcanized rubber under the steel sleeve more vulnerable to shear damage. If put into actual use, the tie plate bolt torque will be somewhat different from the rated torque; because of the difference in the torques coupled with the different vertical load transfer mechanisms between the new and the original tie-plate structures, the precompression and the proportion of the bolt preload force borne by the steel sleeves of the two tie plates will also show different degrees of deviation corresponding to different deviations of the tie plate bolt torque. Therefore, the new tie plate structure needs to be further optimized to make the transfer mechanism of preload force of bolt as consistent with the original tie plate as possible. In addition, the vibration and deformation characteristics and long-term service performance of the new type of plate under the condition of vehicle passing will be studied through a small-scale field trial and systematic dynamic tests.