Three-Dimensional Vehicle–Curved Track Dynamic Model Based on FEM and DEM

In this work, a systematic vehicle–curved track dynamic model is presented, in which the vehicle is modeled as a multi-rigid-body system. The track structure is modeled by finite element method with curved rail beam element considered in geometry. To obtain accurate dynamic behavior of railway ballasted track, the resistance characteristics of ballast bed are revealed by introducing the discrete element method. Besides, a two-step iterative-update method is improved to solve the multi-nonlinearity of the vehicle–curved track dynamic interaction. To improve the computational efficiency, and the improved infinite cyclic calculation method is introduced. Apart from the model validations, the application of this model in engineering practices, such as the vehicle-induced vibration of the continuously welded rail (CWR), has been revealed, and some conclusions are drawn from the numerical studies.

A method for long-term on-line monitoring of temperature stress of continuously welded rail

Continuously welded rail (CWR) has been widely applied in modern railway structures, and its performance is directly related to the safety of railway transportation. After the removal of the rail joints, the CWR cannot expand and contract freely. The longitudinal temperature stress within the CWR turns out to be the core structural parameter in the maintenance and repair of the track. In this study, an ultrasonic theoretical model of the rail temperature force was established, and the mechanism of the critical refracted longitudinal wave to detect the rail temperature stress was analyzed. A numerical simulation calculation was conducted with the three-dimensional finite element model, and the longitudinal wave incidence angle, frequency, and transducer spacing were calculated. The impact of critical factors on the accuracy of refracted longitudinal wave detection temperature stress was investigated. The ultrasonic acoustic propagation under the corresponding stress value of the rail was calibrated to eliminate the influence of residual stress and ensure the accuracy of ultrasonic detection of temperature stress. Finally, an online rail temperature stress monitoring system was built, and a long-term operation was carried out in the Changzhou section of the Shanghai-Nanjing high-speed rail. The monitoring data of the line in 2019 was obtained, and the temperature stress change of the line was recorded. The data showed that the ultrasonic sound obtained by real-time monitoring could accurately reflect the temperature and force changes of the rail. This proposed method is expected to provide a solution for online and remote acquisition of the temperature stress of the CWR. The accumulated long-term monitoring data is of great significance to the prevention plan for rail expansion and rail breakage.

Effect of easement geometry on rail end fillet stress at bolted rail joints for transit track

Continuously welded rail (CWR) has become more popular than bolted joints because of the advantages of continuous geometry and stiffness and the resulting maintenance savings. Due to a variety of reasons, a considerable number of bolted joints are still in service in rail transit systems. With the high frequency of impact loads, rail at bolted joints are vulnerable to defects, such as cracking and head-web separation that could lead to more drastic failures and consequences (i.e. derailments, etc.). To prolong the service life of joint bars and rails, rail-end easements in the center of the bar were proposed and became standard in some freight rail companies. However, the effectiveness of a joint bar easement largely depends on the geometry of the easement. Therefore, the easement designed for freight track may not be effective for rail transit infrastructure. Further, the effect of easement geometry has not been thoroughly investigated and documented. Therefore, this study investigates the stress distribution at the rail end bolt-hole and upper fillet areas for joint bars with different easement geometries through a parametric analysis performed with Finite Element (FE) modeling. The FE model used in this study was developed specifically to study rail joints and was validated through full-scale laboratory testing. Results from this study show that a deeper easement yields lower contact stresses, while a longer easement does not necessarily reduce the contact stresses with the studied combination of rails and bolted joints for transit track. An easement may reduce the service life of the joint if the geometry of the easement is not properly engineered.

Numerical investigation into the effect of ballast properties on buckling of continuously welded rail (CWR)

In this paper, the effect of ballast properties including ballast depth, shoulder width, shoulder height, inter particle friction angle and ballast porosity on track buckling capacity are investigated numerically using discrete element method (DEM) analysis. First, a Single Tie Push Test (STPT) is simulated using DEM and the results are validated with field data. Then a sensitivity analyses is carried out. To investigate the effect of ballast properties on buckling capacity, the STPT responses according to the DEM analysis are introduced as a lateral track stiffness into a finite element model of continuously welded rail track, and a thermal buckling simulation is performed. The results show a significant effect of ballast porosity on buckling temperature.

Appropriate Matching Locations of Rail Expansion Regulator and Fixed Bearing of Continuous Beam Considering the Temperature Change of Bridge

Due to the temperature change of bridges, there is a great additional force in continuously welded rails on continuous bridges. Laying rail expansion regulators is an effective measure to reduce the additional force. The nonlinear finite element model is presented for a continuously welded rail track with a rail expansion regulator resting on the embankment and simple and continuous beams, considering the temperature change of the bridge. Then, a method is proposed to determine the locations of the rail expansion regulator and the fixed bearing of the continuous beam, corresponding to the maximum additional forces of rail reaching minimum values. Their appropriate matching locations are recommended based on the obtained influence laws of any locations of the rail expansion regulator and the fixed bearing of the continuous beam on the maximum additional forces of rail. The results can provide the theoretical basis for the design of the rail expansion regulator and the fixed bearing of long-span continuous bridges.

Experimental determination of longitudinal forces in front of braking train

The number of regularities detected in the experiments described by the author confirms that, despite of the differences in operating conditions between the middle of the 20th century and the present days, the methods of research and assessment of obtained results are still relevant.Features of the superstructure and track operation at the initial stage of introduction of the welded rails and continuously welded rail strings on the railways of the USSR are examined. It is demonstrated that axial displacement forces are occurred during the train movement, which are one of the most dangerous processes taking place in the track during the rolling stock movement. Axial displacement forces are manifested in the axial displacement of rails on the sleepers or displacement of rails with sleepers on the ballast. Knowledge of axial forces resulted from displacement of one rail line or the entire track is required for competent planning of installation and operation of the jointed rail track and continuously welded rail track, especially in the conditions of the Urals and Siberia. Methods and experimental results are provided for determination of additional axial forces acting in the track at the spike fastening and the individual intermediate fastening in front of braking train at the experimental sections of the continuously welded rail track in severe climatic conditions of the West-Siberian railway, where the annual fluctuations of therail temperature amount to 110°C.The following conclusions are made based on the analysis of the experiment results and experience of operation of the continuously welded rail strings: • no additional axial forces in front of braking train were detected in the continuously welded rail strings of the thermalstressed type without any release of thermal stresses on the independent fixation; • experiment confirmed possibility of installation and normal operation of continuously welded rail track on the entire network of railways of the Ministry of Transportation of the USSR; • recent wide introduction of trains of 7,100 t, combined trains of 12,600 and 14,200 tons require special attention to parameters of interaction of track and trains.

Track – Bridge Interaction on High Speed Railways – the ONCF Experience

This paper aims to describe the Moroccan experience on Track – Bridge interaction in railway domain. In fact, that phenomenon may induce a general track instability compromising train security if it’s not taken into account in the study phase. To that end, a numerical method, used to compute the additional longitudinal stresses on a continuously welded rail (CWR) mainly associated to relative displacements between track and deck on account of temperature variations, is presented. Therefore, the conditions of laying an expansion device will be concluded, particularly when the additional rail stresses exceed the maximum limit values defined on the current standards. An application of that method will be performed on MHARHAR viaduct where a non-compliance of track dilatation device laying was noticed. This study will emphasize the beginning of a track grid general instability due to ballast layer deconsolidation, the all based on a track geometry measurement. This study may be widely used in order to conceive properly a bridge supposed to receive a CWR track.

Experimental study on the longitudinal resistance of WJ-8 fasteners subjected to torque and vertical loading in continuously welded rails

The key functions of the fastener system are to hold the rail against the sleepers and to restrain the rail from all forms of movements that could lead to loss of geometry and stability of the track. Thus, fastener resistance is an important parameter in the continuously welded rail technology. This study investigates the characteristics of the longitudinal resistance of WJ-8 fasteners subjected to varying torques and vertical loadings. The vertical loading was applied to the rail section through a reaction frame, while the torque was applied using a digital torque wrench. Two types of fasteners, conventional-resistance and small-resistance fasteners, were tested in this study. The study shows that: (1) The growth rate of the longitudinal resistance of the fastener is independent of the vertical loading until the fastener slips. (2) The slip resistance of fasteners increases as the torque and vertical loading are increased. (3) The relationship between the longitudinal resistance and the displacement of fasteners at varying torques and vertical loadings fits a power index function. (4) The relationship between the longitudinal resistance and the displacement of the fastener exhibits hysteresis. The study serves as a reference for verifying and improving future calculation methods for the longitudinal resistance of fasteners in continuously welded rails.