Unsupported Sleepers Research Articles

Effect of unsupported sleepers on dynamic behavior of running vehicles and ride comfort index

Nowadays, with various advancements in the railway industry and increasing speed of trains, the design of railway tracks and vehicles has become vitally important. One of the frequent problems of ballasted tracks is the existence of unsupported sleepers. This phenomenon occurs due to the lack of ballast underneath the sleepers. Here, a model is presented, in which a flexible track model in a multibody dynamics program is developed, in order to study the dynamic behavior of a vehicle. By utilizing the model, it is feasible to simulate unsupported sleepers on the flexible track including rail, sleeper, and ballast components. In order to verify the results of numerical model, a field test is performed. Findings indicate that, in the case of a single unsupported sleeper through the track, the ride comfort index increased by 100% after increasing the train speed from 30 to 110 km/h. Moreover, when it is needed to have ride comfort index improvement over the uncomfortable level, the vehicle speed should be less than 70 km/h and 50 km/h for tracks with one unsupported sleeper and two unsupported sleepers, respectively.

Calculation of a Railway with Unsupported Sleepers by a Grid-Characteristic Method

Calculation of a Railway with Unsupported Sleepers by a Grid-Characteristic Method

Determination of wheel loading reduction in railway track with unsupported sleepers and rail irregularities

This study investigates the simultaneous effects of unsupported sleepers and rail random irregularities on track displacement and wheel load reduction, by means of numerical simulations with vehicle-track coupling. Vehicles are simulated as multibody systems comprising the major vehicle masses and suspension systems with nonlinear stiffness and damping. Flexible track with rail, sleeper and ballast components is considered using finite element and multibody programs. Numerical results of the simulations are in good agreement with field test measurements. Findings show that in tracks with less than four unsupported sleepers the vehicle is able to move at a speed of 110 km/h; with a higher number of unsupported sleepers the vehicle is vulnerable to derailment. The vehicle speed has no effect on the maximum rail displacement in tracks with less than four unsupported sleepers.

Nonlinear Train-Track-Bridge Interaction with Unsupported Sleeper Group

Nonlinear Train-Track-Bridge Interaction with Unsupported Sleeper Group

Influence of Rail Pad Stiffness and Axle Loads on Dynamic Responses of Train-track Interaction with Unsupported Sleepers

Increasing the axle load causes track deterioration and permanent settlement of the ballast layer. In the ballasted railway tracks, due to the inevitability of unequal settlements in the ballast layer, part of the rail due to high flexural rigidity will become suspended, which causes the formation of the track with unsupported and partially supported sleepers. This situation increases rail vertical displacement and reactions on adjacent sleepers. Several models have been presented to study the effect of unsupported sleepers on dynamic responses of train-track interaction. In this paper, by applying mathematical model, unsupported and partially supported sleepers have been modeled and equations of motions for train-track interaction were written by assuming nonlinear behavior of rail and wheel contact. Following by solving the equations via numerical integration in the time domain, the effect of axle load and pad stiffness on rail vertical displacement were investigated. Results of the analysis suggested that through increasing the axle load rail displacement increased by 13 % in the unsupported sleeper and from 5 to 10 % in the partially supported sleeper. Also, by increasing the pad stiffness rail displacement decreased from 2 to 13 % in the unsupported sleeper and from 1 to 6 % in the partially supported sleeper.

Numerical Investigation of Unsupported Sleeper Detection Method Based on LSTM and Monte Carlo Dropout

Numerical Investigation of Unsupported Sleeper Detection Method Based on LSTM and Monte Carlo Dropout

Assessment of degradation of railroad rails: finite element analysis of insulated joints and unsupported sleepers

Assessment of degradation of railroad rails: finite element analysis of insulated joints and unsupported sleepers

Confirmation of the effect of track specifications on detecting unsupported sleepers and building a calculation method for practical work

Confirmation of the effect of track specifications on detecting unsupported sleepers and building a calculation method for practical work

Dynamic Response of High-Speed Train-Track System Due to Unsupported Sleepers

This paper is concerned with a numerical study on the dynamic response of a high-speed rail (HSR) system subjected to unsupported sleepers using the moving element method (MEM). A three-phase computational scheme in conjunction with the MEM is proposed to account for the motion of the unsupported sleepers in relation to the truncated rail segment in the moving coordinate system. The accuracy of the proposed computational scheme is examined by comparison with available analytical results in the literature and against the finite element method using commercial software. A parametric study is conducted using a computational model consisting of a 10-degree of freedom train model and a three-layer ballasted track model to investigate the effect of unsupported sleepers on the dynamic response of the HSR system. Various factors affecting the response of the HSR system, including the speed of the train, the number of unsupported sleepers and the distance between the unsupported sleepers, are examined and discussed.

Effect of unsupported sleepers on rail track dynamic behaviour

Railway track behaviour with unsupported prestressed sleepers has been investigated in the literature. However, some of the important factors – such as prestressing forces, variations of the sleeper cross-section along its length, losing or recovering contact between the sleeper and the ballast layer – have been omitted. These limitations have been addressed in this research. The effects of unsupported sleepers on the dynamic behaviour of railway track have been investigated, using an improved three-dimensional numerical model of track developed here. The validity of the model is evaluated by comparing the results obtained from the model with experimental results (obtained in this research and available in the literature). The influences of the size of the gap between the sleeper and the underlying ballast, the vehicle speed and the number of unsupported sleepers on the track dynamic behaviour were investigated. The effects of the various unsupported conditions of sleepers on the rail seat load, sleeper bending moment and sleeper–ballast contact force at various train speeds were illustrated. It was shown that consideration of sleeper prestress forces, detailed geometry of the sleepers and a more realistic assumption for the sleeper–ballast contact has considerably improved the accuracy of the results obtained from theoretical models.

Dynamic Performance of Concrete Turnout Bearers and Sleepers in Railway Switches and Crossings

Abstract With constant changes of their geometry and alignment, wheel–rail forces, and track and operational parameters, railway infrastructures are exposed to nonlinear actions by nature. A detrimental type of loading condition that causes cracking in the railway concrete bearers in switches and crossings is the dynamic transient wheel force. The transient wheel forces are often due to the wheel–rail transfer over the dipped trajectory at a crossing nose. It is often found that most track deterioration incurs at the crossing panel. The turnout bearers crack and break. The ballast degradation then causes differential settlement and later aggravates the impact forces acting on partial and unsupported sleepers and bearers. In addition, localized ballast breakages underneath any rail seat increase the likelihood of center-bound cracks in railway sleepers and bearers because of the unbalanced support. This article investigates the dynamic performance of standard-gauge concrete bearers at crossing panel, taking into account the realistic, nonlinear tensionless nature of ballast support. A finite element model was established and calibrated with static and dynamic responses using past experimental results. In this article, nonlinear phenomena caused by topologic asymmetry on both sagging and hogging behaviors of crossing bearers are firstly highlighted. In addition, it is the first to demonstrate the effects of dynamic load impulses on the design consideration of turnout bearers in crossing panel. The outcome of this study will benefit the railway turnout design and maintenance criteria in order to improve train–turnout interaction and reduce unplanned maintenance costs.

Parallel Co-Simulation Method for Railway Vehicle-Track Dynamics

This paper introduces a new parallel co-simulation method to study vehicle-track dynamic interactions. The new method uses the transmission control protocol/internet protocol (TCP/IP) to enable co-simulation between a detailed in-house track dynamics simulation package and a commercial vehicle system dynamics simulation package. The exchanged information are wheel-rail contact forces and rail kinematics. Then, the message passing interface (MPI) technique is used to enable the model to process track dynamics simulations and vehicle dynamics simulations in parallel. The parallel co-simulation technique has multiple advantages: (1) access to the advantages of both in-house and commercial simulation packages; (2) new model parts can be easily added in as new parallel processes; and (3) saving of computing time. The original track model used in this paper was significantly improved in terms of computing speed. The improved model is now more than ten times faster than the original model. Two simulations were conducted to model a locomotive negotiating a section of track with and without unsupported sleepers. The results show that the vertical rail deflections, wheel-rail contact forces and vehicle suspension forces are evidently larger when unsupported sleepers are present. The simulations have demonstrated the effectiveness of the proposed parallel co-simulation method for vehicle-track dynamic interaction studies.

Moving element analysis of high-speed rail system accounting for hanging sleepers

It is very common in the ballasted track system that sleepers are not well supported by the ballast materials due to the uneven settlement of the ballast under repeated train passage. These unsupported track elements are often termed as hanging sleepers and they can lead to undesirable effects due to increased dynamic response of the train-track system, especially when the speed of the train is high. In this paper, we present a computation scheme in conjunction with the moving element method for the analysis of high-speed train-track dynamics accounting for hanging sleepers. The proposed computational scheme will be first verified by comparison with available analytical results. The dynamic response of a high-speed train traveling on a ballasted track considering unsupported sleepers is next investigated. Various factors affecting the response of the high-speed rail system including the speed of the train, the number of hanging sleepers and the pattern of the hanging sleepers will be examined and discussed.

Numerical investigation of the effects of unsupported railway sleepers on train-induced environmental vibrations

Review of technical literature regarding to train-induced vibrations shows that the effects of unsupported railway sleepers on this issue have been less investigated. So, the present study was devoted to numerical investigations of the mentioned issue. In this regard, first the problem of longitudinal train–track dynamic interaction was simulated in two dimensions by using the finite element method and the developed model was validated through comparison of the results with those obtained by previous researchers. In the next stage, a series of sensitivity analyses were accomplished to account for the effects of value of gap beneath the unsupported sleeper(s) and the track support stiffness on increasing the sleeper displacement and track support force. Moreover, the raised sleeper support force was introduced as applied load to a two-dimensional plane strain finite element model of track in lateral section and consequently the train-induced vibrations were assessed. As a result, a series of regression equations were established between the peak particle velocity in the surrounding environment of railway track and the sleeper support stiffness for tracks without unsupported sleepers and with one and two unsupported sleepers.

Ground-Borne Vibrations Caused by Unsupported Railway Sleepers in Ballasted Tracks

As regards the ground-borne vibrations caused by unsupported railway sleepers in ballasted tracks have not been properly investigated till now, so this subject was studied in the current paper. In this matter, two separate finite element models including train-track dynamic interaction and ground-borne vibrations have been developed. At first, the train-track dynamic interaction has been modeled and then this model has been verified with the past work results. Afterward, the effects of various conditions of railway sleeper supports including the track with fully supported sleepers, track with one and two unsupported sleepers have been investigated. In this regard, many sensitivity analyses have been conducted on sleeper support parameters. In continuation, the track sleeper support forces obtained from the first model have been presented as inputs to FEM model of ground-borne vibrations and consequently the ground-borne vibrations have been estimated.

Effects of train bogie patterns on the mechanical performance of ballasted railway tracks with unsupported sleepers

The support condition of railway sleepers has a significant effect on the mechanical behavior of railway tracks due to the passing of different trains. One of the important issues in this regard relates to existing unsupported sleepers on the railway tracks. These sleepers cause changes in the dynamic responses of railway tracks under a moving train. In the literature, the effects of train bogie patterns on the behavior of tracks with and without unsupported sleepers have not been completely investigated till now. Therefore, the present study investigates this issue using numerical analyses. In this regard, first, a finite element model of a railway track is utilized, and the results are verified and validated against those of previous studies. Then, equations of three vehicle models are derived and their interactions with the track model are investigated. These models include vehicles without bogies and vehicles with two- and three-axle bogies. During the numerical analyses, the effects of the unsupported sleepers on the dynamic performance of the track are studied. Finally, based on the achieved numerical results, many regression equations are derived between the train axle loads with rail bending moments, sleeper displacements, and support forces for tracks.

Assessment of sleeper support conditions using micro-tremor analysis

An irregular geometry of the track can influence the safe passage of railway traffic. Therefore, maintenance activities on railways are mostly directed towards the correction of track geometry. It has been shown that unevenly supported and unsupported sleepers make major contributions to the effect of track geometry deterioration. In addition, irregular sleeper support conditions can contribute to ballast fouling, thus reducing its service life. Therefore, assessing the support conditions of the sleepers in a railway track is essential. This paper reviews methods that can be used for this purpose. Then, we propose a method for the assessment of sleeper support conditions and present results obtained in field investigations. The proposed method is based on sampling of the micro-tremor on sleepers and interpretation of obtained data. The obtained results prove that the proposed method is reliable and therefore usable in practice.

Real-Time Distributed Strain Monitoring of a Railway Bridge during Train Passage by Using a Distributed Optical Fiber Sensor Based on Brillouin Optical Correlation Domain Analysis

This study demonstrates the monitoring of distributed strain of rail and girder of a railway bridge occurring during train passage over the bridge’s entire section on a real-time basis by applying a developed distributed optical fiber sensor based on Brillouin Optical Correlation Domain Analysis (BOCDA). The distributed optical fiber sensor system and an algorithm to control as well as to analyze Brillouin gain spectrum signals were also developed. A single-mode optical fiber was attached in the longitudinal direction on the rail and the lower flange of the girder to be used as a sensing fiber of the BOCDA system. Changes in the girder’s strain at the center point of the bridge during the passage of a commercial train were measured at 9 Hz, and the accuracy of this measurement was validated by comparing the measured data with the data from strain gauge. In addition, the distributed strain of a girder and the rail with a length of 40.26 m was measured in real time with a spatial resolution of 31.1 cm. Based on the results of the rail’s strain distribution, the study could identify the location where excessive strain occurred due to an influence of unsupported sleepers on girder of the bridge.

Influence of unsupported and partially supported sleepers on dynamic responses of train–track interaction

One of the major problems of railroad deterioration is uneven settlement which occurs due to various reasons, including existence of defects in substructures, using non-homogenous ballast, or being poorly drained. Sometimes, because of these problems, sleepers remain freely as a part of vertical displacement and contact the ballast with load increase. Different models have been presented for checking the effect of hanging sleepers on the dynamic interaction of rail and train. In this paper, a mathematical model was developed for railway track and differential rail displacement with supported and unsupported sleepers was compared by modeling sleepers such as partially supported ones. On this basis, the motion equations of the train-track system were solved considering the non-linearity of wheel/rail contact form and using numerical integration in the time domain. Longitudinal sections of the track model were coded in Matlab software and the effect of one, two, or three partially supported sleepers and various spacing of sleepers on the sleepers and rail displacement was studied and compared with that of the unsupported one. It was shown that, with increasing the sleeper spacing from 50 to 75 cm, rail displacement increased from 7 to 22% in the unsupported sleeper and 5 to 8% in the partially supported sleeper. Additionally, rail displacement increased from 13 to 74% by changing the number of the unsupported sleeper from 1 to 9. Also, it increased from 6 to 24% in the partially supported sleepers.

3C12 FE-based ballast settlement analysis considering wheel-track dynamic response(Infrastructure)

The FE-based coupling method with ballast settlement elastoplastic analysis and track vibration analysis considering unsupported sleepers is developed to accurately evaluate the sleeper-ballast interaction force in deteriorated track. The present method is used to investigate the evolution of the ballast settlement around a junction of concrete slab and ballast layer. In the analysis considering unsupported sleepers, the maximum of the sleeper-ballast interaction force at the sleeper away from the junction increases in progression of the number of loading cycles at higher rate than that without loose sleepers. A larger maximum force causes a larger permanent deformation of ballast layer. This is because the progression of ballast settlement leads to an increase in the number of unsupported sleepers in neighborhood of a supported sleeper.