Railway Track System Research Articles

Stress intensity factors evaluation for through-transverse crack in slab track system under vehicle dynamic load

The stress intensity factors (SIFs) for through-transverse crack in the China Railway Track System (CRTS II) slab track system under vehicle dynamic load are evaluated in this paper. A coupled dynamic model of a half-vehicle and the slab track is presented in which the half-vehicle is treated as a 18-degree-of-freedom multi-body system. The slab track is modeled as two continuous Bernoulli–Euler beams supported by a series of elastic rectangle plates on a viscoelastic foundation. The model is applied to calculate the vertical and lateral dynamic wheel–rail forces. A three-dimensional finite element model of the slab track system is then established in which the through-transverse crack at the bottom of concrete base is created by using extended finite element method (XFEM). The wheel–rail forces obtained by the vehicle-track dynamics calculation are utilized as the inputs to finite element model, and then the values of dynamic SIFs at the crack-tip are extracted from the XFEM solution by domain based interaction integral approach. The influences of subgrade modulus, crack length, crack angle, friction coefficient between cracked surfaces, and friction coefficient between faces of concrete base and subgrade on dynamic SIFs are investigated in detail. The analysis indicates that the subgrade modulus, crack length and crack angle have great effects on dynamic SIFs at the crack-tip, while both of the friction coefficients have negligible influences on variations of dynamic SIFs. Also the statistical characteristics of varying SIFs due to random wheel–rail forces are studied and results reveal that the distributions of dynamic SIFs follow an approximately Gaussian distribution with different mean values and standard deviations. The numerical results obtained are very useful in the maintenance of the slab track system.

A generalized model for geosynthetic reinforced railway tracks resting on soft clays

SummaryThe present study pertains to the development of a foundation model for predicting the behavior of geosynthetic reinforcement railway track system rested on soft clay subgrade. The ballast and sub‐ballast layers have been idealized by Pasternak shear layer. The geosynthetic layer is represented by a stretched rough elastic membrane. Burger model has been used to characterize the soft clay subgrade. Numerical solutions have been obtained by adopting the finite difference scheme combined with non‐dimensioning the governing equations of the proposed model. The results confirm that the present model is quite capable of predicting the time‐dependent settlement response of geosynthetic reinforcement railway track system placed on soft clay subgrade. The surface settlement profile and mobilized tensile load of geosynthetics has been evaluated by considering variation in the wheel load, sleeper width, thickness of ballast and sub‐ballast layers and shear modulus of ballast and sub‐ballast layers. It has been observed that an increase in the sleeper width by 24% results in the reduction in central settlement and mobilized tensile load by 6.5% and 20.1%, respectively. It was found that with a 50% increase in the thickness of the ballast layer, the central settlement has decreased by 7.3% and the mobilized tension at the zone of maximum curvature has increased by 24.6%. However, with an increase in the thickness of the sub‐ballast layer, a considerable reduction in both central settlement and the mobilization of tension on geosynthetic has been noticed. The pattern of variation of settlement and mobilized tension for an increase in the shear modulus of ballast and sub‐ballast material was found to be almost similar. Copyright © 2014 John Wiley & Sons, Ltd.

Viability of using end-of-life tire pads as under sleeper pads in railway

This research study focused on the design of under sleeper pads made from deconstructed end-of-life tires. The rubber was obtained without grinding up the tires. This cost-effective process has a lower environmental impact and at the same time preserves the mechanical characteristics of the material. The analysis was focused on how certain design parameters of the under sleeper pads affected their static performance (at different stress levels) and their dynamic performance (at different load frequencies). Their long-term performance and durability were also evaluated with a mechanical fatigue test. In addition, a ballast box was used to assess the impact of the pads on lateral resistance and stress distribution in a ballasted railway track system. The results of this study showed that under sleeper tire pads with different static and dynamic stiffness moduli can be obtained by varying pad thickness and by applying different physical treatments to the material. Moreover, the fatigue results revealed that these tire pads are suitable for use in railway systems. In addition, it was found that the pads distributed loads to a higher ballast area and at the same time increased the lateral resistance of the track.

Analysis and Prediction of the Temperature Field Based on In-situ Measured Temperature for CRTS-II Ballastless Track

An effective and accurate prediction of the high-speed railway ballastless track structure (BTS) temperature field can be quite useful in the analysis of stress produced by temperature gradient within the track structure. In this paper, an analytical solution to the conductive heat transfer process in CRTS-II (abbreviation for China railway track system II) is developed from one-dimensional semi-infinite system, subjected to a periodic variation of track slab surface temperature. The measurement of the slab surface temperature from three pieces of track slab on ‘Jing-Hu’ (Beijing-Shanghai) high-speed railway was used to determine the initial condition for CRTS-II heat conduction equation. With the analytical solution and initial condition, the temperature distribution of the CRTS-II track at different time was calculated. Finally, the comparison of the calculated temperature and the measured temperature at depth z=20cm (track slab bottom)showed that the analytical solution to the temperature field is reasonable for temperature profile in the CRTS-II structure.

Effect of Cement Asphalt Mortar Debonding on Dynamic Properties of CRTS II Slab Ballastless Track

The debonding of cement emulsified asphalt mortar (CA mortar) is one of the main damage types in China railway track system II slab ballastless track. In order to analyze the influence of mortar debonding on the dynamic properties of CRTS II slab ballastless track, a vertical coupling vibration model for a vehicle-track-subgrade system was established on the base of wheel/rail coupling dynamics theory. The effects of different debonding lengths on dynamic response of vehicle and track system were analyzed by using the finite element software. The results show that the debonding of CA mortar layer will increase the dynamic response of track. If the length of debonding exceeds 1.95 m, the inflection point will appear on the vertical displacement curve of track. The vertical vibration acceleration of slab increases 4.95 times and the vertical dynamic compressive stress of CA mortar near the debonding region increases 15 times when the debonding length reaches 3.9 m. Considering the durability of ballastless track, once the length of debonding reaches 1.95 m, the mortar debonding should be repaired.

Interface damage and its effect on vibrations of slab track under temperature and vehicle dynamic loads

This paper presents a three-dimensional finite element model to investigate the interface damage occurred between prefabricated slab and CA (cement asphalt) mortar layer in the China Railway Track System (CRTS-II) slab track system. In the finite element model, a cohesive zone model with a non-linear constitutive law is introduced and utilized to model the damage, cracking and delamination at the interface. Combining with the temperature field database obtained from the three-dimensional transient heat transfer analysis, the interface damage evolution as a result of temperature change is analyzed. A three-dimensional coupled dynamic model of a vehicle and the slab track is then established to calculate the varying rail-supporting forces which are utilized as the inputs to the finite element model. The non-linearities of the wheel–rail contact geometry, the wheel–rail normal contact force and the wheel–rail tangential creep force are taken into account in the model. Setting the maximum interface damaged state calculated under temperature change as the initial condition, the interface damage evolution and its influence on the dynamic response of the slab track are investigated under the joint action of the temperature change and vehicle dynamic load. The analysis indicates that the proposed model is capable of predicting the initiation and propagation of cracks at the interface. The prefabricated slab presents lateral warping, resulting in severe interface damage on both the sides of the slab track along the longitudinal direction during temperature drop process, while the interface damage level does not change significantly under vehicle dynamic loads. The interface damage has great effects on the dynamic responses of the slab track.

Analysis of Cement Emulsified Asphalt Mortar Gap on CRTSII Slab Track under Train Loading

The finite element method was used to analyze the deformation and stress of track in different length and height of gaps under the train load. In order to study the influence of gap between the slab and emulsified cement asphalt mortar of china railway track system II slab track on the subgrade, a model of CRTS II slab track was established on the base of elastic foundation beam theory and finite element software ANSYS. The results show that gap between slab and CA mortar has significance effect on the stress and deformation of track structure. The deformation of rail and slab, the longitudinal stress of slab were increase with the increase of gap length, but has less effect on lateral stress of slab. When the length of gap exceed to 1.95m, the deformation and stress have the tendency of increase sharply, the length of gap between slab and CA mortar should not exceed 1.95m. The gap between slab and CA mortar has effect on the durability and lifetime of ballastless track, so the gap should be maintenance timely.

Dynamic Simulation of Ballastless Railway Track System with Local Invalid Sleepers

Considering local sleepers supported invalidly, the dynamic analysis is presented for ballastless railway track system subjected to moving loads. The track is modeled as an infinitely Euler-Bernoulli beam with Kelvin viscoelastic foundation. The restrain conditions of system change suddenly at unsupported sleepers. Numerical simulating was carried out by the finite element discrete and Newmarks-method. Dynamic responses of system were analyzed in the case of single or multi-sleeper to be not working properly. Results show that the maximum value of displacement of track is going up 50% approximately due to an invalid sleeper occurring. The amplitude of vibration is two times increase when three sleepers to be hung up. Hence, there would be a bad effect on the vibration control of ballastless railway track system as some sleepers lose efficacy continuously.

Influence of unsupported sleepers on the dynamic response of a heavy haul railway embankment

It is not uncommon for conventional ballasted railway track systems to have unsupported sleepers due the uneven settlement of the ballast or subgrade. In order to investigate the possible implications of unsupported sleepers, this paper describes the development of a dynamic finite element model which includes wheel/rail friction. The developed model was used to investigate the behavior of a section of existing track on the ballasted Shuohuang heavy haul railway line in China. The investigation showed that the maximum displacement of the rails and sleepers increases significantly with the number of consecutive unsupported sleepers. Furthermore, the magnitude of the displacement between an unsupported sleeper and the ballast is likely to greatly exacerbate ballast/sleeper attrition and reduce the fatigue life of the hanging sleeper. An increase in the number of unsupported sleepers amplifies these effects. In addition, it was found that the sleepers adjacent to unsupported ones carry an additional load resulting potentially in their increased wear and additional damage to the substructure. To better understand the wider implications of the presence of unsupported sleepers on track performance, the stability, safety (in terms of derailment) and potential for rail and substructure damage were computed as a function of the number of unsupported sleepers (one to four) and compared with specifications. The results showed that the number of unsupported sleepers has a significant adverse impact on all four measures. However, while the effects on stability, safety and rail damage were within the limits suggested in specifications, even when four sleepers were modeled, the potential for substructure failure within a typical design life of the railway system was identified.

IMPORTANCE OF NONLINEARITY OF TRACK SUPPORT SYSTEM IN MODELING OF RAILWAY TRACK DYNAMICS

Attention is drawn to the fact that the recent increase in axle loads, speed and traffic volume in railway tracks, as well as concerns over passengers' riding comfort and safety have resulted in fresh challenges that are needed to be addressed. These challenges can only be successfully tackled with a more accurate modeling of the dynamic behavior of railway tracks. Although a significant amount of research involving mathematical modeling of railway track dynamics has been conducted in the last two decades, the nonlinearity of track support systems has not been given sufficient attention. This paper is concerned with the effect of nonlinearity of the support sub-layers on the dynamic responses of the railway track. To this end, a railway track model that considers the nonlinear properties of the track sub-layers is developed. Then, a field investigation into the dynamic responses of the railway track system under moving trains is conducted. The effect of the nonlinearity properties of the track support system on the track responses is investigated by comparing the results obtained by the numerical model, with or without consideration of track support nonlinearity, with those from the field tests. It is illustrated that consideration of the nonlinear properties of the track support system improves the accuracy of the calculated responses by a factor of three. It is also shown that the train axle loads and track accumulative loading have a significant effect on the nonlinearity of the track support system and, as a result, on the modeling of track responses.

On the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads

Installed as the crosstie beam support in railway track systems, the prestressed concrete sleepers (or railroad ties) are designed in order to carry and transfer the wheel loads from the rails to the ground. It is nowadays best known that railway tracks are subject to the impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration, as well as there exists the potential of repeated load experience during the design life of the prestressed concrete sleepers. These have led to two main limit states for the design consideration: ultimate limit states under extreme impact and fatigue limit states under repeated impact loads. Prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, their impact responses and behaviours under the repetitions of severe impact loads are not deeply appreciated nor taken into the design consideration. This experimental investigation was aimed at understanding the residual capacity of prestressed concrete sleepers in railway track structures under repeated impact loading, in order to form the state of the art of limit states design concept for prestressed concrete sleepers. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong as to achieve the purpose. Series of repeated impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from low to high impact magnitudes. The impact forces have been correlated against the probabilistic track force distribution obtained from a Queensland heavy haul rail network. The impactdamaged sleepers were re-tested under static conditions in order to evaluate the residual energy toughness in accordance with the Australian Standard. It is found that a concrete sleeper damaged by an impact load could possess significant reserve capacity sufficient for resisting the axle load of about 1.05 to 1.10 times of the design axle loads. The accumulative impact damage and residual energy toughness under different magnitudes of probabilistic impacts are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented as to implement design guidance related to the serviceability or fatigue limit statesdesign.

Improvement alternatives for railway track formation

The performance of the railway track system results from the complex interaction of its components in response to train loading. The railway track substructure has been given much less consideration, even though it has a major influence on the track deterioration and as a consequence on the costs of track maintenance and renewal. The properties of the substructure components are much more variable and difficult to determine than those of the superstructure. The importance of the track formation properties for track performance is discussed in the first part of the paper. In cases where the formation is too weak, the resulting high cost of track maintenance may dictate the need to improve the formation conditions. The paper contains the alternatives of track formation improvements separated in six groups: altering formation properties in place, reconstruction and replacement, asphalt-concrete application, slip stabilization, insertion of protective layer and geosintetics implementation. In the summary the evaluation process of proper formation improvement method is explained. The goal of the paper is to provide the basis for track formation improvement design, which may result in railway tracks with optimum maintenance effort and traffic operability.

Field investigation of variation of loading pattern of concrete sleeper due to ballast sandy contamination in sandy desert areas

Sleeper is one of the most important components in a railway track system. Thus, for accurate analysis and design of concrete sleepers, knowledge of imposed loading pattern is necessary. Sandy desert areas are critical regions where loading status of concrete sleeper is different from other areas. In these areas, the influence of flowing sand grains between the ballast aggregates increase the stiffness of ballast layer; consequently, rail support modulus increases, so the received share of total axle load subsequently increases on the sleeper which is placed under the wheel load. On the other hand, the pressure distribution underneath the sleeper changes considerably. In this paper, the results of a field investigation about the variation of rail support modulus and also variation of loading pattern of concrete sleeper followed by the variation of bending moment of sleepers in sandy desert regions were presented.

Progress of Filling Layer of Self-Compacting Concrete in CRTS-III Type Track System

In this paper,the functions and performances of filling layer of self-compacting concrete(SCC) in CRTS(China Railway Track System)-Ⅲ type track system were introduced. Developments of SCC including design methods and test method was described in detail. The influencing factors of workability of SCC was analysised. The trends of future development of mix proportion design methods,durability evaluation admixtures,applications were discussed.This paper also pointed that it's importance for SCC to studying the quality control methods and the application.

Cone Penetrometer with a Helical-Type Outer Screw Rod for Evaluation of the Subgrade Condition

AbstractA weak railway subgrade may lead to instability of the railway track system. The condition of a railway subgrade is typically evaluated using trial pit excavation and a portable ballast sampler, which may severely disturb the ballast layer. Also, nondestructive geophysical techniques, such as ground penetrating radar (GPR), are used to investigate the condition of the ballast and subgrade along the track. The objective of this study is the development and application of a cone penetrometer with a helical-type outer screw rod (CPH) that minimizes the disturbance of the ballast layer for the evaluation of the subgrade condition by measuring the resistance of the cone tip. The CPH consists of a helical-type outer screw rod (helical rod) and a mini cone penetrometer inside the rod. The design concerns include easy installation of the helical rod into the ballast layer, the reaction force of the mini cone penetrometer, installation of the strain gauge, and calculation of the cone tip resistance. The he...

궤도 유지보수 주기 예측을 위한 구간 특성에 따른 궤도틀림 표준편차 진전정도 분석

궤도틀림은 열차의 주행안전 및 승차감에 미치는 영향이 크고, 소음 진동의 주요원인으로 작용한다. 따라서 현장에서 발생하는 궤도의 틀림을 체계적으로 분석함으로써 이를 저감할 수 있도록 차량운행 조건과 선로선형 및 궤도구조를 설계하는 것은 중요한 과제이다. 현재 국내에서 EM-120에 의해 검측된 틀림 데이터는 매우 불규칙적인 형태를 나타내며 데이터 분석 시 다양한 문제점을 가지고 있다. 본 연구에서는 궤도의 효율적인 유지관리를 위해 검측된 틀림데이터의 효율적인 처리 기법을 개발하고, 정제된 데이터를 이용해 선로를 구성하고 있는 이음매, 도상, 노반, 체결구 등의 요소를 고려하여 레일 궤도 틀림의 진전 정도를 정량화 하였다. 또한 축적된 검측 데이터로부터 궤도의 건전도를 평가할 수 있는 방법을 정립하고 잔존수명을 예측하여 효율적 유지관리를 실현하기 위하여 검측 데이터의 확률론적 수명 산정 기법 개발 및 데이터를 이용한 구간 특성에 따른 궤도틀림 표준편차의 틀림 진전 정도에 대한 통계 및 확률적 분석을 수행하였다. The irregularity of railway track affects not only the comfort of ride such as noise or vibration but also the safety of train operation. For this reason, it is an interesting research area to design a reliable and sustainable railway track system and to analyze the train movement mechanism based on systematic approaches considering reasons of track irregularity possible in a specific local environment. Irregularity data inspected by EM-120, an railway inspection system in Korea includes unavoidable incomplete and erratic information, so it is encountered lots of problem to analyse those data without appropriate pre-data-refining processes. In this research, for the efficient management and maintenance of railway system, progress rate of standard deviation of irregularity is quantified. During the computation, some important components of railways such as rail joint, ballast, roadbed, and fastener have been considered. Probabilistic distributions of irregularity growth with respect to time are computed to predict the remaining service life of railway track and to be adapted for the safety assessment.

Reliability-based conversion of a structural design code for railway prestressed concrete sleepers

Ballasted railway track is very suitable for heavy-rail networks because of its many superior advantages in design, construction, short- and long-term maintenance, sustainability, and life cycle cost. An important part of the railway track system, which distributes the wheel load to the formation, is the railway sleeper. Improved knowledge has raised concerns about design techniques for prestressed concrete (PC) sleepers. Most current design codes for these rely on allowable stresses and material strength reductions. However, premature cracking of PC sleepers has been found in railway tracks. The major cause of cracking is the infrequent but high-magnitude wheel loads produced by the small percentage of irregular wheels or rail-head surface defects; both these are crudely accounted for in the allowable stress design method by a single load factor. The current design philosophy, outlined in Australian Standard AS1085.14, is based on the assessment of permissible stresses resulting from quasi-static wheel loads and essentially the static response of PC sleepers. To shift the conventional methodology to a more rational design method that involves a more realistic dynamic response of PC sleepers and performance-based design methodology, comprehensive studies of the loading conditions, the dynamic response, and the dynamic resistance of PC sleepers have been conducted. This collaborative research between several Australian universities has addressed such important issues as the spectrum and the amplitudes of dynamic forces applied to the railway track, evaluation of the reserve capacity of typical PC sleepers designed to AS 1085.14, and the development of a new limit states design concept. This article presents the results of the extensive analytical and experimental investigations aimed at predicting wheel impact loads at different return periods (based on field data from impact detectors), together with an experimental investigation of the ultimate impact resistance of PC sleepers required by the limit states design approach. It highlights the reliability approach and rationales associated with the development of limit states and presents guidelines pertaining to conversion of AS 1085.14 to a limit states design format. The reliability concept provides design flexibility and broadens the design principle, so that any operational condition could be catered for optimally in the design.

P1-88 Decrease of railway suicides between 1998 and 2006: evaluation of the German railway suicide prevention project

IntroductionRailway suicides are a suicidal behaviour which strongly impact psychological and socioeconomic aspects of the railway company, its employees and possible eye witnesses. The German Railway Suicide Prevention Project was...

Ultimate Impact Resistance and Residual Toughness of Pre-Stressed Concrete Railway Sleepers

The pre-stressed concrete sleepers (or railroad ties), which are installed in railway track systems as the crosstie beam support, are designed to carry and transfer the wheel loads from the rails to the ground. It is well known that railway tracks are subject to impact loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration. In addition, there exists the potential of repeated load experience during the design life of pre-stressed concrete sleepers. Pre-stressed concrete has played a significant role in maintaining the high endurance of sleepers subjected to low to moderate repeated impact loads. In spite of the common use of pre-stressed concrete sleepers in railway tracks, their impact response and behaviour under repetitions of severe impact loads are not deeply appreciated, nor taken into consideration in design. This experimental investigation was aimed at understanding the residual capacity of pre-stressed concrete sleepers in railway track structures under ultimate impact loading, in order to develop state of the art limit states design concepts for pre-stressed concrete sleepers. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong to achieve this purpose. A series of severe impact tests on in-situ pre-stressed concrete sleepers was carried out, ranging from low to high impact magnitudes. The impact energy was evaluated in relation to the drop heights. The impact-damaged sleepers were re-tested under static conditions in order to evaluate the residual fracture toughness in accordance with the Australian Standard. It was found that a concrete sleeper damaged by an impact load could possess significant reserve capacity sufficient for resisting about 1.05 to 1.10 times the design axle loads. The impact behaviour and residual fracture toughness under different magnitudes of impacts are highlighted in this paper. The effects of track environment, including soft and hard tracks, are also presented together with a discussion related to the ultimate limit states design.

Development of a vehicle–track model assembly and numerical method for simulation of wheel–rail dynamic interaction due to unsupported sleepers

In practice, it is not very uncommon to find railway track systems with unsupported sleepers due to the uneven settlement of a ballasted track system. These unsupported sleepers are among the major vibration excitations for a train and track system when a train moves forwards on a track. The vibration induced by unsupported sleepers can cause a large dynamic contact force between wheels and rails. For heavily loaded high-speed trains, the deteriorated sleeper support may lead to accelerated degradation of the railway track and vehicle components, and may thus impose safety risk to the operation. This paper presents analyses of a coupled vehicle–track assembly consisting of a roll plane vehicle model, a continuous track system model and an adaptive wheel–rail contact model. In order to improve the simulation efficiency, a numerical approach based on the central finite difference method is proposed in this investigation. The developed model assembly and proposed simulation method are utilised to simulate the vehicle–track dynamic interaction in the presence of unsupported sleepers. The dynamic response in terms of the dynamic wheel–rail interaction force due to one or multiple unsupported sleepers is studied. Important factors influencing the dynamic wheel–rail interaction force in the presence of sleeper voids are also investigated. The results show that the vehicle speed, the gap size and the number of unsupported sleepers primarily dictate the magnitude of impact load which can be significant.