Railway Track System Research Articles

Identification of Temperature-Induced Deformation for HSR Slab Track Using Track Geometry Measurement Data.

Slab track is widely used in many newly built high-speed rail (HSR) lines as it offers many advantages over ballasted tracks. However, in actual operation, slab tracks are subjected to operational and environmental factors, and structural damages are frequently reported. One of the most critical problems is temperature-induced slab-warping deformation (SWD) which can jeopardize the safety of train operation. This paper proposes an automatic slab deformation detection method in light of the track geometry measurement data, which are collected by high-speed track geometry car (HSTGC). The characteristic of track vertical irregularity is first analyzed in both time and frequency domain, and the feature of slab-warping phenomenon is observed. To quantify the severity of SWD, a slab-warping index (SWI) is established based on warping-sensitive feature extraction using discrete wavelet transform (DWT). The performance of the proposed algorithm is verified against visual inspection recorded on four sections of China HSR line, which are constructed with the China Railway Track System II (CRTSII) slab track. The results show that among the 24,806 slabs being assessed, over 94% of the slabs with warping deformation can be successfully identified by the proposed detection method. This study is expected to provide guidance for efficiently detecting and locating slab track defects, taking advantage of the massive track inspection data.

Seismic Damage Mechanism of CRTS-II Slab Ballastless Track Structure on High-Speed Railway Bridges

China Railway Track System II (CRTS II) slab ballastless track structure is one of commonly adopted track systems on the high-speed railway bridge, which has been found seismically vulnerable under strong earthquakes. To investigate the earthquake-induced damage mechanism of the CRTS II slab ballastless track structure, a nonlinear numerical model of typical 7-span simply supported bridge–track system was established by the finite element software OpenSees and well calibrated by the test data and relative literatures. The nonlinear time history analysis was employed to calculate seismic responses of bridge and track parts under a suite of 10 seismic records. Results demonstrate that the sliding layer in the track structure is the most damage-prone component, especially at the bridge-subgrade transition section, and the shear alveolar may also sustain earthquake-induced fail. By analyzing the seismic damage mechanism of the track structure, this paper reveals that the nonuniform displacement responses of the girders and friction plate at the bridge-subgrade transition section are main factors that result in the extensive damage of the sliding layer and failure of the shear alveolar. However, the damage of these two components are beneficial to reduce the seismic responses of other components in the track structure and protect them from being damaged. From the perspective of engineering safety, the sliding layer and shear alveolar should be rigorously designed because the residual displacement of the sliding layer increases along with the maximum displacement and the failure of the shear alveolar may make the whole track structure failed.

System dynamics modeling and experimental study of railway track with thermoelectric heater/generator in extreme weather conditions

This paper develops a novel railway fastener system with thermoelectric heater/generator to heat the rail pads with the clean and sustainable electric energy harvested from the ambient thermal radiation. Due to the extremely cold temperature in some areas, the varying dynamic properties of rail pads result in a potential threat to the safe operation of the railway track system. The proposed thermoelectric generator can be used to continuously supply sufficient clean electric power to heat the rail pad, ensuring the railway fastener work within a proper temperature range. The experimental results show that the thermoelectric generator can provide an electric power of 5.8 mW with a low temperature gradient of 8 °C, and the working temperature of the rail pads can be improved by an average of 9.5 °C with 4 heaters of 2.5 W, which is consistent with the theoretical results of the finite volume method by FloTHERM. A fractional derivative Zener model of the coupled vehicle-track system is established to investigate the random vibration of the railway track structure with and without the proposed intelligent fastener system, and the calculated results show that the peak amplitude of wheel-rail contact force changes from 1.37 kN/Hz to 2.34 kN/Hz; whereas the first dominant frequency varies from 56.8 Hz to 68.0 Hz. It indicates that the vibration of the coupled vehicle-track system can be reduced by 41.5% with the proposed fastener system in extreme cold weather conditions.

Measurement of train-induced vibration for track parameter identification: Bayesian probabilistic approach

The train-induced vibration response is used to develop a comprehensive finite element model for the railway track, which considered rail-sleeper-ballast interaction. This model can be further use in the development of an operational monitoring system for railway track by following the Bayesian statistical system identification framework. However, it is believed that the uncertainties associated with the measured train-induced test data and model parameters are relatively high, therefore, the corresponding model updating problem will very likely to be in the category of unidentifiable case. Therefore, Markov chain Monte Carlo (MCMC) simulation was used in generating the samples for the approximation of the posterior uncertainties. The measurements also provide not only reference values suitable for model fitting, but also a good insight into the main features of the dynamic behaviour of the railway track system. Finally, the reliability and accuracy of the proposed method are demonstrated by numerically reproducing the system responses. Modelling assumptions are discussed, together with their implications on numerical results of the time-domain analysis, which were found to be in good agreement with experimental results.

USPs on Damage Reduction of Concrete Railway Sleepers

Ballast is the weakest among all of the railway track components due to its latent dynamic shifting and variation of stiffness along and across the track. Sharp Angular shape of the ballast components hinders evenly distribution of loads from sleeper to ballast, which in turn causes the sleepers to deteriorate over time resulting in higher frequency of railway track maintenance. Previous studies have shown that having an under-sleeper pad (USP) in between sleeper and ballast increases the contact area between them significantly. This by itself reduces the long-term damage on sleepers by a substantial amount. However, concrete sleeper is subjected to cracking due to excessive dynamic load from rail wheels. This paper intends to numerically evaluate whether the cracking of concrete sleepers gets reduced due to installing of USPs in the railway track system. The foremost reason behind cracking of concrete sleepers is the induced dynamic loads due to track irregularities and imperfect wheel rail contact. The most affected portion is at the bottom of the rail seat location of sleeper. Thus, two finite element models (one without USP and one with a 20mm thick USP attached at sleeper bottom) were analyzed while incorporating the concrete damage plasticity in the sleepers’ material. Results have shown better performance of concrete sleepers with USPs. Sleeper pads have shown a tendency to minimize excessive stress developed within naked concrete sleepers. Substantial advantage of using USPs in terms of damage reduction among sleepers were also perceived during conducting this analysis. Consequential reduction of crack formation was observed after installation of USPs.

Micro-mechanical investigation of railway ballast behavior under cyclic loading in a box test using DEM: effects of elastic layers and ballast types

Ballasted tracks are the commonly used railway track systems with constant demands for reducing maintenance cost and improved performance.Elastic layers are increasingly used for improving ballasted tracks. In order to better understand the effects of elastic layers, physical understanding at the ballast particle level is crucial. Here, discrete element method (DEM) is used to investigate the effects of elastic layers – under sleeper pad (text {USP}) at the sleeper/ballast interface and under ballast mat (text {UBM}) at the ballast/bottom interface – on micro-mechanical behavior of railway ballast. In the DEM model, the Conical Damage Model (CDM) is used for contact modelling. This model was calibrated in Suhr et al. (Granul Matter 20(4):70, 2018) for the simulation of two different types of ballast. The CDM model accounts for particle edge breakage, which is an important phenomenon especially at the early stage of a tamping cycle, and thus essential, when investigating the impact of elastic layers in the ballast bed. DEM results confirm that during cyclic loading, text {USP} reduces the edge breakage at the sleeper/ballast interface. On the other hand, text {UBM} shows higher particle movement throughout the ballast bed. Both the edge breakage and particle movement in the ballast bed are found to influence the sleeper settlement. Micro-mechanical investigations show that the force chain in deeper regions of the ballast bed is less affected by text {USP} for the two types of ballast. Conversely, dense lateral forces near to the box bottom were seen with text {UBM}. The findings are in good (qualitative) agreement with the experimental observations. Thus, DEM simulations can aid to better understand the micro-macro phenomena for railway ballast. This can help to improve the track components and track design based on simulation models taking into account the physical behavior of ballast.Graphical

Measurement of Railway Track Geometry: A State-of-the-Art Review

The worldwide increase in frequency of traffic for passenger trains and the rise of freight trains over the recent years necessitate the more intense deployment of track monitoring and rail inspection procedures. The wheel-rail contact forces, induced by the static axle loads of the vehicle and the dynamic effects of ground-borne vibration coming from the track superstructure, have been a significant factor contributing to the degradation of the railway track system. Measurements of track irregularities have been applied since the early days of railway engineering to reveal the current condition and quality of railway lines. Track geometry is a term used to collectively refer to the measurable parameters including the faults of railway tracks and rails. This paper is aiming to review the characteristics of compact inertial measurement systems (IMUs), their components, installation, the basic measures of the quality of the track using motion sensors, like accelerometers, gyroscopes and other sensing devices mounted on different places of the vehicle. Additionally, the paper briefly discusses the fundamentals of inertial navigation, the kinematics of the translational and rotational train motions to obtain orientation, velocity and position information.

Investigation of the Fatigue Behaviour of a Ballastless Slab Track–Bridge Structural System under Train Load

To probe into the time-dependent behaviour of the ballastless track–bridge structural system under train load, based on the import of the static and fatigue damage constitutive model of materials to simulate damage deterioration of the structural system and interface cohesive zone model to the interface layer, a three-dimensional nonlinear finite element model of the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system was established using the equivalent static method. Then, using this model, we developed the numerical simulation analysis of the influence law of material damage deterioration on structural system performance under train load and revealed the fatigue evolution of the structural system. The results show that the beam remains in compressed status for the whole process, the track is in compression in the midspan and in tension at the beam end, and the tensile stress is larger near the shear groove under the double-track static load. Under the fatigue load, stiffness degradation of the structural system is not obvious, and integral rigidity of the structural system is dependent on the rigidity of the beam. Strength reduction of the materials caused stress redistribution of the structural system and had a larger effect on the stress of each layer of track structure than on the stress on the beam. The fatigue degradation of the cement-emulsified asphalt (CA) mortar layer material has a significant impact on the structural system, which directly affects structural layer stress variation with the fatigue loading cycle.

Modelling and in-situ measurement of dynamic behavior of asphalt supporting layer in slab track system

During the last decades, asphalt concrete has been introduced in both ballast and ballastless track (including but not limited to slab track) systems. The use of asphalt concrete provides better damping and waterproofing performance. For this reason, a supporting layer of asphalt concrete (ASL) was introduced to the latest Chinese slab track system. In this paper, an in-depth study of the dynamic behavior of ASL was presented using modelling and in-situ measurement approaches. In the FE model, the train load was simplified to be a time series of concentrated load on rail nodes, and asphalt concrete was modeled as viscoelastic material by Prony series. The FE model was validated against in-situ measurement on a test section, in which a monitoring system was setup during construction. A series of transient analysis were conducted to obtain the dynamic responses of ASL under moving train load. The parametric effects of thickness of ASL was also studied with respect to the dynamic responses of superstructure and substructure, as well as the stability and durability of ASL. The results showed that, under moving bogie load, the reach of the dynamic responses in ASL is about 7.5 m in the longitudinal direction, and the maximum values occur at the position beneath the rails. A thicker ASL is more favorable to ride comfort and structural stability of high-speed railway track system. However, considering the economic and construction factors, an optimal thickness range of 7–10 cm is suggested for ASL in CRTS III slab track.

An Innovative Detection Method of High-Speed Railway Track Slab Supporting Block Plane Based on Point Cloud Data from 3D Scanning Technology

The dimension detection of high-speed railway track slabs is one of the most important tasks before the track slabs delivery. Based on the characteristics of a 3D scanner which can acquire a large amount of measurement data continuously and rapidly in a short time, this paper uses the integration of 3D scanner and the intelligent robot to detect the CRTSIII (China Railway Track System) track slab supporting block plane, then the dense and accurate supporting block plane point cloud data is obtained, and the point cloud data is registered with the established model. An improved Random Sample Consensus (RANSAC) plane fitting algorithm is also proposed to extract the data of supporting block plane point cloud in this paper. The detection method is verified and the quality analysis of the detection results is assessed by a lot of real point cloud data obtained on site. The results show that the method can meet the quality control of CRTSIII finished track slab and the detection standard. Compared with the traditional detection methods, the detection method proposed in this paper can complete the detection of a track slab in 7 min, which greatly improves the detection efficiency, and has better reliability. The method has wide application prospects in the field of railway component detection.

Study on the interlayer debonding and its effects on the mechanical properties of CRTS II slab track based on viscoelastic theory

In this study, a novel viscoelastic finite element model of China Railway Track System (CRTS) II slab track incorporating viscoelastic parameters and a cohesive zone was established. Based on this model, the interlayer debonding between the prefabricated concrete slabs and the cement asphalt mortar layer and its effects on the mechanical performance of track structure were systematically investigated. Firstly, the validity of the viscoelastic model was verified by comparing the simulated results with experimental data. Then, the initiation mechanism of debonding under temperature gradient loading and under coupling actions of temperature and dynamic vehicle loadings was analyzed and then compared with that based on a common elastic model. Finally, typical interlayer debonding cases with different locations and sizes were purposely set up and their effects on the vertical stresses and vertical displacements of the track were discussed. Results show that after introducing viscoelastic parameters, the maximum opening height and the extension width of debonding increase rapidly, while the temperature gradients of initiating debonding keep unchanged but the penetration temperature gradients significantly decrease. On the other hand, the vertical stresses and vertical displacements of track structure are hardly affected by the debonding in the middle, slightly changed by the debonding length at the edge and significantly affected by the debonding width at the edge. With the increase of debonding area, the vertical stresses and vertical displacements significantly increase, especially when the debonding area is larger than critical values. Compared to the elastic model, the use of the viscoelastic model leads to larger vertical stresses and displacements. It is believed that the incorporation of viscoelastic parameters effectively enhances the performance of FEM, which can better predict the initiation of interlayer debonding and the dynamic response of track structure.

Selected laboratory tests on under sleeper pads (USP) used in the railway track system

In the present paper results of the tests for fatigue strength and resistance to severe environ-mental conditions performed on several prototypical under sleeper pads (USP) are presented. The work includes results of the static and dynamic tests carried out on samples of three materials, which were used to produce the USP. The fatigue tests were performed up to 500 thousand load cycles and they aimed at determining which of the analysed USP have favourable properties, taking into account their potential application as the elements used for reduction of stresses in the ballast – especially in the ballast layer directly under the sleeper – and reduction of the material and acoustic vibration emitted to the railway track’s surrounding (vibration and noise). In the climatic tests that were aimed at determining the influence of severe environmental conditions on the properties of USP, the samples were attached to concrete blocks and immersed in water for 24 h and then placed in a climatic chamber, where they were subjected to freeze-thaw cycles. The results show that both the fatigue and climatic tests have influence on the damping-related parameters of the USP, what affects the effectiveness of the vibration isolation.

Interfacial Bonding Strength between Cement Asphalt Mortar and Concrete in Slab Track

AbstractIn China Railway Track System II, the bonding of a cement asphalt mortar (CA mortar) layer to concrete slabs is a decisive factor for its durability and serviceability. In this study, the i...

A model for the stochastic prediction of track support stiffness

As well as guiding the train, one of the key aims of a railway track system is to provide support to the train at the wheel–rail interface that is of near-uniform compliance. Of the various components that make up this compliance, the contribution of the trackbed (ballast and subgrade) is the most difficult to understand and control. This paper presents data from field measurements of the track support system stiffness for a continuous run of 209 sleepers on a high-speed ballasted railway. The data indicate a level of variability, even on a highly engineered and well-maintained route. Statistical analysis of the data is used to demonstrate the dependence of the trackbed modulus at an individual sleeper on the modulus of the sleeper immediately preceding it, and that in statistical terms the effect of sleepers further away is due to correlation between the intermediate sleepers. An optimum trackbed stiffness, close to the overall mean, at which the standard deviation is a minimum is demonstrated for a particular site. As the trackbed stiffness moves away from this optimum value, the likely variation from sleeper to sleeper increases. A framework for implementing a stochastic approach for predicting the variation in track support stiffness from one sleeper to another, based on a Markov model and appropriate probability distribution functions, is then proposed. This framework may be used for the quantitative comparison of different sites and for simulating the plausible values of track stiffness in the vehicle–track interaction analysis.

Arching mechanism of the slab joints in CRTSII slab track under high temperature conditions

China Railway Track System II slab track is widely applied to China high-speed railway. Under the high temperature conditions, it tends to produce different degrees of arch at the joints between prefabricated slabs, which will affect the track irregularity and safe operation of high-speed trains. In this paper, considering the buckling instability of track structure, the arching mechanism of the slab joints was investigated by establishing a 3D finite element model of the CRTSII slab track. Combined with the field investigation, the damage process of joint concrete and its effects on the arching instability were analyzed. The results show: 1) The construction of joint concrete is difficult to control on site, which leads to inferior quality compared to prefabricated slab. The worse quality of joint concrete corresponds to a smaller amplitude of temperature rise causing joints damage and a greater damage area. 2) When the amplitude of temperature rise of the slab is over 37 °C, various damage emerges in the narrow joint and the middle of wide joint, resulting in the eccentric compression. 3) The temperature gradient load will cause the propagation of interface gap between slab and CA mortar layer, which aggravates the arching instability of slab, especially when the height of gap exceeds 1.5 mm. This research is expected to provide guidance for the optimization design, maintenance and damage control of slab track.

Research on Mechanical Performance of CRTS III Plate‐Type Ballastless Track Structure under Temperature Load Based on Probability Statistics

CRTS III (China Railway Track System III) slab ballastless track structure is one of the high‐speed railway ballastless track structures which has Chinese independent intellectual property rights. The mechanical performance of CRTS III slab ballastless track structure under temperature load has not been clear yet. Therefore, through temperature field model and temperature load values selected by statistics analysis based on long‐term meteorological data, the mechanical performance of ballastless track structure is studied under two typical working conditions with different safety probability. It is found that the daily extreme values of monthly axial uniform temperature and the daily maximum temperature gradient obey certain statistical laws. In addition, the maximum tensile stress of the self‐compacting concrete layer is located in the middle and edge of the slab bottom and the side of the slab. The maximum tensile stress of the base plate is located at the edge of the surface of the layer and the inner edge of the limiting groove. The interface normal tensile stress is located at the end and corner of the interface. Furthermore, maximum stress increases with the increase of safety probability.

Analysis of the initiation and propagation of fatigue cracks in the CRTS II slab track inter-layer using FE-SAFE and XFEM

In this study, a novel method for analysing inter-layer defects in slab tracks was proposed, based on fatigue analysis and the extended finite element method. The inter-layer gap of China Railway Track System (CRTS) II slab tracks was analysed. First, a finite element model was established to analyse the stresses in mortar layer under train and temperature loading. Secondly, the results of the stress analysis of the mortar layer were assessed using a fatigue analysis software for calculating the fatigue life of the mortar layer and the areas that fail first. Finally, in an extended finite element analysis, an initial gap was applied over the area that fails first, as determined through the fatigue analysis of the mortar layer. The patterns of the gaps at the ends, in the central part of the edge, and at the corner of the inter-mortar layer were observed and compared. Results show that the new method, which combines fatigue analysis and the extended finite element method, can address the discontinuity problem of the inter-layer slab defects in ballastless tracks, enabling the development process to be simulated. The rate at which the area of gapping increases can be used to characterize the development of the inter-layer gap in slab tracks.

Effects of initial up-warp deformation on the stability of the CRTS II slab track at high temperatures

Initial up-warp deformation is one of the key factors that affect the stability of the China Railway Track System type II (CRTS II) slab track. Through modeling analysis, we studied the effects of different initial up-warp conditions on the deformation and stability of a slab track at high temperatures. Based on the theory of ‘variable span length’ in continuous welded rail (CWR), a vertical stability analysis model of the CRTS II slab track was established using the finite element method (FEM), and a scale model test was conducted. The effects of initial up-warp deformation features, such as rise displacement, span length, and line type on the stability of track slabs at high temperatures were studied through simulation. Results showed that the trends of vertical displacement were almost the same based on the FEM, analytical method, and on-site testing, but there was a better agreement between results from the FEM and the analytical method. When the span length was 6.5 m and the rise displacement of the initial up-warp reached 15 mm, compressional destruction was most likely to occur on the concrete at the bottom of the apex. The rise-span ratio of the slab up-warp reached its maximum when the initial up-warp span was 6.5 m at high temperatures. It is easier for track slabs to maintain their original form at a high temperature when there is an angle at the apex or a smooth boundary. However, with a smooth boundary, the concrete at the bottom of the apex is more likely to suffer compressional destruction. Therefore, to ensure the stability of the CRTS II slab track, an initial up-warp with a span of 6.5 m and a rise of 15 mm should be avoided, and the effects of different line types of the initial up-warp also need to be considered.

Fatigue Performance of the CA Mortar Used in CRTS I Ballastless Slab Track under Simulated Servicing Condition.

The cement and asphalt mortar (CA mortar) used in the China Railway Track System (CRTS) I ballastless slab track may encounter a coupling fatigue effect under the high-frequency vibration, load and high-and-low temperature cycles, and the deterioration under fatigue may happen during service of the high-speed railway. In this study, the performance degradation and its mechanism of the CA mortar with and without polymer emulsion incorporated under the coupling fatigue effects of the high-frequency vibration, load and temperature were studied by using an anti-fatigue testing device specially developed for the CA mortar used in the ballastless slab track of the high-speed railway. The results showed that the deformation capacity of the CA mortar for CRTS I slab ballastless slab track decreased after fatigue test under simulated service environment, presenting a typical brittle characteristic and an obvious reduction of the ductility and toughness. The Scanning Electron Microscopy (SEM) observation and the mercury intrusion porosimetry (MIP) analysis showed that the volume of the macropore decreased whereas that of the micropore increased after the fatigue test. The asphalt in the hardened CA mortar revealed a softening and migration from the bulk paste to fill the pore and make the structure denser and even ooze out of the CA mortar under the high-frequency vibration and high temperature. Through incorporating the polymer emulsion, the anti-fatigue property of the CA mortar was obviously improved, which can prevent the CA mortar from losing its elastic adjustment function too early. Though increase of the strength and elastic modulus for the CA mortar after severe service is beneficial to the stability of train running, the comfort level and safety of the train operation may decline due to the gradual reduction of the ductility & toughness and the gradual loss of the elastic damping adjustment function of the CA mortar between the base concrete slab and the track slab.

Calculation of Reasonable Tension Value for Longitudinal Connecting Reinforcement of CRTSII Slab Ballastless Track

There is confusion in the original design concept for the tensioning of longitudinally connected reinforcement of the CRTSII (China Railway Track System) slab ballastless track. In order to clarify the effect of tension value of longitudinal reinforcement on the mechanical characteristics of the ballastless track, a three-dimensional finite element model, considering the nonlinear interaction between the track slab and cement-emulsified asphalt (CA) mortar of the CRTSII slab ballastless track, was established. The mechanical characteristics of the track structure under longitudinal tension load and temperature gradient load of the longitudinal joint were calculated. A method of applying prestress to post-pouring concrete was proposed according to the concept of prestress loss of pretensioning prestressed concrete, a reasonable tensile force value was proposed after the crack width, and the reinforcement stress of the ballastless track in the operation stage was checked and calculated according to the concrete design principle. When the tension force is greater than 300 kN, it is harmful to the bonding between the slab and mortar layer, which is prone to interlayer damage. In order to add prestress to concrete with wide joints to ensure the longitudinal stability of the ballastless track, and that the reinforcement stress and crack width meet design requirements, it is suggested that the tension force value should be 230 kN. Further, the temperature difference between reinforcement and concrete should be 30 °C before the initial curdle of wide joint concrete.