Non-ballasted Track Research Articles

Modulus of elasticity of non-ballasted track

The main stiffness properties that determine the stresses in the track structure components under loads from a moving train are the modulus of elasticity of the rail slab and the slab-track/rail correlation stiffness coefficient. These parameters have been investigated for a ballasted track and are well established today, in contrast to those of a non-ballasted track. This study aims at determining the stiffness characteristics of a non-ballasted track, comparing them with those of a ballasted track, and assessing their effect on the stress-strain state (SSS) of the elements of a non-ballasted track structure. Field experiments to measure the stresses in the track structure elements were carried out using strain-gauge methods. As a result of the experiments, the modulus of elasticity and the correlation stiffness coefficient of the rail slab and the rail were determined for the RHEDA2000 slab track system. The results obtained prove it possible to apply a rail-as-beamon-elastic-foundation theory and to use well-established calculation methods for designing a non-ballasted track structure suitable for different operational conditions.

Vector Form Intrinsic Finite Element Method for Stochastic Analysis of Train–Track–Bridge Coupling System

In this paper, a train–track–bridge (TTB) interaction model that can account for coach-coupler effect is presented for stochastic dynamic analysis of a train traveling over a bridge. Based on the vector form intrinsic finite element (VFIFE) method, both the bridge and non-ballasted track are discretized into a set of mass particles connected by massless beam elements, in which the fasteners that fixed the tracks on the bridge deck are modeled as a series of linear spring-dashpot units. The multi-body train car is regarded as seven mass particles (1 for car body, 2 for bogies and 4 for wheelsets) connected by parallel spring-dashpot units. Considering the random nature of rail irregularities, the Karhunen–Loéve expansion (KLE) method is used to simulate the vertical profile of the tracks. To calculate the mean and standard deviation of the stochastic response of the TTB system, the point estimated method (PEM) based on the Gaussian integration and dimension reduction method is adopted. The proposed VFIFE–TTB interaction model is then applied to stochastic resonance analyses of a train moving on a bridge. It is shown that the present VFIFE–TTB model is able to analyze the dynamic interaction of the TTB system simply and efficiently. The influence of rail irregularity-induced stochastic vibration on the train and bridge would become significant once the resonant vibration takes place on the TTB system.

Modelling of periodic slab track using time-frequency hybrid Green's function method and its application to vehicle-track dynamic interaction

Periodic slab tracks, as a type of non-ballasted track, are widely used in the high-speed railway and urban subway. Efficient and accurate dynamics modelling of the periodic slab track is a crucial issue for solving the vehicle-track dynamic interaction. In this paper, a time-frequency hybrid Green's function method (GFM) is first developed to model the dynamics of the periodic slab track, in light of the properties of the periodicity, symmetry and attenuation of the Green's functions. By combining with the classical vehicle-rail dynamics model, the simulation of the vehicle-track dynamic interaction is then performed. To improve the computational efficiency, the step-moving window strategy is introduced to characterize the vehicle moving on the infinite length track. The floating slab track, a representation of the periodic slab track, is adopted to reflect the time-spatial distribution of the Green's functions. The truncation errors caused by the presented GFM are analysed by calculating dynamic responses induced by a metro vehicle moving on the floating slab track to determine the truncation parameters. The proposed GFM-based vehicle-track dynamic interaction model is finally validated by comparing with the finite element method (FEM) and the basic dynamic characteristics of the periodic slab track are further investigated. Numerical studies show that the computational accuracy of the GFM-based model is nearly the same with the FEM-based model, but the efficiency can be greatly improved. Moreover, it is concluded that the longitudinal uneven stiffness of the periodic slab track shows a significant influence on the slab displacement and stress, while has a slight influence on the fastener force and slab acceleration.

Influence of nanoparticles on age-associated mechanical properties of cement asphalt mortar

The early-age mechanical properties of cement asphalt mortar (CAM) directly influence the process and quality of non-ballasted track during construction. In order to shorten the long curing period of CAM during the construction of non-ballasted track and accelerate the procedure, nano-SiO2 (NS) and nano-TiO2 (NT) were added to CAM in this study; this also improved the age-related mechanical properties of CAM, especially at early ages. Compressive strength tests were conducted at five different ages to investigate age-related compressive behaviors of CAM with nanoparticles. The results show that NS and NT can greatly enhance the early-age development of CAM and that CAM with nanoparticles accelerates the construction process and optimizes railway management. A stress–strain model of CAM was extracted to describe compressive behaviors of CAM modified by NS and NT at different ages. Finally, the microstructure of specimens was studied with scanning electron microscopy to better understand the mechanism of age-associated mechanical properties of CAM, with and without nanoparticles.

Running Safety of a High-Speed Train within a Bridge Zone

This paper describes the issue of validity of running safety criterion on high-speed railways (HSR). In this research, the 2D model of ‘car–track–bridge’ system is used. A feature of HSR is the practical reaching of the critical speeds that cause resonance of bridge superstructures. The Eurocode establishes the limit of bridge superstructure acceleration below 5[Formula: see text]m/s2 in case of nonballasted track. This limit does not suit in certain conditions such as resonance of the superstructure that is permitted in Eurocode. In this case, there is no correlation between acceleration limit and firm wheel–rail contact. The numerical analysis shows repeated wheel lift-off during train passing a bridge zone. It is resonance of the bridge deck that causes this effect because without resonance, the running train is safe. Lower damping in nonballasted track increases resonant vibration influence.

A three-dimensional modal theory-based Timoshenko finite length beam model for train-track dynamic analysis

An efficient Timoshenko beam model of finite length is developed for train-track interaction dynamics. The rail is reduced to the present beam model and its vertical and lateral bending, shear, and torsion deformations are considered. A moving control volume attached to the train is introduced, which encloses the reduced rail, and a reference coordinate system is established in the reduced rail at the left end. The arbitrary Lagrangian-Eulerian (ALE) method and the modal superposition method (MSM) are adopted, and governing equations of the reduced rail model are derived by Lagrange's equations. Owing to the advantages of the MSM, the number of degrees of freedom of the current formulation is clearly reduced and its efficiency is greatly improved. A long non-ballasted track of finite length subjected to a constant moving load is first considered, and results from the present beam model are in good agreement with those from the traditional finite element method. A three-dimensional train-track interaction problem with consideration of a ballasted track is further studied. Results from the present beam model are compared with those from the commercial software Simpack where the MSM is used, and they are in good agreement with each other. Since the number of modes in the present beam model is much fewer than that in Simpack, the present beam model is more efficient than that in Simpack. It is found that the number of shape functions and the length of the beam model used in calculation can significantly affect the accuracy and efficiency of the present beam model, which should be taken into consideration. The current beam formulation is independent of the moving velocity of the train and can handle train-track dynamics with variable train velocities. The current beam formulation is straightforward and can be easily extended in various complex applications. It is more suitable for dealing with long-term train-track interaction dynamics.

Dynamic Performance of High-Speed Rail Cable Stayed Bridge with Altered Track Assembly

On fast moving world, the interest is being increased for high-speed trains. It provides a sustainable and effective mode of travelling. Till date India was special among the developing nations for not having a high-speed rail corridor. However, by introducing Mumbai–Ahmedabad high-speed rail corridor, it opens up research directed towards efficient design of the supporting structures. In India, construction and upgradation of railways on its top which attracts the researchers for advance research in the same field. Here an attempt is made to understand the railway track formulation and bridging aspect for high speed rail model as per European standards to assess the influence or impact of rail axle load on bridge behavior. Under this scope, a hypothetical case study of “H-Shaped Cable Stayed Bridge” is taken with Rheda 2000 non-ballasted track, vibrating and non-vibrating ballasted track. The analysis is performed by two approaches; first is the track characterized by its finite element model and second is by introducing track through its equivalent weight. The ballast-less track is already a candid approach for rail lines, showing competitiveness against the conventional ballasted track. The reason for the adaptability of the Ballast-less track is its low maintenance and high accessibility of materials. However, on the basis of vibration analysis “Vibrating Ballasted Track” proved decent in terms of performance.

A New Three-Dimensional Moving Timoshenko Beam Element for Moving Load Problem Analysis

Abstract A new three-dimensional moving Timoshenko beam element is developed for dynamic analysis of a moving load problem with a very long beam structure. The beam has small deformations and rotations, and bending, shear, and torsional deformations of the beam are considered. Since the dynamic responses of the beam are concentrated on a small region around the moving load and most of the long beam is at rest, owing to the damping effect, the beam is truncated with a finite length. A control volume that is attached to the moving load is introduced, which encloses the truncated beam, and a reference coordinate system is established on the left end of the truncated beam. The arbitrary Lagrangian–Euler method is used to describe the relationship of the position of a particle on the beam between the reference coordinate system and the global coordinate system. The truncated beam is spatially discretized using the current beam elements. Governing equations of a moving element are derived using Lagrange’s equations. While the whole beam needs to be discretized in the finite element method or modeled in the modal superposition method (MSM), only the truncated beam is discretized in the current formulation, which greatly reduces degrees-of-freedom and increases the efficiency. Furthermore, the efficiency of the present beam element is independent of the moving load speed, and the critical or supercritical speed range of the moving load can be analyzed through the present method. After the validation of the current formulation, a dynamic analysis of three-dimensional train–track interaction with a non-ballasted track is conducted. Results are in excellent agreement with those from the commercial software simpack where the MSM is used, and the calculation time of the current formulation is one-third of that of simpack. The current beam element is accurate and more efficient than the MSM for moving load problems of long three-dimensional beams. The derivation of the current beam element is straightforward, and the beam element can be easily extended for various other moving load problems.

Simplified plastic settlement analysis of non-ballasted slab railroad track foundations on fine-grained soil

ABSTRACTThis study develops a simplified method to evaluate the plastic settlement of non-ballasted slab rail-road track foundations on fine-grained soil. Instead of three-dimensional finite element analysis, a two-dimensional plane strain model is utilized to deduce approximate deviatoric stress profiles for use in plastic strain calculation. From analysis examples of an embedded slab railroad track foundation, it is shown that the proposed method is computationally efficient, greatly reducing the computation load and time. This study also applies this method to perform a parametric study to investigate the design of prepared subgrade in reducing the plastic settlement. The results show that with the same prepared subgrade width as the foundation slab, the effect of the thickness or stiffness of the prepared subgrade on the reduction of settlement is limited; however, once the width of the prepared subgrade is larger than that of the slab, the effect of the prepared subgrade thickness or stiffness can be significantly enhanced.

A comparison of ground vibration due to ballasted and slab tracks

Abstract With the development of non-ballasted track forms (often referred to as slab tracks) over the few last decades, it is important to understand their behaviour with respect to ground-borne vibration compared with the traditional ballasted tracks. This is important in deciding between the use of the two track forms. The present work aims to quantify the differences between slab tracks and ballasted tracks numerically by using the MOTIV model. This is a general and fully coupled three-dimensional model that works in the wavenumber-frequency domain. It can predict the vibration levels of the track and the ground due to the gravitational loading of a passing train and the wheel and rail unevenness. A comparative analysis between the two track types is presented in terms of ground vibration with emphasis given to the influence of the stiffness and inertial parameters of the two track forms. It is shown that, for the same fastener stiffness there are only small differences in ground vibration behaviour, with the mass of the track slab leading to reductions of 1–3 dB at frequencies above 16 Hz. However, if softer rail fasteners are used in the slab track, as is usual, this leads to further reductions above 63 Hz. The critical velocity on soft soil is also considered. Although there is little difference between the different tracks for a homogeneous ground, for grounds with a soft surface layer the critical velocity is increased by the slab bending stiffness. The maximum rail displacement is also smaller for a slab track than the equivalent ballasted track.

STUDI NUMERIK RESPON STRUKTUR MODIFIKASI BANTALAN BETON UNTUK NON-BALLASTED TRACK

According to Rencana Induk Perkeretaapian Nasional (RIPNas), making plans for the development of Indonesian railways until the next 2030. The targets for the development of railway networks and services to be achieved in 2030 include a national network of 12,100 km (spread on Java-Bali, Sumatra, Kalimantan, Sulawesi and Papua). Construction of railway track is generally divided into two main types, namely, ballasted tracks and non-ballast tracks. In this study the non-ballasted track or ballastless track is to modify the width of the sleeper that will be used without using ballasts on the railroad tracks. This is done to reduce the use of coarse aggregates in ballasts so that if used in areas that do not have natural resources in the form of coarse aggregates a railway track can be built. The research will be carried out according to the condition of the soil gravel, dense sand, medium dense sand, silty medium dense dan loose sand. Different types of soil cause different responses or behaviors from the modification of the sleeper that are located above the ground. This study will discuss the analysis of rail displacement and rail bending stress that occur in the modification of railroad concrete sleeper for non-ballast use in some soil conditions. The study was conducted with software SAP2000 version 2014 to analyze displacement and rail bending stress on concrete sleeper modification with dimensions 400 x 2440 mm2; 1200 x 2440 mm2; 2000 x 2440 mm2; 2800 x 2440 mm2 dan 3600 x 2440 mm2 for each different type of soil to determine the dimensions of modification of concrete sleeper that can be used. According AREMA(1999) Result of rail displacement rail may not exceed 6 mm and rail bending stress may not exceed 75 N/mm2.

Investigation of Concrete Base‐Roadbed Surface Contact Variation‐Induced Vibration Characteristics of Vehicle‐Slab Track‐Subgrade System considering Fluid‐Solid Interaction

The excessive pumping of fines in saturated roadbed surface layer, which is induced by the fluid‐solid interaction under dynamic loads from high‐speed train, is a special form of high‐speed railway subgrade defect reported recently. This can deteriorate the interface between nonballasted track structure bottom layer and roadbed surface layer and therefore lead to associated contact variation with the moving of trains. According to the dynamic Biot’s equations known as u‐p formulation and the vehicle‐track coupling dynamics theory, a vertical vehicle‐slab track‐subgrade coupling vibration model is developed to investigate the aforementioned contact variation‐induced dynamic behavior of the whole system considering the fluid‐solid interaction. Dynamic measurements from a field case study are adopted to verify the computation model proposed. Based on the numerical model validated, the effects of three contact variation statuses (continuous contact, vibrating contact, and contact loss) on dynamic responses of track subsystem and subgrade subsystem, such as dynamic pore‐water pressure, vertical accelerations, and dynamic displacements both in time and frequency domains, are investigated. Also, a sensitivity analysis involving rail speeds and lengths of contact loss zone is performed, and the critical length of contact loss zone is suggested.

Water Pressure Variation Properties Research in Non-ballasted Track Crack Interior under Fatigue Loading

Water Pressure Variation Properties Research in Non-ballasted Track Crack Interior under Fatigue Loading

Influence of rail fastener stiffness on railway vehicle interior noise

More attention has been paid in recent years to the interior noise of railway vehicles. It has been observed that the interior noise can increase in some locations where vibration-isolation measures are used in the track structures. In order to assess the influence of vibration isolation measures on the noise levels inside railway vehicles, a field measurement campaign has been carried out. The vehicle interior noise has been measured when a train is running at different speeds over the same non-ballasted track section fitted with two types of rail fastener of different stiffnesses. Additional measurements of axlebox vibration, train floor vibration, exterior noise and rail vibration are used to investigate the influence of the fasteners further. The experimental results are compared with simulations performed using the TWINS model, considering the wheel/rail interaction, by focusing only on the relative differences between the two fastener systems. The axlebox vibration and rail vibration are predicted for a unit roughness input and the differences in rolling noise are also obtained. The predicted differences in axlebox vibration, rail vibration and rolling noise are in broad agreement with the measurement results. The results show that the fasteners with a lower stiffness cause a noisier interior environment. Around 125 Hz and in the frequency range 315–1000 Hz, the noise levels are higher for the more elastic fastener, with an average level difference of 3 dB in the latter frequency range. It appears from the shape of the level difference spectra that airborne noise has most influence between 100 and 400 Hz and structure-borne noise has more influence between 500 and 1000 Hz.

NONLINEAR FINITE ELEMENT ANALYSIS OF CONTINUOUS WELDED RAIL–BRIDGE INTERACTION: MONITORING-BASED CALIBRATION

Continuous welded rail is of high interest to operators of railway infrastructure facilities because of the reduced maintenance work and better train driving dynamics it offers. However, the application of continuous welded rail, in particular associated with its interaction with the superstructures of e.g. bridges, requires special caution with regard to the rail stresses in the transition area between the structure and the free field. These stresses are not only influenced by thermal deformations of the bridges but also by the clamp systems between the rails and e.g. the bridge. In general, these connectors are represented by spring elements during modelling, which: (a) causes singularities in the stress distributions in the rails, and (b) cannot capture all the mechanical system changes occurring due to loading, thermal effects, etc. The target of this paper is to present an alternative way of modelling the connection between rails and bridge superstructure based on composite materials which can overcome the disadvantages of the spring model. In particular, a nonlinear model of the whole system was developed for ballasted and non-ballasted track. Special attention was paid to the calibration of rail–bridge interaction and boundary conditions using measured data and code specifications. The aim of this study was to use the results of in-situ measurements to analyse the admissible stress in rails due to their interaction with a bridge caused by temperature loading.

A mechanical model of vehicle-slab track coupled system with differential subgrade settlement

Post-construction subgrade settlement especially differential settlement, has become a key issue in construction and operation of non-ballasted track on high-speed railway soil subgrade, which may also affect the dynamic performance of passing trains. To estimate the effect of differential subgrade settlement on the mechanical behaviors of the vehicle-slab track system, a detailed model considering nonlinear subgrade support and initial track state due to track self-weight is developed. Accordingly, analysis aiming at a typical high-speed vehicle coupled with a deteriorated slab track owing to differential subgrade settlement is carried out, in terms of two aspects: (i) determination of an initial mapping relationship between subgrade settlement and track deflections as well as contact state between track and subgrade based on a semi-analytical method; (ii) simulation of dynamic performance of the coupled system by employing a time integration approach. The investigation indicates that subgrade settlement results in additional track irregularity, and locally, the contact between the concrete track and the soil subgrade is prone to failure. Moreover, wheel-rail interaction is significantly exacerbated by the track degradation and abnormal responses occur as a result of the unsupported areas. Distributions of interlaminar contact forces in track system vary dramatically due to the combined effect of track deterioration and dynamic load. These may not only intensify the dynamic responses of the coupled system, but also have impacts on the long-term behavior of the track components.

Track–Bridge Interaction Analysis Using Interface Elements Adaptive to Various Loading Cases

In this paper, a numerical model using interface elements is proposed for the sequential analysis of nonlinear track–bridge interaction by taking the loading history into consideration. Longitudinal resistance tests were conducted on track fastening systems to determine changes in track resistance that occur at the instant of application or release of a vertical load. On the basis of the test results, longitudinal track stiffness laws for a nonballasted track were established for different loading cases including constant vertical load, sudden application of vertical load, and sudden release of vertical load. In addition, an interface element adaptive to various loading cases that can be incorporated into a conventional FEM was formulated for modeling the track resistance. Furthermore, a numerical algorithm for a practical solution of the nonlinear system equation was developed. The validity and applicability of the proposed analysis method were verified by conducting extensive parameter studies on a simply supported bridge and a multispan bridge.

Experimental study on dynamic performance of typical nonballasted track systems using a full-scale test rig

This paper presents an experimental study on dynamic performance of China Railway Track System (CRTS) series track systems using a full-scale test rig. The test rig has been constructed based on 55.17 m long full-scale nonballasted tracks composed of four typical CRTS track elements in high-speed railways. First, the dynamic characteristics of different nonballasted tracks are investigated by conducting wheel-drop tests, where a wheel-drop testing vehicle with a dropping wheelset is devised to provide the wheel-drop load. The vibration levels of different track systems are assessed by the root-mean-square acceleration per one-third octave band, and the vibration transmission characteristics of the CRTS series tracks are evaluated by transfer functions. Further, a mathematical track model is used to extract the dynamic stiffness and damping coefficient of the four types of nonballasted track systems based on the wheel–rail impact response. The vibration characteristics, the dynamic stiffness, and damping coefficient of different nonballasted track systems under various wheel-drop heights are compared and discussed in detail.

Experimental study of the frequency-domain characteristics of ground vibrations caused by a high-speed train running on non-ballasted track

An in-situ test to obtain vertical, transversal and longitudinal ground velocities and accelerations caused by high-speed trains was performed alongside the Chinese high-speed railway line between Beijing and Shanghai. The test results indicate that due to excellent track quaity and consolidated infrastructure, whether if the train speed is below or above the Rayleigh wave speed, the dominant frequencies of both the vertical ground velocity and acceleration are both integral multiples of the trainload frequency generated by the centre distance of two neigbouring cars. The frequency-domain distribution of the ground velocity is more sensitive to soil stiffness than is the ground acceleration; this is especially the case for the first dominant frequency. Whether the frequency amplitudes of the vertical ground vibration are higher than the horizontal vibrations depends on the soil stiffness. The greater the soil stiffness, the higher is the frequency-range of the vertical ground vibration compared with that for the horizontal vibration, and the smaller is the difference between the three-dimensional frequency-weighted ground vibration level and the vertical vibration. Thus, effects of horizontal ground vibrations cannot be ignored when the foundation soil is soft.

Experimental investigation into ground vibrations induced by very high speed trains on a non-ballasted track

A field measurement of ground vibration was performed on the Beijing−Shanghai high-speed railway in China. In this paper, the experimental results of vertical ground vibration accelerations induced by very high speed trains running over a non-ballasted track on embankment with speeds from 300 to 410km/h are reported and analyzed in detail for the first time. Characteristics of ground vibration accelerations in both time and frequency domains are analyzed based on the test data. It is shown that the periodic exciting action of high-speed train bogies can be identified in time histories of vertical accelerations of the ground within the range of 50m from the track centerline. The first dominant sensitive frequency of the ground vibration acceleration results from the wheelbase of the bogie, and the center distance of two neighboring cars plays an important role in the significant frequencies of the ground vibration acceleration. Variations of time–response peak value and frequency-weighted vertical acceleration level of ground vibration in relation with train speed as well as the distance from the track centerline are also investigated. Results show that the time-domain peak value of ground vibration acceleration exhibits an approximately linear upward tendency with the increase of train speed. With the increasing distance from the track centerline, the frequency-weighted vertical acceleration level of the ground vibration attenuates more slowly than the time-domain peak value of the ground vibration acceleration does. Severe impact of high-speed railway ground vibration on human body comfort on the ground occurs at the speed of 380–400km/h. The results given in the paper are also valuable for validating the numerical prediction of train induced ground vibrations.