Behaviour Of Railway Track Research Articles

A semi-analytical model of a discretely supported railway track

The dynamic behaviour of railway track plays an important role in the generation of rolling noise as well as the development of rail corrugation. A semi-analytical model is presented that includes vertical, lateral and axial dynamics and takes account of the discrete supports provided by the sleepers. The rail is represented by a semi-analytical beam model that includes vertical and lateral bending, extension and torsion, with warping and shear-centre eccentricity. A receptance-coupling method is used to couple the rails, through damped springs that represent the rail pads, with a finite number of flexible sleepers that are in turn supported on an elastic foundation. The model also accounts for the coupling between the two rails through the sleepers. Results are presented in terms of the point mobilities in different directions, including the vertical-lateral cross mobility, as well as the track decay rates, and the results are validated by comparison with measurements. The inclusion of torsion and warping is shown to have a significant effect on the lateral rail mobility, leading to better agreement with the measured results. The response on one rail due to excitation on the other rail is also explored and the results agree well with the measurements. It is found that the coupling between the two rails has only a limited effect on the resultant track response.

Analysis of Indonesia’s Railway Track Structure Behavior Under Double-Stack Freight Train Loading

The growing number of freight transported using railway transport is massive. Indonesia targeted 995,500,000 tons of freight transported using the railway mode. Double-stack train is one solution to increase thefreight tonnage of the train without adding the number of operations of the train. The 3D ANSYS model ismade to see the structural behavior of railway tracks under the double-stack train load using 1067 mm and 1435 mm gauge from Indonesia’s railway track regulation. It was also modeled with several speeds to observe its influence on the structure. It is known that in all output parameters of deformation, stress, and strain, the 1435 mm gauge actsbetter for the structure than the 1067 mm gauge. The subgrade service life also became longer in the 1435 mm gauge structure. Lower speed also gives a better impactonthe structure of the track and possible to give longer service life for subgrade.Further research isneeded to observe the railway track structural behavior in cyclic loading and the possibilityofreinforcing the subgrade. The lab-scale test also needed to validate the analysis.

Monitoring and Expertise of Sections with a Sudden Change in Railway Track Stiffness—Transition Zones of Bridges

The subject of the research is the investigation of the behavior of railway tracks in places with a significant change in the stiffness of the track. These parts can be designed from various structural elements and their materials, and this mainly results in a height change of the track level during its operation. These transition zones are monitored and expertly examined to detect undesirable deformations of the geometrical position of the track caused by the trains running. The transition zones are at the points where the fixed track transitions to the classic track bed, in our case it is their combination with bridge structures, especially at their supports. In Slovakia, under the conditions of the Railways of the Slovak Republic, the issue is topical within the framework of the modernization of trans-European railway corridors. The results of experimental measurements and their analysis will provide relevant data for subsequent research solutions for their new numerical modelling, which will ensure a smooth passage through these points of change without height fluctuations, vibrations, and shocks from the wheels of train sets.

An Analysis of Dynamics of Retaining Wall Supported Embankments: Towards More Sustainable Railway Designs

Retaining walls are structures used to retain earth materials on a slope. Typically, they are designed for static loads, but for highway and railway infrastructures, vehicle-induced dynamic responses are also relevant. Therefore, retaining wall structures are often designed with a factor of safety that is higher than necessary, because it can be challenging to quantify the magnitude of expected dynamic stresses during the design stage. This unnecessary increase in material usage reduces the sustainability of the infrastructures. To improve railway retaining wall sustainability, this paper presents the results from a field monitoring campaign on a heavy-haul rail line with a retaining wall, studying the dynamics induced in response to 30-ton axle load trains running at speeds of between 5 km/h and 100 km/h. The site comprises an earth embankment supported by a gravity retaining wall, with accelerometers on the sleepers, roadbed surface, and retaining wall, velocity sensors on the roadbed, and strain gauges on the rail web to record wheel–rail forces. The vibration intensities collected from various locations are processed to explore the peak particle velocities, maximum transient vibration values, and one-third octave band spectrums. Two transfer functions define the vibration transmission characteristics and attenuation of vibration amplitude along the propagation path. The long-term dynamic stability of the track formation is studied using dynamic shear strain derived from the effective velocity. The peaks of observed contact forces and vibrations are statistically analyzed to assess the impact of train speed on the dynamic behavior of the infrastructure system. Next, a 3D numerical model expresses the maximum stress and displacements on the roadbed surface as a function of train speed. The model evaluates the earth pressures at rest and vehicle-induced additional earth pressures and horizontal wall movement. The investigation provides new insights into the behavior of railway track retaining walls under train loading, and the field data are freely available for other researchers to download. The findings could facilitate the design of more sustainable retaining walls in the future.

Laboratory and numerical investigation on the behavior of reclaimed asphalt pavement (RAP) as railway track subballast layer

The use of asphalt mixtures in different places of the structure of railway tracks has been increased, given their acceptable performance and properties. Using bituminous materials in subballast layers is of great importance due to the structurally, vibrationally, and geometrically improving properties of these infrastructures. In order to enhance the mechanical behavior of railway tracks under heavy loads and high-speed trains, the tendency to use sustainable development approaches such as reuse of discarded and recycled materials has increased. The asphalt is recycled in the maintenance activities of road pavements and, in some cases, reused in the road construction and pavement industry, raising the question of whether reclaimed asphalt pavement (RAP) mixtures can be utilized in railway tracks? Has not been so extensively studied on RAP materials to be used as an interlayer in the structure of railway tracks. Accordingly, the present study seeks to investigate the behavior of these materials as the railway tracks subballast by experimental and numerical through structural approach. Given the complex behavior of these materials due to their bitumen aging, researchers are concerned about the quantity of them that can be reused. In this study, subballast layers containing RAP with percentages varying from 25 % to 100 % without any additive material and thicknesses from 5 cm to 20 cm were numerically modeled. At first, the behavioral models of the RAP materials without any additive material in a laboratory were determined for the model inputs. Using the dynamic modulus and relaxation behavior remarkably helped to identify the behavior of these materials. Numerical models were developed for RAP materials by assuming the linear elastic (LE) behavior for granular materials and linear viscoelastic (LVE) behavior for RAP materials. A conventional ballast track model with granular subballast was also simulated for validation and comparison. Eventually, by evaluating the effect of using RAP on the track settlement, the tensile strain of the bottom of the subballast layer, and compressive stress imposed on the subgrade, the subballast layer with 100 % RAP and a thickness of 20 cm was found to have the best performance, reducing the mentioned Strain and Stress parameters by 40 %. Accordingly, such a layer can be utilized as a simple permanent solution to improve the stiffness and performance of tracks.

A Methodology Linking Tamping Processes and Railway Track Behaviour

Today’s railway transport is built upon high-performance infrastructure. Cost-effective yet sustainable infrastructure presumes tracks with a precise and durable geometry. At ballasted tracks, the geometry is created and restored through tamping machines, which position the track panel and compact the ballast beneath the sleepers. It is commonly agreed that the ballast compaction plays an important role in the long-term stability of the track. Yet, there is no method available which allows a direct correlation between the compactness of the ballast and the stability of the track geometry. Available studies either model track behaviour without considering the bedding, or analyse ballast compactness locally while disregarding its influence on the track geometry. This paper presents a new methodology which establishes a relation between these two topics—ballast compaction during tamping and subsequent track behaviour. A state-of-the-art tamping machine has been equipped with an experimental measurement setup, constantly recording relevant data during every tamping process. These data can be used to derive an indication for the achieved compaction under every sleeper. Utilising the tamping machine’s internal measuring system for track geometry documentation, every tamping process (every sleeper) is assigned to the precise position along the track. The data set is merged and synchronised with regular track geometry measurements of the infrastructure manager. The result is a comprehensive data set which allows precise analyses between tamping machine measurements and track behaviour. This data set provides the foundation for future research, aiming towards a better understanding of the tamping process and its influence on the quality and durability of the established track geometry.

Vibration Behaviour of Railway Track under High Speed Moving Load

Vibration Behaviour of Railway Track under High Speed Moving Load

Structural response of monoblock railway concrete sleepers and fastening systems subject to coupling vertical and lateral loads: A numerical study

Monoblock prestressed concrete sleepers are the most dominant type of sleepers in ballasted railway tracks. As such, it is important to provide optimized designs to the concrete sleepers and the associated fastening systems to ameliorate railway safety and to save both capital and maintenance funds. Therefore, a three-dimensional finite element railway model was created and verified. The response of both concrete sleepers and fastening components to coupling vertical and lateral loading was quantified. Such loading form typically occurs at horizontal railway sections causing damage to the railway track components. The influences of the sleeper spacing, elastic modulus of the rail pad, and friction coefficient at the contact surfaces of the rail and sleeper with the rail pad under varied lateral loadings were investigated. The interaction influence between parameters was thoroughly discussed. Among the studied parameters, the finite element model outcomes showed that the elastic modulus of the rail pad and the coefficient of friction are the most critical parameters with respect to the lateral load path and the local response of concrete sleeper and fastening system, especially at high lateral loadings. By using a relatively soft rail pad (elastic modulus = 100 MPa), the concrete material remained below the compressive and tensile fatigue limits even under high lateral loadings provided that the coefficient of friction remains limited to 0.3. By contrast, for a given lateral to vertical loading ratio, a continuous increase in the developed stresses of the concrete material and rail pad was detected as the elastic modulus changed from 100 MPa to 2000 MPa and the coefficient of friction increased from 0.3 to 0.9. The influence of sleeper spacing on the behaviour of railway tracks is only tangible on the distribution of the vertical wheel load. Lastly, the peak stress magnitudes of the ballast bed could be increased by 50% as the lateral to vertical loading ratio reached 0.6 compared to the case where the lateral load is absent. The experience gained from this article would help to formulate specific recommendations to improve the design of concrete sleepers, fastening systems, and ballast bed.

Experimental and numerical investigations of dual gauge railway track behaviour

The dual gauge track, in which a third rail is added to the conventional track section, has recently been installed in large sections of the Spanish railway network, allowing the passage of trains of two different track gauges. With increasing train speeds and axle loads, the new dual gauge track must share the main characteristics of current track systems while minimizing the drawbacks, in order to ensure a real step forward in railway track design. Thus, this paper presents a research study on the dynamic behaviour of a dual gauge track generated by the passage of trains. To accomplish this task, an extensive experimental and numerical investigation was conducted in a stretch of the Spanish railway network. The experimental work includes the characterization of the rail and sleeper mechanical behaviour during train passage. In addition, results from the experimental investigations were also compared with a fully three-dimensional numerical model. The model uses SOLID95 elements with elastoplastic Mohr–Coulomb behaviour and yields a rMSE of 25% between measured and calculated responses, hence showing a good agreement. Concerning the vibrational response, the presence of the third rail have a significant effect, since the maximum rail vertical accelerations significantly increased on the side where two rails are close together. Finally, the contact pressure between the sleeper and the ballast bed is 35% higher in the common rail when the train runs on the Iberian gauge, but 50% higher on the dedicated rail when the train runs on the standard gauge.

Finite Element Modeling of the Dynamic Response of Critical Zones in a Ballasted Railway Track

The critical zones are the discontinuities along a railway line that are highly susceptible to differential settlement, due to an abrupt variation in the support conditions over a short span. Consequently, these zones require frequent maintenance to ensure adequate levels of passenger safety and comfort. A proper understanding of the behavior of railway tracks at critical zones is imperative to enhance their performance and reduce the frequency of costly maintenance operations. This paper investigates the dynamic behavior of the critical zone along a bridge-open track transition under moving train loads using two-dimensional finite element approach. The influence of different subgrade types on the track behavior is studied. The effectiveness of using geogrids, wedge-shaped engineered backfill and zone with reduced sleeper spacing in improving the performance of the critical zone is evaluated. The numerical model is successfully validated against the field data reported in the literature. The results indicate that the subgrade soil significantly influences the track response on the softer side of the critical zone. The difference in vertical displacement between the stiffer and the softer side of a track transition decreases significantly with an increase in the strength and stiffness of the subgrade soil. The subgrade layer also influences the contribution of the granular layers (ballast and subballast) to the overall track response. As the subgrade becomes stiffer and stronger, the contribution of the granular layers to the overall track displacement increases. The mitigation techniques that improve the stiffness or strength of granular layers may prove more effective for critical zones with stiff subgrade than critical zones with soft subgrade. Among all the mitigation techniques investigated, the wedge-shaped engineered backfill significantly improved the performance of the critical zone by gradually increasing the track stiffness.

Dynamic Behavior in Transition Zones and Long-Term Railway Track Performance

Transition zones between embankments and bridges or tunnels are examples of critical assets of the railway infrastructure. These locations often exhibit higher degradations rates, mostly due to the development of differential settlements, which amplify the dynamic train-track interaction, thus further accelerating the development of settlements and deteriorating track components and vehicles. Despite the technical and scientific interest in predicting the long-term behavior of transition zones, few studies have been able to develop a robust approach that could accurately simulate this complex structural response. To address this topic, this work presents a three-dimensional finite element (3D FEM) approach to simulate the long-term behavior of railway tracks at transition zones. The approach considers both plastic deformation of the ballast layer using a high-cycle strain accumulation model and the non-linearity of the dynamic vehicle-track interaction that results from the evolution of the deformed states of the track itself. The results shed some light into the behavior of transition zones and evidence the complex long-term response of this structures and its interdependency with the transient response of the train-track interaction. Aspects that are critical when assessing the performance of these systems are analyzed in detail, which might be of relevance for researchers and practitioners in the design, construction, and maintenance processes.

Experimental investigation of the dynamic behavior of railway track with sleeper voids

The deterioration of the sleeper support on the ballasted track begins with the accumulation of sleeper voids. The increased dynamic loading in the voided zone and the ballast contact conditions cause the accelerated growth of the settlements in the voided zones, which results in the appearance of local instabilities like ballast breakdown, white spots, subgrade defects, etc. The recent detection and quantification of the sleeper voids with track-side and onboard monitoring can help to avoid or delay the development of local instabilities. The present paper is devoted to the study of the dynamic behavior of railway track with sleeper voids in the ballast breakdown zone. The result of the experimental track-side measurements of rail acceleration and deflection is presented. The analysis shows the existence of the dynamic impact during wheel entry in the voided zone. However, the measured dynamic impact is subjected to the bias of the track-side measurement method. Both the mechanism of the impact and the measurement aspects are explained by using the one-beam model on viscoelastic foundation. The void features in the dynamic behavior are analyzed for the purpose of track-side and onboard monitoring. A practical method of the void parameter quantification is proposed.

Numerical investigation of the behavior of stone ballast mixed by steel slag in ballasted railway track

Recently, implementing steel slag ballast has been proposed as an appropriate material to substitute stone ballast. In this regard, one of the technical concerns is the behavior of steel slag ballast in both time and frequency domains that needs to be assessed, properly. Furthermore, the combination of stone ballast and steel slag is unavoidable in steel slag ballasted tracks during track maintenance concerning the limitation of steel slag resources. Therefore, this paper suggests an optimal stone ballast-steel slag (SB-SS) combination regarding the dynamic behavior of five SB-SS combinations as 0%SS, 25%SS, 50%SS, 75%SS and 100%SS by weight of ballast using a finite element method (FEM) model of a 50-meter test track. Moreover, using elasticity modulus and Moher-coulomb parameters obtained via a series of plate load and shear strength tests for each SB-SS combination turns FEM model to be more close to the real test track results.Experimental results show that adding steel slag particles to stone ballast increases elasticity modulus and friction angle of ballast layer resulting in the improvement of mechanical behavior of railway track. Consequently, the maximum deflections and root mean square (RMS) of accelerations decrease by increasing steel slag content. Analyzing free vibration of ballast layer combinations reveals that damping ratios of 100%SS ballast layer is the maximum value as 0.25 followed by 75%SS, 50%SS, 25%SS and 0%SS combinations. Moreover, the dominant frequencies of each ballast layer combinations determine that 0%SS, 25%SS and 50%SS coincides within the track excitation frequency range made by wheel sets, while 75%SS and 100%SS are out of which. Finally, according to all results, 75%SS ballast layer is proposed as the optimal SB-SS combination.

An analysis of railway track behaviour based on distributed optical fibre acoustic sensing

Trackside monitoring of railways provides useful data for understanding the condition and mechanical behaviour of railway track, prior research has shown that railway track performance varies significantly along its length, primarily owing to changing support conditions. Understanding the changing performance along track offers the potential for improved track design and maintenance. Different technologies are used to investigate this. For example, inertial sensors, or high-speed filming with digital image correlation (DIC) for track deflection, and traditional strain gauges for loads. The latter usually rely on in-situ calibration. These techniques are suitable for measurements at discrete locations along the track length but are not suited to measuring performance variability even along a few hundred meters of a railway line. This paper investigates the use of a recently developed sensing system known as distributed acoustic sensor (DAS) that uses optical fibres. This method has the potential to be used over very long lengths of track; offers high sample rates; and has a gauge length and spatial resolution suitable for investigating the load-deflection behaviour of the track. This study presents DAS optical fibre strain measurements from a study site and presents novel methods for determining the rail deflection and the load per sleeper end. The DAS results are compared with point location measurements using a traditional strain gauge and deflections determined using imaging and DIC. The DAS system offers reliable distributed strain measurement that convert to estimates of track deflection and load with the potential for continuous spatial and temporal coverage over significant lengths of track.

The influence of sleeper material characteristics on railway track behaviour: concrete vs composite sleeper

Composite sleepers and bearers formed of polymers and sometimes steel or fibre reinforcement are an alternative to traditionally used timber or prestressed concrete counterparts. Composite materials offer the combined benefits of the compliant sleeper/ballast contact of timber with the longer service life of concrete. However, composite and timber sleepers have lower bending stiffness compared with concrete, and this affects their track performance. To better understand the influence of sleeper material on performance, a concrete and a composite sleeper were tested in the Southampton Railway Testing Facility. Test results were interpreted with the aid of finite difference and discrete element method numerical modelling. It was found that composite sleepers can provide a more compliant sleeper/ballast interface with increased numbers of ballast grain contacts of larger area that attenuate the peak contact forces. However, owing to their lower bending stiffness, they have more exaggerated deflection profiles and a tendency to become centre-bound compared with stiffer prestressed concrete counterparts.

Impact Evaluation of Track Girder Bearing on Yeongjong Grand Bridge

The line track bearings used in the Yeoungjong Grand Bridge experienced cracks and deformations, which result in significant accelerations and displacements of the track. This study measured an acceleration and a displacement of 0.5 g and 0.5 mm, respectively. Three-dimensional finite element analysis was performed to predict the behavior of railway tracks. However, when low-maintenance cylindrical bearings were used instead of line bearings, the displacement was decreased by 93%, and the acceleration was decreased by 82%. Furthermore, it turned out that the maximum displacement of the track girder was decreased by 45% when cylindrical bearings were used.

EXPERIMENTAL INVESTIGATION ON DYNAMIC BEHAVIOUR OF HEAVY-HAUL RAILWAY TRACK INDUCED BY HEAVY AXLE LOAD

The damage to the track structure and the influence to the line deformation have greatly deteriorated with the increase of the axle load compared with that of the ordinary trains. However, there is a paucity of experimental research on the dynamic influence of the heavier haul freight trains on the railway tracks. The objective of this study is to investigate the dynamic behaviour of heavy-haul railway track induced by heavy axle load by field experimental tests. The wheel–rail dynamic force, the track structure dynamic deformation and the track vibration behaviour are measured and analysed when the train operates in the speed range from 10 to 75 km/h and the axle load of vehicles varies from 21 to 30 t. Comparisons between the results for the axle conditions of 25 and 30 t are made in this paper to reveal the axle load effects. It is demonstrated that part of the indicators reflecting the dynamic behaviour of the railway track increases approximately linearly with the train running speed and axle load, while others are influenced negligibly

Analytical modelling of rail track to account for nonlinear properties of structure

It is known that nonlinear and stochastic properties of structures should be taken into account in the analysis of their dynamic behaviour. This statement remains valid for railway infrastructure, where trains acting on rail track cause their strong dynamic variations. It becomes even more important when one deals with high frequencies and speeds of trains. The recent HSR networks need new technologies and materials in order to increase train speeds and, in the same time, to protect the environment against negative factors produced by operational lines. Therefore all important aspects of new railway constructions should be analysed, especially in terms of mechanical vibrations and noise attenuation. The elements of rail tracks, such as sleepers, under sleeper pads, rail dampers, fastening systems and others, have nonlinear properties. Their influence on dynamic behaviour of railway tracks is still insufficiently researched. For this purpose, various analytical models are proposed which can give a new insight into detailed dynamic characteristics of such structures.

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.

A model for the mechanical behaviour of the railway track in the lateral plane

This paper deals with a mechanical model for the analysis of the railway track behaviour built by exploiting the periodicity of the track-structure. The starting point of this study are the inner forces transferring modes. They have been determined by the unit principal vectors analysis of the base cell transfer matrix. The main outcome on bending moments is that they are transferred through the track without deforming the sleepers and fasteners and are composed of two parts: the first one, referred as primary bending moment, is generated by the couple of axial forces acting on each nodal section while the second is due to the curvature changes of the rails. Shear forces are engendered by two independent mechanisms that are associated respectively with the unit changes of the total and primary bending moments. The constitutive properties of the equivalent medium are derived by an averaging and limiting process of the transferring modes strain energies, avoiding any a priori assumption on the kinematics of the substitute medium. Finally, the equilibrium equations are achieved by the virtual work principle.The proposed model is able to reproduce accurately the track behaviour in transferring its inner forces. However, solutions that are equilibrated but not kinematically admissible are obtained from it when transversal loads are applied. In additions, only boundary conditions compatibles with the track transferring modes can be satisfied. This inconsistency is eliminated by superposition of some corrective deformed shapes. These are derived by the eigenvectors of the transfer matrix pertaining to self-equilibrated systems of bending moments decaying along the track.The application field of the proposed track model is also discussed, and the results of a validation study carried out by F.E. analysis are finally presented.