Railway Structures Research Articles

Numerical parametric study for ballast assessment using SVM applied to GPR data

Abstract This study explores novel radar-based methodologies for ballast fouling evaluation and structural anomalies in railway structures. Ground Penetrating Radar (GPR), coupled with numerical modeling, is utilized to provide insights into ballast condition and structure. Various data processing methods, including the Matrix Pencil Method (MPM) and Full Waveform Inversion (FWI), are investigated for their effectiveness in detecting fouling. Support Vector Machine (SVM)-based machine learning approaches are employed to enhance classification accuracy. The results demonstrate that integrating raw GPR signals with MPM yields the most accurate classification results, facilitating efficient assessment of ballast condition and contributing to improved railway maintenance strategies.

Impact of typical environments in China's western mountainous areas on the durability of railway concrete: a review

PurposeThis study aims to analyze the impact mechanism of typical environments in China's western mountainous areas on the durability of railway concrete and propose measures to improve durability.Design/methodology/approachWith the continuous promotion of infrastructure construction, the focus of China's railway construction has gradually shifted to the western region. The four typical environments of large temperature differences, strong winds and dryness, high cold and low air pressure unique to the western mountainous areas of China have adverse effects on the durability of typical railway structure concrete (bridges, ballastless tracks and tunnels). This study identified the characteristics of four typical environments in the western mountainous areas of China through on-site research. The impact mechanism of the four typical environments on the durability of concrete in different structural parts of railways has been explored through theoretical analysis and experimental research; Finally, a strategy for improving the durability of railway concrete suitable for the western mountainous areas of China was proposed.FindingsThe daily temperature difference in the western mountainous areas of China is more than twice that of the plain region, which will lead to significant temperature deformation and stress in the multi-layered structure of railway ballastless tracks. It will result in cracking. The wind speed in the western plateau region is about 2.5 to 3 times that of the plain region, and the average annual rainfall is only 1/5 of that in the plain region. The drying effect on the surface of casting concrete will significantly accelerate its cracking process, leading to serious durability problems. The environmental temperature in the western mountainous areas of China is generally low, and there are more freeze-thaw cycles, which will increase the risk of freeze-thaw damage to railway concrete. The environmental air pressure in the western plateau region is only 60% of that in the plain region. The moisture inside the concrete is more likely to diffuse into the surrounding environment under the pressure difference, resulting in greater water loss and shrinkage deformation of the concrete in the plateau region. The above four issues will collectively lead to the rapid deterioration of concrete durability in the western plateau region. The corresponding durability improvement suggestions from theoretical research, new technology development and standard system was proposed in this paper.Originality/valueThe research can provide the mechanism of durability degradation of railway concrete in the western mountainous areas of China and corresponding improvement strategies.

<b>Outline of Design Standard and Commentary for Railway Structures (Concrete Structures)</b>

<b>Outline of Design Standard and Commentary for Railway Structures (Concrete Structures)</b>

Assessing the Feasibility of Removing Graffiti from Railway Vehicles Using Ultra-Freezing Air Projection

Unauthorised graffiti is a challenge in urban environments, affecting railway structures, stations, tracks, and vehicles. Inefficient cleaning methods increase the costs and downtime of railcars, limiting passenger transport. In turn, they are harmful to the operator’s health and the environment, due to the VOCs they release. This study focuses on the feasibility of dry-ice blasting, replacing carbon dioxide with ambient air as an innovative and sustainable solution to remove graffiti from rail vehicles. Experimental tests have been carried out with 13 different aerosols, controlling the temperature (<−80 °C), pressure (up to 3 bar), projection distance (0.5 cm) and exposure times (30″/1′/2′/4′/6′/8′/++). The results showed that ultra-freezing with ambient air preserved the integrity of the support materials and altered the topography, colourimetry and adhesion of the aerosols tested, achieving the total removal of one of the paints. Preliminary results suggest that ultra-freezing with ambient air could be a viable and sustainable solution for graffiti removal on railway structures, transferable to other urban environments.

Monitoring For Strain-Based Railway Structure Assessment Approach Using Optical Fibre Sensor

Railway transportation is essential and continually evolving with new technologies to achieve high efficiency and passenger safety. Monitoring railways can be challenging, especially when dealing with delicate equipment. This study outlines a basic guideline and real-time monitoring process for railway tracks, serving as precautionary measures. The research employs Fiber Bragg Grating (FBG) sensors directly attached to the railway track’s web surface, which have the potential to cause failures. Before sensor installation, several critical steps were taken to ensure the fragile FBG sensors remained intact. These steps involved preparing sensor arrangements and positioning them before installation. Additionally, a calibration test for FBG is performed using the Universal Tensile Machine (UTM) with a mild steel sample, achieving a measurement of almost 1.2 picometers/micro-strain. As a result, a shift in wavelength was successfully measured and collected, enabling the calculation of strain-stress data for the rail structure during operation. The collected data exhibited no irregularities or anomalies data, indicating the success of the monitoring process. The data obtained from a well-prepared installation greatly differs from that of an underprepared one. This study underscores the necessity of thorough preparation when handling delicate equipment like FBG sensor. Therefore, the FBG sensor has the capability to measure the strain-stress behavior of rail structures, allowing for more accurate predictive assessments to prevent rail failures.

Temperature effects on noise radiated by concrete railway structures

In recent years, concerns have arisen regarding the periodic deformation of high-speed railway tracks owing to the temperature effects caused by the solar radiation. This phenomenon has prompted investigations into temperature-induced changes in the dynamic responses of vehicle–track–bridge systems. Previous studies have commonly taken the additional track irregularity caused by thermal deformation as the sole factor affecting dynamic responses while neglected changes in the structural frequency response characteristics. Structural radiation noise is also a prominent issue that affects the lives of people and the environment. However, studies on track–bridge-borne noise rarely consider the influence of temperature. To address the impact of temperature on structure-borne noise radiated by tracks and bridges, this study employed a sequentially coupled multi-physics analysis method. This approach allowed a comprehensive exploration of the temperature effects on track irregularities, structural frequency responses, and sound radiation efficiency. A full-scale temperature deformation field test of a CRTS III slab was also conducted to determine the necessary initial thermodynamic boundary conditions. The analysis results revealed that the thermally induced deterioration of track irregularity and changes in structural frequency response characteristics were the primary factors affecting structure-borne noise radiated by track–bridges under local climate conditions.

Innovative Trends in Railway Condition Monitoring

Provision of functional safety of a railway track requires complementing the existing system of assessment of the railway track condition with the stress-strain behaviour assessment of the rail substructure, i.e. the assessment of the effect of track structure elasticity on the change of its geometric parameters during rolling stock passage over time. There is a lack of available theoretical and practical information about any pivotal changes in this field of science. The subject of the study is the in-situ elasticity indicators of a railway track and geometric monitoring indicators of railway structure condition or similar indicators obtained by numerical processing of data provided by the measuring systems of a track recording car and enabling the determination of change of irregularity parameters over time taking into account of the tonnage passed. The outcome of the investigation is the proposed approach to the development of an unparalleled diagnostic loading system which has been the missing part of the “puzzle” in the existing system of integrated assessment of the technical condition of a railway track.

Durability evaluation for existing railway engineering: a review

PurposeThis study aims to analyze the factors, evaluation techniques of the durability of existing railway engineering.Design/methodology/approachChina has built a railway network of over 150,000 km. Ensuring the safety of the existing railway engineering is of great significance for maintaining normal railway operation order. However, railway engineering is a strip structure that crosses multiple complex environments. And railway engineering will withstand high-frequency impact loads from trains. The above factors have led to differences in the deterioration characteristics and maintenance strategies of railway engineering compared to conventional concrete structures. Therefore, it is very important to analyze the key factors that affect the durability of railway structures and propose technologies for durability evaluation.FindingsThe factors that affect the durability and reliability of railway engineering are mainly divided into three categories: material factors, environmental factors and load factors. Among them, material factors also include influencing factors, such as raw materials, mix proportions and so on. Environmental factors vary depending on the service environment of railway engineering, and the durability and deterioration of concrete have different failure mechanisms. Load factors include static load and train dynamic load. The on-site rapid detection methods for five common diseases in railway engineering are also proposed in this paper. These methods can quickly evaluate the durability of existing railway engineering concrete.Originality/valueThe research can provide some new evaluation techniques and methods for the durability of existing railway engineering.

Towards real-time condition monitoring of a transition zone in a railway structure using fibre Bragg grating sensors

Differential settlement of ballast and subgrade is a common issue in ballasted railway tracks. In transition zones between two different track forms, such as between a ballasted track and a slab track, a dip in longitudinal level often develops on the ballasted side. To ensure the safety of railway operation and reduce maintenance and life cycle costs, it is necessary to monitor the condition of the transition zone in an economical manner and to detect any operational change at an early stage. In recent years with the advancement of fibre-optic technology, fibre Bragg grating (FBG) sensors have been more commonly applied in condition monitoring of railways due to their high precision and high acquisition rates. In this study, an FBG-based setup for in-situ long-term condition monitoring of track bed degradation in a transition zone has been developed and implemented to provide data for verification and calibration of a simulation model. The system is designed for measurements in an operational railway track in harsh conditions in the north of Sweden. The instrumentation along the transition includes four clusters, each with an optical strain gauge array on the rail web in one sleeper bay, and an accelerometer and a displacement transducer on the sleeper. It is shown that the implemented displacement and strain sensors are able to effectively capture the overall dynamic range of the system, indicating that the collected data can accurately represent the dynamic response of the transition zone in the short term and long term and be applied for the calibration of a simulation model.

Implementation and analysis of viscoelastic damping in a 2D + 1D model of railway track vibrations

One of the most important technological challenges in the railway context nowadays is reducing the noise produced by the interaction between the train wheels and the track surface, that is the rolling noise. Introducing viscoelastic damping in the railway structure is one method to mitigate this rolling noise. In the paper, we investigate the impact of damping in the vibrational response of railway tracks using different viscoelastic models and parameters available in the literature. For this purpose, the main focus here is on developing an advanced numerical model in which viscoelastic models representing the rail foundation and/or pad are implemented in the framework of the Semi-Analytical Finite Element (SAFE) method. Linear or nonlinear viscoelastic models are considered, compared and effectively implemented for accelerance computation. The obtained numerical strategy leads to affordable and accurate predictions on dynamic features of the railway structure compared to classical methods.

Optimizing Mixed Group Train Operation for Heavy-Haul Railway Transportation: A Case Study in China

Group train operation (GTO) applications have reduced the tracking intervals for overloaded trains, and can affect the efficiency of rail transport. In this paper, we first analyze the differences between GTO and traditional operation (TO). A new mathematical model and simulated annealing algorithm are then used to study the problem of mixed group train operation. The optimization objective of this model is to maximize the transportation volume of special heavy-haul railway lines within the optimization period. The main constraint conditions are extracted from the maintenance time, the minimum ratio of freight volume, and the committed arrival time at each station. A simulated annealing algorithm is constructed to generate the mixed GTO plan. Through numerical experiments conducted on actual heavy-haul railway structures, we validate the effectiveness of the proposed model and meta-heuristic algorithm. The results of the first contrastive experiment show that the freight volume for group trains is 37.5% higher than that of traditional trains, and the second experiment shows a 30.6% reduction in the time during which the line is occupied by trains in GTO. These findings provide compelling evidence that GTO can effectively enhance the capacity and reduce the transportation time cost of special heavy-haul railway lines.

The Heritage Value of Railway Structures and Western Practice

The Heritage Value of Railway Structures and Western Practice

Recent advancements in the applications of fiber‐reinforced polymer structures in railway industry—A review

AbstractThe application of fiber‐reinforced polymer (FRP) composite materials and structures in various industrial sectors is expanding significantly to meet the rising demand for efficient, reliable, and functional building materials. Using FRPs can be an excellent strategy for enhancing railway structures and equipment because of their high strength‐to‐weight ratio, tailorable mechanical properties, and suitable long‐term characteristics. However, the railway industry appears to be hesitant to adopt composite materials compared to other transportation sectors like aerospace. It seems that there is still a long way to go before FRPs reach their full potential in railway applications. The goal of the current study is to explore the current uses of FRPs in the railway industry and the significant challenges, obstacles and difficulties that must be overcome to put FRP‐based concepts into practice for structural and rail vehicle applications.HighlightsApplications of FRPs in railway vehicles and rail lines are reviewed.Main challenges for utilization of FRP in railway industry are studied.Future trends and applications of FRPs in the railway sector are introduced.

Performance evaluation of rail trackbed stiffness: pre and post stabilisation

Excessive deflection of a rail in response to axle loading can lead to discomfort for passengers and increased wear of both railway structures and trains. These oscillations are often caused by poor trackbed stiffness which may be due to either soft subgrade and/or contaminated ballast. A variety of trackbed stabilisation (TBS) techniques are available to remediate soft subgrades and increase the safety of tracks within the railway network. Traditional TBS methods require track removal, which is expensive, disruptive and often inefficient maintenance works. Micro-piling, using screw piles installed between sleepers, is an innovative low disruption TBS technique. This paper investigates the performance of a soft subgrade and contaminated ballast section of rail line in the UK, before and after screw pile TBS. Pre and post remediation, a computer vision-based system was used to measure rail vertical deflections during train passages and then analysed to quantify the trackbed stiffness. Additionally, 3D finite element models are created and validated by the site measurements. The finite element models are used to simulate a range of different scenarios exploring how changes to the TBS piling layout and/or further works, such as ballast improvement could add further improvements or design efficiencies. Site measurements show TBS reduced rail deflection by 20–30%, indicating that micro-piling is an effective technique for soft subgrades. The finite element analysis revealed the efficiency of micro-piling is highly dependent on the conditions of ballast, strength of the ground at the pile toe, and the pile arrangement. When the aforementioned are optimised the rail deflection could be reduced to approximately 50% of the pre TBS condition.

Multiphase assessment of post-mining effect on railway structures: A case study of Jharia Coalfield

Multiphase assessment of post-mining effect on railway structures: A case study of Jharia Coalfield

Investigation on smoothed finite element methods using linear tetrahedral elements for high-speed train hollow axle strength analysis

PurposeThis paper aims to investigate the performance of two novel numerical methods, the face-based smoothed finite element method (FS-FEM) and the edge-based smoothed finite element method (ES-FEM), which employ linear tetrahedral elements, for the purpose of strength assessment of a high-speed train hollow axle.Design/methodology/approachThe calculation of stress for the wheelset, comprising an axle and two wheels, is facilitated through the application of the European axle strength design standard. This standard assists in the implementation of loading and boundary conditions and is exemplified by the typical CRH2 high-speed train wheelset. To evaluate the performance of these two methods, a hollow cylinder cantilever beam is first used as a benchmark to compare the present methods with other existing methods. Then, the strength analysis of a real wheelset model with a hollow axle is performed using different numerical methods.FindingsThe results of deflection and stress show that FS-FEM and ES-FEM offer higher accuracy and better convergence than FEM using linear tetrahedral elements. ES-FEM exhibits a superior performance to that of FS-FEM using linear tetrahedral elements, showing accuracy and convergence close to FEM using hexahedral elements.Originality/valueThis study channels the novel methods (FS-FEM and ES-FEM) in the static stress analysis of a railway wheelset. Based on the careful testing of FS-FEM and ES-FEM, both methods hold promise as more efficient tools for the strength analysis of complex railway structures.

Microstructure characteristics and evolution of the bonding interface between SCC and steam-cured concrete

The microstructure of the bonding interface in CRTS III ballastless track structures is critical to the mechanical properties and durability of high-speed railway structures. The microstructure evolution of the bonding interfacial zone between steam-cured concrete and SCC (self-compacting concrete) is widely studied. This paper investigates the pore structure and phase evolution of the bonding interface zone using backscattered electronic and energy dispersive spectroscopy (BSE + EDS). Based on the nanoindentation test, the microstructure characteristics of the bonding interfacial zone were studied. The results show that the microstructure reveals a gradient change at the bonding interface zone, and the gradient characteristics of the microstructure weaken as curing age increases (especially at 7 days and 56 days). The width of the bonding interface zone is about 15 μm, and the width is more about 20 μm at 1 day. The elastic modulus of C-S-H at the bonding interface zone is low and the C-S-H is mostly LD C-S-H. VMA is beneficial to improve the elastic modulus of C-S-H.

Assessing the Impact of a Railway Tunnel on Groundwater Flow Regime in Urban Areas: A Case Study of Bratislava’s TEN-T Track and Proposed Mitigation Measures

The Bratislava region in Slovakia aims to improve its transport infrastructure by connecting the airport with the railway network. As part of the Trans-European Network for Transport project (TEN-T), an underground railway line is proposed to be constructed on both sides of the Danube River, connecting the airport in Bratislava to the Petržalka region on the river’s right side. However, underground construction is likely to have an impact on the groundwater flow regime. This construction, which will be built below the ground surface, should be built by excavating from above under the protection of sealing walls to prevent significant changes to the groundwater level regime (GWL). Therefore, a numerical model based on the finite element method (FEM) was established to evaluate the effect of the planned underground construction on the GWL, and technical measures were introduced to mitigate any potential impacts. The results of the model revealed possibilities for controlling the groundwater level in the aquifer affected by the railway structure during and after the construction.

Расчет движения подвижного состава по железнодорожному пути сеточно-характеристическим методом

The application of a grid-characteristic method is proposed for numerical simulation of the movement of rolling stock along a railway track laid on an earth and a bridge. In the study, the railway track is presented using a dynamic system of equations of the theory of elasticity of hyperbolic type. The grid-characteristic method relies on the characteristic properties of the system under consideration and uses finite-difference schemes of high order of accuracy to obtain a space-time solution. The features of railway structures are considered by changing the boundary conditions and conditions at the contact borders. To simulate the areas of contact of wheel pairs of rolling stock with the rail – the "wheel-rail" system – a previously developed pressure boundary condition is applied, modified so as to consider multi-element rolling stock. As a result of computer simulation of the movement of rolling stock along the railway track of various types, full-wave stress distribution in the track structure is obtained, which makes it possible to predict dangerous sections of rolling stock movement.

Thermal-mechanical coupled XFEM simulation of low temperature cracking behavior in asphalt concrete waterproofing layer

Asphalt concrete waterproofing layer (ACWL), which is used to reduce the moisture impact on high-speed railway structure, tends to crack at low temperatures and thus reduces its durability. Therefore, understanding the low-temperature cracking behavior of ACWL from both the material and structure perspectives is of great significance. In this study, thermal-mechanical coupled simulation based on extended finite element method (XFEM) was employed for research on this aspect, with the experimental and numerical monotonic-loading overlay test (ML-OT) to determine the fracture parameters of railway asphalt concrete materials and full-scale model to characterize the thermal cracking behaviors of ACWL. The results firstly showed that both the ML-OT and thermo-mechanical simulation on ACWL structure presented a four-stage fracture process, i.e. elastic response, crack initiation, crack propagation and final failure stage, at the temperature of −20 °C. Secondly, the effects of material formulation and structure design on the low-temperature cracking resistance was investigated: 1) In terms of material formulation, the binder B and gradation AC-13 was superior to their counterparts; 2) In terms of structure design, the ACWL layer thickness of 8 cm was the most unfavorable in the range of 6–16 cm, and the increased temperature difference accelerated the thermal cracking propagation in ACWL at the average temperature of −20 °C. In addition, two thermal stress mitigation strategies, namely laying the geotextile at base joints and setting expansion joints, were found to effectively prevent and delay the emergence of thermal cracks in ACWL at low temperatures. For recommendation, the developed thermal-mechanical coupled simulation framework, the custom-designed railway asphalt concretes, and the recommended ACWL thickness of 12 cm were applicable in future studies and engineering projects.