Types Of Sleepers Research Articles

The Influence of an Unsupported Sleeper on the Vertical Bearing Characteristics of Heavy-Haul Railway Ballast.

In order to study the influence of an unsupported sleeper on the vertical bearing characteristics of heavy-haul railway ballast, a three-dimensional discrete element model (DEM) was established for a ballasted track, by removing ballast particles that come into contact with the bottom of the sleeper from the model to simulate the unsupported sleeper. Vertical bearing characteristics for ballast on different types of unsupported sleepers were studied. The results showed that an unsupported sleeper could reduce the bearing area of the ballast below the sleeper and reduce the number of ballast particles that were in contact. It could also lead to an increase in the maximum contact force between the particles, accelerating the deterioration of the particles (thus affecting the overall performance of the ballast) and reducing the vertical stiffness of the ballast. As the unsupported length and width increased, vertical stiffness gradually decreased. The vertical ballast stiffness for an unsupported sleeper was then used in a dynamic coupled vehicle/track model, and the effect of the unsupported sleeper on wheel/rail interaction was analyzed. Results showed that increasing the unsupported length and width leads to a decrease in the supporting force on the unsupported sleeper and to an increase in the supporting force on the adjacent sleepers.

Comparison of lateral resistance between I-shaped and X-shaped sleepers using finite element and discrete element coupling method

The lateral resistance of ballasted track is a key factors to maintain the stability of continuously welded rails. In this study, a new type of X-shaped sleeper was developed to increase the lateral resistance compared to conventional I-shaped sleepers. Multi PD3D (Particle discrete 3D) elements were bonded by rigid Beam-type multi-point constraints (MPCs) to implement irregular shaped ballast. The performance of the X-shaped sleeper was examined using track panel push-out tests simulations. The results showed that the X-shaped sleeper could provide 27% greater lateral resistance compared to double I-shaped sleepers. This is due to the V-fork arms which distribute the central and lateral crib ballasts more effectively, enhancing the stability of the sleeper. Crib ballasts play a crucial role in the lateral resistance of X-shaped sleeper, providing nearly double the lateral resistance compared to double I-shaped sleepers. Overall, the proposed X-shaped sleeper has stronger lateral resistance and stability, making it a promising option for future applications.

Influence of ballast shoulder width and track superelevation on the lateral resistance of a monoblock sleeper using discrete element method

Railway tracks must resist lateral horizontal forces associated with curving and wind loading of trains and provide lateral restraint to prevent rail buckling in hot weather. On a ballasted railway, the required resistance is provided at the sleeper-ballast interface and is influenced by the shape and type of sleeper and the characteristics and profile of the ballast bed. In this study, numerical simulations of Single Tie Push Tests (STPTs) were carried out using the discrete element method (DEM) to investigate the effect of shoulder width and track superelevation on the lateral resistance of unloaded monoblock sleepers. Few previous studies of lateral resistance have considered the effect of superelevation, which is perhaps surprising as the horizontally-curved track is usually superelevated (canted) so that the downslope component of the train weight provides some of the centripetal force needed for the train to travel in a curved arc. It is found that the lateral resistance of a single sleeper increased with the degree of superelevation, by about 100% at 2 mm sleeper displacement for a superelevation of 150 mm compared with an uncanted sleeper. Most of this increase came from the shoulder ballast; the contribution from the crib increased slightly while that from the base reduced slightly. Widening the ballast shoulder from 300 to 500 mm resulted in an increase in resistance of about 27% regardless of the superelevation. The results indicate the importance of maintaining the ballast shoulder, especially in superelevated track sections.

Investigation of the Track Gauge in Curved Sections, Considering Hungarian Railway Lines

In this paper, the authors examined the change in track gauges in curves for several railway lines with low and high traffic in Hungary (i.e., secondary lines and main lines). They covered the processing of raw data as well as statistical calculations. The considered curved sections were transition curves (TCs) and circular curves (CCs), as well as—in some cases—entire curves (ECs), including TCs and CCs, but not dividing them into parts. The change of track gauge parameter as a function of elapsed time was analyzed based on the distribution functions by calculating the Vaszary-type shape number. A statistical test with the Kolmogorov–Smirnov test was performed, in which the question as to whether the measurement data of the railway lines followed a normal or lognormal distribution was examined; additionally, the skewness and kurtosis parameters were calculated and analyzed. The authors also took into account the impact of the track system and the sleepers. For the selected curves, the authors observed how the average track gauge changes and categorized them according to tolerances. In presenting and summarizing the tests, the authors formulated a conclusion for each study fulfilled. Despite higher traffic loads, the value of track degradation over time is lower for mainline curves than for secondary line curves. It is because the main line has stricter tolerances due to the higher speeds allowed, and more maintenance work is carried out on these lines. The authors concluded that the type of the track system and the sleeper type also influence the change in track gauges in curves. The accurate deterioration ratios for all analyses are contained in the paper.

Effect of Critical Factors Influencing Longitudinal Track Resistance Leveraging Laboratory Track Panel Pull Test Experimentation

There are, on average, 12.5 Federal Railroad Administration reportable derailments per year on U.S. mainlines and sidings caused by “defective or missing spikes or rail fasteners.” Because fastener failures are most commonly caused by a combination of vertical, lateral, and longitudinal loads, it is important to quantify all loads placed on the fasteners to reduce the number of failed fasteners and increase rail safety. Multiple researchers have developed analytical models that leverage longitudinal track resistance and stiffness to quantify the fastener demands. Therefore, to support the refinement of these analytical models that leverage longitudinal track resistance and stiffness, track panel pull tests (TPPTs) were executed in the laboratory to expand on the values within the available literature. These TPPTs quantified the effect of sleeper type (i.e., timber versus concrete), given that 88% of previous studies have focused on concrete. Further, these novel tests quantified the effect of the fastening system, crib ballast height, shoulder width, and ballast condition on the panel’s longitudinal resistance and stiffness. From these experiments and the resulting analysis of data, multiple conclusions were drawn. For example, concrete sleeper panels exhibit 20% higher resistance than timber sleeper panels, disturbing ballast reduced the longitudinal resistance by 13% and stiffness by approximately 80%, and the crib, shoulder, and bottom ballast provide approximately 65%, 5%, and 30% of the total longitudinal resistance, respectively.

Performance studies on two types of prestressed concrete railway sleepers using finite element model

Prestressed concrete sleepers [PCS] are widely used in ballasted railway tracks across the world. Sleepers distribute the load coming from the rails to the ballast. PCS have advantages like high durability, stability, and strength compared to other types of sleepers. Concrete sleepers in their life span may undergo utmost loading conditions due to high-speed rails, high-magnitude wheel loads, and rail irregularities. Cracks in sleepers may occur at the rail seat region and mid-span region because of the high positive bending moment and high negative bending moment, respectively. PCS may satisfy the excepted performance standards during short-term serviceability, but long-term durability and premature failures are still an issue. Hence, selecting a suitable sleeper that performs better during harsh loading conditions becomes crucial. In the present study, two kinds of railway sleepers, namely, Indian sleeper (RT2496/60 kg) and Chinese type III prestressed concrete sleeper [CT III PCS], are considered to assess the performance under harsh loading conditions which arise due to modern high-speed or semi-high-speed rails on ballasted tracks. The finite element models of two kinds of sleepers were done using ANSYS, and the performance of the sleepers was assessed. The numerical results show that the CT III PCS performed slightly better than the Indian sleeper that has been studied in the present investigation.

Combined effect of supported and unsupported sleepers on lateral ballast resistance in ballasted railway track

The lateral resistance of a ballast bed significantly affects the lateral stability of ballasted railway tracks. Hence, a precise evaluation of the lateral ballast resistance is essential for predicting rail buckling potential. Differential ballast settlement can cause the sleeper bottom to separate from the ballast, thereby causing the sleeper to become an “unsupported sleeper” suspended from the rail. The gap between the ballast and sleeper bottom results in zero frictional force at the bottom, which reduces the lateral ballast resistance. However, sleepers near unsupported sleepers are subjected to the additional weight of the unsupported sleepers and the rail load borne by the unsupported sleepers. Consequently, they become over-supported. Additional loads may change the lateral ballast resistance of the supported sleepers. Previous studies did not consider the combined effects of supported and unsupported sleepers on the lateral ballast resistance. Therefore, in this study, experiments are conducted on 1/5-scale ballasted track models to investigate these combined effects. Analytical methods for evaluating the lateral ballast resistance when panels incorporate both supported and unsupported sleepers are presented. Pullout tests conducted on panels incorporating supported and unsupported sleepers reveal that unsupported sleepers adversely affect the lateral ballast resistance. The lateral ballast resistance decreases as the number of unsupported sleepers increases, irrespective of sleeper type. Moreover, the analytical results reveal that the lateral ballast resistance of the panel is underestimated when only the decrease in the lateral ballast resistance due to unsupported sleepers is considered. Meanwhile, the analyses considering the combined effects of supported, unsupported, and over-supported sleepers provide reasonable estimates of the lateral ballast resistance, similar to the experimental results. This indicates the importance of comprehensively considering the effects of the support conditions of the sleepers on the lateral ballast resistance to estimate rail buckling potential.

Influence of Type of Sleeper–Ballast Interface on the Shear Behaviour of Railway Ballast: An Experimental and Numerical Study

The shear resistance at the sleeper–ballast interface of a ballasted track is an important contributor in maintaining track stability under faster and heavier axle loads where the ballast undergoes significant lateral sliding. Different types of sleeper–ballast interfaces based on the type of sleeper arrangements, such as concrete sleepers, timber sleepers, and under sleeper pads (USPs) attached to the concrete sleepers influence the lateral stability of railway tracks. Therefore, in this study the shear and degradation behaviour of ballast at concrete–ballast, timber–ballast, and USP–ballast interfaces were examined in the laboratory using large-scale direct shear tests under 60 kPa normal stress. The use of waste materials in the construction of civil infrastructure is gaining a lot of interest in the engineering community. Therefore, in addition to commercial USPs manufactured using raw materials, recycled USPs manufactured from granulates of end-of-life rubber tyres were also tested in this study. The discrete element modelling (DEM) approach was used to predict the shear behaviour of ballast at 30, 90, 120, 150, and 180 kPa normal stresses. The bonded particle model (BPM) was adopted in the DEM to simulate the effects of particle breakage during shearing. The results exhibited that both commercial and recycled USPs significantly improve the shear resistance at the sleeper–ballast interface while reducing particle degradation compared to concrete and timber sleeper interfaces.

Progressive failure analysis of partially pre-stressed concrete railway sleepers

Billions of sleepers are used on railways around the world today. As the importance of railways in the transportation sector is increasing, the demand for sleepers is also increasing. Although wooden and steel sleepers were used in rail systems in the past, today the most widely used sleeper type in the world is reinforced concrete sleepers. Among these reinforced concrete sleepers, pre-stressed sleepers are the most widely used, popular type of sleeper that can be produced in many countries. The two main production methods of pre-stressed sleepers are the ribbed reinforced system and the non-ribbed reinforced anchor plated system. In this study, B70 type pre-stressed concrete sleepers, have been investigated with the positive moment determination tests at the rail seat with progressive failure observations according to EN 13230-2:2016 standard. After tests, detailed cracking, failure, and fatigue analyzes under increasing test loads were performed with ANSYS® finite element analysis results for both types of pre-stressed sleepers. According to results, A-type sleepers have 50% more compression stress at the first crack formation load (Frr) than N-type sleepers and According to the first 0.05 mm permanent crack formation load (Fr0.05), it is seen that 25% higher stresses occur in A-type design than N-type design under Fr0.05 load. The results obtained through the analysis have been compared with the actual field measurement results, which have become more and more popular in the world in recent years. In this direction, various suggestions have been made for the development of concrete railway sleeper models.

Fatigue life modelling of railway prestressed concrete sleepers

Railway sleepers, which transfer wheel loads to the formation, are an essential component of railway track systems. Prestressed concrete is the most commonly used type of railway sleepers around world. Crushing is a common damage (under resultant compressive stress) in concrete sleepers, which is attributable to excessive flexural, shear, pre-stress and bond actions. Dynamic impact loading conditions are often the cause of failure in the concrete sleepers. However, accumulated damage due to cyclic loads can also cause concrete crushing. Most previous research has investigated the impact load characteristics and the ultimate limit states of prestressed concrete railway sleepers. There is a knowledge gap with respect to serviceability limit states and fatigue failure of prestressed concrete sleepers. This study presents new results of extensive numerical, analytical, and experimental investigations aimed at predicting fatigue lives under cyclic loads. A numerical study validated by 30 full-scale experimental tests is executed and extended to assess fatigue limit states, while theoretical fatigue analysis methods based on S-N curve and Miner linear cumulative damage are additionally introduced for benchmarking. This paper is the world's first to demonstrate a remaining fatigue life assessment for prestressed concrete sleepers and benchmark with the theoretical methods. Parametric studies are conducted to unprecedentedly illustrate influences of support conditions, dynamic load distribution, and track stiffnesses on the remaining fatigue lives of prestressed concrete sleepers. This paper highlights the rationales associated with the development of fatigue limit states. The insights will provide design flexibility and improve railway sleeper maintenance and inspection criteria.

Verification of Longitudinal Level Irregularity Suppression Effect at the Structural Boundary by Ballasted Ladder Track

The ladder sleeper, which is a type of longitudinal sleeper with long beams in the longitudinal direction of the rail, was developed for the maintenance-labor saving of ballast tracks. In this study, to quantify the load distribution performance of the ladder sleepers at the structural boundary, full-scale model tests were conducted to quantify the vibration transmission reduction effect of the ladder sleepers. Following that, numerical experiments were carried out using a three-dimensional numerical analysis model and it was revealed that the ladder sleeper can reduce the pressure on the sleeper bottom plane by approximately 70% when compared to conventional prestressed concrete sleepers. Furthermore, when laying the ladder sleeper at the structural boundary, it was shown that laying across the structural boundary may be more effective in reducing the pressure on the sleeper bottom plane than laying it in front of the structural boundary. Finally, ladder sleepers were installed on the commercial line and long-term measurements of the longitudinal level irregularity verified the effect of suppressing the longitudinal level irregularity of the ballasted ladder track.

Discrete element method analysis of lateral resistance of different sleepers under different support conditions

With the increasing speed of trains and the axle load of railways, the need to provide lateral stability of railways becomes more important. Small-radius curves on conventional tracks and temperature fluctuations pose a significant threat to the lateral stability of railway tracks as they increase lateral and longitudinal forces, leading to track buckling. Therefore, the lateral resistance of ballasted railway tracks must be improved in every way possible. To this aim, many approaches have been proposed, including modifying ballast and sleeper materials, changing the ballast layer geometry, and replacing conventional sleepers with specialized ones. Compared to conventional B70 sleepers, applying HA110, winged and middle-winged sleepers improved the lateral resistance by 31%, 50% and 17%, respectively, according to the findings of a Single Tie Push Test (STPT). Ballast supports often fail to ideally cover the sleeper bed. Thus, the lateral resistance of four different types of sleepers (i.e., HA110, winged, middle-winged, and B70) under four different support conditions (i.e., lack of rail seat support, full support, lack of center support, high center binding) with/without shoulder and crib ballasts was investigated by discrete element method (DEM). The results revealed that winged and HA110 sleepers showed similar behavior in providing the lateral track resistance without considering crib and shoulder ballasts in the absence of center and high center binding support conditions, while winged sleepers exhibited the highest lateral resistance in the presence of crib and shoulder ballasts in full support, lack of rail seat support, and lack of center support.

Suitability of recycled materials as a composite sleeper: A scoping review

The railway transportation system is the most convenient transportation system due to its easy accessibility and construction mode. Sleeper is the most important and vulnerable part of the railway transportation system due to its load-bearing and load distribution characteristics. Several types of materials are used nowadays as sleeper materials, such as timber, concrete, and steel. Each type of sleeper has some disadvantages and is sometimes harmful to the environment. For that reason, a composite sleeper with different materials has recently been developed by other sleeper manufacturing companies. Different composite sleeper materials are geopolymer concrete, recycled polymer, and CarbonLoc composite. The use of plastic can be an excellent alternative to conventional sleeper material. Still, the only use of recycled plastic as a sleeper material cannot be suitable due to less stiffness, higher cost, voids formation, porosity, spike loosening, and permanent deformation due to creep and less modulus of elasticity. The structural properties of this type of sleeper can be improved by using recycled rubber, fibre reinforced foamed Urethane (FFU), and epoxy polymer resin as a composite material. Composite sleepers with recycled and reinforced materials can be a good alternative for the railway track with critical locations such as crossings, switches, bridge transom, and areas with constraint clearance. Though composite sleeper has been used for several decades in different parts of the world, it is not gaining popularity due to the lack of standards and confusion between buyers and sellers based on acceptance criteria and qualifications. Therefore, this scoping review will give some idea about different composite sleeper types and review the significant features based on the mechanical, physical, and structural properties. Finally, it will highlight other comparative characteristics of composite sleepers with recycled and reinforcing materials and their properties.

Numerical and Experimental Analysis of Lateral Resistance of Single Y-Shaped Steel Sleeper on Ballasted Tracks

AbstractLateral track stability is a critical parameter in ballasted railway tracks considering track buckling. The sleeper type has a direct impact on lateral track stability. Due to the Y-shape s...

Numerical studies to evaluate crack propagation behaviour of prestressed concrete railway sleepers

The prestressed concrete sleeper is a primary type of sleeper for railway systems around the world. Compared with wooden and composite sleepers, concrete sleepers are of good elasticity and sufficient longitudinal and lateral resistance to ensure the stability of the track. As the railway system is developing to a heavier load and higher speed system, the cracking of concrete sleepers under dynamic load and long-term service is becoming more and more critical. It is essential to evaluate the crack behaviour of prestressed concrete sleepers. In this paper, three-dimensional FEM models have been established using Abaqus based on the brittle cracking model. After the validation by experimental results, the numerical research is performed to evaluate the crack propagation behaviours of prestressed concrete sleepers with different concrete compressive strength, different prestressing force magnitudes, and different loading rates. The results reveal that the cracking resistance of a concrete sleeper turns enhanced by improving the compressive strength of concrete and the initial prestressing force of tendons. It is also observed that the cracking becomes more progressive as the loading rate increases.

Intermittent cyclic load testing of polymer railway sleepers

Before a new type of railway sleeper can be used in track, standardised laboratory tests must be carried out to determine its suitability. In addition to static load tests, assessments usually include cyclic load tests consisting of millions of load cycles, representing passing trains during the sleeper’s service life. In these laboratory tests, the loading cycles are applied continuously without resting periods to condense the test time. Traditional sleeper materials (timber, concrete) possess elastic properties for which such testing is appropriate. However, polymer sleepers exhibit viscoelastic properties, such as creep, a loading rate-dependent stiffness and heating due to non-linearity of the stress-strain curve. Subjecting polymer sleepers to continuous cyclic load tests with a load frequency reflecting permissible track speed can cause the sleeper to heat up. Intermittent testing with pauses between numbers of load cycles is proposed in this paper as a possible solution. The aim is to propose a laboratory loading procedure that adopts a traffic-resembling load of a railway line, considering an effective compromise between polymer visco-elastic behaviour and time consumption of the laboratory tests. The loading frequency is kept at the desired strain rate for track evaluation, giving a representative sleeper stiffness and strength assessment. Exemplary tests with varying test arrangements and loading procedures were performed to quantify the effects of intermittent loading in comparison with continuous loading. The proposed method eliminated most of the test-induced creep and heat accumulation, resulting in a more representative stiffness and strength assessment, which justifies the proposed intermittent testing for polymer sleepers. The proposed intermittent procedure is an optional test regime in ISO 12856-2 for polymer sleeper testing.

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 study on lateral resistance of frictional sleeper with arrowhead groove

To enhance the stability of continuous welded rail (CWR) tracks, frictional sleepers have been developed. The frictional sleepers are new types of sleepers with grooves on the bottom, and different bottom grooves improve lateral resistances at different magnitudes. In this study, single sleeper push test (SSPT) and its model with discrete element method (DEM) were carried out to confirm how much arrowhead groove frictional (AGF) sleeper increases the lateral resistance of ballasted track. The SSPTs were performed to confirm the lateral resistance results, and also to validate and calibrate the DEM models. With the validated models, the groove factors influencing the lateral resistances were studied, including groove sizes (depth, width), arrowhead groove direction and groove numbers. The reason of lateral resistance improvement was studied at mesoscopic level, including the ballast-sleeper contact numbers and contact force chains. Results show that applying the AGF sleeper is able to improve lateral resistance by 7–24%, and it can provide enough lateral resistance after reducing ballast shoulder width from 500 mm to 300 mm. The AGF sleeper can improve the sleeper-ballast interaction by increasing sleeper-ballast contact number. The study is helpful for frictional sleeper design, further improving track stability.

Application of Deep Learning Networks to Segmentation of Surface of Railway Tracks.

The article presents a vision system for detecting elements of railway track. Four types of fasteners, wooden and concrete sleepers, rails, and turnouts can be recognized by our system. In addition, it is possible to determine the degree of sleeper ballast coverage. Our system is also able to work when the track is moderately covered by snow. We used a Fully Convolutional Neural Network with 8 times upsampling (FCN-8) to detect railway track elements. In order to speed up training and improve performance of the model, a pre-trained deep convolutional neural network developed by Oxford’s Visual Geometry Group (VGG16) was used as a framework for our system. We also verified the invariance of our system to changes in brightness. To do this, we artificially varied the brightness of images. We performed two types of tests. In the first test, we changed the brightness by a constant value for the whole analyzed image. In the second test, we changed the brightness according to a predefined distribution corresponding to Gaussian function.

Modal and harmonic response analysis of new CFRP laminate reinforced concrete railway sleepers

Nowadays high-cost sleeper applications are becoming indispensable because of railway operation conditions and high frequency train loads. For the protection of sleepers and other railway components, “non-prestressed” sleepers have the potential to reduce railway maintenance costs and exhibit a longer service life compared to their prestressed competitors. But the disadvantage of this process is steel reinforcement defects due to corrosion and fatigue. A new type of sleeper with non-pre-stressing process with non-corroding carbon fiber reinforced polymer (CFRP) laminate reinforcements can overcome these disadvantages. Rail seat static positive moment tests have been performed for these new types of sleepers before and it was determined that they can provide the desired static strength parameters even in high speed train lines. In this study, modal and harmonic response analysis has been performed and the results compared with prestressed sleepers with equivalent concrete cross-section dimensions. According to the results this new sleeper model has higher damping advantages and is expected to be beneficial in extending the service life of the railway components, reducing maintenance needs, and harmful effects on the environment.