Railway Sleepers Research Articles

Influence of Non-Homogeneous Foundations on the Dynamic Responses of Railway Sleepers

In a railway track, the sleeper’s responses on a non-homogeneous foundation have been investigated by researchers focusing on the foundation behavior along the rails. However, the foundation can also vary along the sleeper length, particularly when the track is newly tamped. The foundation at the sleeper center is often weaker than those under the rails and this non-homogeneity directly affects the sleeper responses. This paper presents a new model to calculate the influence of such foundations on the dynamic responses of the railway sleepers. This model is developed by combining a finite element model for the sleepers and foundation and a model of periodically supported beams subjected to moving loads for the rails. In this paper, the foundation contains three parts with different mechanical behaviors. The sleeper’s responses can be calculated by transforming the finite-element dynamic stiffness matrix to the one considering the boundary conditions and the relation between the rail seat forces and rail displacements governed by the beam model. This method reduces all the degrees of freedom of the railway track to its one period which gives a substantial reduction in computational time. The numerical applications show that the more homogeneous (so-called consolidated) the foundation is, the larger the sleeper strain is at its center. This result shows the potential application of the sleeper responses to estimating the consolidation level of the foundation.

Pull out and pre-tightening force tests for plastic dowel of the railway sleeper considering the influence of installing torque and frost force

The reliability connection of the plastic dowel and the bolt largely determines the normal function of the railway fastener system. However, the failure of the dowel and the uplift of the bolt are found during railway operation. Therefore, a series of pull-out and pre-tightening force tests for plastic dowel of the railway sleeper are carried out. Not only the relationship between the bolt ultimate pull-out capacity and the effective anchorage length is obtained, but the failure pattern of the plastic dowel is analysed. In addition, the relationship between pre-tightening force and installing torque, and the influence of freeze-thaw cycles on pre-tightening force are investigated. The above relationships could be described by linear equations, the failure of the dowel during pull-out test is dominated by bending failure pattern and the freeze-thaw cycles for the space between the bolt and the dowel with full of water (9 mL) could cause reduction of the pre-tightening force.

Mechanical Properties of Coal Ash Particle-Reinforced Recycled Plastic-Based Composites for Sustainable Railway Sleepers.

This experimental research investigates the mechanical properties of municipal plastic waste-based particulate composites reinforced with coal ash (CA), the by-product of thermal power plants, for sustainable railway sleepers. Six series of sustainable composites filled with inorganic mineral fillers, including CA, were prepared by a twin-screw extruder and a compression molding machine. The effect of mix design variables—such as filler type, contents and the particle size of the filler—on mechanical properties—including tensile, compression and flexural properties—and morphology were characterized. The scanning electron microscopy (SEM) was employed to examine the morphology of the composites, which revealed the uniform dispersion of fillers in the polymer matrix. The study results conclude that the recycled plastic-based composite with the addition of CA up to 60% is suitable for railway sleeper applications. This experimental study may provide new insight into the railway applications of the developed composites under service loading conditions including traffic loading and earthquake.

A Method of Classifying Railway Sleepers and Surface Defects in Real Environment

Rail transport is an efficient and safe way to move large quantities of goods and people over long distances but it still suffers from maintenance issues, mainly due to assets of great extent, quantity, weight, and geographic dispersion. Because of this, some initiatives in automatic inspection of railway assets have been developed in recent years/in the last decade. In particular, the automatic inspection of railway sleepers still needs improvement and consolidation. This work presents a method for sleepers inventorying, identification of the type and defects based on image processing, heuristics and feature fusion in an unsupervised way. The Haar transform and integral images are used, as well as other image processing techniques such as edge detection, and entropy computation along with aspects of railroad topology. The algorithm was developed using real images of daily railway, previously unclassified, and that were subject to various noises and variations of a real railway operation. The method was validated through experiments with an image set comprising 32,917 sleepers in 10,116 images. The results are promising in which 97% accuracy is reached, for the identification of the type of sleepers, and 93% accuracy for the identification of visible defects in sleepers.

Utilization of Wood Railway Sleepers Using a Supercritical Fluid Extraction Process

In this work, we propose an alternative method for the utilization of sleepers, based on the use of a supercritical fluid extraction process. The preference for the implementation of a supercritical fluid extraction process for “extractable-extractant” systems exhibiting I–II types of phase behavior is given. On the example of supercritical fluid extraction of the impregnation material of spent wood railway sleepers, the efficiency of replacing the carbon dioxide participating as an extractant with a propane/butane mixture, which provide the desired change in the type of phase behavior in relation to such components of the impregnation material as phenol, anthracene and naphthalene is shown. The phase equilibria of thermodynamic systems involving carbon dioxide and a propane/butane mixture on the one hand and coal oil components such as phenol, anthracene, and naphthalene on the other are studied. The proposed method of processing spent railway sleepers allows you to select from it up to 97 % of the mass impregnation source material.

Investigations on Fiber-Reinforced Rubcrete for Railway Sleepers

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Parametric Studies Into Creep and Shrinkage Characteristics in Railway Prestressed Concrete Sleepers

Prestressed concrete is very suitable for railway sleepers because of its many superior advantages in high performance, maintenance, sustainability, and construction. Prestressed concrete improved the structural performance which has stronger tensile resistance in comparison with common concrete. However, the long-term performance largely depends on creep and shrinkage responses. The effects of time-dependent phenomena on prestressed concrete sleeper are investigated. In the past, many investigators have proposed various material models to predict creep and shrinkage but those were mostly based on general reinforced concrete concept. The popular uses of prestressed concrete have led to a concern of practitioners whether those existing predictive models could be realistically applied to prestressed concrete. Due to high initial elastic shortening in prestressed concrete, the creep and shrinkage effects should be critically re-evaluated in flexural members. This study investigates and compares the effects of creep and shrinkage on railway prestressed concrete sleepers. The comparison between prediction models underpinned by European Standard Eurocode 2, American Standard ACI, and Australian Standard AS3600-2009 provides the new insight into the time-dependent performance of concrete sleepers installed in various locations. The outcome of this study will help rail track engineers to better design and maintain railway infrastructure, improving asset management efficacy.

Моделирование поведения сегмента рельсовой плети при динамическом воздействии

The paper presents a mathematical model for behaviour of a rail string segment bound by several railway sleepers. The model makes it possible to account for prestressing due to joining rail sections into a string, for anisotropic properties of the rail-and-sleeper assembly, and effects caused by the rolling stock for various initial loading conditions. We considered eleven functions describing wheel--rail contact. These functions enable us to select the most accurate model to describe the effects that vehicles have on railway segments that may differ in design specifics, mechanical properties of materials used, operation modes, and the presence of flaws on the rail tread and wheelset tread. The wave equations used to describe the behaviour of a rail string segment can simulate the process of elastic wave propagation after wheelset contact takes place, which is considerable in the case of high vehicle velocities. The investigation conducted allowed us to plot the wheel--rail interaction force for various contact models. The functions specified make it possible to select the optimum force ratio, taking into account the following: geometrical, mechanical and design parameters of the railway segment; operation modes; and the functions sought for in terms of obtaining the desired maximum contact force, contact duration, and loading and relief times

Effect of steel fiber content on structural and electrical properties of ultra high performance concrete (UHPC) sleepers

This experimental research investigates the structural and electrical responses of ultra-high performance concrete (UHPC) railway sleepers with three different levels of steel fiber content. The UHPC sleepers used in this research were fabricated using a conventional concrete sleeper manufacturing process including the post-tensioning method. They were then evaluated via static bending tests at the rail-seat section and via electrical insulation performance tests. Test results indicate that UHPC sleepers with all three levels of steel fiber content sufficiently meet international requirements. The results from the first cracking load and the load when a crack width becomes 0.05 mm indicate that an amount of steel fiber greater than 1% is required to effectively control early-stage crack development in UHPC sleepers. In addition, the relationship between fiber volume fraction and normalized strength highlights that the material characteristics of UHPC, especially its tensile capacities, correlate strongly with the structural behavior of UHPC sleepers.

Recycling Tire-Derived Aggregate as elastic particles under railway sleepers: Impact on track lateral resistance and durability

The use of recycled Tire-Derived Aggregate (TDA) under railway sleepers has been demonstrated to be a sustainable and effective way to improve the durability and mechanical behaviour of ballasted train tracks. This solution enables the optimization of a track’s vertical performance, as different rubber quantities can be employed depending on track vertical requirements, while recycling a waste material abundantly available. However, before the widespread adoption of TDA, joined to previous studies focused on track vertical behaviour, it is still necessary to assess its influence on the lateral resistance of the track, given the importance of this parameter on the infrastructure’s quality and safety. Thus, the present paper focused on determining the effects on the lateral resistance of the section when employing varying quantities of rubber particles under the sleeper, along with its impact depending on the level of track degradation. For this study, laboratory tests were carried out to simulate realistic traffic conditions on full-scale sections. Results showed that TDA under sleepers could lead to higher lateral oscillations of the track due to the flexibility of the rubber particles, but resulting in similar, or even lower, permanent displacements to those in conventional ballasted tracks, as long as not excessive rubber volumes are applied. Particularly, for the study cases assessed in this article, it was seen that quantities up to around 1500–2000 cm3 (applied under half sleeper) could reduce permanent lateral movements due to dynamic efforts up to 45% in reference to traditional ballasted tracks, while increasing close to 130% the number of loads required to reach a lateral displacement of 10 mm (selected as example of failure criteria).

Process Simulation-Based Design, Mold Construction and Mechanical Performance Evaluation of an Insert-Injection Molded Thermoplastic Polyurethane Part

Abstract This paper presents a case study of simulation-based design and experimental validation of the insert-injection molding process of a complex polyurethane part. The part under consideration is a dowel holder which is a machine element used in the concrete railway sleepers production. A simulation study was carried out to define the relevant mold design options and optimal molding parameters as well as to evaluate their influence on the part's quality indexes. Simulation was performed using the software Moldex3D. The mold was constructed according to the optimization analysis and a batch of pieces was manufactured under the optimized conditions. A mechanical testing experiment – representing the actual service loading conditions – was designed and performed to validate the mold and process designs and the part performance. Simulation and statistical analysis results allowed determining those conditions that lead to a better assembly between the part and the metallic insert and to its structural integrity. The mechanical performance evaluation demonstrated that the part meets all its functional and structural requirements, validating simulation predictions.

Experimental and Numerical Investigations into Dynamic Modal Parameters of Fiber-Reinforced Foamed Urethane Composite Beams in Railway Switches and Crossings

Dynamic behaviors of composite railway sleepers and bearers in railway switches and crossings are not well-known and have never been thoroughly investigated. In fact, the dynamic properties of the full-scale composite sleepers and bearers are not available in practice. Importantly, the deteriorated condition or even the failure of composite materials and components in the railway system can affect the functional limitations or serviceability of the switches and crossings. Especially, it is important to identify the dynamic modal parameters of Fiber-reinforced Foamed Urethane (FFU) composite railway sleepers and bearers so that track engineers can adequately design and optimize the structural components with their superior properties, for benchmarking with the conventional sleepers and bearers. This paper is the world’s first to investigate the vibration characteristics of full-scaled FFU composite beams in healthy and damaged conditions, using the impact hammer excitation technique. This study also determines the dynamic elastic modulus of FFU composite beams from experimental dynamic measurements. It is found that the first bending mode in a vertical plane obviously is the first dominant mode of resonance under a free-free condition. The dynamic modal parameters reduce when damages occur. In this study, finite-element modeling has been used to establish a realistic dynamic model of the railway track incorporating FFU composite sleepers and bearers. Then, numerical simulations and experimental campaigns have been performed to enable new insights into the dynamic behaviors of composite sleepers and bearers. These insights are fundamental to the performance benchmarking as well as the development of vibration-based condition monitoring and inspection for predictive track maintenance.

Analysis of influential parameters for accelerated degradation of ballast railway track

Several various examples of anomalies on ballast railway tracks resulting in accelerated degradation of railway sleepers and ballast layer are described in the paper. Initially, some locations on the Slovenian railway network (SRN) where the degradation occurs were identified. Afterwards, various experimental field investigations (georadar, geometry measurements, measurements of displacements and accelerations on the track, visual assessment of ballast degradation) have been used to measure the characteristics of the railway track and the parameters of its behavior. Based on the experimentally obtained data a simplified numerical model which interconnects the individual measured and estimated parameters of the railway track and also the processes of further degradation has been developed using the artificial neural network. Influential factors for the model’s individual parameters influencing the degradation were identified. The proposed model is able to assist in the evaluation of critical areas on the railway infrastructure and further enables a better understanding of the process and prediction/estimation of degradation of railway sleepers and ballast.

Potential for improving the environmental performance of railway sleepers with an outer shell made of recycled materials

An innovative sleeper with a pre-stressed reinforced concrete inner structure wrapped by an outer shell manufactured with end-of-life tires powder and recycled plastics has been recently designed by the Greenrail company. The external protection is aimed at increasing its lifetime and reducing the maintenance requirements of the railway lines. This study evaluates the environmental performances of this sleeper, under different operational conditions, in comparison with traditional pre-stressed reinforced concrete sleepers, using the Life Cycle Assessment methodology.The assessment includes 16 environmental, energy, and human health impact categories. It is performed considering the following functional unit: 1 railway sleeper, including the fastenings of the rail to the sleeper and the portion of the track bed underneath it, over one year of operation. The evaluated system includes the sleeper production, its installation, the railway maintenance, the sleeper removal at its end-of-life and the final recovery. Moreover, the ballast is included in the analysis considering its mining and transportation to the railway line, the partial replacement during maintenance operations, the removal during a track renewal, and the end-of-life management.For the worst operational conditions of the Greenrail sleeper, the potential impacts between the two sleeper typologies differ by <10% for most of the examined categories, meaning that no significant environmental differences are observed. In the average conditions, impact reductions for the Greenrail sleepers result bigger than 10% for 7 out of 16 categories. Finally, for the best conditions, benefits are in the range 20% - 30% for 11 impact categories.

Preparation and Hydration Mechanism of Low Shrinkage Railway Sleeper Concrete Containing Hot Steaming Steel Slag

The cascade grinding technology was used to product cementitious materials with hot steaming steel slag (SS), iron ore tailings (IOT), granulated blast furnace slag (GBFS), cement clinker (CC) and flue gas desulfurization gypsum (FGDG). The effect of SS on the mechanical properties and autogenous shrinkage of railway sleeper concrete and the mechanism of SS inhibiting the autogenous shrinkage of railway sleeper concrete were studied by means of X-ray diffraction (XRD), flourier transform-infrared spectroscopy (FT-IR), and scanning electron microscope (SEM). The results show that the compressive strength of IOT railway sleeper concrete mixed with SS (SIRSC) is lower than that of IOT railway sleeper concrete unmixed with SS (UIRSC) at the same age. However autogenous shrinkage of SIRSC is significantly lower than that of UIRSC, autogenous shrinkage value of SIRSC at 28 d was 230×10-6, while that of UIRSC was 593×10-6. The hydration mechanism analysis shows that the hydration expansion of a small amount of inert f-CaO and f-MgO phase contained in the SS is the main expansion source to restrain the autogenous shrinkage of SIRSC. The f-CaO and f-MgO phases are highly dispersed after superfine grinding SS is mixed with concrete. In the middle and later stage of concrete hardening, the synergistic growth of ettringite (AFt) and C-S-H gels inhibits the autogenous shrinkage of SIRSC and improves the mechanical properties.

Automatic concrete sleeper crack detection using a one-stage detector

Crack is the most common defect in the railway sleeper inspection work. However, it is still lack of effective algorithms to automatically detect. Two deep learning based methods were popularly used to detect cracks: two-stage methods and one-stage methods. However, they both have their corresponding shortcomings: for the two-stage methods, they are too slow; for the one-stage methods, their accuracy is a problem. In this paper, we propose using a divide-and-conquer strategy of labels to improve the accuracy of the one-stage methods. A one-stage crack detector called CF-NET is proposed by us including two main innovations: a new detection pipeline (CF module) and modified loss function smooth-flat. Finally, the proposed model CF-NET achieves 98.1% accuracy with 17 FPS real-time speed. The accuracy of CF-NET is matched with the two-stage method Faster R-CNN, but faster at least 3 $$\times $$ . The meaning of our work is that we provide a real-time and high-accuracy crack detector to better meet the actual demands of the railway sleeper crack detection task.

Wireless cement-based sensor for self-monitoring of railway concrete infrastructures

In this study, we developed a cement-based wireless sensing system for self-monitoring of concrete infrastructures in a railway environment. The cement-based sensor was developed by inserting electrodes into cement composites incorporating 1.0 vol% multi-walled carbon nanotubes (MWCNTs) as conductive fillers. We designed and fabricated a wireless signal transmission module that can be mounted/dismounted directly on/from the cement-based sensor and a wireless reception module that receives and saves wireless sensor signals. The wireless transmission/reception module was applied to the cement-based sensor, and sensing response during the cyclic compression test was compared with that in a wired environment. The sensing response and the gauge factor in the wireless environment were found to be very similar to those in the wired environment. The loss rate of wireless transmission data was tested according to the distance between the transmitter and the receiver to determine applicability in an actual railway environment. Based on the test results, the distance of stable wireless transmission was evaluated for the open space, railway station, and railway sleeper. When the developed cement-based wireless sensor is applied to the railway sleeper, the wireless sensing system is expected to be used up to 3.5 years when the battery needs to be replaced.

Influence of creosote-polluted substrate on the bioremediation-potential microscopic fungi in the rhizosphere of plants

Wooden sleepers used in railways are impregnated with preservatives with fungicidic and bactericidic properties, which contain a large amount of harmful polycyclic aromatic hydrocarbons (PAHs). The aim of this research was to reveal the type of fungi in the rhizosphere of plants, which tolerate pollutants and can be involved in bioremediation process of creosote-contaminated used wooden railway sleepers. Tagetes patula grown in the substrate with 12.5% creosote impregnated used wooden sleepers chips additive is characterized by the most intensive root development and the biggest population of active fungi, therefore it is recommended for further investigation. Number of colonies of fungi in the rhizosphere of investigated plants decreased in many cases by increasing the amount of sleepers chips additive in substrate, however it was greater in the substrates with creosote treated wooden sleepers chips additives (12.5, 25 and 37.5% wooden sleepers chips) than in the pure substrate and various substrates with additives of pure Pinus sylvestris chips. This is a pioneering study searching for the local fungi species in Lithuania, which can be further utilized for the bioremediation of PAHs.

Damage Detection in Fiber-Reinforced Foamed Urethane Composite Railway Bearers Using Acoustic Emissions

To a certain degree, composite railway sleepers and bearers have been recently employed as a replacement for conventional timber sleepers. Importantly, attributed to the rise in traffic demand, structural health monitoring of track structural members is essential to improve the maintenance regime and reduce risks imposed by any structural damage. A potential modern technique for detecting damage in railway components by using energy waves is called acoustic emission (AE). This technique has been widely used for concrete structures in other engineering applications, but the application for composites is relatively limited. Recently, fiber-reinforced foamed urethane (FFU) composites have been utilized as railway sleepers and bearers for applications in the railway industry. Neither does a design standard exist, nor have the inspection and monitoring criteria been properly established. In this study, three-point bending tests were performed together with using the AE method to detect crack growth in FFU composite beams. The ultimate state behaviors are considered to obtain the failure modes. This paper is thus the world’s first to focus on damage detection approaches for FFU composite beams using AE technology, additionally identifying the load-deflection curves of the beams. According to the experimental results, it is apparent that the failure modes of FFU composite beams are likely to be in brittle modes. Through finite element method, the results were in good agreement with less than 0.14% discrepancy between the experimental and numerical data. The attractive insights into an alternative technique for damage assessment of the composite components will help railway engineers to establish structural monitoring guidelines for railway composite sleepers and bearers.

Experimental and Analytical Investigations of Innovative Composite Materials Using GFRP and Iron Slag for Railway Sleepers

This paper presents further results of experimental testing and analytical investigation on the mechanical properties of fiber composite sleeper in order to evaluate its strength and behavior. Recycled high density polyethylene, iron slag, calcium carbonate, styrene and polyester resin were used with different percentages for manufacturing the proposed composite sleepers. Adding glass fiber ropes and woven laminates as a reinforcement to enhance the flexural capacity of the proposed composite material. Negative bending at center and positive rail seat compression were performed on full scale sleeper. Two full scale sleepers were proof loaded up to 72, 82 KN under negative bending test without any generated cracks. Also, under positive rail seat compression test, first crack occurred at load ranged from 170, 195 KN and failure load happened at load 270, 250 KN. That's mean that the strength of sleeper ranged from 36.39 to 39.30 MPa. This result showed that the proposed composite material of sleeper has sufficient strength to hold mechanical connections. Nonlinear finite element analysis (NLFEA) predicted the behavior up to failure load of the proposed composite sleeper reasonably well. This confirms that the behavior and failure modes of composite sleeper can be well predicted by simplified analysis procedures. Comparison of proposed composite with commercially available composite and timber sleepers' behavior was presented. It is found that proposed composite sleeper performance is near or similar to that of timber and better than that of commercially available composite sleepers. It is concluded that the proposed composite sleeper can be effectively used for timber sleeper replacement.