Conventional Sleepers Research Articles

Mechanism of cross-level settlements and void accumulation of wide and conventional sleepers in railway ballast

AbstractThe cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses. However, the mechanism of the irregularities initiation and development is unclear. The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track. The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track. However, wide sleepers had higher twist and cross-section level irregularities. The present paper aims to explain the phenomenon by discrete element method (DEM) modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form. The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one. Nevertheless, the cross-level differential settlements are almost the same for both sleepers. The particle loading distribution after all loading cycles is concentrated on the smaller area, up to the half sleeper length, with fully unloaded zones under sleeper ends. Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities. The mechanism of initiation of the cross-level irregularity is proposed, which assumes the loss of sleeper support under sleeper ends. The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes: ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper. The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.

Effect of post-peak flexural toughness on the residual performance of macro synthetic fibre reinforced concrete sleepers subjected to impact loading

Dynamic impact loading is one of the predominant causes of premature failure of concrete railway sleepers, demanding a fair portion of the railway budget. Therefore, macro synthetic fibre reinforced concrete (MSFRC) is suggested as an alternative owing to its improved post-peak flexural capacity, ductility and crack arresting properties. In such adaptation, the residual behaviour after dynamic impacts caused by wheel-rail irregularities governs the reusability and the life cycle of the sleepers. Correspondingly, the residual performance of impacted MSFRC sleepers was evaluated experimentally compared to conventional prestressed concrete sleepers. The residual behaviour of the sleepers was further supported by a series of material-scale flexural experiments. The fracture toughness of MSFRC increased with the crack-opening width because of the tension stiffening associated with fibre bridging. As a result, the residual capacity, stiffness, and toughness of MSFRC sleepers were higher than conventional sleepers, thereby improving their adaptability to the rail network.

Life cycle cost analysis of macro synthetic fibre reinforced concrete for railway sleeper applications

Over the last decade, restructuring of railway systems has resulted in infrastructure management assets demanding increased performance and reliability while adopting budget limits and reduced time available for maintenance. In fact, the current routine and major programmed maintenances are such capital-intensive activities that transport operating companies always attempt to optimise the operational procedures and related assets’ performances towards minimising the costs. Characteristically, the use of macro synthetic fibre reinforcement is proposed to improve the structural performances and service life of the sleeper component. Accordingly, this study addresses the economic feasibility of implementing macro synthetic fibre reinforced concrete (MSFRC) as an alternative material for railway sleeper applications. Through a life cycle costing (LCC) approach, the study evaluates the impact of different asset phases such as acquisition, operation and maintenance, and end-of-life towards a cost comparison of MSFRC with conventional sleeper materials. Hence, the most financially viable option is identified, although key economic parameters are varied to simulate future market values.

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.

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.

Experimental Investigation on Effect of Winged Sleeper on Lateral Resistance of Ballasted Track

Nowadays, the benefits of continuous welded rails and engineers’ tendency toward such types of tracks have increased the importance of railways’ lateral stability. For increasing railways’ stability, lateral resistance development mechanism should be reinforced. One of the methods for reinforcing the passive pressures’ mechanism at sleeper’s end and, therefore, increasing tracks’ durability is the utilization of winged sleepers. In this paper, lateral resistance of conventional and winged sleepers is examined and compared using laboratory and field tests. The tracks’ lateral resistant force was measured by single sleeper push test and track panel loading test. In the laboratory, single sleeper push tests showed 101% increase in lateral resistance in the winged sleeper compared with the conventional sample. In the field test, the test track was divided into three parts, namely conventional sleeper part, winged sleeper part and mixed part. The lateral resistance of each part was measured by LTPT. In the field test, 96% increase in lateral resistance was obtained. Winged sleeper panels and mixed sleeper panels showed 71% and 59% resistance increase, respectively, compared with the conventional panel. By using winged sleepers in tracks, lateral displacements decreased by increasing the shoulder and crib ballast’s volume through the passive pressure mechanism.

Multivariate Heteroscedasticity Models for Functional Brain Connectivity.

Functional brain connectivity is the co-occurrence of brain activity in different areas during resting and while doing tasks. The data of interest are multivariate timeseries measured simultaneously across brain parcels using resting-state fMRI (rfMRI). We analyze functional connectivity using two heteroscedasticity models. Our first model is low-dimensional and scales linearly in the number of brain parcels. Our second model scales quadratically. We apply both models to data from the Human Connectome Project (HCP) comparing connectivity between short and conventional sleepers. We find stronger functional connectivity in short than conventional sleepers in brain areas consistent with previous findings. This might be due to subjects falling asleep in the scanner. Consequently, we recommend the inclusion of average sleep duration as a covariate to remove unwanted variation in rfMRI studies. A power analysis using the HCP data shows that a sample size of 40 detects 50% of the connectivity at a false discovery rate of 20%. We provide implementations using R and the probabilistic programming language Stan.

Benefits of blast furnace slag and steel fibers on the static and fatigue performance of prestressed concrete sleepers

This study investigates the influence of the use of steel fibers and ground granulated blast furnace slag (GGBFS) on the static and fatigue performance of prestressed concrete sleepers. Two series of sleepers with a partial replacement of type III cement by GGBFS (56% by weight of the binder) were tested and the performances of these sleepers were compared to conventional railway sleepers. One series of sleepers were reinforced with the same number of prestressing strands (sixteen strands) as conventional railway sleepers, while the other series of sleepers had a reduced number of strands (fourteen strands). Each series consisted of two types of sleepers with (vf=0.75%) and without steel fibers. Static and fatigue tests causing positive moments at the rail seat section and additional static tests causing negative bending moments at the center section of the sleepers were carried out. The sleepers produced with GGBFS showed improved static flexural and fatigue performance at the rail seat section compared to conventional sleepers with Type III cement. The addition of steel fibers instead of conventional stirrups resulted in increased flexural and fatigue capacity at the rail seat section by controlling crack propagation and by preventing brittle shear failure. The performances of all sleepers at the center section were quite similar. The combination of the reduced number of strands together with steel fibers improves the performance and achieves greater economy.

Sleep duration and resting fMRI functional connectivity: examination of short sleepers with and without perceived daytime dysfunction.

BackgroundApproximately 30% of the U.S. population reports recurrent short sleep; however, perceived sleep need varies widely among individuals. Some “habitual short sleepers” routinely sleep 4–6 hr/night without self‐reported adverse consequences. Identifying neural mechanisms underlying individual differences in perceived sleep‐related dysfunction has important implications for understanding associations between sleep duration and health.MethodThis study utilized data from 839 subjects of the Human Connectome Project to examine resting functional connectivity associations with self‐reported short sleep duration, as well as differences between short sleepers with versus without reported dysfunction. Functional connectivity was analyzed using a parcellation covering the cortical, subcortical, and cerebellar gray matter at 5 mm resolution.ResultsSelf‐reported sleep duration predicts one of the primary patterns of intersubject variance in resting functional connectivity. Compared to conventional sleepers, both short sleeper subtypes exhibited resting fMRI (R‐fMRI) signatures consistent with diminished wakefulness, potentially indicating inaccurate perception of functionality among those denying dysfunction. Short sleepers denying dysfunction exhibited increased connectivity between sensory cortices and bilateral amygdala and hippocampus, suggesting that efficient sleep‐related memory consolidation may partly explain individual differences in perceived daytime dysfunction.ConclusionsOverall, current findings indicate that R‐fMRI investigations should include assessment of average sleep duration during the prior month. Furthermore, short sleeper subtype findings provide a candidate neural mechanism underlying differences in perceived daytime impairment associated with short sleep duration.

Discrete element method of improved performance of railway ballast bed using elastic sleeper

With the development of high-speed and heavy-haul railway in China, problems like insufficient thickness of ballast bed and overlarge track stiffness are obvious. Ballast may break into small particles and their contact status will deteriorate under cyclic loading, resulting in ballast degradation. Discrete element method (DEM) was used to research improved performance of ballast bed using elastic sleeper. Clusters were generated by bonding spheres to model real ballasts, while broken bonds were utilized to distinguish breakage. Two kinds of ballast beds with elastic sleeper and conventional sleeper were established, respectively. After applying cyclic loading to the models, differences of mechanical properties between two models were analyzed by contrasting their dynamic behavior indexes, such as particle contact force, sleeper settlement, vibration velocity and acceleration, breakage characteristic. The results illustrate that compared with conventional sleeper, elastic sleeper increases sleeper settlement, while reduces ballast vibration and contact force between particles, which could depress ballast breakage.

Optimization of Bogie Frame in Indian Railway

Our project was carried out at “Integeral Coach Factory Chennai” at shell division in shop no 21. Our project is entitled as Optimization of Bogie Frame in Indian Railway. The bogie frame is an important and integral member of bogie. The main purpose of the bogie frame is to withstand and/or transfer the various forces acting on it. Each coach under frame requires two Body frame. An attempt to optimize the current conventional sleeper bogie frame and to compare already optimized Fiat bogie frame with the conventional bogie frame is done in this project. Optimization of the conventional sleeper frames is done by making changes in their side structural member’s cross section. Currently the side member in conventional sleeper frames are in shape of I section, which has been converted into channel section. Fiat bogie frames are currently imported in India from Germany. In this project we are recommending the usage of the better bogie frame in keeping the view of increased safety. This comparison will be made by analyzing the behavior of the frames under static load conditions using analysis software. Modeling and analysis will be done using PRO-E and ANSYS respectively. Both the frame will be first modeled using modeling software PRO-E. The solid model will be then imported to ANSYS by saving the file in IGES format. Using the boundary and load conditions, finite element analysis will be done. The results obtained for the frames will be compared to find the optimized model. In total, by adopting better frame which give less deflection and less induced stress value, the safety and operation at higher speed can be insured in addition to reduction of weight that happen in case of Fiat frame.

Design of a new high lateral resistance sleeper and performance comparison with conventional sleepers in a curved railway track by means of finite element models

The lack of lateral resistance in a curved railway track can produce misalignment problems due to the centrifugal forces when the trains pass through. Moreover, most of the times continuous welded rails (CWR) are used in nowadays railway tracks, which can induce the track buckling as a result of thermal loads caused by high temperature gradients. A new sleeper has been designed to provide higher lateral resistance of the track. A finite element model has been developed to analyze the lateral movements of an actual curved track subjected to lateral resistance problems. Then, variations on the finite element model have been made to study the response of the track when different sleepers are used. Thus, the performance of the different sleepers in the modeled track has been analyzed, resulting that the inclusion of the new sleeper in the track can improve the lateral resistance between 39 and 55 % with respect to a track with conventional sleepers made of wood or concrete.

Utilizing the track panel displacement method for estimating vertical load effects on the lateral resistance of continuously welded railway track

The safe operation of continuously welded rail depends on its ability to laterally resist forces generated by vehicles. In recent decades, considerable improvement has been made in increasing the lateral resistance and stability of track. This has been achieved by using elastic rail fastenings, increasing the height and width of the ballast shoulder, and modifying the shape of the sleeper. This paper deals with the effect of the vertical load on the lateral resistance and stability of a railway track using frictional sleepers (with a ribbed underside) in comparison with conventional sleepers (with a flat underside). The test results prove that the vertical load has a significant effect on the increase in the track’s lateral resistance in both types of sleepers; however, it is more effective in the tracks with frictional sleepers.