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Laboratory investigation on contribution of fastening system and sleeper in longitudinal resistance of ballasted railway tracks
Abstract
Track longitudinal resistance is defined as the resistance generated by sleeper-ballast and rail-sleeper interactions against the imposing forces, which cause longitudinal displacement. This component is one of the important indicators of the continuously welded rail (CWR) track's stability and lateral resistance against buckling. In this paper, the track longitudinal resistance (TLR) and track longitudinal stiffness (TLS) have been investigated to determine the contribution of the fastening system and sleeper in TLR and TLS through laboratory tests and a numerical model. A track panel with one to eight sleepers fastened with 100, 80 and 60 Nm prestressed torqe-force applied to fastening screws was loaded. The average contribution of the sleepers in TLR in the case with a rail-pad for 100 and 60 Nm torque-forces is approximately 30% and 75%, respectively, and the average contribution of the fastening system in the same state is approximately 70% and 25%, respectively.
... In the paper of Safizadeh et al. [27], the track longitudinal resistance (TLR) and track longitudinal stiffness (TLS) have been investigated to determine the contribution of the fastening system and sleeper in TLR and TLS through laboratory tests and a numerical model. ...
Where railway tracks pass through tunnels, the temperature conditions on the railway superstructure are different from those on the connecting track sections. Due to the temperature difference at the tunnel, dilatation movements occur even in cases of construction of continuously welded rail (CWR) tracks. The aim of this research is to determine the magnitude of the movements resulting from heat expansion and the normal force in the rail in the region of the tunnel gates, both in the tunnel and in the sections of track on the connecting earthworks. Ballasted and straight tracks with rail section of 54E1 are assumed in this paper.
... The causal sequence of rail stressing-buckled rail-track buckling has been described and formalized in the form of a mathematical model in a fundamental way, for example, in [1,7,8]. Laboratory studies of the rail-sleeper system in terms of the rail stressing phenomenon are presented, for example, in [9,10]. When it comes to rail stressing, no publications have been found proposing an analytically supported approach to reducing this phenomenon by changing the shape of the rail during production. ...
Highlights
The paper concerns the possibility of using an innovative railway rail structure in a contactless track:
The correct operation of CWR track, due to the occurrence of additional thermal stresses with a value dependent on changes in rail temperature, requires a systematic diagnosis of its condition;
The paper presents the research of longitudinal force load tests for a classic rail and for two cases of an innovative railway rail solution.
The research presented in the paper shows that:
The proposed proprietary design of the rail used for the railroad track can enable the reduction in the longitudinal force occurring as a result of high ambient temperatures;
The use of an innovative rail conception will allow for less steel consumption, which means less emissions into the atmosphere during its production (lower carbon footprint).
Abstract
This paper presents the concept of a modified 60E1 rail dedicated to continuous welded rail (CWR) track. The presented solution is the subject of a patent application by the authors of the publication. The paper describes problems associated with the operation of CWR track and the phenomena of so-called “rail stressing”, i.e., stresses created in the rail due to thermal shrinkage that, in extreme cases, can lead to the buckling of the rail track. Simulation calculations of longitudinal track loads to represent the occurrence of thermal force as a result of the occurrence of high air temperatures were carried out for the constructed conventional model of the railroad track as well as the track with the proposed solutions. A discussion of the simulation results is presented, indicating the possibility for the wider application of both varieties of modified rail.
... Parameters that can depend on the performance of the ballast-sleeper interaction are the aggregate type, density, geometry, humidity, folding, sleeper type, and shape [28]. This resistance of the ballast contributes in large scale to the stability of the track, which means less chances of buckling. ...
Continuously welded rail (CWR) is among the most used railroad systems worldwide with great improvements compared to jointed tracks, including refined ride quality, increased fatigue life of track and rolling stock, and reduced maintenance costs. Rail buckling is one of the key remaining issues for CWRs to further reduce safety hazards and infrastructure deterioration, and save required track retrofit material and efforts. CWR buckling is induced by combined longitudinal, lateral, and torsional forces on the track that are caused by the synergy of rail components, the loading from moving trains, the interaction between track and substructure, and the effect of thermal variations. A systematic evaluation of factors that contribute to rail longitudinal, lateral, and torsional stiffnesses and a thorough investigation of their interactions are critical to understand rail buckling and enhance buckling resistance on CWR. This paper compiles, summarizes, and interprets existing research related to rail buckling resistance, considering parameters such as time-dependent neutral temperature of the tracks, the type of trains, various track resistors (rails, sleepers, and ballasts), and other accessories (anchors and fasteners). A discussion of previous experiments that studied resistors and rail buckling resistances is presented, which guides development of an experimental arrangements as part of an on-going large-scale rail resistance testing project in Edinburg, Tx. The information summarized in this article greatly points out additional needs for experimental and numerical studies, enlightens future research, and provides structured background for prospective improvements on rail buckling and stiffnesses of CWR.
As extreme temperatures increase, there is an increased need to ensure that continuous welded rail (CWR) stresses are more accurately set and better maintained. Therefore, to improve the management of CWR rail stresses and to increase safety through the reduction of buckled track derailments this paper documents the results from a field experimentation program of controlled single rail breaks (SRBs). SRBs were conducted at multiple field site locations to quantify the longitudinal resistance on both timber and concrete sleeper track. Accurate longitudinal resistance values are critical, because if the wrong value is selected, the rail neutral temperature could easily be set to a low value, increasing the probability of a track buckle or rail pull-apart, further compounding the impact of extreme temperatures. The results presented quantify the effect of sleeper and fastener type as well as ballast consolidation, and compare them with relevant results from the literature. From this, it was found that well-maintained concrete sleeper track exhibited a longitudinal resistance greater than the currently recommended value. Further, well-maintained timber sleeper track with anchors on every other sleeper exhibited a longitudinal resistance 44% lower than concrete sleeper track and 30% lower than timber track with anchors installed on every sleeper. Additionally, disturbing the ballast reduced the longitudinal resistance by 15%. Finally, the results indicated that slip was primarily occurring at the rail–sleeper interface for unanchored timber sleepers and at the sleeper–ballast interface for anchored timber sleepers and concrete sleepers.
In this paper, the effect of different thicknesses of Deconstructed Tires Under Sleeper Pads (DT-USP) and different Unconfined Compressive Strength (UCS) values of mother rocks of ballast aggregates were studied in the degradation of railway ballast. For this purpose, in the first step, both static and dynamic bedding modulus of DT-USP's were extracted in the laboratory according to DIN standard requirements. In continuation, the physical and mechanical properties of the three different ballast types taken from Shahriar, Anjilavand, and Kouhin quarries in Iran were obtained via a series of standard lab tests. The UCS of core specimens taken from the mother rocks of the mentioned queries were ranked as low (159 MPa), medium (216 MPA), and high (285 MPa) respectively. Finally, 36 ballast box test experiments with and without the presence of DT-USPs in three thicknesses of 7, 11, and 13 mm were carried out and their results were compared up to 200,000 loading cycles to investigate the cyclic behavior of ballast samples. Experiment results were elicited in the form of settlement, Hardin breakage index (Br), ballast stiffness, and ballast Damping Ratio (DR). The results demonstrate for ballast of Shahriar quarry by increasing of the DT-USP's thickness from 7 to 13 mm, settlement, Br, and stiffness have decreased by 38.4%, 6.9%, and 80.5% respectively and DR has increased by 199.2% while these reported percentages, i.e. settlement, Br, and Stiffness have decreased and DR has increased after strengthening the ballast mother rock in the cases of Anjilavand and Kouhin quarries. On the other side, based on the achieved results for all three categories of ballast strengths, the DT-USP with 11 mm thickness has shown the most suitable performance.
The objective of this study has been to develop an approach to the allocation of an effective maintenance limit for track geometry maintenance that leads to a minimisation of the total annual maintenance cost. A cost model was developed by considering the cost associated with inspection, preventive maintenance, normal corrective maintenance and emergency corrective maintenance. The standard deviation and extreme values of isolated defects of the longitudinal level were used as quality indicators for preventive and corrective maintenance activities. The Monte Carlo technique was used to simulate the track geometry behaviour under different maintenance limit scenarios and the effective limit was determined which minimises the total maintenance cost. The applicability of the model was tested in a case study on the Main Western Line in Sweden. Finally, a sensitivity analysis was carried out on the inspection intervals, the emergency corrective maintenance cost and the maintenance response time. The results show that there is an optimal region for selecting an effective limit. However, by considering the safety aspects in track geometry maintenance planning, it is suggested that the lower bound of the optimal region should be selected.
This paper was devoted to investigating and comparing the dynamic lateral resistance (DLR) of various types of sleepers under lateral impact loading conditions. In this regard, a series of impact tests were conducted on concrete, wooden and steel sleepers in the laboratory, using an inventive pendulum loading test device (PLTD). In loading tests, different masses and triggering angles for the PLTD hammer, the impact load, inertia force and lateral displacement of sleepers were recorded by instrumenting the hammer and sleepers. Furthermore, in order to compare the ballast–sleeper interaction force diagrams in dynamic and static states of loading, a number of single tie (sleeper) push tests (STPTs) were accomplished in a similar circumstance. The laboratory results showed the insufficiency of steel sleeper in providing the DLR against impact loads in comparison with concrete and wooden sleepers. Moreover, the maximum DLR of concrete, wooden and steel sleepers were calculated as 12.2, 5.1 and 2.35 kN, which were considerably higher than their static lateral resistances (SLRs) of 6.2, 3.1 and 1.75 kN, respectively. Assuming an impact coefficient as the DLR/SLR ratio, the values of 1.98, 1.65 and 1.34 were attained for the mentioned sleepers, indicating a very good agreement with the value of 200% suggested by the American Railway Engineering and Maintenance-of-Way Association [AREMA. (2006). Manual for railway engineering. Lanham, MD: Author] for a concrete sleeper.
The Technical Specifications of D.12/H. of Hungarian StateRailways specifies that a continuously welded rail track can be constructed through a bridge without being inter-rupted if the expansion length of the bridge is not longer than 40 m. If the expansion length of a bridge is greater than 40 m, the continuously welded rail should normally be interrupted; a rail expansion joint has to be constructed. The goal of this research is to provide technical solutions of track structureson bridges so a continuously welded rail can be constructed through the bridge from an earthwork without interruption, so rail expansion joints can be omitted.
Track stiffness plays an important role in design and construction stages of the railway track. Smoother travel and longer life time of a track depend on the immutable track stiffness. Nevertheless, changing the track stiffness is inevitable, especially in the transition zone, where the slab track connects to a conventional ballasted track. In this zone track stiffness changes abruptly and it causes differential settlement, which is the main cause for degradation of tracks and foundations at transition zones. A number of remedies have been proposed or used to provide gradual stiffness transition, such as the use of gradual pad stiffness, long sleepers and auxiliary rail in the transition zone. The emphasis of this study is held on the assessment of the behavior of different types of the transition zone under the train moving loads. For that reason, well-known commercial finite-element method package has been used to investigate the dynamic behavior of the transition zone under the passage of high-speed trains. The results of the dynamic analysis are presented and compared in two circumstances; one considering the common improvement in the superstructure by installing auxiliary rails or gradually increasing the length of the sleepers in transition area, and the other by enhancing the substructure through constructing two-part transition section.
The longitudinal resistance of ballasted tracks is due to the longitudinal interaction of rail-fastener and ballast-sleeper. Longitudinal resistance is under the effect of various factors as well as the applied vertical load of the running train over the track structure. In this paper, the effect of vertical load on the longitudinal resistance of the ballasted railway track is experimentally and numerically investigated. First, the longitudinal resistance of a 3-m test panel with five B70 concrete sleepers under 0, 100, 200, and 300 kN vertical load were investigated. Second, a three-dimensional model of the track was developed using Abaqus software. Finally, the results of experiments and modeling were compared and the numerical modeling is validated based on tests’ results. In each test, track longitudinal stiffness (TLS) and track longitudinal resistance force (TLRF) were calculated. According to laboratory results, TLS was increased by 3.36, 3.63, and 3.83 times with increasing the vertical load as 100, 200, and 300 kN, respectively. In the mentioned order the increment values for TLRF were increased 2.1, 2.74, 2.97 times. Likewise, the numerical results of TLRF for the above-mentioned load order illustrated increasing values as high as 2.1, 2.6, and 2.81 times, respectively.
In this paper, a new test method and a measurement technique were proposed to evaluate the track longitudinal resistance (TLR). The three-stage track longitudinal behavior was assessed. The track longitudinal stiffness (TLS) and track longitudinal resistance force (TLRF) were defined based on the analyses of force-displacement curves in each test. Next, the effect of ballast geometry on these two parameters was scrutinized. The resisting mechanism was described. Finally, the share of ballast geometry components in providing the TLS was determined, and contribution percentages were verified by comparing the results with those of previous studies. Nine test conditions were considered. The ballast depth (BD) was set at 30 cm, 40 cm, and 50 cm. In each ballast depth, the TLR was evaluated with and without the crib and shoulder ballasts. The average values of TLS and TLRF were obtained as 22.94 kN/mm and 35.52 kN, and the total share of the base, crib, and shoulder ballast was calculated as 21%, 67%, and 12%, respectively. It was found that the crib ballast had the most impact on the TLS and enhanced the TLS and TLRF up to 4.11 and 3.25 times.
Track buckling is a complicated phenomenon that is caused by a wide range of parameters including the nature of track loading and the lateral and longitudinal resistance of a track. In this paper, the results of a field study on a test track in the Aprin railway station (in the southwest region of Tehran city) are presented to investigate the lateral and longitudinal resistance of the ballasted track. The lateral resistance of the track is measured by using both the single tie (sleeper) push test and the sleeper lateral pull test, and the results of the two methods are found to be compatible. The contributions of the ballast shoulder, crib, and the base part in the total lateral resistance are obtained for the loose and compacted ballast conditions, which showed good consistency with the presented data of literature. The longitudinal resistance is measured by using an innovative setup prepared on the test track. The measured longitudinal stiffness per sleeper is approximately twice of what was measured in the previous studies on track panels. The measured longitudinal stiffness during the unloading process is found to be 40% of the loading stiffness.
In service, railway tracks must withstand the transverse and longitudinal forces that are caused by running vehicles and thermal loads. The mechanical design that adopts any of the track models available in the technical literature requires that the strength of the track is fully characterised. In this paper, the results of an experimental research activity on the sleeper–ballast resistance along the lateral and the longitudinal directions are reported and discussed. In particular, the work is aimed at identifying the strength contributions offered by the base, the ballast between the sleepers, and the ballast shoulder to the global resistance of the track in the horizontal plane. These quantities were experimentally determined by means of an ad hoc system designed by the authors. Field tests were carried out on a series of track sections that were built to simulate scenarios in which the ballast was removed from the crib and/or the shoulder. The results of this study indicate that the strength percent contributions from the crib, the sleeper base, and the shoulder are, respectively, equal to about 50%, 25%, and 25% in the lateral direction, and 60%, 30%, and 10% in the longitudinal direction. Moreover, the comparison of the acquired data with literature results reveals that a detailed knowledge about the testing conditions and the activated ballast failure mechanisms is needed in order to correctly use the test data for the design purpose.
Lateral resistance of railway track is one of the most important parameters in lateral stability. This parameter depends on the conditions of different components of ballasted railway track (such as density of ballast layer, sleeper spacing, type of sleeper, etc.). From this perspective, type of sleeper has an important effect on lateral resistance. However in some conditions, in technical and economical investigations, using a special type of sleeper is not avoidable. In this research, concrete, wooden, and steel sleepers are studied using experimental and numerical analysis by finite element method. According to the experimental results, concrete sleeper B-70 with 2.06 tons has the most lateral resistance among three types of sleepers. Steel and wooden sleepers with the amounts of 1.32 and 1.10 tons are in the next ranking. On the other hand, numerical analysis (modeled according to field conditions) shows that the lateral resistance of concrete, steel, and wooden sleepers is equal to 2.10, 1.36, and 1.15 tons, respectively.
This paper aims at studying the behavior of a railroad track concerning the action of longitudinal forces, targeting the determination of the track-ballast resistance, in a real scale standard track model. This research, was developed at the São Paulo State University, and consisted of a comparative study of track-ballast resistance for railroad tracks built with four different types of sleepers. The first set of sleepers was made of steel, the second one was made of wood, the third one of prestressed-concrete and the fourth one of two-block concrete. In order to carry out this research, four 1600 mm gauge models were built with two TR-68 rails, fastened to seven sleepers by means of elastic fasteners and base plates. The sleepers, all of the same type for each model, were embedded in 0.35 m thick ballast, which was supported by a layer of 30 cm thick compacted soil. The computerized data acquisition system allowed displacement and force values to be obtained in real time. By convention, the maximum longitudinal track-ballast resistance corresponds to a displacement of 15 mm. The prestressed-concrete sleeper setup showed the greatest longitudinal track-ballast resistance per sleeper. The second best performance was obtained by the two-block concrete sleeper setup, followed by the wooden and the steel sleeper setups. The force-displacement curves showed an exponential rise to a maximum shape. The displacement corresponding to the maximum track-ballast resistances were different for each kind of sleeper setup. Correlations between forces and displacements (N= f (d)) were obtained for each type of sleeper. The relative displacements between the rails and sleepers were negligible, showing that the adopted elastic fasteners can bear the forces originated from the displacements of the track setup embedded in the ballast. The measured and analyzed data provided unpublished important parameters for the project of modern and permanent railroads using welded long rails.
Several national guidelines set the non-linear horizontal spring values between the railway track and a railway bridge. In Finland that is not the case. Consequently, one of the objectives of the research funded by the Finnish Rail Administration was to determine the spring values both during the elastic phase in the beginning of displacement and during the plastic phase. These values are needed, for example, to calculate the behaviour of an integral bridge-track structure. In autumn 2007 researchers from the Department of Civil Engineering at Tampere University of Technology performed field tests to measure the track resistance at a railway yard in Mellilä, Finland. The main objectives of the experimental study were 1) to determine the longitudinal track resistance and the load-displacement relation, 2) to compare the measured values to those reported by the International Union of Railways (UIC), and 3) to determine the transverse track resistance and the load-displacement relation. The railway yard had three track test locations, two for longitudinal loading and one for transverse loading. At each location the rails were cut to a length of six to seven metres. During the longitudinal loading the track was loaded with two adjacent hydraulic jacks. Altogether eight longitudinal tests were conducted, three without a vertical load and five with a vertical load. The vertically unloaded track reached the plastic phase due to the axial load. The vertically loaded rails moved axially in their fasteners while the sleepers moved only a little in relation to them. Consequently, the track did not reach the plastic phase. The results of the longitudinal tests were reported as horizontal and vertical displacements and axial rail stresses along the rail at different phases of the axial loading. The results were presented also in tables where initial stage stiffness was presented as an elastic value [kN/m/m] and plastic track resistance in kN/m. The maximum forces per metre affecting the track without a vertical load were 13 to 15 kN/m. The maximum forces per metre affecting the track with a vertical load were 26, 15 and 31 kN/m. During transverse loading the track was loaded horizontally with an excavator bucket. Altogether five loadings with three different arrangements were performed. The loadings clearly caused curvature of the track. The results of the transverse tests were reported as displacements at different locations during different phases of loading.
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