摘要 :
In a conventional railway system, timber sleepers have been widely used for ballasted railway tracks to carry passengers and transport goods. However, due to the limited availability of reliable and highquality timbers, and restri...
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In a conventional railway system, timber sleepers have been widely used for ballasted railway tracks to carry passengers and transport goods. However, due to the limited availability of reliable and highquality timbers, and restrictions on deforestation, the ``interspersed" approach is adopted to replace ageing timbers with concrete sleepers. The replacement of ageing timber sleepers is frequently done over old and soft existing formations, which have been in service for so long, by installing new stiff concrete sleepers in their place. This method provides a cost-effective and quick solution for the second and third track classes to maintain track quality. Presently, railway track buckling, caused by extreme temperature, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. According to the buckling evidences seen around the world, buckling usually occurs in ballasted track with timber sleepers and thus there is a clear need to improve the buckling resistance of railway tracks. However, the buckling of interspersed tracks has not been fully studied. This unprecedented study highlights 3D finite element modelling of interspersed railway tracks subjected to temperature change. The effect of the boundary conditions on the buckling shape is investigated. The results show that the interspersed approach may reduce the likelihood of track buckling. The results can be used to predict the buckling temperature and to inspect the conditions of interspersed railway tracks. The new findings highlight the buckling phenomena of interspersed railway tracks, which are usually adopted during railway transformations from timber to concrete sleepered tracks in real-life practices globally. The insight into interspersed railway tracks derived from this study will underpin the life cycle design, maintenance, and construction strategies related to the use of concrete sleepers as spot replacement sleepers in ageing railway track systems. (C) 2021 Elsevier Ltd. All rights reserved.
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In the past several decades, many lateral track buckling studies have been conducted in an effort to determine an allowable safe temperature increase for preventing the occurrence of buckling. The present analysis builds on some o...
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In the past several decades, many lateral track buckling studies have been conducted in an effort to determine an allowable safe temperature increase for preventing the occurrence of buckling. The present analysis builds on some of these studies, but uses recently derived frame-type equations that more accurately represent the response of the rail-tie structure in the lateral plane, The presented analysis takes into account the effects of the torsional stiffness of the rail fasteners, the lateral bending stiffness of the cross-ties, and the track gauge to model more accurately the lateral response of the track panel to temperature increases. It determines effective ways to raise the allowable safe temperature increase, whether by increasing the axial and lateral resistances or by increasing the rotational stiffness of the fasteners. Also, the effect of lateral tie-stiffness on the safe temperature increase is examined.
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Railway tracks are vulnerable to buckling when subjected to temperature increases, as occurs frequently during heatwaves. This paper presents an investigation of the lateral buckling and postbuckling response of railway tracks und...
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Railway tracks are vulnerable to buckling when subjected to temperature increases, as occurs frequently during heatwaves. This paper presents an investigation of the lateral buckling and postbuckling response of railway tracks under thermal loading that includes the restraining effect of the ballast in the longitudinal and lateral directions. The principle of stationary total potential is used to develop the differential equations of equilibrium, as well as the bifurcation buckling from this equilibrium, and these equations are shown to be highly non-linear. The buckling analysis shows that first-order symmetric and antisymmetric modes may govern the buckling, and that for very long members the two buckling loads are the same. The highly non-linear equations for the postbuckling response are solved by making recourse to a shooting technique, and it is shown that following the bifurcation buckling under displacement control the response is initially unstable, followed by a stable branch of the postbuckling equilibrium response. Under thermal loading, which occurs in practice, the response is one of snap-through buckling to the remote stable path, and the solution is shown to capture the localisation of the buckling modes that is observed in practice. The effects of the lateral and longitudinal ballast resistance are quantified, and it is shown that the lateral resistance is predominant when compared with the longitudinal resistance. The influence of lateral track imperfections is also studied, which is shown to have considerable effect on the critical temperature. (C) 2016 Elsevier Ltd. All rights reserved.
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Many of the railway installations seriously suffered from the 1995 Hyogoken-Nanbu Earthquake. It is important to prevent railway installations from being damaged by earthquakes not only to secure the essential role of railway, but...
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Many of the railway installations seriously suffered from the 1995 Hyogoken-Nanbu Earthquake. It is important to prevent railway installations from being damaged by earthquakes not only to secure the essential role of railway, but also to protect the safety of passengers. Prevention of the fatal destruction of infrastructures of railway has been considered fundamental to accomplish these aims and many actual measures have been taken from that point of view. However, even if there is no serious damage done to railway structures, the safety of train operation might be influenced by the deformation or the vibration of track. Characteristics of track deformation and running safety of train under earthquakes so far made clear will be discussed in the paper.
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摘要 :
Presently, railway track buckling, caused by extreme heat, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR...
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Presently, railway track buckling, caused by extreme heat, is a serious issue that causes a huge loss of assets in railway systems. The increase in rail temperature can induce a compression force in the continuous welded rail (CWR) and this may cause track buckling when the compression force reaches the buckling strength. It is important to ensure the lateral stability of railway track in order to tackle the extreme temperature. However, in fact, railway track can be progressively degraded over time resulting in poorer track stability. This includes the larger lateral track misalignment and component deteriorations. This unprecedented study highlights 3D Finite Element Modelling (FEM) of ballasted railway tracks subjected to temperature change considering different ballast fouling conditions. The buckling analysis of ballasted railway tracks considering ballast fouling conditions has been investigated previously. This paper adopts the lateral resistance obtained from the previous single sleeper (tie) push test simulations to the lateral spring model. The influences of the boundary conditions and rail misalignment on the buckling temperature are also investigated. The results clearly show that the ballast fouling may increase the likelihood of track buckling even if the fouled ballast is accumulated at the bottom of the ballast layer. More importantly, the allowable temperature can be reduced up to 50% when the ballast is completely fouled. The results can be used to predict the buckling temperature and to inspect the conditions of ballast. The new findings highlight the buckling phenomena of interspersed railway tracks and help improve the inspection regime of ballast conditions especially in summer to encounter the extreme heat.
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Track lateral stability is one of the most critical considerations for safe and reliable railway infrastructures. With increasing exposures to high temperatures globally, a greater expansion in continuous welded rails can induce a...
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Track lateral stability is one of the most critical considerations for safe and reliable railway infrastructures. With increasing exposures to high temperatures globally, a greater expansion in continuous welded rails can induce a higher risk of track buckling, especially when track defects exist. In ballasted track structures, ballast layer holds sleepers in place and provides lateral support and stiffness to the track. Note that there are several factors influencing the lateral resistance of ballasted railway tracks. However, the effects of the progressive degradation of the ballast on the track's lateral resistance have thus far never been fully investigated. Note that the fouling conditions can be due to the accumulation of ballast breakage or external contamination, such as subgrade intrusion or coal dust, and difficult to inspect in the field. It is evidenced that track buckling can incur even if the railway track and ballast seem to be in a good condition by visual inspection. Therefore, this paper presents a more realistic model to study Single Sleeper (Tie) Push Test (STPT) conditions using the Discrete Element Method (DEM) with the objective to evaluate ballasted track lateral resistance considering different fouling scenarios. Note that coal dust, acting as a lubricant, is considered as a fouling agent. The lateral force-displacement curves of sleepers are analysed. The lateral force is derived from the sleeper-ballast contact forces obtained from three main components: sleeper bottom friction, sleeper side friction, and sleeper end force. The fouling conditions are employed by adapting appropriate model parameters to the ballast layer that represents the fouled ballast condition by coal dust in the DEM simulations. Note that the fouling layer is considered to start from the bottom of the ballast layer and is applied all the way to the top to represent the completely fouled ballast layer condition. The results indicate that fouled ballast can significantly undermine the lateral stability of ballasted tracks by more than about 50%. Track lateral stiffness may be reduced significantly due to fouled ballast layer conditions that cannot be inspected visually in the field. This may reduce track restraint and increase the likelihood of track buckling even though the degraded ballast does not have direct contact with the sleeper. Finally, the study will enrich the development of inspection criteria for ballast lateral resistance and support conditions, improve safety and reliability of rail network, and mitigate the risk of delays due to track buckling leading to unplanned maintenance. (C) 2021 Elsevier Ltd. All rights reserved.
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Last year's hot summer saw an increased number of reported buckling failures of rail track. Similar restrained thermal buckling problems are experienced in concrete road pavements, buried land-based and subsea pipelines, bituminou...
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Last year's hot summer saw an increased number of reported buckling failures of rail track. Similar restrained thermal buckling problems are experienced in concrete road pavements, buried land-based and subsea pipelines, bituminous pavements, parquet and laminate floors, the earth's crust and even ice sheets. For all of these phenomena the underlying mechanics is very closely related, of considerable analytical challenge in its complexity and yet capable of a fairly simple interpretation. The following short note outlines an alternative way of representing the non-linear buckling behaviour that has the merit of being both simple and yet capable of producing explicit analytical representations of the imperfection sensitive buckling loads. Since a similar form of buckling can be exhibited in many commonly employed structural components, for example in sandwich composite panels, this approach may be of interest.
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The use of continuous welded rails (CWR) is increasingly common and is particularly important when it comes to high-speed ballasted tracks. As the longitudinal displacements are restricted in CWR tracks, a considerable rise in tem...
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The use of continuous welded rails (CWR) is increasingly common and is particularly important when it comes to high-speed ballasted tracks. As the longitudinal displacements are restricted in CWR tracks, a considerable rise in temperature induces compressive stresses in the rails that can lead to track buckling. Given the nonlinear behavior of the ballast, usually represented by a linear plastic model, the problem of snap-through buckling may occur, for which only a few nonlinear analysis methods can trace the full response of the track structure. However, these methods fail to yield convergent solutions for problems with thermal loads when implemented in their conventional algorithm. For this reason, a new methodology is presented allowing the calculation of the safe temperature. In addition, some analytical results are also derived for comparison with the numerical results, obtained using three-dimensional finite element beam models provided by ANSYS.
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Continuously welded rails (CWR) are sensitive to thermal and train loads which could destabilize the track and cause buckling. The study of track buckling in the literature, however, is mostly focused on static analysis of CWR tra...
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Continuously welded rails (CWR) are sensitive to thermal and train loads which could destabilize the track and cause buckling. The study of track buckling in the literature, however, is mostly focused on static analysis of CWR tracks under thermal loads. Yet in reality, train dynamic loads in lateral, vertical and longitudinal directions can have a major impact on track buckling behaviour. Moreover, track and wheel defects can aggravate the dynamic train track interaction loads, and reduce the safety against track buckling. The aim of this paper is to have an in-depth comparison of static and dynamic track buckling by employing a multi-body train-track dynamic model and a 3D finite element track model. Various scenarios are elaborated, base scenario dealing with static thermal analysis, dynamic analysis for a steady motion of a wagon with constant speed, dynamic analysis for a wagon with defect free wheels during braking, and dynamic analysis for a wagon with out of round defect wheels during braking. For each scenario, a sensitivity analysis of relevant parameters is also presented. Based on the results, it is concluded that train loads can significantly change the buckling temperature, as well as the safe temperature. For a severe braking of a wagon with out of round wheel defect of order 3, buckling temperature is almost 5.5 degrees C less than that of the static case. The drop for safe temperature in this case is 6.7 degrees C.
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With more than 3,200 km of track, the Spanish high-speed rail network is the longest network in Europe and the second largest in the world after China. Due to its geographical location in southern Europe, the entire network is exp...
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With more than 3,200 km of track, the Spanish high-speed rail network is the longest network in Europe and the second largest in the world after China. Due to its geographical location in southern Europe, the entire network is exposed to periods of elevated temperatures that can cause disturbances and severe disruptions such as rail deformation, or in the worst case, lateral track buckling. In this study, the vulnerability of the current Spanish high-speed rail network is analysed in terms of track buckling failures with a Monte Carlo simulation. Downscaled temperature projections from a range of Global Climate Models (GCMs), under three Representative Concentration Pathways (RCP4.5, RCP6.0 and RCP8.5), were forced in a buckling model and particularized for different segments of the network. With that, the proposed methodology provides the number of rail buckles expected per year by assuming current maintenance standards and procedures. The result reveals significant increase in the occurrence of buckling events for future years, mainly in the central and southern areas of mainland Spain. However, relevant variations are found in different climates and time horizon scenarios in Spain. The anticipated buckling occurrences highlight the vulnerability of the Spanish rail network in the context of global warming scenarios. Overall, the proposed methodology is designed to be applicable in large-scale railway networks to identify potential buckling sites for the purpose of understanding and predicting their behaviour.
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