Understanding track loading requirements to achieve better track design

This paper reviews current track loading requirement (ballasted and ballastless) Typical vehicle-track interaction loads are described along with their influential factors. Limits and influential factors are analysed against statistical evidence from vehicle dynamics measurement. Additional load combinations are presented as potentially relevant for track design. Discussion are made on the potential reduction of load from improved vehicle performance and slab track improved geometry, areas which might bear some benefits in terms of cost reduction for future slab track designs. This paper demonstrates that both vehicle measurement and simulations can provide an important source of information in terms of expected track loading and their limit values to help achieve cost reduction in track design

Development of non-prestressed fibre-reinforced concrete sleepers

Railway sleepers are one of the essential parts of the ballasted railway tracks that provide support to the rails, retain the track gauge, and transfer the rail-seat loads uniformly to the underlying ballast layer. Prestressed concrete (PSC) sleepers are currently the most well-known railway sleepers used by the railway industry. It is estimated that there are around 400 billion prestressed concrete sleepers used in railway tracks worldwide and this number is increasing rapidly. The manufacturing process of the PSC sleeper requires relatively spacious indoor area with expensive machinery. Additionally, this manufacturing process needs heat curing and, therefore, is energy-consuming and pollutes the atmosphere due to the emission of greenhouse gases. This research proposes the application of non-prestressed concrete sleepers as an alternative to the currently used PSC railway sleepers. For manufacturing non-prestressed concrete sleepers, ultra-high tensile strength concrete is needed to resist the significant flexural tensile stresses generated within the sleeper under the design wheel load. In this research study, the reactive powder concrete (RPC) material, also called ultra-high performance fibre-reinforced concrete (UHP-FRC), is utilised for manufacturing the proposed non-prestressed concrete sleeper. In the first stage, the optimal UHP-FRC mix design is determined through experimental testing of trial concrete mixes and a mathematical optimisation algorithm. Then, the standard rail-seat positive moment and the cyclic/fatigue tests are carried out for the prototype UHP-FRC sleepers. The prototype sleeper satisfies the criterion to pass the standard rail-seat static test. However, the fatigue performance of the UHP-FRC sleeper needs further improvements. Indeed, the prototype UHP-FRC sleeper sample failed under fatigue (cyclic) loading after around 200,000 load cycles, while according to the Australian Standard, concrete sleepers are expected to resist at least 3 millions of load cycles

Hybrid numerical-analytical approach for predicting the vertical levelling loss of track geometry in a heavy-haul railway

Post-construction track geometry deterioration is one of the major problems for railway track maintenance. Increasing train velocities, frequencies of railway transport, and axle loads can accelerate rapidly this deterioration due to repeated traffic loadings. Technically, this trend requires higher standards not only for each individual track component but also for the track geometry. An important contribution to the track geometrical deterioration is the ballast settlement, which impacts on the track geometry, specifically on one of the most important track geometrical parameters: the vertical levelling (VL). Any weakness in the railway track support sub-system will affect negatively the railway track vertical profile. It means inferior ride comfort quality and excessive dynamic forces for railway track and vehicles components, resulting inevitably in a less attractive and safe railway. Track geometrical vertical levelling loss (VLL) is defined as a parameter of how much the rail losses its vertical position in the track physical space. The track conditions (smooth, unsupported-sleeper, and uneven tracks) plays a significant role in accelerating the VLL. With an emphasis on the combined degradation of railway track geometric elements and components, an innovative hybrid numerical-analytical approach is proposed for predicting the VLL. In contrast to previous studies, this research unprecedentedly considers the effect of unsupported sleepers (US) and the influence of initial track irregularities (ITI) on VLL under cyclic loadings, elastic-plastic behaviour, and different operational dynamic conditions. The nonlinear numerical models are simulated using an explicit finite element (FE) package, and their results are validated by experimental data. The outcomes are iteratively regressed by an analytical logarithmic function that cumulates permanent settlements, which innovatively extends the effect of track condition on VLL in a long-term behaviour. Additionally, a power function factor innovatively extends the response of US on VLL over a long term. New findings reveal that this innovative numerical-analytical approach can very well predict the VLL long-term performance considering not only the number of cycles or MGT but also different dynamic conditions to support the development of a specification to proceed the investigation of track geometrical degradation. This approach can also support more complex analysis of track geometry elements with a minimal need of carrying out expensive field experiments. Moreover, the proposed methodology can accurately predict both the effect of US and the influence of initial track irregularities on the track geometrical VLL considering different railway operational conditions (and configurations). Finally, this hybrid numerical-analytical approach can be applied to enhance the development of new practical maintenance and construction guidelines to support the maintenance activities in a heavy-haul ballasted railway track for a minimum effect on VLL extending the railway track service life

Composites for Timber-Replacement Bearers in Railway Switches and Crossings

Recent developments in composite materials have resulted in their pilot adoption in railway industry, such as ‘fibre-reinforced foamed urethane (FFU)’, ‘geopolymer concrete’, ‘recycled polymer’, and ‘CarbonLoc composite’. Railway track support systems are critical for safe and reliable operations of railway tracks. There are two types of support structures, which can be designed to be either a slab or a cluster of discrete bearers or sleepers. The choice of turnout support system depends on asset management strategy of the rail operators or maintainers. The aim of this paper is to present the criteria, fundamental and multi-disciplinary issues for the design and practical selection of composite materials in railway turnout systems. As a case study, a full-scale trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, ‘fibre-reinforced foamed urethane (FFU)’ bearers, is presented. Influences of the composite bearers on track geometry (recorded by track inspection vehicle ‘AK Car’ and based on survey data), track settlement, track dynamics, and acoustic characteristics are highlighted in this paper. Comparative studies of composite materials for railway track applications are reviewed and presented in order to improve material design process. This state-of-the-art review paper will also focus on practicality and environmental risks of composite components in railway built environments. It embraces the requirement considerations of new materials for use as safety-critical track elements

A Review of Numerical Models for Slab-Asphalt Track Railways

Higher train speeds and heavier axle loads trigger elevated stresses and vibrations in the track, potentially increasing track deterioration rates and maintenance costs. Alternative track forms made of combinations of reinforced concrete and asphalt layers have been developed. A thorough understanding of the slab and asphalt tracks is needed to investigate track performance. Thus, analytical and numerical models have been developed and validated by many researchers. This paper reviews numerical models developed to investigate railway track performance. The synthesis of major finite element models is described in detail, highlighting the main components and their outputs. For slab track models, the use of a structural asphalt layer within the railway track remains an active research topic and firm conclusions on its efficacy are not yet available. It can be expected that slab track structures will also be affected by train-induced ground vibrations. There is thus a gap in the literature regarding the measurement of dynamic effects on high-speed railway lines, and further research is needed to investigate the dynamic behaviour of slab–asphalt track systems. In this review, novel solutions for mitigating the vibrations in high-speed rail are discussed and compared. The use of asphalt material in railways appears to have beneficial effects, such as increasing the bearing capacity and stiffness of the structure and improving its dynamic performance and responses, particularly under high-speed train loads

Development of numerical and experimental tools for the simulation of train braking operations

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Performance Appraisal of Ballasted Rail Track Stabilised by Geosynthetic Reinforcement and Shock Mats

Rail tracks serve the principal mode of transportation for bulk freight and passengers in Australia. Ballast is an essential constituent governing the overall stability and performance of rail tracks. However, large repetitive loads from heavy haul and passenger trains often lead to excessive deformation and degradation of the ballast layer, which necessitate frequent and expensive track maintenance works. In Australia, the high cost of track maintenance is often associated with ballast degradation, fouling (e.g. coal and subgrade soil) and associated poor drainage, differential settlement of track, pumping of subgrade soils, and track misalignment due to excessive lateral movements. With increased train speeds, the track capacity is often found to be inadequate unless more resilient tracks are designed to withstand the substantially increased vibration and repeated loads. A field trial was conducted on a section of track in Bulli, New South Wales, and findings indicated that the moderately-graded recycled ballast when used with a geocomposite resulted in smaller deformations in both vertical and lateral directions in comparison to uniformly-graded fresh ballast. Installing resilient (shock) mats in the track substructure led to significant attenuation of high impact forces and thereby mitigated ballast degradation. In addition, a series of full-scale field experiment was undertaken on track sections near Singleton, New South Wales to investigate the effects of geosynthetics on the performance of the track built on subgrade soils with varying stiffness. The finding suggested that geogrids can decrease vertical strains of the ballast layer and a few selected types of geogrids can be used more effectively with soft subgrade soils. This state of the art & practice (SOAP) paper describes the results of two unique full-scale field trials, series of large-scale laboratory tests and numerical models to assess the improved performance of ballasted rail tracks using synthetic grids and shock mats

Resilience of ballasted railway tracks exposed to extreme temperature

At present, railway track buckling, caused by extreme heat, is a serious concern that can lead to the huge loss of lives and assets. With increasing exposures to high temperatures globally, a greater expansion in Continuous Welded Rails (CWRs) can induce higher risk of track buckling, especially when track defects exist. Note that track lateral stability is one of the most critical considerations for safe and reliable railway infrastructures. In ballasted railway tracks, ballast layer holds sleepers in place and provides lateral resistance and stiffness to the track. This doctoral thesis aims at investigating the buckling behaviour of ballasted railway tracks under extreme temperatures to clearly understand this vulnerability in order to improve the ballast track’s resilience to extreme temperatures. This doctoral thesis first presents 3D Finite Element Modelling (FEM) of traditional and interspersed railway tracks exposed to extreme temperatures, through realistic modelling. The new findings highlight the buckling phenomena and failure mechanism of interspersed railway tracks, which are usually adopted during railway transformations from timber to concrete sleepered tracks in real-life practices around the world. All possible phenomena observed in the field are captured. The novel in-depth insight unprecedentedly instigates vulnerability and resilience of traditional and interspersed railway track systems exposed to extreme weather conditions. Moreover, the coupling DEM-FEM modelling are developed to deeply investigate the effect of ballast degradation and vulnerability on track lateral stability. This shows that the inspection of ballast profile is essential even though ballast condition seems to be good according to a visual inspection, as the hidden degraded ballast in the bottom layer can still undermine the buckling strength unexpectedly, resulting in increasing vulnerability to track buckling. The obtained results can be used for stability and misalignment management of ballasted railway tracks. The key findings will enhance the development of inspection criteria for 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. Lastly, this doctoral thesis also proposes a new type of resilient material to effectively increase track resilience and reduce the likelihood of track buckling

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

Risk-Based Optimal Scheduling for the Predictive Maintenance of Railway Infrastructure

In this thesis a risk-based decision support system to schedule the predictive maintenance activities, is proposed. The model deals with the maintenance planning of a railway infrastructure in which the due-dates are defined via failure risk analysis.The novelty of the approach consists of the risk concept introduction in railway maintenance scheduling, according to ISO 55000 guidelines, thus implying that the maintenance priorities are based on asset criticality, determined taking into account the relevant failure probability, related to asset degradation conditions, and the consequent damages