The influence of support conditions on short- and long-term track behaviour

Railway track support conditions are known to deeply affect the dynamic performance of vehicle-track interaction, influencing the state of the track system both in the short and in the long term. Exactly how much and how is not precisely understood and the notion of track stiffness, although thought to be a key parameter of the track quality, is currently not being monitored systematically. This paper seeks to analyse the influence on the ballast behaviour of track vertical stiffness and especially its spatial non-uniformity, using available experimental data measured at different sites. Mathematical models are developed and the effectiveness of applying under sleeper pads is also investigated. Finally, an iterative procedure based on Guerin’s settlement law is used to take into account the long-term behaviour of the ballast. Such models can help to understand mitigation solutions as well as predicting track quality evolution over time

Assessing the Role of Longitudinal Variability of Vertical Track Stiffness in the Long-Term Deterioration

The performance of the railway system in terms of dynamic loading is depending mainly on the track support conditions. Usually, the track stiffness is used as the main parameter to describe the support conditions and is defined as the ratio of the load applied to the rail over the vertical rail deflection. Ideally that parameter is constant, but in reality this condition is very unlikely to happen. Therefore, there is non-uniform track loading and non-uniform track deterioration, generally known as differential settlement, leading to a general increment of maintenance and renewal costs. Even if it plays a major role in the system dynamics, it is very difficult to derive a measure of the actual variability of the track stiffness along the railway. There are many techniques to experimentally acquire those values, for example using the Falling Weight Deflectometer (FWD) equipment or the Swedish Rolling Stiffness Measurement Vehicle (RSDV) measuring train. However, these measures are usually very costly and limited in extension. The measuring data may not be long enough to be statistically representative, and thus it is not possible to have a clear correlation between the physical properties of the railway system and its long-term behaviour without running simulations with extended track data. The main aim of the present study is to assess the role of longitudinal variability of the vertical track stiffness in the long-term behaviour of the track degradation. In particular, new sets of track stiffness data which can appropriately reproduce the statistical properties of the real ones will be simulated. Then, the variability of the outputs of the vehicle dynamic model depending on the variability in the inputs will be statistically analysed. This is inspired in past research that highlighted the role of vertical stiffness in track deterioration, but not looking at the actual longitudinal variability of vertical stiffness as a contributing factor

The interaction between railway vehicle dynamics and track lateral alignment

Track geometry deteriorates with traffic flow, thus it needs to be regularly restored using tamping or other method. As the deterioration is mainly in the vertical direction this aspect has been widely studied and models for its analysis developed, however, the lateral deterioration of track is not as well understood. This research aims to develop a method that can be used to analyse and predict the lateral deterioration of railway track caused by traffic flows, and investigate the influences of different railway vehicles, running speeds, traffic types and wheel/rail contact conditions

Virtual testing environment tools for railway vehicle certification

This paper describes the work performed in Work Package 6 of the European project DynoTRAIN. Its task was to investigate the effects that uncertainties present within the track and running conditions have on the simulated behaviour of a railway vehicle. Methodologies and frameworks for using virtual simulation and statistical tools, in order to reduce both the cost and time required for the certification of new or modified railway vehicles, were proposed. In particular, the project developed a virtual test track (VTT) toolkit that is capable of both generating a series of test tracks based on measurements, which can be used in vehicle virtual testing using computer simulation models, and also automatically handling the output results. The toolkit is compliant with prEN14363: 2013. The VTT was used as an experimental tool to analyse cross-correlations between track data (input) and matching vehicle response (output) based on data recorded using a test train. This paper discusses the issues encountered in the process and suggests avenues for future developments and potential use in the context of European cross-acceptance. The VTT offers benefits to the areas of design development and regulatory certification

Dynamic response of vehicle-track coupling system with an insulated rail joint

The dynamic behavior of vehicle and track systems is studied in the presence of an insulated rail joint through a two-dimensional vehicle-track coupling model. The track system is described as a finite length beam resting on a double layer discrete viscous-elastic foundation. The vehicle is represented through a half car body and a single bogie. These sub-systems are solved independently and coupled together through a Hertzian contact model, where the irregularity caused by the rail joint is modelled as a second order polynomial. A parametric study is carried out in order to understand the influence by the main track and vehicle parameters to the P1 and P2 peak forces. Finally, the results in terms of P2 force from the present model have been compared not only with measured values but also with both other simulated and analytical solutions and an excellent agreement between these values has been found

Impact of wheel shape on the vertical damage of cast crossing panels in turnouts

Impact forces generated in the load transfer area of railway crossing panels lead to a range of degradation modes from wear and fatigue of the contacting materials, fatigue of supporting components to ballast/subgrade deterioration. A simplified modelling approach has been developed to first analyse the geometrical problem of the axle rolling through the crossing geometry, and in a second step to predict the vertical dynamic force produce from the interaction between the wheel unsprung mass and the track system. The force is analysed in the frequency domain to estimate the level of damage in different parts of the track system. A parametric analysis of wheel shapes was carried out showing that the axle lateral displacement has a significant influence on the produced level of damage and also that characteristics such as the wheel flange thickness and the equivalent slope in the area of contact also leads to increased damage. It is suggested that such a measure in combination with the simplified algorithms developed here could be used, possibly in combination with track side monitoring system, to highlight traffic instances leading to increased asset damage

Designing future turnouts – where research capabilities meet industry needs

Railway switches and crossings (S&C) are the most costly items for railway infrastructure managers. In the UK over 20% of the planned maintenance and renewal budget for 2014-19 is taken by S&C despite the fact that they only represent a small proportion of the network in terms of km-installation. They are complicated and expensive assets, representing a bottle neck with potential for costly traffic disruptions while attracting a large proportion of the networks failures (e.g. Point Operating Equipment - POE related). Recent European projects (e.g. Innotrack, Sustrail, Drail, Capacity4Rail) and the new H2020/Shift2Rail opportunities for funding are enabling industry and research institutes to work together with infrastructure managers and suppliers to help rethink and redesign a technology which in some aspects remains truly embedded in the middle of last century. What was then a satisfactory design is now being proven beyond its intended design capacity, with ever increasing loads, traffic speed and frequency; while at the same time the window for maintenance and intervention is being drastically narrowed. One fundamental aspect emerging from these previous research programmes is that a lot of the observed failures surrounding S&C have their root cause explained by the discontinuities experienced by the vehicle at S&C. The nature of these is related to the varying geometrical interface between the vehicle wheels and the guiding rails (e.g. load transfer between stock and switch rails), as well as the uneven vertical support offered to the vehicle through the S&C (e.g. uneven loading of long bearers, increased bending stiffness of cast crossings). A large number of reliability issues find their source in the physical vibrations and dynamically amplified loads occurring because of these two facts, this includes some of the gradual deterioration experienced by POE. Research institutes, including the Institute of Railway Research at the University of Huddersfield, have helped develop advanced simulation tools capable of confidently predicting these phenomena and assess contributory factors to degradation modes as well as iteratively work on remedial actions. These might either be small step changes to existing designs or they might be radical concept changes, covering short, medium and long term vision for 2050 railways in Europe. The author will summarise some of the outcome of recent EU projects, give examples of were simulation technology might be used to assess future improvements and radical changes, as well as opportunities for validating these and other wheel-rail interface research projects using advanced testing techniques

Development of a new running gear for the Spectrum intermodal vehicle

The European Union (EU) Seventh Framework Programme (FP7) project Spectrum [12] set out to develop a freight vehicle which would facilitate the exploitation of the low density, high value (LDHV) goods market. Key to the performance criteria for the vehicle were: increased speed to enable mixed running with passenger services; improved ride quality to avoid damage to the LDHV goods; and reduced track damage for longevity and sustainability on increasingly stressed infrastructure. This paper presents aspects of the development of a novel running gear arrangement for the Spectrum vehicle, focussing on the dynamic performance of a Vampire vehicle model and the steps to realising stable running. Finally, the estimated performance of the Spectrum vehicle concept is compared against calculations for a conventional freight wagon with respect to curving, vertical track forces and potential savings in track access charges through implementation of Network Rail’s Variable Track Access Charge Calculator. It was found that the novel Spectrum concept could offer savings in Variable Usage Charges of between 8% and 16% compared to the conventional equivalent

Optimization of support stiffness at a railway crossing panel

Turnouts are a key element of the railway system. They are also one part of the railway system with the highest number of degradation modes and failures for a number of reasons, including dynamic loads generated from non-linearities in the rail geometry and track support stiffness. It is therefore necessary to optimise the performance of the system in terms of its dynamic behaviour taking into account effects on long-term term damage evolution. The main aim of this study is to optimise the rail-pad stiffness in the crossing panel in order to achieve a decrease in the main indicator for ballast settlement, which is ballast pressure. A three-dimensional vehicle/track interaction model has been established, considering a detailed description of the crossing panel support structure. Genetic algorithm has been applied to find the optimum rail-pad combination for a specific case where variation in travelling speed and support conditions have been considered