A Petri net asset management framework for railway switches and crossings

Switches and Crossings (S&C) are a fundamental part of any railway network, they allow trains to switch between tracks and to cross over other tracks. They consist of various electrical and mechanical components to which there is a substantial maintenance cost. Failure of an S&C unit can cause significant disruption to traffic and have large financial implications. Therefore, planning their maintenance is of critical importance to railway asset managers. This research proposes an asset management framework, which models the degradation, failure, inspection and maintenance for the S&C unit. The framework comprises nine Petri net sub-models for the S&C component availability and predicts the number of maintenance interventions in a given time period. This can be used to inform maintenance decision making, with the aim of reducing the life cycle cost of the S&C

A reliability study of railway switch and crossing components

Within any railway network Switches and Crossings (S&C) are essential. They allow trains to change tracks, allowing different routes to be selected. Despite their necessity, they generally have a lower reliability than plain line track and are often subject to breakdowns due to the high number of interlinking electrical and mechanical components they contain. Due to their location such as station throats and major junctions, S&C breakdown is generally very disruptive to traffic causing significant delays. Ensuring that S&C units are maintained correctly and minimising their risk of failure, is therefore of critical importance to railway asset managers. This research uses maintenance and failure data to determine probability distributions for the degradation, failure, inspection and maintenance of nine critical components within S&C units. These distributions can then be used within an asset management framework to simulate the expected operational behaviour of an S&C unit under a given set of conditions, allowing more informed asset management decisions to be taken

An alternative approach to railway asset management value analysis: application to a UK railway corridor

Railway networks are complex systems and the management of such systems is a challenging task for railway asset managers. It is their responsibility to ensure that the network delivers the highest level of performance for all stakeholders, whilst adhering to strict safety regulations and financial constraints. Historically, Reliability, Availability, Maintainability and Safety (RAMS) analysis has been used to assess the performance and safety of railway networks, nonetheless there is a lack of consistency in approaches across the industry, with analysis often influenced by the key stakeholders at the time. This research demonstrates an application of an Extended RAMS framework on the UK Railway Network, the Extended RAMS frameworks aims to consolidate various extensions to the traditional RAMS approach in to a single universal approach, which is beneficial to all stakeholders. This paper explores the data currently available within the rail industry and how it can be used to assess the ten metrics within the framework. The final part of the paper explores how the parameters within the ExRAMS framework can be used as the bases of a value analysis, which can be used to assist with asset management decisions

An alternative approach to railway asset management value analysis: framework development

The management of a diverse asset portfolio is a demanding task for railway asset managers. They must ensure that the network delivers a high level of performance for customers and adheres to safety limits. Reliability, availability, maintainability and safety (RAMS) analysis is regularly used to assess the performance of systems, including railway networks. However, currently there are a wide range of different approaches to RAMS analysis in the railway industry. This research seeks to identify and consolidate any potential extensions to the traditional RAMS approach into a single framework: extended RAMS. The framework comprises ten parameters, RAMS and six additional parameters of particular interest to railway asset managers, including capacity and train performance. The framework is intended for use by asset managers to evaluate the attributes and current status of the railway infrastructure and enable comparison between different parts of the network and to evaluate different stakeholder needs

Modelling the stiffness development in asphalt concrete to obtain fatigue failure criteria

The study of fatigue is critical to good usability and durability of asphalt pavements. Inaccurate calculation of the fatigue failure criteria can cause incorrect evaluation of the fatigue performance, leading to inaccurate prediction of the pavement performance and poor maintenance planning. This paper develops a stiffness change tendency method (SCTM) that can be used to model the stiffness evolution in asphalt concrete and determine critical laboratory fatigue failure points to characterise different fatigue damage stages. A logistic model was selected to represent the relationship between the log of the stiffness (E) and the log of the number of cycles (N) obtained from two-point bending (2PB) fatigue tests. The measured stiffness reduction versus loading curves were determined for a range of asphalt mixtures in unaged, aged and moisture damaged conditions by testing at various temperatures and strains. By analysing the derivatives of the logistic model, it is possible to identify three transition points associated with fatigue progression. There is good agreement between the laboratory data and the logistic model proposed, confirming that the logistic model is a good approximation to the stiffness reduction curves. The number of loading cycles associated with the first two transition points in the SCTM (NP1 and NP2) were compared to the value of N1 and Nfm obtained from the energy ratio (ER) method and the ratio of dissipated energy change (RDEC) method, respectively. There are no statistically-significant differences between the SCTM and two energy-based methods, proving that P1 can be viewed as the number of cycles to micro-crack initiation and propagation, and P2 can be defined as the macro-crack generation point (the true failure point). Three different mixtures are subjected to four-point bending (4PB) fatigue tests to demonstrate the applicability of the SCTM with different bitumen types, mixture grades and test methods. The SCTM provides a method to model stiffness development, obtain different fatigue failure criteria and characterise different fatigue damage stages, which could be useful in a simulation of pavement deterioration

RFQ Reaction Cells for AMS: Developments and Applications

The use of anion-gas interactions in Radiofrequency Quadrupole (RFQ) ion guide reaction cells has been shown to be very effective in the elimination of a number of atomic and molecular isobars which have caused difficulties for Accelerator Mass Spectrometry (AMS) measurements [1,2]. This presentation begins with a review of the early work leading to the use of ion-gas reactions and continues with a discussion the recent measurements of the efficacy of this technique, some of which involve fluoride molecular anions. However, the transformation of the equipment used for these proof-of-principle measurements into a system suitable for routine analysis has required attention to aspects of the ion beam transport and gas handling subsystems. For example, the cross sections of the ion-gas reactions, involving both the analyte ion as well as the isobar, are critically dependent on the ion energy which has to be reduced from the ion source energy, usually between 20 and 80 keV, to energies typically in the range of several eV, a task complicated by the energy spread and divergence of beams from AMS sputter sources. With simulations using SIMION 8.1 [3] and tests of promising configurations in a laboratory system, principles for the design of the retarder optics have been developed. These are discussed, along with their planned implementation in a next generation analytical system

The Dalradian rocks of the central Grampian Highlands of Scotland

The central Grampian Highlands, as defined here, are bounded to the north-west by the Great Glen Fault, to the south-west by Loch Etive and the Pass of Brander Fault and to the south-east by the main outcrop of the Loch Tay Limestone Formation. The more arbitrary northern boundary runs north-west along the A9 road and westwards to Fort William. The detailed stratigraphy of the Dalradian Supergroup ranges from the uppermost Grampian Group through to the top of the Argyll Group, most notably seen in the two classic areas of Loch Leven–Appin and Schiehallion–Loch Tay; Southern Highland Group strata are preserved only in a small structural inlier south of Glen Lyon. Major F1 and F2 folds are complicated by co-axial northeast-trending F3 and F4 folding, as well as by locally important north- or NW-trending folds. In the Loch Leven area, nappe-like F1 folds verge to the north-west, whereas to the south-east the major recumbent F1/F2 Tay Nappe verges to the south-east. The trace of the upright Loch Awe Syncline lies between the opposing nappes, but in this region a large mass of late-Caledonian granitic rocks obscures their mutual relationship. Three tectonic ‘slides’ are identified that are certainly zones of high strain but which in part could be obscuring stratigraphical variations. The regional metamorphism ranges from greenschist facies on the western seaboard of Argyll to amphibolite facies in most of the remainder of the region. The study of garnets, together with kyanite and staurolite in the Schiehallion area, has enabled a detailed history of the metamorphism and structure to be unravelled. Stratabound mineralization occurs in the Easdale Subgroup, where there is also evidence of changes of sedimentary environment associated with volcanicity and lithospheric stretching. The region is dissected by a series of NE-trending, dominantly left-lateral, faults, subparallel to the Great Glen Fault, whose movement history is illustrated here by that of the Tyndrum Fault