Michael Burrow

Reliability analysis and maintenance decision for railway sleepers using track condition information

This paper describes the development of a model which can be used to evaluate the reliability of a sleeper system when the sleeper condition is known. Two cases that are of particular interest to the railway industry are investigated. These are the failure of a sleeper system caused by at least two consecutive failed sleepers and by at least three consecutive failed ones, respectively. A model to optimize sleeper maintenance is proposed, which minimizes the number of sleepers restored during immediate maintenance subject to meeting the requirements of reliable and safe sleeper operation. Finally, an example is given to illustrate the model.

A comparison of railway track foundation design methods

Abstract One of the primary functions of the layers that make up the trackbed in a conventional railway track system is to distribute wheel/rail contact forces so that the stresses in the subgrade are of an acceptable level. To ensure that the trackbed layers perform this task adequately, there are a number of design procedures that may be used to calculate an appropriate thickness of the layers. This paper describes and compares five such design procedures from the USA, UK, Europe, and Japan. The comparisons show that the design procedures give large differences in the calculated layer thicknesses which are due to the design methodologies used in each procedure. Consequently, to enable an appropriate design procedure to be adopted for a given set of conditions, it is necessary to have a thorough knowledge of the methodologies employed together with their inherent assumptions.

Developing Formative Assessments for Postgraduate Students in Engineering

This paper outlines an approach taken to produce computer-based formative assessments for two modules in a one-year taught MSc programme in Road Management and Engineering. It presents the aims of the assessments, the taxonomy adopted to ensure that the formulation of the questions addressed learning outcomes related to the development of higher order skills and the choice of software used. Further, the students’ qualitative perception of the assessments is presented together with a discussion on key elements that affected the implementation procedure. This included an understanding of the higher order skills assessed, knowledge of the facilities offered by the software to be used, and the commitment needed to designing, delivering and improving flexible learning materials.

Measurements and simulation of the dynamic responses of a bridge–embankment transition zone below a heavy haul railway line

Chinese Railways is seeking to increase the capacity of many of its heavy haul railway lines by increasing their utilization and at the same time increasing axle loads from 250 to 300 kN. These projected increases in railway traffic may result in accelerated deterioration of the railway network. A vulnerable part of the network, are bridge–embankment transition zones which frequently experience high degradation rates. To investigate the possible implications of the forecasted increases in railway traffic on these structure, a study was carried out which consisted of instrumenting a transition zone to measure accelerations under existing loads and building a three-dimensional finite element dynamic model of the bridge–embankment transition to predict the effects of the anticipated future traffic. The results of the study indicated that commonly used measures of stability, safety and substructure damage would remain within specified limits, despite the projected increases in axle load. However, excessive wear of the wheel and or rail may occur.

A genetic-algorithm-based approach for scheduling the renewal of railway track components

This article describes a procedure that may be used to help synchronize the renewal of railway track components so that the costs of the renewal processes are minimized. To this end a model has been developed to maximize the cost benefit by combining renewal activities for a section of track. As the problem may be considered to be a mixed integer program with constrains, a genetic algorithm (GA)-based approach was used to find the solution. Techniques that may be used to reduce the computational effort required to perform the analysis are also described. The applicability of the approach to optimize the renewal of railway track components is shown by means of an example.

Probabilistic Model for Predicting Rail Breaks and Controlling Risk of Derailment

A model is developed to analyze the risk of derailment of railway vehicles by using a probabilistic approach to model the development of rail defects leading to rail breaks and further to derailment. The risk of derailment is measured by the expected number of rail breaks multiplied by the severity of rail break. To evaluate the risk, four submodels are combined to predict the rate of occurrence of rail defects and breaks. These submodels include one to predict the expected number of weld defects, considering the effect of rail repair; a fatigue model of the rails; and a grinding model to take into account removal of defects through maintenance. The fourth submodel concerns the impact of inspections that are imperfect and of nonconstant frequency. The performance and application of the proposed combined model are illustrated by an example that shows the effectiveness of alternative measures in reducing the risk of derailment. It also shows that the proposed model can be used as a tool for quantitatively evaluating the risk of derailment and for decision making on control of the risk.

Influence of unsupported sleepers on the dynamic response of a heavy haul railway embankment

It is not uncommon for conventional ballasted railway track systems to have unsupported sleepers due the uneven settlement of the ballast or subgrade. In order to investigate the possible implications of unsupported sleepers, this paper describes the development of a dynamic finite element model which includes wheel/rail friction. The developed model was used to investigate the behavior of a section of existing track on the ballasted Shuohuang heavy haul railway line in China. The investigation showed that the maximum displacement of the rails and sleepers increases significantly with the number of consecutive unsupported sleepers. Furthermore, the magnitude of the displacement between an unsupported sleeper and the ballast is likely to greatly exacerbate ballast/sleeper attrition and reduce the fatigue life of the hanging sleeper. An increase in the number of unsupported sleepers amplifies these effects. In addition, it was found that the sleepers adjacent to unsupported ones carry an additional load resulting potentially in their increased wear and additional damage to the substructure. To better understand the wider implications of the presence of unsupported sleepers on track performance, the stability, safety (in terms of derailment) and potential for rail and substructure damage were computed as a function of the number of unsupported sleepers (one to four) and compared with specifications. The results showed that the number of unsupported sleepers has a significant adverse impact on all four measures. However, while the effects on stability, safety and rail damage were within the limits suggested in specifications, even when four sleepers were modeled, the potential for substructure failure within a typical design life of the railway system was identified.

An investigation of subgrade differential settlement on the dynamic response of the vehicle–track system

The construction of non-ballasted slab railway track on existing subgrade soils, or on embankments, is at an early stage of development on Chinese railways. Developing appropriate standards for the allowable amount of subgrade differential settlement that takes into account the dynamic response of the train–track system is one of a number of issues that need to be addressed. To inform the development of such standards, a model based on the theory of vehicle–track coupling dynamics, which considers the weight of the track structure, was created to investigate how differential settlement, in terms of the amplitude, wavelength and position of the settlement along the track, can affect various railway performance-related criteria, including ride quality, stability, vehicle safety and potential damage to the wheel of the train and the rail (i.e. forces at the wheel–rail contact and in the fasteners). The performance of the model was favorably compared with other widely used models described in the literature. The analysis of the study to inform design standards using the developed model demonstrated that the magnitude of the differential settlement influences passenger comfort the most compared with other performance criteria. For the considered CRTS I track, there exists a particular wavelength (8 m for the specific conditions considered) that results in all measures of performance being at their maximum values. Furthermore, the longitudinal position of the settlement waveform in relation to the joints between two concrete slabs, a factor which is not considered in design standards, was shown to influence component deterioration, passenger comfort and safety. The greatest propensity to cause component damage occurs when the beginning or end of the differential settlement waveform corresponds with the inter-slab joint of a concrete base. Accordingly, it is recommended that current design standards should be modified to specify appropriate combinations of amplitude, wavelength and position of the differential settlement to give acceptable measures of performance.

The unmet travel needs of the older population: a review of the literature

ABSTRACT Unmet travel needs can be defined as trips and activities that people need or would like to do more, but for a variety of reasons they are prevented from doing so. This paper provides a critical evaluation of the literature focused on unmet travel needs, with the aim of assessing the scope of existing studies on this topic and better understanding the full context of older people’s mobility. This narrative review identifies how travel needs in later life have been assessed, and the barriers that affect the ability of older people to fulfil these needs. Due to the heterogeneity of older people and differences in research approaches, the analysis of the literature is not conclusive in terms of identifying the real impact of the analysed variables and measures on unrealised mobility. Nevertheless, of the studies analysed, on average at least one-third of older people report unmet travel needs. This situation was found to worsen with age, and women were reported to be more affected than men. The pursuit of leisure, and in particular visiting friends and family, was found to be the activity most associated with unmet travel needs.

A Computational Intelligence Approach to Railway Track Intervention Planning

Railway track intervention planning is the process of specifying the location and time of required maintenance and renewal activities. To facilitate the process, de- cision support tools have been developed and typically use an expert system built with rules specified by track maintenance engineers. However, due to the complex interrelated nature of component deterioration, it is problematic for an engineer to consider all combinations of possible deterioration mechanisms using a rule based approach. To address this issue, this chapter describes an approach to the intervention planning using a variety of computational intelligence techniques. The proposed system learns rules for maintenance planning from historical data and incorporates future data to update the rules as they become available thus the performance of the system improves over time. To determine the failure type, historical deterioration patterns of sections of track are first analyzed. A Rival Penalized Competitive Learning algorithm is then used to determine possible failure types. We have devised a generalized two stage evolutionary algorithm to produce curve functions for this purpose. The approach is illustrated using an example with real data which demonstrates that the proposed methodology is suitable and effective for the task in hand.