Life-time monitoring of in service switches and crossings through field experimentation

Abstract

In financial year 2011/2012, Switches and crossings (S&C) cost the UK rail infrastructure owner, operator and maintainer, Network Rail, over £220m in maintenance and £189m in renewals. This represented 24% of the total track maintenance budget, whilst accounting for only 5% of the network mileage. The large costs are due to the complex S&C design that allows network flexibility whilst supporting a vehicle traversing from the switch rail to the stock rail and through the crossing. The motivation for undertaking this research was to understand how S&C reacts to dynamic loading imposed by the vehicles, and to gain a better knowledge of the deterioration of the asset. The understanding and measurement of S&C degradation has never been scientifically measured in real time before, which means that currently the maintenance schedules are cyclic or reactive. The outcome from this investigation could be used to provide a finely calibrated pre-emptive schedule for more effective S&C maintenance and investment. Eight sites were outlined in the design of experiments, of which four were instrumented as part of the first phase of the research in this thesis. High wear and fatigue rates from prior failure statistical analysis showed the need to understand the loading and degradation of S&C. Strain gauges, geophones and accelerometers were used to understand the system reaction to loading, through strain and the sleeper deflection within S&C. The results show that the largest increase in strain over time was at the stock rail with the closed switch rail. The degradation is due to the increased dynamic forces of the vehicle transferring from one line to another. The change in strain indicates that the additional vibrations / frequencies will occur over time, increasing the rate of material change. As speed increases through switches and crossings, a reduction in the strain generated is seen at the gauge locations. This indicates that switches demonstrate lower levels of wear with a higher speed at the locations of the gauges. Degradation of vertical motion of sleepers at the crossing is shown, with no change in the bending strain generated due to the whole asset deforming at a similar rate.

Key words: S&C instrumentation, deterioration, strain gauge, vertical displacement