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An investigation is presented of the use of finite element models in the time domain to represent a load moving on a railway track on a flexible ground. A systematic study is carried out to compare different sizes and shapes of finite element mesh, different boundary conditions intended for suppressing reflections from the truncated model boundaries, and different models of soil damping. The purpose is to develop guidance to assist in selecting appropriate finite element models for moving load problems. To prevent reflections from the boundaries of the finite domain two approaches are compared. A 40 m radius hemispherical finite element mesh has been used first with infinite elements around the perimeter. This approach gives good results for a point harmonic load at the centre of the domain but some problems are highlighted when it is used for moving load calculations. An alternative approach has therefore been investigated based on a cuboid mesh. The base was fixed to prevent rigid-body motions of the model and, rather than use infinite elements at the sides, these were also fixed. It is shown that, provided that a suitable damping model is used, the spurious reflections from the sides of the model can be suppressed if the model is wide enough. On the other hand, if infinite elements are used, the calculations are found to be considerably more costly with little added benefit. Different models of soil damping are also compared. It is shown that a mass-proportional damping model gives a decay with distance that is independent of frequency, making it particularly suitable for this application. The length of model required to achieve steady state has been investigated. For a homogeneous 2 half-space it is found that the required length increases considerably in the vicinity of the critical speed, up to 130 m in the present example, whereas for the layered ground a more modest length is sufficient for all speeds.

Train run-throughs on railway switches is a special issue where a train passes through non-trailable railway switches in the wrong direction. This has the potential to causes severe damage and can lead to derailment. In order to undertstand the impact of train run-throughs on railway switches, a three-dimensional (3D) Finite Element (FE) model using explicit analysis has been developed. A detailed switch model has been developed that includes all key components: stretcher bars, supplementary drive, point operating equipment. The model was validated through a specifically designed experiment where switch run-throughs were emulated on a real switch; a good agreement was found between the experimental data and the model. The model has been used to make an assessment of the locking mechanisms. The forces in each component have been assessed and investigated, and the observations of failure location and component during run-through analysis are indicated. During a run-through the supplementary drive rod and stretcher bar encounter a significant plastic deformation, and it is recommended that they should be redesigned in order to avoid plastic behaviour.

Railway switches and crossings constitute a small fraction of linear track length but consume a large proportion of the railway track system maintenance budget. While switch and crossing (S&C) faults rarely prevent trains from running, switches and crossings are the source of many faults and need continual attention. On the rare occasions when trains are prevented from running the cost of the disruption is very high. Condition monitoring of the point operating equipment that moves the switchblades has been in use for many years but condition monitoring of the state of the switch in terms of the support and mechanical damage as trains pass over has only recently started to become possible. To this end, it is important to understand the correlation between S&C faults and sensor data that can detect those faults. This paper assesses some of the data collected from multiple sensors variously positioned on and around a switch and crossing on the UK mainline for a few days of normal train operation. Accelerometers, geophones, and strain gauges were installed at the locations where they were anticipated to be most useful. Forces at the load transfer point on the crossing nose were estimated from two separate strain gauge bridges and possible use of acceleration on the crossing is discussed. Correlations between different data are analysed and assessed and correlation between peak estimated load transfer forces and accelerations is presented. Based on the analysis, conclusions are drawn about the different types of dynamic information around S&Cs that can be obtained from a variety of sensor types.

When trains run on soft ground, large deflections of the track and vibration of the ground can occur when the train speed approaches the speed of Rayleigh waves in the ground. Modelling is helpful to understand and mitigate such critical velocity effects. Here, a three-dimensional time-domain model of a load moving on a track and ground has been developed with the finite element software ABAQUS. This allows nonlinear soil properties to be considered. In order to validate the approach, the vibration of the track and ground induced by a high speed train is compared with those from the site measurements carried out in the late 1990s at Ledsgård, Sweden. Due to the particularly soft soil at this site, it is necessary to adopt a nonlinear soil model due to the large deflections induced by the high-speed train. It is shown that using a linear model based on the small strain soil parameters leads to results which underestimate the displacements. Laboratory test data allow the nonlinear characteristics to be obtained. These have previously been used by various authors in an equivalent linear model. Here this approach is compared with a fully nonlinear model.