Assessing the deflection behaviour of mechanical and insulated rail joints through finite element analysis

Rail joints constitute a weak component in the railway system. In this paper three- dimensional (3D) finite element analyses (FEA) are carried out to study the structural deflection performance of rail joints under a fatigue static test through vertical stiffness assessment. Four different types of 4-bolted joints are investigated under a dynamically enhanced static load including a glued insulated rail joint (IRJ), a dry encapsulated IRJ, a dry non-glued IRJ and a mechanical RJ. The analysis focused on the accurate simulation of the contact types between the interfaces of rail joint components, namely among the rail, fishplate faces, bolts, insulating materials and on the effect of the elastic supporting structure of the joint on the overall joint deflection. The effect of bolt pretension is included in the model. The vertical displacement of IRJs is measured experimentally both by dial gauges and Video technique both in laboratory and in field. The numerical modelling investigated the effect of different contact types on the interfaces of the rail joint components during the performance of fishplates, and of the rail in the vicinity of the RJ under a given support condition. The vertical displacement of the rail joint were presented and assessed against specified endurance tests’ limits and field measured deflection values that validate the model. Stress distribution in the fishplates was presented that could allow the calculation, through a stress-life approach, the fatigue life of the fishplates and consequently of the joints due to repeated wheel passage. A comparison of the performance of the aforementioned RJ types is included. The results indicate this FE model to be practical to be routinely applied to industry, as it was used in UK Rail industry study to allow designers to optimise life expectancy of IRJs

The application of track deflection measurements made by the video gauge

This paper presents direct track deflection data measured by the Video Gauge (VG), (a Digital Image Correlation method) that is used to remotely determine track stiffness characteristics. Two cases are discussed. Firstly, the deflection performance of two novel ballastless trackforms are coupled with an analytical model to assess their stiffness properties for known train loads. Secondly, the performance of a bridge transition is evaluated under live train passages by the VG; the traffic loads are assumed based on train type to allow track stiffness interpretation from a number of train passes. A track deflection bowl is assessed to show the performance of the transition. The paper initially discusses the DIC technique and the importance and assessment of track stiffness. It then presents the VG deflection data, the global support stiffnesses and deflection bowls. It shows these novel methods to be consistent with other approaches of track stiffness evaluation. It concludes on how this methodology can be utilised in the railway industry for assessing trackbed performance of critical zones without the need for track possessions

Potential for external reinforcement of insulated rail joints

This paper aims to investigate alternative ways of reducing the deterioration and failure of railway track insulated rail joints (IRJs). Joints deteriorate faster than rail initially due to the structural discontinuity present. This weakness results in both extra displacement as a consequence of applied load and the dynamic force that results as a consequence. Over time this situation worsens as the impacts and applied stresses both damage and soften the ballast and supporting subgrade under the joint. This study initially presents a static finite element model designed to simulate the mechanics of IRJs and a comparison between plain rail and a suspended insulated rail joint under various support stiffnesses. Product design options of reinforced IRJs are then chosen as input variables of the model. Results of the model are compared with field and laboratory data acquired via the Video Gauge, which is a new high-resolution optical measurement technique. Results show that the use of strap rails or more robust I-beam sections in the vicinity of the IRJ to stiffen the support structure can significantly reduce the displacement and the subsequent dip angle seen at an IRJ. This potentially presents a means of improving the IRJ behaviour. Their impact becomes more significant for soft support conditions. Although these results are indicative for new IRJ conditions, field measurements indicate that the magnitude of deflection of IRJs is a result of the structural discontinuity of the rail, the dynamic P2 force, the wheel condition, the degraded ballast and it significantly increases with time under repeated load. Thus, it is recommended that careful field implementation and testing will indicate the effect of an external enhancement on the timely degradation of insulated rail joints

Applicability of video gauge for the assessment of track displacement

Numerous techniques have been used for the measurement of the track displacements and consequently the assessment of track stiffness. Some of the most commonly employed are linear variable displacement transducers (LVDTs), geophones and older video monitoring techniques based on Particle Image Velocimetry (PIV). In this paper, the application of the Video Gauge, a relatively new technique, is investigated. This technique can be seen as a quick and reliable way to capture data of high quality and resolution, which can be directly employed for the evaluation of track displacement and hence stiffness.The Video Gauge is used at three different track sites measuring different ballasted track components under various train speeds and types