The effects of railpad nonlinearity on the dynamic behaviour of railway track

Abstract

Introduction—Railway tracks are commonly constructed with railpads that attenuate the level of vibration and impact transmitted to them from railway vehicles. The stiffness and damping properties of railpads have significant effects on track vibration and forces transmitted to the track substructure and underlying soil. When modelling track dynamic behaviour, it is most common to assume that these properties are linear and homogeneous. However, many studies, including Fenander (1997) 1, Thompson et al. (1998) 2 , Maes et al. (2006) 3, etc., have shown that railpads exhibit pronounced nonlinear behaviour and their properties are dependent on preloads, among other factors like frequency and temperature. Characterising these dependencies is, to a large extent, subjective to a particular data set and is by no means a generic process. Therefore, this process should be carried out with the scope set to particular applications, for e.g. in railway track dynamics, the scope may be to predict the vibration levels in a track for which experimental data is available for the railpads. The preload dependent behavior of a railway track with nonlinear railpads and ballast was studied by Wu and Thompson (1999) 4.

The preload dependent stiffnesses of the railpads were calculated using an equivalent continuous elastic foundation model. These were then used in a discretely supported track model in the frequency domain to obtain the track receptances and decay rates.

In this paper, a similar process is followed but the analysis is carried out in the time domain. In section 2, the stiffness and damping properties of the railpad are characterised for a studded rubber railpad that is commonly used on European railway tracks. Empirical expressions for the static and dynamic stiffnesses for a railpad are derived based on experimental data. A time domain based nonlinear Finite Element model is then developed in section 3 which incorporates the nonlinear railpads. The model consists of a rail that is discretely supported on railpads with preload dependent stiffness and damping under combined static and dynamic load to study the effects of nonl inearity on track dynamics. The model is solved in the time domain using a time integration scheme. Results are presented for the track dynamic response for various preload levels in section 4.

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