Modelling options for ballast track dynamics

Accurate modelling of railway ballasted track dynamics is an important issue for a variety of applications such as the assessment of wheel/rail contact force and critical speed of the vehicle. Track design and assessment against safety and stability criteria can now rely on a number of advanced and validated dynamic models. However, there is a large range of different models that can be used to predict ballasted track dynamics. They vary from fast and simple rigid multi-body models as used in commercial Multibody System approach (MBS) vehicle dynamics calculations, to more complex and expensive three-dimensional (3D) Finite Element (FE) models. This paper investigates the influence of different modelling options up to 2000 Hz for characterising ballasted track dynamics with the aim of providing guidelines for simplifying the model and summarising the advantages and limitations of each option. Five different models, a two-degrees-of-freedom (2 dof) multi-body track model, 2D FE model, 3D FE models with/without consideration of sleeper flexibility, and a 3D FE track model with homogeneous ballast layer are used to represent the ballasted track as a two-layer support and compared against an analytical solution. Consideration is given to the flexibility of the sleepers, inclusion of ballast density and geometry, element discretization level and FE model length. Equivalent parameters to convert input data from one model to another are summarized.