Dynamic train/track/ballast interaction - Computer models and full-scale experiments

A numerical method has been developed by which the vertical dynamic behaviour of a railway track subjected to the loading of a moving train may be investigated. The interacting train and track are both modelled as dynamic systems and the compound train/track system is treated as a whole. In the track model, the rail is treated as a Rayleigh-Timoshenko beam discretely supported, via railpads, by rigid sleepers. Below each sleeper, a rigid mass accounts for the mass of the ballast and those parts of the subgrade that participate in the vibration. The rigid mass is connected to the adjacent masses, to the foundation and to the sleeper by linear springs and viscous dampers. The mass, stiffness and damping of these track components and also the sleeper spacings can be arbitrarily varied. The contact between the wheelsets and the rail is modelled by non-linear Hertzian spring elements. The model permits calculation of deflections, accelerations and forces in various track components, and also enables engineers to investigate how parameters such as train speed, axle load, bogie wheelbase, rail corrugations, wheel flats and so on influence the track and vehicle components. To verify the computational method, two full-scale measurement programmes were carried out on the Swedish West Coast Line in 1993 and 1995. Track parameters are determined by use of measured frequency response functions. Measured and calculated frequency response functions show acceptable agreement. Variations in measured parameter values are discussed.