Dynamic Train-Track Interaction: Linear and Non-Linear Track Models with Property Scatter

Doctoral thesis, 2001

A numerical method was developed to investigate the vertical dynamic behaviour of a railway track subjected to the loading of a moving train. The numerical simulations are carried out in the time-domain with what is known as a moving mass model. This doctoral thesis emphasises especially the influence on the train-track dynamics of the ballast mass (giving rise to inertia forces when a train passes), the influence of the non-linear characteristics of the railpad and of the sleeper support, and the part played by scatter in some track structure properties, such as varying railpad stiffness, varying ballast stiffness and varying sleeper spacing. Full-scale measurements in the field sometimes reveal a track resonance at low frequency (somewhere in the region of 20 to 150 Hz). This resonant behaviour cannot be modelled unless the ballast-subgrade inertia is included in the track model, which is done here. Both laboratory and full-scale field measurements have shown that the load deflection behaviour of the railpad and the sleeper support are non-linear. In a realistic demonstration example, the influence of a state dependent railpad on railpad compression and rail wear was investigated. It was shown that, for a weakly state dependent railpad, the difference in results compared with those obtained for a linear model is negligible. Measurements have also shown that track parameter values are not constant along the track. In fact, very dissimilar properties have been observed even between neighbouring sleepers. It is concluded that, if one wants to investigate the mean values and variations of selected track parameters, a method that does not restrict the variation and distribution of the stochastic variables is, while not necessary, certainly preferable.