Methods of predicting the dynamic forces are developed for the cases of
vehicles negotiating vertical and lateral track irregularities.
The bounds of validity of various models of the track are evaluated, from
single degree of freedom, lumped parameter models to the case of a two layered
beam on elastic foundation with a moving dynamic load. For the case of the
lateral response of a vehicle negotiating a track switch, a finite element model of
the track is also developed.
The vehicle model developed for-the vertical case contains all the rigid
body modes of a four axle vehicle for which primary and secondary suspension
can be included with viscous or friction suspension damping. Solution of the
vehicle/track interaction problem for these non-linear models is obtained by
numerical integration, vehicle and track being connected by the non-linear
wheel/rail contact stiffness. The most significant forces are shown to arise from
the interaction of the unsprung mass and track resilience, with the vehicle
modes also making a significant contribution, particularly in friction damped
For the lateral case use is made of an existing model of transient vehicle
behaviour containing the wheel/rail contact non-linearities, to which track
resilience is added in order to predict the track forces. The model is used to
predict the forces which would be anticipated at discrete lateral irregularities
such as those to be found at track switches. Once again the interaction with the
track introduces modes of vibration which are significant in terms of wheel/rail
Comparison is made with experimental results obtained from full scale
tests in the field. In one experiment the vertical track forces due to a range of
vehicles negotiating a series of dipped welds in the track were measured, and in
a second the lateral forces were recorded at the site of an artificially introduced
A particular application of the results is in the prediction of the rate of
deterioration of vertical and lateral geometry due to dynamic forces. This is to
offer an improved understanding of the deterioration mechanism in order to
influence the future design of vehicles and track to reduce maintenance costs.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.