Simulation of vertical dynamic interaction between railway vehicle and slab track

Licentiate thesis, 2018

The usage of slab track for high-speed railway lines has increased in recent decades. In Sweden, the building of new railway lines for higher speed and the selection of track design for such lines are currently being debated. Slab track has, so far, only been applied in small scale in Sweden, which implies that the knowledge and experience of such track are limited. This thesis aims to improve the understanding of the dynamic interaction between railway vehicle and slab track.

The vertical dynamic vehicle–track interaction is simulated in the time domain using an extended state-space vector approach. By using a complex-valued modal superposition technique for the considered linear, time-invariant and two-dimensional track models, the computational cost of solving the associated initial-value problem is reduced. Two generic slab track models, including one or two layers of concrete slabs, are presented. The upper layer of the two-layer slab track model is described by decoupled beams of finite length, while the lower layer is a continuous beam. From the solution of the initial-value problem, wheel–rail contact forces, bending moments in the concrete panel and load distributions on the supporting foundation are evaluated. The presented models are applied to calculate the influences of track design parameters on various track responses. Furthermore, the influences of longitudinal track stiffness gradients and rail imperfections causing periodic and transient excitations are analysed.

Transition zones between the one-layer slab track model and a ballasted track model are analysed. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. From the solution of the optimisation problem, a non-dominated front of the objective functions is obtained illustrating potential for a significant reduction of the dynamic loads. Since the transition zones are optimised neglecting the influence of wheel and rail irregularities, a methodology is proposed to assess the robustness of the optimal design by evaluating its performance when periodic rail irregularities with different combinations of wavelength and phase, relative to the position of the transition, are applied in the model.