Transition zones in railway tracks are locations with an abrupt change in stiffness in the vertical rail supporting structure. These locations are typically located as approaches near engineering structures where there is a sudden change in track substructure. Due to these abrupt changes the dynamic forces of the wheel-rail interaction on the railway track are significantly amplified resulting in the deterioration of track geometry. With higher operational velocities, the degradation process of the track is accelerated. The goal of this research is the investigation of the relationship between vertical acceleration from the axle box of the vehicle bogie (axle box accelerations - ABA) and track geometry changes at transition zones. While most studies investigate the behavior of railway transition zones making use of finite element models, this study focuses on the use of a more computational efficient multi body simulation (MBS) software (VI-Rail flextrack).
After the software is tested and the results validated, different stages of the service life of a transition zone (new - used - heavily used) are simulated. From the results two main conclusion can be drawn. First, the vertical acceleration is able to show the changes in differential settlement and stiffness that are occurring at transition zones. The indicators for these changes are the frequency responses with a wavelength between 1.2 < 𝜆 < 5 meters. This shows that ABA is a powerful non-invasive monitoring technique for long wavelength track irregularities. Second, the multi body simulation software is able to model complex railway tracks. The software shows the same characteristic frequencies as the measurement data does.
The results of this investigation could especially be of interest for asset owners and contractors. By showing that ABA measurements tends to be an effective way of monitoring transition zones, predictive maintenance could be implemented which saves time and high costs.

In recent decades, rail transport has become a popular mean of transportation due to its efficiency and environmental friendliness technology which lead to increasing the axle loads, speed and recurrence of the trains. These enhanced service provisions resulted in new challenges to the sustainability of the railway systems. Insulated rail joint (IRJ) is one of the crucial structural components of the railway track with the function of serving the signaling control by securing the occupancy of the track with one and only train in each divided block. An IRJ includes the application of two joint bars being bolted with the purpose of connecting two adjoining rails. In addition to the insulation layers between the joint bars and the rail, the end post which is positioned between the end-to-end rails, assure the disruptions of current flow between two blocks. The emerge of discontinuity in the stiffness and geometry at IRJs influence the service life of this component due to the introduced high dynamic forces. Subsequently, the IRJ is considered as one of the weak spots of the railway tracks which requires the allocation of great concern in their maintenance. In order to attain understanding of the wheel-rail dynamic interaction at IRJs, various analytical, experimental and numerical studies have been conducted in the past few years. The application of the finite element method (FEM), as a flexible numerical tool, reveals distinct advantages for understanding the behavior of the track structure under the pass-by wheel. This M.Sc. thesis utilizes an explicit finite element analysis to investigate the influence of the sleeper spacing and traffic speed on the impact force and vibration of the track. The FE model includes the detailed demonstration of the rail, joint bars and sleepers while simulated spring and damper elements are preferred to the rail pads and ballast to reduce the complexity of the model. Besides, the detailed illustration of the wheel and axle as well as the effects of the carbody and bogie are considered in the FE model. Based on the parametric studies conducted in this thesis, the impact force as well as the low (0–3kHz) and high (3-10kHz) -frequency vibrations are prominently influenced by the application of non-uniform sleeper spacing and various traffic speed. With considering the two factors; sleeper spacing and traffic speed, a typical statistical approach -Design of Experiment- is implemented to attain an optimized track model with the aim of reducing the impact force and the impact vibration of the track, and thus to reduce the maintenance necessity and noise generation as well as to increase the passenger comfort. The performance of the nominated optimized model has been observed under the application of two typical trains operated on the Dutch railway network. Finally, the conclusions are presented and recommendations for future research are proposed.