Transition zones in railway tracks are locations with considerable changes in the vertical stiffness of the rail support. Typically they are located near engineering structures, such as bridges, culverts and tunnels. In such locations, the vertical stiffness of the track support varies, resulting in amplification of the dynamic forces acting on the track, which ultimately leads to deterioration of the vertical track geometry. Also, differential settlement of the track sub-structure on both sides of the transition contributes to the deterioration of the vertical geometry. The deterioration process accelerates with increase of the operational velocities of the passing trains. Finally, all these result in increase of the maintenance efforts on correction of the track geometry in the transition zones.
To analyze the dynamic behavior of transition zones due to the differential settlement, a finite element dynamic model (using explicit integration) of a track transition zone is developed. The model is also accounting for the effect of hanging sleepers. The model is verified against the measurement results performed using the Video Gauge System (VGS). With the developed model, the differential settlement of ballast and soil has been introduced and the effects of this settlement on performance of the track are analyzed. The resulting wheel forces and the dynamic responses of the track components are obtained and analyzed. Special attention has been paid on the stresses of ballast, which is one of the most vulnerable track components in the transition zones. Finally, conclusions on the effect of the various internal and external factors on the degradation process of the track in transition zones are drawn. With the developed model, the differential settlement of ballast and soil is induced and hence, the effects of the differential settlements can be analysed. The contact forces of wheel-rail interaction and the dynamic response of track components are obtained and analysed. Special attention has been paid on the stresses of ballast which are one of the most vulnerable components in the track transition zones. Finally, conclusions on the effect of the various internal and external factors on the degradation process of the track in transition zones are drawn.