Analysis of a bridge approach: long-term behaviour from short-term response

Transition zones are locations where trackbed support conditions change abruptly, for example from an earth embankment onto a bridge. The track geometry at these sites degrades faster than regular railway track, requiring more frequent and costlier maintenance. To improve understanding of the underlying causes and improve maintenance and design methods, numerical studies are often carried out, although it is computationally expensive and generally not feasible to mimic a sufficient number of loading cycles to represent reality. This paper explores an approach to predicting the long term performance of a bridge approach based on a short term simulation. Three novel performance indicators are suggested, based on existing empirical settlement equations. The dynamic response of a real ballasted railway bridge transition was studied using a Finite Element (FE) model, and the effects of train speed, sub-base soil and under sleeper pads (USPs) were investigated. Results show that both the train speed and the sub-base material affect transition performance. In accordance with previous studies, a stiffer, wedge-shaped backfill was found to mitigate the adverse effects of the support stiffness variation at the bridge approach under idealised conditions. Adding USPs appeared to have a relatively minimal influence on track long term performance.