Abstract:
This work utilizes a Finite Element model to investigate the effect of Under Sleeper Pads (USPs) on the dynamic forces within a railway track, with a specific focus on areas of changing vertical stiffness. The analysis, performed using LS-DYNA software on a model representing thirty sleepers, examines three distinct scenarios: the transition from a soft embankment to a stiff bridge, a track with randomly varying ballast stiffness, and sections with unsupported "hanging" sleepers. For each case, the study calculates and evaluates the wheel/rail contact force and the ballast contact force, comparing results for tracks with no USPs against those with stiff, medium, and soft USPs. The findings show that medium-stiffness USPs are most effective at reducing the peak wheel/rail contact forces caused by stiffness transitions and hanging sleepers, while softer USPs significantly decrease the maximum ballast contact forces by distributing the load over more sleepers and a longer duration. The investigation concludes that while USPs can positively influence track interaction forces, their stiffness must be chosen carefully to achieve optimal performance, as pads that are too stiff have little effect and pads that are too soft can lead to other undesirable oscillations.
