Keywords: railway, track, railway superstructure, polymeric sleeper, plastic tie, viscoelasticity, track stiffness, sleeper optimization.

Polymer sleepers can combine a stiffness behaviour comparable to timber sleepers with the consistency and lifespan of concrete sleepers, but their specific characteristics and potential advantages should be considered: material viscoelasticity, bending stiffness range, and freedom of shape. Due to viscoelasticity, laboratory tests on polymer sleepers should be performed dynamically, at strain rates applicable to in-track conditions. Cyclic loading should be performed intermittently, introducing pauses between cycling to reduce heating, creep effects and to give track representative results. In analyses, polymer (and timber) sleepers should be considered a beam on an elastic foundation, because of their limited bending stiffness. To accommodate analytical calculations, a simplified calculation method was derived, using a sleeper flexibility factor to account for sleeper bending effects on track deflections. As a result of repeated train loads, a gap arises between the rail seat location and ballast, and the sleeper shapes according to this gap (i.e. beds-in) on every train passage, causing equalization of the contact stresses over the sleeper length and ballast. Optimisation show that balancing the sleeper (prevention of centre-bound) can reduce resilient rail seat displacements by up to 40% without increasing material usage but only utilizing moulding processes allowing the freedom of sleeper shape.

download the full-text of this paper (PDF, 15 pages, 1434 Kb)

go to the previous paper
go to the next paper
return to the table of contents
return to the volume description