Keywords: stress analysis, fastening solutions, pre-stressed concrete, sleepers, bearers, finite element analysis, acoustic tensor analysis, material instability. .

The use of such plastic inserts (such as Vossloh dowels and other soft fastening solutions) in pre-stressed concrete sleepers and crossing bearers has become widespread within the United Kingdom, Europe and the rest of the world. This paper uses a bespoke finite-element analysis tool to, for the first time, investigate the stress state around these plastic inclusions specifically focusing on the likelihood of discontinuity development. Most continuum stress analysis methods are over simplistic, in that they assume that fracture occurs in a direction normal to the major (most tensile) principal stress once it exceeds some limiting threshold. However, simply using a limiting stress approach fails to interpret the problem from the viewpoint of material instability analysis. A more physically realistic approach requires examination of the inelastic material stiffness, to determine the direction in which the initial fractures will propagate. This rigorous continuum-discontinuum approach, combined with an efficient instability search algorithm, is used in this paper.

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