Chapter 6 - Nonlinear 3D finite-element modeling for structural failure analysis of concrete sleepers/bearers at an urban turnout diamond

Abstract

Railway turnouts are special track systems that are used to divert a train to other directions or other tracks. A featured subset of the turnout system acting as an “intersection” between tracks is commonly called “diamond.” In any modern turnout systems, concrete sleepers/bearers tend to be the dominant components supporting steel works and redistributing dynamic forces onto ballast, and formation. The wheel-rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The field maintenance data have showed that a number of concrete bearers failed under repeated impact loadings, especially under turnout diamonds. This has caused major downtime, high cost of turnout renewal, and reduced reliability of train operations. On this ground, a nonlinear 3D finite-element model has been developed, using commercial finite-element package STRAND7, to evaluate the design methods and to analyze the failure mechanism of the concrete sleepers/bearers at an urban turnout diamond. Track components, that is, steel rails, crossings, and concrete bearers were modeled by solid elements. Contact elements were used between rails, baseplates, and sleepers. Track support elements were modeled by using nonlinear surface pressure, which was correlated back to actual track modulus obtained from field measurements. The finite-element analysis results show that the load action could reach the allowable sleeper/ballast contact pressure under the variation of dynamic loading condition by 20-30%. Such variation could potentially damage the supporting ballast and result in a premature flexural failure mode of concrete bearers. This study recommends a higher impact factor (>2.5) for the design of turnout bearers.