Wheel–Rail Impact Loads and Track Settlement in Railway Crossings
Doctoral thesis, 2019
The current work aims to provide a methodology to increase the understanding of track settlement in railway turnouts. Different numerical models are used to simulate the dynamic vehicle--track interaction and predict the wheel--rail impact loads in the crossing panel.The calculated contact pressure between sleepers and ballast is used as input for calculating the track settlement. Both empirical and constitutive settlement models are applied to predict settlement for a large number of load cycles (wheel passages). The material behaviour of the track substructure under repeated loading is investigated using a three-dimensional finite element model. A parameter study is performed to determine the influence of train and track parameters on the impact load generated at the crossing. The investigated train parameters include vehicle speed, lateral wheelset position and wheel profile, while the track parameters are rail pad stiffness, sleeper base area and implementation of under sleeper pads (USP). The study shows that the magnitude of the impact load is influenced more by the wheel--rail contact geometry than by the rail pad stiffness. Among the investigated parameter combinations, the most effective mitigation measures to reduce sleeper--ballast contact pressure are the implementation of USP and increasing the sleeper base area.
material modelling of ballast
Switches and crossings
Chalmers, Mechanics and Maritime Sciences (M2), Dynamics
Simulation of track settlement in railway turnouts
Vehicle System Dynamics,; Vol. 52(2014)p. 421-439
Three-dimensional modelling of differential railway track settlement using a cycle domain constitutive model
International Journal for Numerical and Analytical Methods in Geomechanics,; Vol. 40(2016)p. 1758-1770
Simulation of vertical dynamic vehicle-track interaction in a railway crossing using Green's functions
Journal of Sound and Vibration,; Vol. 410(2017)p. 318-329
X. Li, J. C. O. Nielsen and P. T. Torstensson. Simulation of wheel--rail impact load and sleeper--ballast contact pressure in railway crossings using a Green's function approach. Journal of Sound and Vibration. DOI: http://doi.org/10.1016/j.jsv.2019.114949
Railway turnouts (switches and crossings, S&C) are critical components in the railway system. They provide flexibility in traffic routes by allowing trains to switch from one track to another. To serve this purpose, the turnout consists of both movable and fixed mechanical parts, as well as systems for mechatronics and signalling. In Sweden alone, there are about 14 000 S&Cs in the 16 600 km of railway network.
Turnouts stand for significant contributions to the number of reported track faults and the total cost for railway maintenance. In 2018, the cost for maintenance of turnouts in Sweden was MSEK 530, corresponding to about 10 % of the total railway maintenance cost. Further, it was the railway component that caused most train delays. One of the main drivers for the high maintenance costs is the need to repair and replace switch rails and crossings as these components are subjected to a severe load environment resulting in the degradation of rail profiles and track geometry.
One contribution to the degradation of track geometry in turnouts is differential track settlement. This is a phenomenon where the horizontal level of the supporting track substructure decreases in height over time when subjected to repeated traffic loading. Dynamic wheel–rail contact forces with high magnitudes are generated in the switch and crossing panels due to the discontinuities in rail profiles that are necessary to allow for the rerouting of traffic. Because of the turnout design and the variation in track support conditions, the load transferred into the track bed is not uniform, thus resulting in a variation in settlement along the track and irregularities in track geometry. Poor quality in track geometry induces higher dynamic wheel--rail contact forces that further increase the degradation of rail profiles and track geometry.
The present work aims to provide a methodology to improve the understanding of differential track settlement in railway turnouts. This includes predictions of the high-magnitude wheel--rail impact loads on the crossing generated by passing trains with worn wheel profiles, the distribution of contact pressure between sleepers and ballast, and the accumulated permanent deformation of the track substructure.
Another objective is to provide an accurate and generic simulation environment accounting for the multiple wheel–rail contacts in the crossing panel and considering the high-frequency dynamic interaction between the vehicle and the complete railway turnout. This simulation environment offers a safe and time-efficient complement to expensive field experiments. It also allows for an optimisation of the turnout design. Examples of design aspects considered in this thesis are selection of rail pad stiffness, implementation of under sleeper pads, and design of the bearers (sleepers). A better understanding and mitigation of wheel–rail impact loads and differential settlement in turnouts can also contribute to the reduction of other track degradation mechanisms, such as wear, plastic deformation and rolling contact fatigue of the rails.
Research into enhanced track and switch and crossing system 2 (In2Track-2)
Swedish Transport Administration, 2018-11-01 -- 2021-10-31.
European Commission (EC) (EC/H2020/826255), 2018-11-01 -- 2021-10-31.
Areas of Advance
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: Ny serie nr. 4631
Opponent: Dr Yann Bezin, Head of Railway Research Institute of Railway Research, School of Computing and Engineering, University of Huddersfield, United Kingdom