Page 162 - Handbook of Materials Failure Analysis

158 CHAPTER 6 Failure analysis of concrete sleepers/bearers

impact loads on the railway turnout and its components. The field maintenance
reports have demonstrated that a number of concrete bearers failed under repeated
impact loadings, especially under turnout diamonds. Such an incident has caused
major downtime, high cost of turnout renewal, and reduced reliability of train oper-
ations. As a result, 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. The finite-element modeling of the bearers and the diamond crossover has
shown that the contemporary design methods may underestimate the vertical quasi-
static loads for design of concrete bearers. The finite-element analysis results illus-
trate that the dynamic load action could be at or higher than the allowable sleeper/
ballast contact pressure due to the variation of dynamic loading condition by 20-
30%. It is highly likely that the variation could damage the supporting ballast and
result in a premature flexural failure mode of concrete bearers. As a result, the out-
come of this study recommends that a higher impact factor (>2.5) for the design of
turnout bearers be adopted in railway industry. This adoption can potentially save
millions of dollar from prioritized maintenance and unplanned renewal and from
the penalty costs associated with the turnout diamond failure.

ACKNOWLEDGMENTS
The authors are grateful to Sydney Trains and Transport for NSW for the technical support.
Sakdirat Kaewunruen wishes to thank Australian Government’s Department of Innovation for
supporting his Endeavour Executive Fellowships at Department of Civil and Environmental
Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA, and at Railway
Mechanics Centre, Chalmers University of Technology, Gothenburg, Sweden.

REFERENCES
[1] Andersson C, Dahlberg T. Wheel/rail impacts at a railway turnout crossing. Proc Inst
Mech Eng F J Rail Rapid Transit 2003;212F:135–46.
[2] Remennikov AM, Kaewunruen S. A review of loading conditions for railway track struc-
tures due to train and track vertical interaction. Struct Control Health Monit 2007;15
(2):207–34. http://dx.doi.org/10.1002/stc.227.
[3] Wu TX, Thompson DJ. On the impact noise generation due to a wheel passing over rail
joints. J Sound Vib 2003;267(3):485–96.
[4] Kaewunruen S, Remennikov AM. Dynamic properties of railway track and its compo-
nents: recent findings and future research direction. Insight Non Destr Test Cond Monit
2010;52(1):20–2. http://dx.doi.org/10.1784/insi.2010.52.1.20.
[5] Thompson DJ. Railway noise and vibration. Amsterdam, The Netherlands: Elsevier;
2010.
[6] Kaewunruen S, Remennikov AM. Dynamic flexural influence on a railway con-
crete sleeper in track system due to a single wheel impact. Eng Fail Anal 2009;16
(3):705–12. http://dx.doi.org/10.1016/j.engfailanal.2008.06.002.