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The high-speed train travel has become increasingly popular in continental people’s daily life, for it does not only greatly shorten the inter-city travel time without causing traffic congestion but also being environmental more friendly than the conventional car travel. The rapid increase in speed, however, also gives rise to concerns regarding the train-travel safety and increased demand on railway system maintenance. For example, the vibration of rails induced by a passing train would disturb the pavement of ballast materials [1]. According to [1], the ballast would undergo non-elastic deformation under vehicle passage which eventually leads to uneven track settlement and voids under sleepers. Literature has shown that it is very common that sleepers are not well supported by the ballast [2, 3]. The gaps between sleepers and ballast put the safety of train operation in question, and the risk of disaster is believed to be amplified with regards to the increase in the running speed of the train.

The existence of unsupported sleepers, also known as hanging sleepers, has attracted railway engineers’ attention, and quite a few research studies, both experimental and numerical, were carried out to investigate the effect of hanging sleepers on the dynamic response of a train-track system [4-6]. These works mainly assume that the hanging sleepers only appear in a consecutive arrangement. In reality, however, it is common that the sleepers are not aligned in a consecutive manner. In other words, well-bedded sleeper(s) may be surrounded by hanging sleepers. Unfortunately, such scenario has been rarely studied.

In this paper, we present a computational study using the moving element method on the dynamic response of a high-speed train traveling on ballasted tracks accounting for hanging sleepers. This paper will present and discuss the effect of various factors affecting the dynamic response of the high-speed rail system. This includes the speed of the train, the number of hanging sleepers, and the number of well-supported sleepers that are surrounded by the hanging sleepers. Furthermore, the maximum wheel-rail contact force and its occurring location will be discussed.


References:
[1] A. Lundqvist and T. Dahlberg, Load impact on railway track due to unsupported sleepers. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, Vol. 219, 2005, pp. 67-77.
[2] S. Augustin, G. Gudehus, G. Huber and A. Schunemann, Numerical model and laboratory tests on settlement of ballast track. In: System Dynamics and Long-term Behaviour of Railway Vehicles, Track and Subgrade, Berlin, Springer, Vol. 6, 2003, pp. 317-336.
[3] E.-L. Olsson and P. Zackrisson, Long-term measurement results, Final report. Banverket, Technical report 2B/000120/T2/DA for the EUROBALT II project, Sweden, 2002.
[4] J.J. Zhu, A.K.W. Ahmed, S. Rakheja and A. Khajepour, Development of a vehicle-track model assembly and numerical method for simulation of wheel-rail dynamic interaction due to unsupported sleepers. Vehicle system dynamics, Vol. 48, No. 12, 2010, pp. 1535-1552.
[5] J.Y. Zhu, D.J. Thompson and C.J.C. Jones, On the effect of unsupported sleepers on the dynamic behaviour of a railway track. Vehicle system dynamics, Vol. 49, No. 9, 2011, pp. 1389-1408.
[6] J.A. Zakeri, M. Fattahi and M.M. Ghanimoghadam, Influence of unsupported and partially supported sleepers on dynamic responses of train-track interaction. Journal of Mechanical Science and Technology, Vol. 29, No. 6, 2015, pp. 2289-2295.