Dynamic responses of railway prestressed concrete sleepers with under sleeper pads to high intensity impact loads

Under sleeper pads (USPs) has recently been adopted as a component installed under the concrete sleepers generally to improve railway track resilience. The initial development in Europe, particularly the pilots in Austria, has been benchmarked around the world. In practice, the component has commonly been used in certain applications, mainly to moderate track stiffness in special locations such as turnouts, crossings, and level crossing. In heavy haul operation, the heavier wagons result in sturdier bogie structures, higher unsprung mass, and then higher level of wheel-rail interaction forces. With imperfect wheel or rail, the impact load imposed is rather of high intensity. Statistically, the impact load could exist over 25% of annual track load spectra. Accordingly, the application of USPs to mitigate detrimental impact load consequence on track structure is presented in this paper. A field trial aimed at mitigating rail joint impacts using the USPs with a thickness of 10mm and bedding modulus of 0.2 N/mm3 has been conducted in NSW Australia since October 2011. It was found that the track structure and its heavy-duty components were designed to cater heavy load burden of 30t axle load with rail pad stiffness of 800 MN/m (HDPE pads). This paper will present a 3D finite element model of sleepers with under sleeper pads, using LS-Dyna. The model has been validated by experimental results. Although the studies have found that the sleepers with USPs tend to have lesser flexures, the field data also confirms that a railway track with USPs could experience a large amplitude vibration, especially when excited by a high-frequency impact force. These behaviours imply that the use of USPs may have a trade-off impact that could aggravate dynamic behaviour of sleepers with under sleeper pads.