Effects of under sleeper pads on dynamic responses of railway prestressed concrete sleepers subjected to high intensity impact loads

摘要

Exposed to operational uncertainties, the investment in railway infrastructure is increasing to improve track resilience, to mitigate long-term consequences, to prolong the track service life, and to reduce unplanned maintenance costs and carbon footprint. Under sleeper pads (USPs) have been widely used in several countries as a resilient component placed underneath concrete sleepers. However, it is well-known that, with any imperfection of either wheel or rail, railway tracks usually are incited by impact loading conditions. Accordingly, the application of USPs to mitigate the detrimental impact load consequences on track structure is unprecedentedly highlighted in this paper. Despite the common uses of USPs in various countries in Europe, the dynamic behaviour of the USPs under high-intensity impact loading conditions has not been fully investigated. Note that not only does this study focus on serviceability condition but it also instigates an extreme condition, which can occur when there are coupled effects of short and long wavelength defects (e.g. dipped rail joint coupled with track settlement, switches and crossings, etc.). This paper thus establishes a 3D finite element model of prestressed concrete sleepers with USPs, using LS-Dyna. This study has confirmed field measurement data that the sleepers with USPs tend to have lesser flexures, contact force and impact energy. However, this study is the world's first to reveal that the vibration of sleeper with USPs could be amplified by the large amplitude impact force, which can be induced especially when excited by a high-speed train travelling over short-pitch rail defects, rail joints, coupled defects or crossings. It is also noteworthy that a very stiff pad with a bedding modulus of 1 N/mm(3) can be alternatively used as USPs as recommended by the results obtained. Based on both numerical and field measurement results, it demonstrates that the applications of USPs should be very carefully considered since the USPs could trade off the desired benefits by aggravating dynamic behaviours of sleepers with USPs. The new insights will help track engineers to make appropriate decision on the design and usage of USP.