Evaluation of remaining fatigue life of concrete sleeper based on field loading conditions

The main functions of the sleepers in ballasted tracks include transferring loads, securing rail gauge and maintaining railway track geometry. Sleepers can be manufactured using timber, concrete, steel or other engineered materials, but concrete is most commonly used around the world. There are a number of researches on the impact load characteristics and the ultimate load carrying capacity of prestressed concrete sleepers, but research on the fatigue life of prestressed concrete sleepers is very limited. A prestressed concrete sleeper's fatigue damage is mainly due to the repeated loads derived from dynamic wheel-rail interactions, especially when either wheel or rail irregularity is present. Fatigue failure is thus a time-dependent limited state where a concrete sleeper accumulates damage to a failure point over its service life. Concrete sleepers could usually suffer from the dynamic fatigue loading spectra throughout their whole lives, and simultaneously, both static and dynamic load-carrying capacities of concrete sleepers degrades over time. Therefore, a fatigue life assessment is an important and complicated research frontier. Field loading conditions, material time-dependent and dynamic properties, and the dynamic bending moments of prestressed concrete sleepers are quantitatively analysed in this study. This paper also presents an updated fatigue life assessment method for concrete sleepers, and provides a case study based on actual field loading conditions and the time-dependent behaviour of materials. The new insights obtained from this study will improve concrete sleeper maintenance and inspection criteria, and provide a new reference for a rational dynamic design principle of railway concrete sleepers and bearers.