Dynamic design guidelines for prestressed concrete sleepers

Current design philosophy, outlined in AS 1085.14, is based on the analysis of permissible stresses resulting from quasi-static wheel loads and essentially the static response of concrete sleepers. In general, cracking can incur when the bottom fibre stress is larger than tensile strength of concrete. Premature cracking of prestressed concrete sleepers has been detected in railway tracks. The major cause of cracking is the infrequent but high-magnitude wheel loads produced by a small percentage of “out-of-round” wheels or railhead surface defects, which are crudely accounted for in AS 1085.14 by a single load factor. Based on the current design method, the cracked sleepers must be replaced by new ones, resulting in a costly maintenance budget each year. The collaborative research between the University of Wollongong (UoW) and Queensland University of Technology (QUT) has addressed such important issues as the spectrum and amplitudes of dynamic forces applied to the railway track, evaluation of the reserve capacity of typical prestressed concrete sleepers designed to the current code AS 1085.14, in order to develop a new limit states design concept that is taking care of the realistic loading conditions and the true capacity of the sleepers. This paper presents a new limit states design concept for prestressed concrete sleepers. The paper also de-scribes the dynamic design guideline and unified design diagrams for railway concrete sleepers. The unified design diagrams have been developed for practical purpose in dynamic design and analysis of railway sleep-ers. The numerical investigations and case scenarios have been performed using a package for dynamic analy-sis of railway tracks, D-Track. The package was an achievement of the collaboration within the framework of the Australian CRC for Railway Engineering and Technologies. The dynamic design guideline covers the various effects on railway tracks due to a wide range of track occupancies, support conditions, vehicle types, rail gauges, and wheel/rail irregularities.