Conversion of AS1085.14 for prestressed concrete sleepers to limit states design format

Premature cracking of prestressed concrete sleepers has been found in railway tracks. The major cause of cracking is the infrequent but high-magnitude wheel loads produced by a small percentage of “bad” wheels or rail head surface defects which are crudely accounted for in AS 1085.14 by a single load factor. The current design philosophy, outlined in AS 1085.14, is based on assessment of permissible stresses resulting from quasi-static wheel loads and essentially the static response of concrete sleepers. In order to shift the conventional methodology to a more rational design method that involves more realistic dynamic response of concrete sleepers and performance-based design methodology, a significant research effort within the framework of the CRC for Railway Engineering and Technologies is currently underway to perform comprehensive studies of the loading conditions, the dynamic response, and the dynamic resistance of prestressed concrete sleepers. 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, and the development of a new limit states design concept. This paper presents the results of the extensive investigations at UoW and QUT aimed at predicting wheel impact loads at different return periods (based on the field data from impact detectors) together with an experimental investigation of the ultimate impact resistance of prestressed concrete sleepers required by a limit states design approach. The paper also describes the reliability concepts and rationales associated with the development of limit states format codes and the issues pertaining to conversion of AS 1085.14 to a limit states design format