Development of reliability-based design for railway prestressed concrete sleepers

Faster and heavier train services are a driven improvement aspect for leaner and more profitable transport logistics of either passengers or freights. Ballasted rail track has been adopted for modern railways because of its many superior advantages in design, construction, shortand long-term maintenance, sustainability, financial capital and life cycle cost. An important element of the railway track system, which distributes the wheel load to the formation and holds the rail gauge, is the railway sleeper. Field data has raised concerns about design techniques for prestressed concrete (PC) sleepers. Most current design codes for these rely on allowable stresses and material strength reductions. In contrast, premature cracking of PC sleepers has been found in railway tracks. The major cause of cracking is the infrequent but high-magnitude wheel loads produced by the small percentage of irregular wheels or rail-head surface defects; both these are crudely accounted for in the allowable stress design method by an over-conservative single load factor. The current design philosophy, outlined in either Australian or American Standard, is based on the assessment of permissible stresses resulting from quasi-static wheel loads and essentially the static response of PC sleepers. To change the conventional methodology to a more rational and economical design method that involves a more realistic dynamic response of PC sleepers and performance-based design concept, comprehensive studies of the loading conditions, the dynamic response, and the dynamic resistance of PC sleepers have been conducted. This collaborative research has addressed such important issues as the dynamic load spectra applied to the railway track, evaluation of the reserve capacity of typical PC sleepers designed to Australian AS 1085.14, and the development of a new limit states design concept. This paper highlights the development of reliability-based design philosophy and rationales associated with structural limit states; also it presents a limit states design guideline. This approach has been proven to be sustainable by not only saving material costs, but also reducing the waste and the usage of cement, of which the production emits carbon towards global warming.