Reliability-based conversion of a structural design code for railway prestressed concrete sleepers

Abstract

Ballasted railway track is very suitable for heavy-rail networks because of its many superior advantages in design, construction, short- and long-term maintenance, sustainability, and life cycle cost. An important part of the railway track system, which distributes the wheel load to the formation, is the railway sleeper. Improved knowledge 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. However, 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 a single load factor. The current design philosophy, outlined in Australian Standard AS1085.14, is based on the assessment of permissible stresses resulting from quasi-static wheel loads and essentially the static response of PC sleepers. To shift the conventional methodology to a more rational design method that involves a more realistic dynamic response of PC sleepers and performance-based design methodology, comprehensive studies of the loading conditions, the dynamic response, and the dynamic resistance of PC sleepers have been conducted. This collaborative research between several Australian universities has addressed such important issues as the spectrum and the amplitudes of dynamic forces applied to the railway track, evaluation of the reserve capacity of typical PC sleepers designed to AS 1085.14, and the development of a new limit states design concept. This article presents the results of the extensive analytical and experimental investigations aimed at predicting wheel impact loads at different return periods (based on field data from impact detectors), together with an experimental investigation of the ultimate impact resistance of PC sleepers required by the limit states design approach. It highlights the reliability approach and rationales associated with the development of limit states and presents guidelines pertaining to conversion of AS 1085.14 to a limit states design format. The reliability concept provides design flexibility and broadens the design principle, so that any operational condition could be catered for optimally in the design.

Risks of Climate Change with Respect to the Singapore-Malaysia High Speed Rail System

“…To develop this new form of transportation, the Malaysian government needs to ascertain that its new HSR system can cope with and adapt to climate change. In addition, the complexities of climate change and predictions of climate model outputs have introduced an additional measure of uncertainty for railroad operators [1,2]. Extreme weather has affected railway operations and safety, including fatalities, injuries and property damage.…”

Reply to Giannakos, K. Comment on: Toughness of Railroad Concrete Crossties with Holes and Web Openings. Infrastructures 2017, 2, 3

“…Based on the international railway practices, there are two main design principles that have been commonly used to describe or predict the behaviour of railway sleepers (using any type of materials) [4,5]. The traditional design method that has been used for over many decades is based on the 'permissible stress design principle' while the new performance-based design method considers 'limit states design concept' [28,29].…”

Fatigue Life Assessment Method for Prestressed Concrete Sleepers

“…The important functions of sleepers include the following: uniform transfer and distribution of loads from the rail foot to ballast bed, provision of an anchorage for the fastening system, and the restraining of lateral, longitudinal, and vertical movement of the rails (Kaewunruen, 2007;Kaewunruen et al, 2017). The sleepers can be manufactured using timber, concrete, steel, or other engineering materials (Esveld, 2001;Remennikov et al, 2011), and concrete is commonly used around the world.…”

“…Since the permissible stress method does not take into account the dynamic load accurately, while also underestimating the strength of the material, much research has been performed to develop the limit states design approach for concrete sleeper (Wang, 1996;Wakui and Okuda, 1997;Gustavson, 2002). The concept of the limit states design is based on a probabilistic model of the resistance and loads factors and it takes into account a reliable distribution statistic of loads and resistance (Remennikov et al, 2011).…”