Relationships between wheel/rail interface impact and railseat flexural moment of railway prestressed concrete sleepers

Wheel/rail interactions often generate interface impact forces to railway tracks due to the wheel/rail abnormalities. Accordingly, the damage of track components, especially for the concrete sleepers, is often observed and unpredictable as its current design concept relies mostly on the quasistatic behaviour. Limit states design concept then provides more logical entity for the design approach associated with the behaviours of such sleepers. This paper presents the experimental and analytical investigations, in order to evaluate the relationships between wheel/rail impact forces and resultant railseat flexural moment of railway prestressed concrete sleepers. It enables and enhances the methodology to analyse and design for the prestressed concrete sleepers at ultimate limit states. INTRODUCTION Over the years the tracks have been deteriorating due to increased traffic frequency, heavier wheel loads and improper maintenance. Increased wheel load leads to an increasingly detrimental response of the track system, resulting in a premature failure of its components. When increased wheel loading is expected on a given line, it is necessary to evaluate the feasibility all the components can sustain. A major component of railway track structures to distribute loads from rail foot to the ballast bed is railway prestressed concrete sleeper, or so-called ‘railroad tie’ (see Fig.1). In practice, railway concrete sleepers have been suspected for their untapped, reserved strength. It has also been observed that cracks in concrete sleepers are attributed to the infrequent but high-magnitude wheel loads produced by a small percentage of wheel/rail abnormalities. Current design philosophy for prestressed concrete sleepers is based on permissible stress principle taking into account only the static and quasi-static loads, which are inconsistent to the nature of loadings on tracks. Thus, the more rational design method is required on the basis of limit states approach, which will substantially improve the reliability and sustainability of the sleepers in their life cycle. In order to devise a new, innovative limit states design concept, the research efforts are required to perform comprehensive studies of the loading conditions, static and dynamic performance, impact resistance, and risk of the prestressed concrete sleepers [1]. To compliment the main goal, this paper carries out the fundamental concept on the relationships between impact forces applied and resultant bending moments, enabling further studies presented in the companion papers [2,3]. ANALYTICAL STUDIES The analytical studies have been carried out using DTRACK, the package for dynamic analysis of railway tracks, developed under a collaborative research project of the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail CRC). A benchmark study has been done recently by Murray [4]. The further analysis of those data is presented in Fig. 3. Figure 1 Typical ballasted track structure Figure 2 Drop-weight impact machine y = 0.0572x R = 0.8991 y = 0.0413x R = 0.5948 y = 0.0291x R = 0.8509