Behaviour of timber-alternative railway sleeper materials under five-point bending

Abstract

Timber alternative composite sleepers available in the market have very distinct material properties. These differences affect the track performance when used interspersed with timber sleepers in a railway track. This research employs a newly developed five-point bending test to evaluate the failure behaviour and overall structural performance of timber, low-profile prestressed concrete, synthetic composite and engineered plastic sleepers. The Digital Image Correlation technique was used to capture the full-field profile deformation and was validated with strain data at centre and rail seat locations. The results showed that sleepers with bending modulus higher than timber will exhibit a U-shaped or nearly flat bending profile while those with lower modulus will have a pronounced W-shaped bending profile. This effect is more profound on the centre part than the rail seats. Alternative sleepers also have significantly lower rail seat flexural failure load than timber, i.e. low-profile prestressed sleepers (85%), synthetic composites (56%) and lastly, engineered plastic sleepers (42%). Moreover, each sleeper materials exhibited distinct failure mechanisms, i.e., rail seat flexural crack for timber, longitudinal shear cracks along the length for synthetic, permanent deformation at both the rail seat and centre for engineered plastic, and a combination of shear and flexural cracks for the low-profile concrete sleeper. Foam-based composite sleepers also suffers permanent indentation under the rail seat due to high pressure in these areas. The observations and the findings from this research will enrich the understanding of the behaviour of timber alternative composite sleepers, providing useful guidance to railway track engineers, asset owners and sleeper manufacturers.