Characterising native hardwood timber bridges in New South Wales, Australia

During the period 1855-1930, in NSW, Australia many larger timber bridges with spans up to 100 m and overall lengths of 500 m were designed and constructed with local timbers. To justify the safety factors of these structures, the early characterisation of Australian timbers undertaken in the late 1800s is compared with contemporary characterisations. In this paper, a historical background to the early characterisation of Australian hardwoods is contextualised and compared with a more contemporary approach to demonstrate how to assess extant timber bridges. The strength of round structural bridge girders can be inferred from their in-service elasticity, and such knowledge can be incorporated both in new designs and in maintaining those extant. As a girder deteriorates, its modulus of rupture against modulus of elasticity vector will follow a predictable path. By interpreting this path the current and predicted carrying capacity of extant heritage-listed timber bridges can be assessed by loading with a low-mass vehicle precluding the need for proof testing.