About 30% of Australia’s 10,000-plus timber bridges are in poor condition, but instead of replacing decades-old hardwood trusses with concrete, the answer could lie in replacing long-span hardwoods, which are in critically short supply, with new and emerging types of timber technologies like stress-laminated timber.
That is according to Professor Keith Crews, an internationally recognised expert who has published over 350 papers and technical reports on the use, assessment, safety, and reliability of bridges and timber structures and buildings: “There are (numerous types of) timber-based technologies that can be used to meet the requirements of the national (AUSTROADS) bridge design code.”
Published as part of AS 5100.9:2017, Bridge Design, Part 9: Timber, the code sets out the requirements for the design and construction of timber bridges and associated structures, including members that contain steel connectors and the design of stress-laminated timber (SLT) decks and bridges.
Over the past 25 years, safe, strong, durable timber bridges have enjoyed a revival—and not just for environmental reasons. Better connectors and the ease and speed of off-site construction have made timber a compelling alternative to precast concrete, which has seen many countries experience serious structural issues with concrete bridges that are less than 50 years old.
“Although a girder in a traditional timber girder bridge built in Australia may have had an average life expectancy in the order of (just) 30 years, and may not have been able to carry even T44 vehicular loadings when assessed with limit state design methods, bridges designed in accordance with this Standard are designed for the full 100-year design life and for the full vehicular loadings as outlined in AS 5100.2”
Foreword to AS 5100.9:2017, Bridge Design, Part 9: Timber – which can be downloaded from Standards Australia’s website.
Why replace bridges when we can repair and restore them instead?
On Monday, Wood Central spoke to the directors of Timber Restoration Services, which plays a key role in repairing and restoring bridges. “When built and maintained properly, wooden bridges can last 200 years,” pointing to the Bodoga Wooden Bridge in Sri Lanka, which has survived since the 16th Century, and numerous 200-year-old bridges in the United States.
Armed with the rights to use 42 patents in timber restoration and reinforcement, they argue that “structures shouldn’t be destroyed just because they’re old. Like the trees from which they originated, we believe that timber structures acquire grace and story as they age.”
Please note: Wood Central will have more information about timber bridge design options in the coming days.
