Concrete Providing Solution to Australia's Aging Timber Bridge Problem

Across Australia, the replacement of aging timber road and rail bridges is a challenge for regional councils and state governments alike.

According to the Australian Local Government Associations most recent State of the Assets report (2018), 21 per cent of timber bridges are in poor to very poor conditions.

And as the cost of repairs grows with the age of these structures, the imperative to act increase exponentially.

On the NSW North Coast, Kempsey Shire Council is well into a program of progressively replacing its 85 timber bridges. The latest and largest to be completed in the current four-year replacement cycle is the $4 million Turners Flat Bridge, jointly funded by the Shire and the Federal Government. 

Turner's Flat is the last of the five downstream bridges over the Macleay River to be replaced - all in concrete.

The original timber structure, built in 1913, was washed away in flooding in 1949. A 130-metre, 11- span replacement timber bridge was commissioned in the early 1950's, but was closed for a lengthy period after two spans washed away in 2009.

Faced with an increasing maintenance burden, in 2017 Council applied for Commonwealth funding. Once this funding was secured and a tender process completed, civil contractor Waeger Constructions was chosen to design and construct the new bridge, with site work commencing in April 2019.

Officially opened to traffic in January, the new bridge is 144 metres long, with six 24-metre spans. It's constructed from pre-stressed concrete beams and concrete headstocks sitting on bored piles, with an insitu concrete deck.

Notwithstanding that the new concrete structure is slightly higher (1.8 metres) than the timber bridge it's replacing, Council still expects it to 'go under' a couple of times a year.

February 14 Flood

Old Timber Bridge

In fact, it withstood its first flood test in February (2020) when the river rose about 600mm over the top of the deck. (The yet-to-be-demolished old bridge standing alongside went under by about two metres.)

With the river capable of rising another eight or nine metres, it would have been cost prohibitive to design and build a completely flood resistant bridge.

But taking all the practical and cost factors into consideration, including strength and longevity, the choice of concrete over alternatives (timber, steel and composites) was a 'no brainer' for Kempsey Shire Council - as it is for most regional councils burdened with the task of replacing dilapidated timber bridges.