ONE of the world’s most pre-eminent timber bridge experts claims Fremantle’s old Traffic Bridge could be restored for the same cost Main Roads has spent on just the design phase of a concrete replacement.

Wood Research and Development senior wood technologist and structural engineer Dan Tingley says the bridge’s central pylons could also be removed and the structure “spanned” to remove the unsafe jig that boats are forced into in order to navigate the nearby train bridge.

Dr Tingley believes that could give the heritage-listed bridge an extra 100 years.

While giving supporters of the Save Old Fremantle Bridge Alliance a ‘tour’ of the bridge’s underbelly on Thursday, Dr Tingley also took a shot at Main Roads’ WA’s maintenance over the years, saying elements such as concrete “potting” around the base of the pylons had shortened their life by 66 per cent.

• Part of Thursday’s bridge ‘tour’ included local soprano Penny Shaw singing it Happy Birthday in celebration of its opening on December 15, 1939. Photo by Steve Grant

He’d warned the department about the method while providing training for its engineers years ago, he said.

Holes drilled into the timber for testing were also unnecessary.

“Don’t make Swiss cheese out of this bridge; use non-destructive testing.

“There’s ways today to send a compression wave through the wood to find the cavities; find decay without ever harming it.”

Dr Tingley believes Main Roads’ engineers have suggested replacing the bridge with a steel and concrete version because they don’t get much training in timber structures any more so take the “path of least resistance”.

Roman numerals

To highlight his point, he recalled a meeting under the bridge with an engineer who completely misinterpreted a series of Roman numerals carved into its pylons to indicate how deeply they’d been sunk into the ground.

“When I’m working with engineers that have been trained in steel and concrete – with no timber experience – and I’m standing under a bridge and the engineer thinks this is the year that it’s built, you’ve got trouble.

“How else would you rate the bridge for capacity if you didn’t know how deep the piles were?”

Dr Tingley drilled his own holes in arguments that steel and concrete bridges were longer-lasting than timber bridges, while noting that in today’s carbon-conscious economy, timber was starting to come back into its own.

• Timber bridge expert Dr Dan Tingley.

“The civil infrastructure in Australia; some 42,000 hardwood timber bridges with an average age of 82 years, have provided the grid iron that Australia has been built on.

“In the back roads or rural Australia, right today, there are timber bridges built like this one that are carrying sm 1600 loads – that’s transport loads, bus loads – and their original design was for 12 tonnes.

“Now what material… could be designed for 12 tonnes and carry 44 tonnes for an average age of 82 years and still be in service?”

Dr Tingley says Nova Scotia in Eastern Canada has even introduced a prohibition against steel being used on bridges near the oceans because of rusting issues.

“Rust resistant steel doesn’t work, we know that now; it develops a patina on it and is very susceptible to rust.

“There’s more embodied carbon in this bridge here, than the combined production of all the plastic straws for a year in the world.

“Why would we have a program that takes that embodied carbon and moves it back into the atmosphere? Why not keep this embodied carbon going by restoring it with new timber pieces that are coming from sequestered carbon that has been there when the tree is growing because of photosynthesis, converting CO2 into food for the tree and giving off oxygen.”

Dr Tingley claims building a concrete bridge is “21 times less carbon-friendly” than a timber equivalent, while estimating that 75 per cent of the existing bridge’s structure could be saved.

Wood Research and Development have been involved in more than 1300 bridge restorations across the globe, while Dr Tingley says he’s devoted his working life to restoring timber structures.

“Nobody’s paying me to be here. Why do I want to be here? It’s because this bridge has to have a voice.

“This grand old bridge when we look up, we see something that really always impresses me, and that’s actually this great width made out of timber.

“Rarely do you see a timber bridge in Australia as wide as this one.

“This bridge is a gateway Fremantle; it’s the way people get in and out of it, and because of that, there’s a lot of history to it.”

by STEVE GRANT