11 May 2021
Experts are calling for a review of building processes in Western Australia, after Tropical Cyclone Seroja tore through the state's Mid West region last month, damaging more than 600 properties.
According to the Bureau of Meteorology, Cyclone Seroja was one of the worst storms to hit the region in more than five decades.
Wind speeds were up to 170 km/hr when the cyclone hit the coast of WA between Kalbarri and Gregory at roughly 8 pm on Sunday 11 April. It continued moving south-east and was downgraded from a Category 3 system to a Category 2 at about 11 pm.
By the time it was downgraded to a tropical low, Cyclone Seroja had already completely destroyed or severely damaged 170 homes and businesses, and moderately or slightly damaged a further 491. WA’s Department of Fire and Emergency Services Commissioner Darren Klemm estimated the clean up would cost nearly $200 million.
What went wrong?
What’s particularly concerning about Cyclone Seroja, says Chartered engineer Dr Geoff Boughton FIEAust CPEng, Adjunct Associate Professor at James Cook University’s Cyclone Testing Station, is that the contemporary buildings in Kalbarri should have been able to withstand the winds.
“Our estimation of the wind speeds in Kalbarri was at about 80 to 90 per cent of their design level,” he said.
“So the event should not have taken them past what they were designed for.”
And yet, 10 per cent of these buildings suffered moderate to severe damage, according to Boughton.
“To get that level of damage when the wind speeds were 10 per cent lower than the design wind speed tells us something is systematically wrong with the way the buildings have performed,” he said.
Boughton and his team at the Cyclone Testing Station are investigating exactly what happened to cause so much damage. Their theory is that the buildings could not handle the internal pressure caused during the tropical cyclone.
If a window breaks, either due to strong winds or debris crashing into it, then the pressure from the windwall enters the building and pushes up on the ceiling. This increases the tie-down forces needed to stop the roof from coming off.
“If this isn’t anticipated in the design then the roof is going to disappear,” Boughton said.
“So the number one lesson for engineers is to look really carefully at what openings could develop in extreme wind events, and make sure the rest of the structure is going to be able to cope with it.”
Reconsidering building standards
Engineers Australia’s WA General Manager and Chartered engineer Susan Kreemer Pickford FIEAust CPEng believes the damage caused by Cyclone Seroja is a warning for the industry to take a look at building standards and whether construction and inspection is to those standards.
“We really need to be asking if the current standards, construction techniques and inspections regimes are meeting the requirements,” she said.
“If the winds from Seroja were allegedly not strong enough to do the damage it evidently did, then perhaps those design levels need to be re-tested.”
The incident has once again highlighted the importance of a mandatory registration scheme for engineers in all states and territories. But Kreemer Pickford said it’s too soon to know if that could have mitigated the situation.
“To say that would have definitely changed the outcome is pure speculation at this time; we need to do some more investigation,” she said.
Engineers Australia hopes to address the question of what happened at a forthcoming roundtable with industry experts.
Representatives from a number of government departments and associations, including the Department of Mines, Industry, Regulation and Safety; the Master Builders Association WA; and the Housing Industry Association will be in attendance.
The Mayor of Karratha, Peter Long, will also share his experience dealing with Severe Tropical Cyclone Damien last year, while Chartered engineer Xihong Zhang MIEAust CPEng, Senior Research Fellow at Curtin University’s School of Civil and Mechanical Engineering will provide expert commentary.
Kreemer Pickford aims to bring an engineering eye to the problem and assess where the gaps might be.
“What we know is that large projects by mining and construction companies don’t have this issue, so we need to ask why we aren’t applying the same rigour to residential projects,” she said.
The roundtable is part of Engineers Australia’s remit to “advance the science and practice of engineering to the benefit of the community,” Kreemer Pickford said.
“We want to answer the question, ‘How can we as engineering professionals work with other industries to make sure we don’t see this kind of devastation again?’.”