With bushfire season approaching, and after the devastating fires over the black summer of 2019–2020, new research into how and why houses are destroyed during bushfire events is welcome news.
Professor Mahen Mahendran from QUT’s School of Civil and Environmental Engineering is spear-heading emerging research that could lead to improved Australian building standards and safer homes by determining why buildings structurally fail during fire events.
Earth, wind and fire
When buildings are destroyed by bushfires, it’s not always due to the flames — often, buildings are structurally damaged by powerful bushfire-generated winds, which can tear roofs off buildings as they rip across the landscape.
On its own, wind can impact a bushfire by propelling the fire faster, carrying embers into buildings and vegetation to spread the fire, or changing direction, which can change the shape and intensity of the fire front.
However, there’s also a powerful reverse mechanism whereby the bushfire can also make the wind faster.
“When we see some buildings significantly damaged in bushfires, a lot of structural damage comes from this high wind force,” Mahendran explained.
“Generally, higher winds are expected before a bushfire arrives, and the heat from the fire creates additional energy that propels that wind even faster.
“As the fire approaches, the building’s exterior envelope gets hotter and becomes weaker from this heat.
“When the bushfire nears the building, the wind has become so strong that it can blow off the roof or other structural parts of the building, causing significant damage.”
Safe as houses
National building standards currently call for non-combustible steel cladding on the walls and roof of buildings in bushfire-affected areas, but this only addresses fire resistance and not the potential damage caused by wind.
The Australian Research Council has funded Mahendran and his research team, including Dr Anthony Ariyanayagam and Lisa Pieper, to investigate ways to make buildings more resistant to the damage caused by combined wind and bushfire actions.
Early estimates place the bushfire-enhanced wind at more than 50 per cent faster than the unaffected winds.
But although the effect has been clearly observed during past bushfire seasons it has not been completely quantified, meaning researchers will need to cover more possibilities and develop solutions that manage the resulting significant wind pressure increases.
Mahendran hopes that the research will improve the Australian building standards for external building envelopes — the exterior walls and roof of an edifice.
From the test facility to policy
Mahendran’s team will test the strength of steel building envelope in a purpose-built lab where they’ll simulate the pressure of wind action and heat stress.
“We have a large air box where we can place the roof or wall cladding and heat it with electric blankets to emulate the heating of the building envelope in bushfires,” Mahendran said.
“We can then subject the cladding to simulated wind pressures to understand its performance under combined wind and heat actions.
“Alternatively, we can also use our radiant panel to simulate a more realistic bushfire intensity together with a wind pressure simulator.”
While research is in the early stages, there is precedent for policy change to mitigate the impact of severe weather events in parts of Australia.
“Cyclones have caused immense damage in the Northern Territory before, destroying hundreds of buildings and causing substantial loss of life,” Mahendran said.
“Insurance companies work with homeowners and councils to improve buildings and make them much safer in the face of natural disasters, and we’d like to see the same thing happen with bushfires.
“We can’t solve all bushfire-related problems and we can’t stop bushfires from happening, but we can increase our understanding of how buildings can best survive bushfire conditions.”
More information
Contact Professor Mahen Mahendran
See more research from QUT’s Wind and Fire Engineering Laboratory
Explore research at QUT’s Centre for Materials Science
Explore more research at QUT
