When cars crash into buildings: how new materials can reduce damage caused by vehicle collisions
When a car collides with a building at speed, the damage is catastrophic: the vehicle punches through the brick and mortar exterior causing structural damage to the building, and potentially injuring or killing the driver, passengers, and building occupants.
Damage from these collisions runs to almost $50M each year, based on the estimated 2,000 intrusions each year recorded in Australia.
A new building material being developed by a QUT research team can be applied to the front façade of a building, leading to less damage to the car, the vehicle’s occupants and the building itself in the event of a collision.
The emerging research is supported by a $415K Australian Research Council Discovery grant and will be tested at a world-first impact testing facility currently being built in Brisbane’s north.
More city, more problems
As our cities grow bigger and more densely populated, there are more cars on the road and more buildings constructed closer together on smaller lots.
Lead researcher Professor David Thambiratnam and his team, Professor Tommy Chan, Dr Tatheer Zahra and Dr Mohammad Asad, believe that the solution lies in auxetic materials: a synthetic substance that is combined with building mortar to create an impact-resistant building material.
“Auxetic materials have a special property called negative Poisson ratio,” explained Thambiratnam.
“Normally, if you have a block of rubber and you stretch it horizontally, it will lose height to accommodate the new width. Similarly, if you stretch it vertically it will become thinner as it becomes taller.
“Material with a negative Poisson ratio expands equidistantly in all directions as it’s stretched, because of a wider spacing between the material’s particles.”
When combined with mortar it gives a building’s surface flexibility to absorb impact and recover, as opposed to denser materials like brick, which can shatter under impact.
This auxetic composite render on the street-facing wall only needs to be 1–2cm thick, and costs about $190/m2, making it incredibly cost effective.
While auxetic materials have been used in other industries — thick protective casts for broken bones, or the soles of certain sneakers — this will be the first application in the building construction industry.
“The data around building collisions from cars is frightening, and only increasing — with more drivers on the road, especially drivers who are drunk, or in a hurry, or driving in slippery conditions, these accidents will keep happening,” said Thambiratnam.
“Building owners could put up fences or walls as a barrier, but they’re expensive, can be unsightly, and take up too much physical space — and they won’t stop the damage to the car and its occupants.
“Our solution will protect the driver, the car and the building and its occupants through simple physics.”
Something’s got to give
“There’s a very basic equation for what happens when a collision occurs,” explained Thambiratnam.
“The energy of the impact is made up of the energy absorbed, the energy transferred into damage or destruction, and the energy transferred into vibration.
“In a standard car collision, that impact might be 80% damage, 10% vibration and only 10% of the impact will be absorbed.
“We want to change the distribution of energy in this equation — so, with the auxetic material, we’d hopefully see the damage drop to 10%, while absorption goes up to 70% and vibration to 20%.”
This means that while the building will shake, the bricks won’t shatter, and the car and its occupants will suffer less harm as the auxetic material absorbs the energy from the impact.
To mitigate the shaking, Thambiratnam is investigating alternative materials for the building’s other walls that can dampen vibration and lessen the disruption to its inhabitants.
Making an impact
Initially, the technology was shown to work through computer simulations and small-scale testing.
To further demonstrate the strength and flexibility of the auxetic render, Thambiratnam and his team will take the project to a world-first impact testing facility currently being built in Brisbane’s north.
The facility is due to be completed in late 2020, and is jointly funded by QUT, Australian Research Council, and 10 other Australian Universities: Monash University, University of Sydney, University of Queensland, Griffith University, University of Newcastle, Swinburne University, University of NSW, Western Sydney University, University of Wollongong and Curtin University.
The facility will be equipped with a large pneumatic machine that can reach speeds of 50m/second, replicating impacts from collisions, bomb blasts, and other potentially catastrophic events.
“We’ll be able to build walls using the auxetic render and subject them to impact from the testing machine, which will show us the difference in damage patterns with and without the render,” said Thambiratnam.
“We can then look at adding dampers to the edges of the wall to reduce vibration, and optimise the composition and thickness of the render to achieve the safest, most cost-effective protection.”
The testing facility will be able to look at impact dynamics across a range of scenarios, with other research teams lined up to investigate bomb blasts on armoured vehicles and ship collisions with bridge pylons.
Once the research team’s new auxetic render has undergone testing at the facility, the team hopes to have it ready to share with the construction industry in 2022.
More information
Explore more research at QUT’s Science and Engineering Faculty
