A cost-effective solution to strengthen Aotearoa New Zealand's riskiest buildings has been identified by researchers at Waipapa Taumata Rau, University of Auckland.
PhD candidate Victor Li, Dr Enrique del Rey Castillo and Dr Rick Henry from the Faculty of Engineering found that wrapping weak spots in concrete walls with carbon-fiber strips can strengthen high-rise buildings to resist earthquakes well beyond the demands of the building code.
The research was funded by Toka Tū Ake EQC to help find the most efficient and cost-effective ways to strengthen thin concrete walls.
The findings are likely to draw significant interest in the engineering sector as over 100 multi-story buildings in Wellington’s CBD alone are well below modern code.
Li says that thin concrete walls can deform out of plane due to their inherent instability, and just one percent of lateral displacement can cause catastrophic collapse.
“Technically it’s called ‘axial failure’. It can still happen in a newer building, as we saw in Christchurch’s Grand Chancellor Hotel, but the pre-1982 design methods mean the risk is higher in those older buildings,” says Li.
“Up until now there has been no guidance on how these walls could be strengthened, but our research has shown that with the carbon fiber solution, the wall cannot buckle in the out of plane direction.”
The engineers wrapped at-risk walls in carbon fiber and tested 56 different combinations of concrete, steel and carbon fiber to see when and how they would break. The team also tested the walls up to twice the building code for seismic resilience.
“This gave us the data we needed to model how to strengthen a particular wall, and the results have even been better than we anticipated,” says Li.
“Finding a solution that is cost-effective was another important aspect of the research,” says Dr del Rey Castillo. “Using carbon fiber to strengthen concrete walls is a much less invasive process than other means, which helps to keep costs down.”
Dr Natalie Balfour, Toka Tū Ake EQC Head of Research, says that many older commercial buildings are being converted to apartments, so it is vital to ensure that people live in homes that meet modern earthquake standards.
“Toka Tū Ake EQC decided to fund this research because it will deliver practical guidance on how at-risk walls in older buildings can be strengthened cost-effectively. It will also establish a consistent way of doing these fixes across New Zealand,” says Dr Balfour.
Practicing engineers will now have the scientific data to use the new technology with confidence to repair old walls, says Li. His team has had support from industry players like Concrete NZ, Mapei, Sika, Holmes and BBR Contech, who wanted to ensure that the testing would deliver real-world results.
“Thanks to the input from people working in the industry, we have delivered something that can be put to practical use right away,” says Li.
Funding: Toka Tū Ake EQC
Published in journal: None
Source/Credit: University of Auckland
Reference Number: eng041823_02
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