New Zealand concrete research set to offer new way of fixing earthquake-hit buildings

Precast concrete hollow-core floor
"We hope it will give building owners confidence to start repairing." Photo credit: Supplied / EQC

A collaboration of New Zealand researchers will publish its findings this week, promising a new way to fix issues with earthquake-prone buildings.

Precast concrete hollow-core floors are a distinctly New Zealand problem and are a reason many earthquake-hit buildings in Aotearoa have been demolished rather than fixed.

But the project team, led by experts from the Universities of Canterbury and Auckland, will publish its findings in the Structural Engineering Society NZ (SESOC) journal in order to provide guidance for engineers and building owners considering retrofitting rather than demolishing.

"The seismic issues around hollow-core floors are not new but were brought into the spotlight by the damage caused in the Wellington CBD by the Kaikōura earthquake," Nicholas Brooke, coordinator of the ReCast Project, said.

The project has spent four years testing and verifying retrofit solutions to strengthen buildings with precast floors, which have been widely used in New Zealand construction since the mid-1980s.

"We focused on the least complex and most affordable retrofit solutions, tested them, verified them and developed design guidance for the different technologies," Brooke said.

The research was also supported by funding from the Earthquake Commission (EQC),  Building Research Association of New Zealand (BRANZ) and Concrete NZ.

"Precast hollow-core floors have been recognised as a seismic risk for many years and EQC has been eager to support any research that will tackle this issue," said EQC chief resilience and research officer, Dr Jo Horrocks.

"We hope it will give engineers and building owners, especially in the Wellington area, the confidence to start repairing a building instead of demolishing them.

"New Zealand has suffered devastating impacts from earthquakes over the past 11 years, but from that trauma we have learned a huge amount and developed world-leading science and engineering solutions," she continued.

"Many owners may have been holding off investing in repairs, in fear of having to do more repairs later, but now they can be confident a retrofit will work."

Brooke said precast concrete hollow-core floors had been a favourite in Aotearoa's construction since the 1980s, but the country was an outlier.

"The rest of the world was not so excited about hollow-core floors, so this is really a distinct New Zealand issue," Brooke said.

The weakness of the system was exposed in the 1994 Northridge earthquake in North America where buildings with hollow-core floors were severely damaged, he said.

Professor Des Bull at the University of Canterbury was concerned about the New Zealand context and spent nearly two decades investigating hollow-core floors, ultimately developing guidance on their assessment with Professor Richard Fenwick.

"Unfortunately, they published their findings shortly before the Darfield earthquake and their findings were a bit lost in the chaos of those earthquakes," Brooke said.

It was only after the damage caused by the Kaikōura earthquake that authorities and researchers galvanised into taking action.

"It is the culmination of 25 years of research, building on the work of Des Bull and funding by EQC, that will be hugely valuable to seismic engineers in New Zealand and abroad," Brooke concluded.