Earthquake News

New Zealand concrete research could lead to a new technique of repairing earthquake-damaged structures.

This week, a group of New Zealand academics will publish their findings, providing a new way to address difficulties with earthquake-prone structures.

Many earthquake-damaged buildings in Aotearoa have been demolished rather than repaired because of precast concrete hollow-core floors, which are a uniquely New Zealand hazard.

However, the project team, which includes experts from the Universities of Canterbury and Auckland, will publish its findings in the Structural Engineering Society of New Zealand (SESOC) journal to help engineers and building owners who are considering retrofitting rather than demolition.

"The seismic difficulties surrounding hollow-core flooring are not new, but the devastation caused in the Wellington CBD by the Kaikura earthquake brought them into the focus," Nicholas Brooke, coordinator of the ReCast Project, stated.

The team has spent four years researching and testing retrofit solutions for precast floors, which have been widely employed in New Zealand construction since the mid-1980s.

"We evaluated, verified, and developed design recommendations for the different technologies, focusing on the least complex and most cheap retrofit solutions," Brooke stated.

The Earthquake Commission (EQC), the Building Research Association of New Zealand (BRANZ), and Concrete NZ all contributed to the research.

"For many years, precast hollow-core floors have been recognized as a seismic danger, and EQC has been ready to assist any study that would address this issue," said Dr Jo Horrocks, EQC's chief resilience and research officer.

"We hope it will inspire engineers and building owners, particularly in the Wellington area, to begin restoring rather than removing structures."

"Over the past 11 years, New Zealand has been devastated by earthquakes, but we have learned a great deal and produced world-leading science and technical solutions as a result of that pain," she concluded.

"Many owners may have been putting off repairs for fear of having to do more later, but they can now rest assured that a retrofit will work."

Precast concrete hollow-core floors had been popular in Aotearoa construction since the 1980s, according to Brooke, but the country was an oddity.

"The rest of the globe isn't crazy about hollow-core floors," Brooke added, "so this is truly a New Zealand issue."

Buildings with hollow-core flooring were extensively damaged in the 1994 Northridge earthquake in North America, exposing the system's flaws, he said.

Professor Des Bull of the University of Canterbury was worried about the New Zealand context and spent nearly two decades researching hollow-core floors, eventually collaborating with Professor Richard Fenwick to give recommendations on their assessment.

"Unfortunately, they released their findings just before the Darfield earthquake, and their conclusions got lost in the midst of the pandemonium," Brooke added.

Authorities and experts were only motivated to act after the Kaikura earthquake caused significant damage.

"It's the result of 25 years of research, built on Des Bull's work and funded by EQC, that will be extremely useful to earthquake engineers in New Zealand and around the world," Brooke said.

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