New fix for flooring flaw creating quake risk in Wellington buildings

New Zealand researchers have found solutions for a construction flaw threatening more than 150 central Wellington buildings.

After the Ministry of Education's head office in central Wellington was found to be below standard, the Wellington City Council announced at least another 150 other central city buildings were built with the same precast concrete hollow-core floors.

Nicholas Brooke is the coordinator of the ReCast Project, which has spent the past four years testing and verifying retrofit solutions to strengthen buildings with precast floors – a popular construction technique in New Zealand since the mid-1980s. They now cover about 1.5 square kilometres of buildings floors around the country.

"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.

READ MORE: * Hospital audit didn't use up-to-date engineering guidelines * The Government is looking at whether more buildings may be earthquake-prone * Kaikōura highlighted potential deadly problems with precast concrete floors

The seismic issues around hollow-core floors are not new, but were brought into the spotlight in Wellington by the Kaikōura earthquake in 2016.

The project team, led by experts from the Universities of Canterbury and Auckland, and supported by funding from the Earthquake Commission, BRANZ and Concrete NZ, is set to publish its findings in the Structural Engineering Society NZ (SESOC) journal to provide guidance for engineers and building owners considering retrofit options for existing buildings.

EQC chief resilience and research officer Dr Jo Horrocks said precast hollow-core floors were cheap and fast to build, and before as much was now known about Wellington's seismic risk, seemed a good option. After 2006, building code changes meant they were no longer used.

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

"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."

Former research projects hadn't received sufficient industry attention, Brooke said. The Kaikōura earthquake galvanised authorities and researchers into action.

This research now formed the largest SESOC journal, with 11 articles and more than 200 pages of design guidance for seismic engineers.