The ReCast Project, led by experts from the Universities of Canterbury and Auckland and supported by funding from the Earthquake Commission, BRANZ and Concrete NZ, has spent the last 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.

This week, the project team will 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.

“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,” says Nicholas Brooke, coordinator of the ReCast Project. “We focused on the least complex and most affordable retrofit solutions, tested them, verified them and developed design guidance for the different technologies.”

EQC Chief Resilience and Research Officer, Dr Jo Horrocks, says that the Recast Project strikes at the heart of EQC’s vision of investing in research that will strengthen buildings and protect people.

^{The above video is a timelapse of precast hollow-core concrete floors being reinforced.}

“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,” says Dr Horrocks. “This research is incredibly valuable and detailed and 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. 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.”

Horrocks says that Aotearoa has suffered devastating impacts from earthquakes over the past 11 years but, from that trauma, has come a huge amount of learning and the development of world-leading science and engineering solutions. “We will continue to fund excellent research like this because we know it saves lives and protects property – it’s all part of our role to help New Zealand to be better prepared for the next earthquake.”

Brooke says that precast concrete hollow-core floors have been a favourite option for the New Zealand construction industry and developers since the mid-1980s and cover about 1.5 square kilometres of buildings floors around the country.

“The rest of the world was not so excited about hollow-core floors so this is really a distinct New Zealand issue,” says Brooke, who explains that the weakness of the system was exposed in the 1994 Northridge earthquake in North America, where buildings with hollow-core floors were severely damaged.

With the help of EQC funding, Professor Des Bull at the University of Canterbury has spent nearly two decades investigating hollow-core floors before developing guidance on their assessment with Professor Richard Fenwick. The findings were published shortly before the Darfield earthquake and the subject did not receive sufficient industry attention until the damage caused by the Kaikōura earthquake galvanised authorities and researchers into action.

The ReCast Project was launched with the universities in Canterbury and Auckland dedicating four PhD students and a Masters students for four years. “It was truly a unique collaboration with PhD students from Canterbury working in the Auckland lab and vice versa, which we believe had not happened previously to anything like the same extent,” says Brooke.

The result is the largest SESOC journal published to date, with 11 articles and over 200 pages of design guidance for seismic engineers. “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.”

The Earthquake Commission (EQC)

The country’s EQC scheme was set up in 1945 to provide affordable, natural hazard insurance to help communities recover. Today, EQC’s mission still reflects that same commitment: to reduce the impact on people and property when natural hazards occur. EQC is a Crown Entity that operates under the Earthquake Commission Act 1993. It invests in natural hazard research and education to help communities to reduce their risks, and it provides natural hazard insurance cover for damage to residential properties caused by earthquakes, volcanic eruptions, hydrothermal activity, tsunamis, as well as damage to land from storms and floods.