Research into the technique used to connect reinforced concrete walls to their foundations is set to have a significant impact on the New Zealand construction industry.

Researchers at the University of Canterbury are conducting earthquake testing to better understand the performance of a construction technique called staggered lapsed splices, which is used to connect the steel bars in reinforced concrete walls to the steel bars coming out of the foundations.

The practice is no longer used overseas, but allowed under the New Zealand building code.

'The connections between the walls and the foundation are created by overlapping the steel bars and they rely on the concrete around the bars to transfer the seismic forces from one bar to the other,” says University of Canterbury Department of Civil Engineering lead researcher Professor Santiago Pujol, whose research has been funded by Toka Tū Ake EQC.

'This configuration is economical and easy to build but does not always provide the toughness for the walls to resist the demands of an earthquake."

The lines mark the cracks after three days of seismic testing on the concrete wall. Photo: Supplied.

Professor Pujol says that structures using this configuration have collapsed in previous earthquakes in Turkey, Chile, Japan and Alaska.

'When these connection fails, the outcomes are often catastrophic.”

He says that New Zealand has fortunately not seen similar catastrophic failures of lapsed spliced walls in the Canterbury and Kaikōura earthquakes, but it is vital to test the seismic strength of staggered lap splices in a controlled environment.

University of Canterbury researcher and PhD student Charlie Kerby is carrying out the testing at the Seismic Engineering Laboratory by attaching the walls to hydraulic actuators which mimic the effects of a major earthquake by pushing and pulling the walls until they fail.

'We are not interested in how much force is needed to make the wall fail, but how much the wall can deform before failure occurs,” says Charlie.

'Buildings need to be able to move with the earthquake and we are looking at how much a lap splice can deform until it fails.”

The research is funded by Toka Tū Ake EQC as part of its contestable Biennial Grants, which supports research in improving the resilience of buildings to New Zealand's natural hazards to better protect people and property.

'Our organisation invests around $19 million each year into research to better understand our natural hazards. Professor Pujol's project is a great example of research that identifies potential risks, but also informs better engineering solutions for reinforced concrete buildings, which many of us live and work in,” says Toka Tū Ake EQC Chief Resilience and Research Officer Dr Jo Horrocks.

Charlie says engineers have alternative options like welding the steel bars together or using a mechanical connection to transfer seismic forces, but says that tradition and economics dominate most of what happens in the construction industry.

'These lap splices have been used for over a century and from an economic viewpoint, an extra meter of steel virtually costs nothing compared to a specifically designed connection.”

Charlie says the question of whether lap splices actually perform well in earthquakes has only been raised fairly recently, so the research at the University of Canterbury will provide vital new insights to inform engineers and construction standards.

Professor Pujol says his team will not only put the spotlight on a potential problem but also provide solutions for the industry by designing and testing alternative configurations.

'We will find out what works best to enable greater confidence in building design.”

More information about Toka Tū Ake:

• The forerunner to Toka Tū Ake EQC was set up in 1945 to provide affordable natural hazard insurance to help communities recover. Today, our mission still reflects that same commitment: to reduce the impact on people and property when natural hazards occur.
• Toka Tū Ake is a Crown Entity that operates under the Earthquake Commission Act 1993. We invest in natural hazard research and education to help communities to reduce their risks, and we provide natural hazard insurance cover for damage to residential properties caused by earthquakes.
• The Public Inquiry into the Earthquake Commission recommended the organisation change its name to better reflect that our scope extends beyond earthquakes to deliver insurance and expertise for a range of natural hazards, including volcanic eruptions, hydrothermal activity, tsunamis, land slips, as well as damage to land from storms and floods. Toka Tū Ake means the foundation from which we stand strong, together.
• In order to support us to build familiarity with our new name, we invite you to refer to us as Toka Tū Ake EQC at first reference, and Toka Tū Ake thereafter. Please avoid acronyms for Toka Tū Ake, and note that it should not take a possessive apostrophe.