Exciting new research has demonstrated cross-laminated timber (CLT) walls are feasible and cost-competitive with steel or concrete systems in low-rise buildings, and offer significant environmental benefits.
The findings from EQC-funded research by Associate Professor Minghao Li and his team at the University of Canterbury (UC) could have far-reaching implications for the construction and forestry industries, and New Zealand’s quest to become a carbon-neutral economy.
Associate Professor Li and his PhD student Ben Moerman have been testing large CLT shear walls in the UC Structural Engineering Laboratory to find out how these multi-storey walls behave in significant earthquakes.
“We loaded the walls horizontally to create a similar scenario of multi-storey CLT buildings in big earthquakes like the ones in Christchurch,” Li says.
He points out that the weight of timber is only one-fifth of concrete, meaning much lower earthquake loads, but engineered timber has similar strength as concrete.
“With the right connections, CLT buildings can be really strong and resilient in an earthquake.”
The research team designed innovative high capacity connections to resist earthquake forces and protect the integrity of the timber walls.
“We have tested those large-capacity connections that tie the walls down to the foundations to study their performance in an earthquake,” Moerman says.
He was excited to see that steel dowels in the connections bent to absorb energy and prevent the walls from being significantly damaged or collapsing.
“The main benefit is that after an earthquake you can simply replace the dowels and the buildings will be just as strong as they were before the earthquake,” Moerman says.
The research in Christchurch has major environmental implications as the construction industry contributes around 40% of global CO2 emissions, while New Zealand’s building industry contributes around 20% of the country’s carbon footprint.
“If we can put more wood from sustainable plantations into buildings, we can lock carbon into those buildings for at least 50 years, which will have great benefits for New Zealand to achieve our carbon-neutral goals,” Li says.
“New Zealand has 2.1 million hectares of plantation forests and we grow a lot of high quality timber like radiata pine that we can use for construction.
“We hope our research will convince the building industry to use more timber, which will also benefit our forestry industry.”
Li acknowledges that currently engineered timber materials might be slightly more expensive than other materials, but the speed of construction and limited resources required may also make timber a cost-competitive building solution.
“The walls are prefabricated off-site, and you only need a handful of staff to put the walls together, so you make savings and can build much faster by using timber.
Ben Moerman shows how the steel dowels in the specially designed connections bend to absorb seismic energy and prevent the walls from being significantly damaged or collapsing.