Photo: 123rf.com
Research into how buildings sway during earthquakes is recommending they be built more stiffly.
Some Wellington buildings that swayed a lot suffered extensive interior damage in the 2016 Kaikōura earthquake, and some were later demolished.
Canterbury University - with help from Taiwan - has done a large scale test on the sort of steel frame and concrete multistories common in New Zealand.
The researchers say small design changes that cost only a fraction of a building's total cost can end up saving billions of dollars in damage.
Professor Santiago Pujol said the results could be dramatic.
"It only costs one or two percent extra to make a building that is much better, one you can live in after a quake, not one you have to abandon," Pujol said in a statement on Monday.
Limiting the sideways movement between floors to under one percent can save doors and window that jam or break even if the structure remains standing.
"As long as the storey-drift ratio was less than one percent, the damage was quite tolerable, even in materials as brittle as gypsum board [plasterboard]," Pujol said.
The key was testing this in a real-world way, not on a idealised model. The National Centre for Research on Earthquake Engineering in Taiwan helped with that.
New Zealand had for decades followed the philosophy of designing slender, flexible buildings.
The rationale was "one way to help buildings deal with the large amounts of energy released in earthquakes, is to design them to move", said Te Hiranga Rū QuakeCoRE research centre, which worked with Pujol's team.
But the 2011 Christchurch earthquake and 2016 quake had forced a reappraisal.
"Drifting might sound like a good idea, but it leads to damage for both the structure and non-structural building components such as facades, cladding, windows, and partitions. There is some thought that elements such as ceiling panels, sprinklers, and lighting experience more damage in rigid buildings, but does that need to be the case?."
Pujol said New Zealand was currently looking at introducing tighter "drift limits", as they are called.
Japan and Chile have had tighter limits for decades.
Studies have compared how buildings perform between countries with different drift limits.
"Observations of the performance of reinforced concrete ... buildings after the 2016 Kumamoto earthquake in Japan showed buildings designed to Japanese specifications resulted in less damage and downtime compared to buildings following the 2010/2011 Christchurch earthquakes in New Zealand even though the earthquakes were of comparable magnitude," one study for the NZ Society of Earthquake Engineering said in 2023.
The Ministry of Business, Innovation and Employment and the Natural Hazards Commission have developed guidelines for low-damage seismic design that encourage the use of small drift limits to control damage to buildings in earthquakes.
The first guidelines came out last year, while parts two and three are due out later this month.
MBIE was not directly involved in the research at Canterbury.
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