A groundbreaking international study led by Te Whare Wānanga o Waitaha | University of Canterbury (UC) researcher Professor Santiago Pujol has found that limiting how much buildings sway during earthquakes could dramatically reduce damage across New Zealand.
Working in collaboration with the National Center for Research on Earthquake Engineering (NCREE) in Taiwan and the Te Hiranga Rū QuakeCoRE research centre, Professor Pujol and his team carried out a large-scale structural test, combining steel framing and reinforced-concrete walls to replicate the kind of buildings being constructed here New Zealand.
“The main goal was to conduct a large-scale test representing, as well as possible, a building that reflects what’s actually being built out there, not an idealised model,” Professor Pujol says. “Thanks to the Taiwanese generosity, we were able to focus on current New Zealand practice.”
Their findings showed if engineers can keep storey drift, the sideways movement between floors, below about one percent of the storey height, most damage to current building components becomes cosmetic rather than structural.
“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.
“When drift exceeds that, you start seeing cracked walls, jammed doors and broken windows, even though the building might still stand.”
“It only costs one or two percent extra [from the total building cost] to make a building that is much better, one you can live in after a quake, not one you have to abandon,” Professor Pujol says.
“That small investment at the design stage could save billions of dollars in rebuilding and insurance costs after major seismic events.
“When you buy a car, if someone offered you one percent off but it didn’t have airbags or seatbelts, would you buy it?”
The study reinforces what earthquake engineers have long suspected; controlling drift, not just strength, is key to keeping buildings usable after major earthquakes.
The implications reach beyond engineering. Insurance companies and policymakers are already looking for clear definitions of ‘damage’ to inform future regulations and coverage. Professor Pujol’s work provides crucial data as New Zealand moves to tighten drift limits, which are expected to come into force by 2027.
“Right now, we’re looking at introducing tighter drift limits in New Zealand and in the US,” he says. “Japan and Chile have had strict limits for decades, and they’ve proven effective.
“You can retrofit [buildings], but it’s expensive and difficult,” he says. “We’re researching ways to add stiffness externally, for example, by tying new concrete walls to the outside of existing buildings. However, it’s better to build more robust buildings to begin with, especially if we admit that our estimates of the seismic hazard are just that: estimates.”
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