Building better to save lives
The Christchurch and Kaiko¯ura earthquakes have done a lot to change building owners’ and developers’ views when it comes to designing for earthquake safety, a Wellington engineer says.
As the third anniversary of the Kaiko¯ura earthquakes nears, people are reportedly asking for better materials and techniques that exceed what the Building Act requires.
Hamish McKenzie, principal, structures, at Holmes Consulting, says the act is predominantly aimed at reducing deaths rather than damage, but it doesn’t have to stop there.
‘‘I think people have learned the need for good design, the benefits of going a bit further than the Building Act minimum and risk-to-life safety imperatives. We need to keep learning the lessons so that we continue to build better buildings for the future.’’
Five years after Christchurch’s devastating 2011 earthquake, Kaiko¯ura’s 2016 quake created widespread business disruption in its epicentre and in Wellington.
Many businesses were forced to leave the capital’s centre temporarily and buildings were unoccupied for long periods.
At least eight buildings were deemed irreparable, including the city’s BNZ building, a modern building on reclaimed land, which is only now being demolished.
The buildings in Wellington most affected by that quake were mid-rise buildings (six to 10 storeys) sitting on softer, more flexible soils.
While preventing death is all important, owners and insurers are now asking how buildings can also get back to normal more quickly after a major shake, McKenzie says.
Materials and structural solutions that are less vulnerable to damage and easier to repair include ‘‘base isolators’’, the lead-rubber bearings already used by Te Papa and Parliament House.
Another option are ‘‘viscous dampers’’, which reduce shaking in higher, more flexible buildings, whereas the base isolators are better for low-rise or squat buildings, McKenzie says.
Braced steel and rocking concrete wall systems are also becoming more common, and there is more interest being shown in lightweight timber options.
Although some of these technologies have traditionally been thought of as too expensive, McKenzie says structure accounts for only about one-fifth of a building’s cost, and base isolators might increase those structural costs by 5- to 10 per cent.
‘‘It’s not necessarily a big cost premium to use some of these technologies when you look at the cost
of still being able to use a building after an earthquake.’’
He says insurance, which has traditionally been relatively easy to get in New Zealand, is also getting harder to secure, and that adds some incentive for building owners to go the extra mile.
McKenzie, who was in Wellington when the Kaiko¯ ura earthquake
We need to keep learning the lessons so that we continue to build better buildings for the future. Hamish McKenzie Principal, structures, at Holmes Consulting, right
hit at midnight on November 14, 2016, has worked on many buildings impacted by the damage, including the Majestic Centre.
His company has also worked on the retrofitting of the city’s old Town Hall, the Aurora Centre on Lambton Quay, and it continues to work on the restoration of Bowen Campus next to Parliament.