Rebuilding stronger, safer, smarter

DAVID KILLICK
Last updated 07:56 20/08/2014
Base isolator
IAIN MCGREGOR/Fairfax NZ

FIRST BASE: Henri Gavin, an associate professor at Duke University in the United States, inspects the rubber base isolators in the basement of Christchurch Women’s Hospital.

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OPINION: Christchurch has a first-class opportunity to lead the world in earthquake-resistant design - by building back stronger, safer and smarter.

Are we doing that? Could we be doing more? It is crucial we don't put short-term costs - by building cheaply - ahead of long-term gains.

As devastating as the earthquakes were, the Christchurch death toll could have been far higher.

We can thank building regulations, developed over decades, and the use of predominantly lightweight timber construction that it wasn't.

The most lives were lost in one building, the CTV building, an atrocious design which should never have been built.

Unreinforced or poorly reinforced masonry, stone and brick buildings failed and collapsed or were seriously damaged.

Building owners, businesses and regulators should have known that some buildings would not be able to withstand a big quake, but thought that was unlikely, so took a calculated risk and did nothing.

Now, nearly four years after that first shocking early morning wake-up call, it is critical that new buildings are as safe and earthquake-resistant as possible. It's a fundamental issue that affects everyone - homeowners and business owners, those wanting to rebuild or buy new.

The challenge is not only to design buildings that keep their occupants safe, but that can also survive a big quake with little or no damage.

Building back better is an insurance policy that could pay big dividends.

You had better hope that the designers of the new proposed $500 million Christchurch Convention Centre get it right.

The site is swampy ground in the central city close to the river and not too far from the existing Town Hall, the fate of which is uncertain.

Some critics have questioned the suitability of building in the central city again at all.

Fortunately, the owners of some new buildings going up around Christchurch are doing their best to future-proof their investment by incorporating the best earthquake- resistant design in excess of simply what regulations dictate.

You don't necessarily see the features from the outside, but they certainly make a difference. Some of the designs are exciting and there is a definite buzz among those involved in their development that progress is happening.

Last month, I wrote about the Trimble building, designed by Opus Architecture.

The building is constructed from post-tensioned, pre-stressed laminated timber (Pres-Lam), a system developed at the University of Canterbury.

Steel "dissipators", tendons and brackets take up the energy in a quake and can easily be adjusted or replaced.

University of Canterbury professor emeritus of engineering, Andy Buchanan, showed me through another building, the Merritt building in Victoria St, which uses the same technology.

Buchanan says this laminated timber construction, using a sustainable locally produced resource, has great potential, both in New Zealand and around the world.

Other systems are also taking off. Opus Architecture principal architect Colin Corsbie and practice manager Julian O'Sullivan showed me some other new developments.

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The Waimairi Beach Golf Clubhouse - in part of the city badly hit by the quakes - is a new single-storey building that sits on a stiffened concrete raft on remediated ground.

Yes, you can still build in many areas if you build for the conditions.

A four-level reinforced concrete office building at 138 Victoria Street, next to the Merritt building, is base isolated with lead rubber bearings and is piled to 26 metres "to provide the highest level of seismic protection possible".

Base isolators look rather like giant shock absorbers.

They substantially reduce the impact of earthquake forces on the structure, minimising damage to the building itself.

New Zealand engineer Dr Bill Robinson developed base isolation technology in the 1970s, but until recently only a few buildings in this country have used it.

One reason cited has been cost. However, Corsbie says this is a misconception; he says cost is similar in most cases or only around 2 per cent higher.

(Wellington's Te Papa and the Christchurch Women's Hospital are base isolated. The new four- storey Triangle Centre will also have base isolators.)

In Japan, I saw advances in base isolation technology allowing buildings to better resist both up- and-down and sideways movement.

Sometimes you need deep piles down to solid rock. The new Opus office on Moorhouse Ave has a piled foundation to 26m.

New piling technology is reported to provide "improved foundation performance and reduced environmental impact".

Seismic sliders, base isolators, viscous dampers, buckling restraint braces and deep piling are part of the new language of architecture in Christchurch. So the technical details may not sound as sexy as smart facades, but they do really matter.

The world is still watching. A recent delegation from Sichuan, in China, was keen to know more about what Christchurch is doing.

By developing and sharing technology, Christchurch can literally build itself a better future.

- The Press

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