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Innovative Christchurch buildings designed to beat quakes

Rescue workers at the collapsed CTV building Image copyright AFP
Image caption More than half of the 2011 earthquake's victims died in the Canterbury Television Building

A severe earthquake off the north-east New Zealand coast last week served as a stark reminder of why the country is nicknamed the Shaky Isles.

More than 15,000 earthquakes are recorded in the South Pacific nation each year, but only about 150 are large enough to be felt.

The 7.1 quake sparked a tsunami warning and reportedly caused some damage to property but no injuries.

It is a far cry to the magnitude 6.3 quake that struck Christchurch in February 2011, killing 185 people.

In Christchurch today, a white powdery compound, a cathedral made of cardboard and a hangar-like laboratory where earthquakes are created are all part of New Zealand's response to that catastrophe five-and-a-half years ago.

The commercial hub of the South Island sits to the east of the Alpine fault that snakes beneath the Southern Alps. But the tremor that left much of central Christchurch in ruins came from a previously unknown perpendicular fault that sent a devastating seismic wave through the ground.

As disaster struck, 115 people - more than half of the earthquake's victims - died in a single office block, the Canterbury Television (CTV) Building.

Its crumpled shell has become a defining image of one of New Zealand's worst natural disasters.

'Dream'

Academics, architects, the government and the construction industry are all striving to make buildings safer places to work, study and live.

Image copyright Geoff Rodgers
Image caption Geoff Rodgers at the University of Canterbury with rocking steel frames

"Our dream is to have a society that is much more resilient to this, and we're much better prepared and we suffer much less," explains Geoff Rodgers, from the department of mechanical engineering at the University of Canterbury.

We're in the new structural engineering laboratory on the campus a short drive from the city centre. It is huge.

In one corner of this cavernous space, mighty concrete barriers have been erected that will feel the force of simulated earthquakes, along with large-scale tests on internal steel beams and joints that make up a building's skeleton.

Steel beams

Geoff and his team talk of damping devices and energy dissipators - engineering terms for techniques that will help industrial and commercial premises absorb and repel the worst effects of damaging tremors, while steel-framed buildings would rock and sway but not give way.

Then there is what's called base isolation, where a large office block can mostly stand firm while the earth underneath moves.

"We'll be creating earthquakes on structures of small size, of big size and we'll be pushing them backwards and forwards, high speed, low speed to simulate all the aspects of the behaviour of a structure in a real earthquake," says associate professor Greg MacRae.

Image copyright Geoff Rodgers
Image caption A low-damage steel beam column connection using a lead extrusion damper to absorb energy

He shows me how special steel beams are being tested to see if they can safely slide and shift under pressure rather buckle and break.

"What we are doing is providing a special friction connection here so that as the building moves the beam rotates, and instead of buckling and twisting and having to be thrown away after an earthquake like we have with traditional construction, the friction just means that we get sliding on some surfaces.

"So the beam is actually okay, the plates should be okay and if something does need to be replaced it is just the bolts," he tells the BBC.

Magnesium oxide

Thousands of suburban homes were also left uninhabitable following the 2011 quake in New Zealand's second biggest city.

Timber frames and brick cladding have long been the staple of Kiwi residential building but architect Dean Buckeridge is crafting houses to better withstand earthquakes. The key ingredient is magnesium oxide, a white powdery compound.

"It is reinforced with fibreglass, bonded either side of a polystyrene core and that makes it extremely strong. It has the right balance of rigidity and elasticity so that it is able to withstand the earthquake shocks," he explains, outside a single-storey property he recently built.

Image copyright Dean Buckeridge
Image caption Architect Dean Buckeridge is crafting houses to better withstand earthquakes

"We have used the lessons in this house to completely re-evaluate the way we design and build," he says. "We've got houses now that we are offering that are going to be cheaper to build and will have almost no running costs in terms of electricity."

This warm, well-insulated new home is owned by Janet and Jeff Norton, an expatriate couple from the UK.

"It was obviously a very different thing to come to a country where earthquakes are almost part of everyday life. I have felt a few rumbles. I'm extremely pleased to be in this house and I don't think we could be in a better place to be honest with you," says Janet.

I ask her husband how safe he would feel if a major earthquake were to occur.

"The amount of engineering that has gone into this house is way over what I have experienced in the past so this house is very, very durable and it will literally be one of the last houses standing," he tells me.

'Airy'

In the centre of Christchurch the multi-billion dollar reconstruction continues, and near the CTV site, rising skywards there is a beacon of hope, and durability.

It's quite possibly the world's newest cathedral and the only one made of cardboard that was built as a temporary replacement for the city's badly damaged Anglican Cathedral, which remains wounded and mostly untouched.

Inside the giant A-framed church built of recycled cardboard (and bolstered by laminated timber and reinforced steel) rows of pews face a large cross, which is, naturally, fashioned from cardboard.

Image copyright Getty Images
Image caption Christchurch cardboard cathedral has a "Zen Buddhist" feel to it, the Dean says

"It is a wonderfully light space, an airy space. It has got this sort of lovely almost Zen Buddhist feel to it," says the Very Reverend Lawrence Kimberley, the Dean of the Christchurch Transitional Cathedral.

"Earlier this year on 14 February we had another strongish aftershock. You could barely tell that anything had happened when you're in here and most people felt so safe they didn't want to get out and they just carried on doing their thing. So it feels safe and it is a safe building," he says.

Christchurch's response to disaster will help others in earthquake-prone regions - including those in central Italy still coming to terms with last month's catastrophe - not only recover from tragedy, but be more resilient in the future.

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