Taking The Shake Out of Quakes

By Bridget Gourlay

One of the deadliest earthquakes of all time occurred in Portugal’s capital in 1755. Believed to be nearly a nine on the Richter scale, the Lisbon earthquake was followed by fires and a tsunami, killing up to 100,000 people in the surrounding countries it affected.

The Portuguese empire never recovered.

Three hundred years later, and our buildings are made of much stronger stuff, as we’ve witnessed in Christchurch. Other than the collapse of the CTV and PGG Wrightson buildings, most of our modern buildings held up extremely well.

Current building design protects lives via sacrificial damage, protecting the occupants much like cars in a crash. The buildings stay up through earthquakes but later need repair or to be knocked down.

But just like in 1755, big earthquakes leave extensive damage. Homes can’t be lived in, businesses can’t open, hospitals can’t provide critical services, and in Christchurch the entire CBD has been shut for months. The damage to New Zealand’s economy from this event will last for years.

“If you look through time to the Lisbon earthquake there were thousands of deaths,” Canterbury University’s Dr Geoff Chase says.

“According to a study I read, it cost them about 20-25 percent of GDP. Today the lives lost as a percentage of population have gone down to become extremely small. That’s not to diminish the 181 who lost their lives here, but it has become extremely small. “Meanwhile, the actual cost of GDP to a country has stayed the same. Christchurch’s earthquakes will be about 15-25 percent of GDP. We’ve got very good at saving lives. The next step — and it sounds mercenary — is about saving money.”

accuators

Retro-fit accuators: Concrete and steel connections using lead extrusion dampers directly in the joint to save buildings.

Energy absorbtion

That’s why Chase and a team of Canterbury engineers — Lance Cleeve, Geoff Rodgers, Greg MacRae and Doug Heaton — have created a new type of building dissipator. “Using a high capacity energy dissipating device (with lead inside) fitted into the joint itself, these dissipators absorb energy with every shake, causing almost no damage to the structure.

Unlike other damage-free earthquake engineering technologies, these dissipators only cost between $100 and $400 and can be retro-fitted to existing buildings.

The team believes that with these dissipators, if there is another big earthquake, then people will be able to go back to work quickly afterwards. The devastating affect the earthquakes have had on businesses, especially SMEs, would be minimised.

“Our fathers and grandfathers had some great ideas about how to make buildings life safe,” Greg MacRae says.

“What was done in the 1980s with 80s technology was to make buildings that would stay up during an earthquake and everyone would get out.

“What we’re trying to work towards is a building that is made with 2000s technology that will not only protect life, but mean the structure is useable after an earthquake.

“Think of a cellphone from 1980s — they worked but were clunky and expensive and the batteries needed to be charged all the time,” MacRae says.

Lance Cleeve and Doug Heaton have set up a business selling the dissipators but the team has had a hard time getting the industry to change its thinking, even though their design has held up well to extensive testing. “The words ‘first mover’ and ‘civil engineer’ don’t usually go in the same sentence unless there’s something like ‘are not’ in between. That’s the real problem,” Chase says.

“Design codes have done a lot to increase consistency and improve performance of structures but they’ve now regimented people’s thinking that things can only be done in one way.”

For more information contact lance.cleeve@cmtechnologie.com

Author: magazinestoday

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