Safer designs affordable - expert

Last updated 05:00 14/03/2012
Des Bull

NEW WAYS: Canterbury University concrete design engineer Des Bull says buildings should be designed and built differently in future.

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Technology to help new buildings in Christchurch survive earthquake damage is affordable, a structural engineer says.

New technology for the central-city rebuild was yesterday discussed before the Canterbury earthquakes royal commission.

Low-damage designs discussed included base isolation – a design method that allowed a building to move on its base and absorb ground shaking – and precast seismic structural systems (Presss), which allows controlled rocking of a structure's joints.

Engineering company Structex designed the endoscopy unit at Christchurch's Southern Cross Hospital using Presss technology.

Director Gary Haverland told commissioners the building, completed in August 2010, used precast concrete walls and post-tensioned frames.

The build was $30,000 under the $7.2 million budget and was completed ahead of schedule.

The February 2011 quake caused "minor" cosmetic damage, and Haverland believed the structural system performed well.

Structural engineer John Hare, of Holmes Consulting Group, said new building technology was "well established but not well used".

Holmes had designed six buildings using base isolation at a rate of one about every five years.

"Assuming we ask ourselves the question and do want better performance from our buildings, we have to ... be sure the new technologies we go to are actually going to perform better, otherwise we might repeating some mistakes of the past," Hare said.

The existing technology "hasn't really let us down".

"If a building was regular, well-conceived, well-detailed, well-constructed and on good ground, by and large it's performed very well even though it's been through loads potentially up to twice what they were designed for," he said.

Des Bull, a professor of civil and natural resources engineering at Canterbury University, told the commission design changes were needed.

"The whole issue is should we continue to build conventional buildings as they've done for 30 years? Personally, I don't think we should," he said. "There are plenty of options with new technologies for future buildings just to rearrange the connections between the walls, beams, columns and foundations such that we don't have these intrinsic, systemic problems that we have with all our current building stock," he said.

Damage to building connections could not be repaired in most cases and resulted in demolition, Bull said.

The effect was like bending a paperclip until it snapped.

"They might be able to survive a subsequent series of smaller aftershocks, but could they survive another major event in the next 20 or 30 years? Highly unlikely, and that's some of the reasons these buildings have been brought down. They have nothing left in them to resist big earthquakes and are too expensive to repair," Bull said.

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- The Press


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