Clarendon Tower 'a horror story'

Tower was failing before February quake

MARC GREENHILL
Last updated 17:41 13/03/2012
Clarendon Tower
Dean Kozanic
CONCRETE HORROR: Clarendon's reinforcing was failing in September.

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Christchurch Earthquake 2011

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The performance of Christchurch's Clarendon Tower in the February 2011 earthquake was a ''bit of a horror story'', an inquiry has heard.

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

Academics, senior practising engineers and professional engineering organisations have been invited to debate building design philosophies, such as life safety versus building survivability, and associated economic impacts.

Des Bull, a professor of civil and natural resources engineering at the University of Canterbury, told commissioners the loss of floor support in quake-affected buildings was a ''major issue''.

He used the Clarendon Tower, a 17-storey central-city building now being demolished, was an example of a ''textbook'' concrete building built after 1980.

The quake collapsed internal stairwells in the building, forcing people to wait hours to be rescued as aftershocks rumbled across the city.

Cracks up to 35 millimetres wide - large enough to see through to the storey below - appeared after a beam in the tower's northwest corner elongated and separated the column from the pre-cast concrete floor, Bull said.

The reinforcing used, which was common in buildings built in the past 30 years, was ''quite brittle''.

''At best, it can expect 5mm [movement] before breaking. To be honest, conventional reinforcing today, which is quite tough, can only handle 15mm worth of crack before it snaps,'' he said.

''The reinforcing in this particular building was failing all over the floors even in September [2010], let alone what happened in February.''

The building ''ballooned'' and the bulging caused the floor to drop 35mm, Bull said.

''When it was surveyed, the building was 100mm wider in the middle between level seven and level eight than it is at the ground up to level 18.''

The floor separation was general problem with all reinforced-concrete buildings around the world, he said.

The Clarendon Tower was a ''bit of a horror story'', but changes to the concrete code in 2006 helped ensure floors would not fall even if supporting beams separated, he said.

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