Call for Stats House floor hangers to be banned

Tuesday, 10 October 2017

Statistics House on Wellington's waterfront had not completed retrofitting of its floor plates fast enough to avoid a failure associated with its pigtail bindings.

The Ministry of Business Innovation and Employment (MBIE) wants to ban a building technique that caused in a modern Wellington building to partially collapse during the November Kaikoura earthquake.

'Pigtail' floor supports, which were found in the two partially collapsed floors of Wellington's Statistics House were highlighted by an independent expert panel for their poor performance in the 7.8 magnitude quake.

The pigtail, or loop bar connection, failed in Statistics House, contributing to a partial floor collapse during the Kaikoura earthquake.

The technique uses an embedded steel loop, or 'pigtail', which binds together concrete flooring and pillar supports.

The expert panel found the pigtail connection contributed to the Statistics House's concrete floors partially collapsing.

Dunning Thornton managing director Adam Thornton said an 'outright ban' was not the answer.

Two floors in the five-storey Statistics House partially collapsed following the 7.8-magnitude earthquake last November.

* 'Unacceptable' performance of Stats House in 2016 quake: Building Minister Nick Smith

* CentrePort warned of 'critical issue' in Statistics House in 2013

Engineering New Zealand chief executive of Susan Freeman-Greene supports a ban of the pigtail hanger.

* Steel stretched in Wellington high rise during Kaikoura quake

* Stats NZ boss: I'm asking the same questions that you're asking about our headquarters**

Building and Construction Minister Nick Smith said in March that the performance of Statistics House, which was completed in 2005, 'was unacceptable and could have caused fatalities'.

The building's owner, CentrePort Wellington, confirmed this week the badly damaged building would be demolished.

But some structural engineers did not think an 'outright ban' on the pigtail connection was the right answer in preventing a collapse in the future.

Dunning Thornton, the engineering firm that assessed the building in 2013 and 2016 recommended modifying the pigtail floor supports with extra brackets within five to 10 years.

At the time of November's earthquake, a retrofit program to improve the supports of the pre-cast floor units had been underway at Statistics House for two months.

An MBIE spokeswoman said: 'It is worth noting the floors whose retrofit work had been completed did not fail during the earthquake.'

Dunning Thornton director Adam Thornton said strengthening elements could be added to existing pigtail connections, and even replacement technology still suffered the weakening effects of 'beam dilation', a condition where the concrete beam stretches under pressure.

'I'm not sure that an outright ban is the right answer'.

Thornton said shear walls and bracing could lower risk, and more rigid beams would better maintain the integrity of concrete flooring in an earthquake.

The MBIE spokeswoman said if the ban went through, each building containing the pigtail connections would be assessed on an individual basis, and even buildings with the same floor system as Statistics House could be safe.

Alternatives to pigtails were understood be be 'cost neutral', she said.

MBIE has opened public consultation on the ban and is accepting submissions until November 20.

Engineering New Zealand, formerly IPENZ, chief executive Susan Freeman-Greene said the organisation supported the Government's move to ban pigtails.

'Engineers had raised some concerns about pigtails before the Kaikoura earthquake, and their use was being phased out.'

A ban on pigtail hangers has been floated by the industry for years.

In 2008 the New Zealand Structural Engineering Society said, '[The pigtail] has been used extensively in New Zealand for approximately 35 years and has performed well under gravity loading'.

'However some designers and pre-casters have recently abandoned it, citing manufacturing and safety concerns in particular with seismic loads.

'Therefore, it is recommended that until further research demonstrates otherwise, designers and precast manufacturers should avoid pigtail hangers.'