Ban floated after quake building fail
The Ministry of Business, Innovation and Employment (MBIE) wants to ban a building technique that resulted in a modern Wellington building to partially collapse in the November Kaikoura earthquake.
‘‘Pigtail’’ floor supports, which were found in the two partially collapsed floors of Statistics House were highlighted by an independent expert panel for their poor performance during the 7.8-magnitude quake.
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 building’s concrete floors partially collapsing.
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 that the badly damaged building would be demolished.
But some structural engineers did not think an ‘‘outright ban’’ on the pigtail connection was the solution.
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 programme to improve the supports of the pre-cast floor units had been under way 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 replacement technology still suffered weakening from ‘‘beam dilation’’, when the beam stretches under pressure.
‘‘I’m not sure that an outright ban is the right answer. The issues arise when the concrete floor stretches … It’s a known cause of failure in [concrete flooring],’’ he said.
Thornton said shear walls, bracing and more rigid beams could lower risk, but no building was earthquake-proof.
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.
MBIE is accepting public submissions on the ban until November 20.
Engineering New Zealand 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,’’ she said.
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 precasters 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 pre-cast manufacturers should avoid pigtail hangers.’’