More than half of the 342 buildings earmarked for review following the devastating earthquake in New Zealand in 2011 have either been cleared or excluded, according to NZ Building and Construction Minister Maurice Williamson.
The review of buildings with non-ductile columns is being led by the Ministry of Business, Innovation and Employment. The Ministry is seeking to establish whether there are any buildings with similar design flaws to the Canterbury Television Building, which collapsed in the February 22, 2011 earthquake, killing 115 people.
Testing of circular concrete columns following the Canterbury Earthquakes showed that those in structures designed between 1982 and 1995 may fail in a sudden non-ductile manner initiated by the buckling of the reinforcing steel at lower than expected loads and drifts.
The move was commended by Dr Clark Hyland, director of specialist fatigue and earthquake engineers with Hyland Consultants, but he has encouraged continued vigilance on the part of building owners.
“It is good to see progress with identifying the problem buildings, and the Minister's role in this is commendable,” he said. “But it is important to recognise that the criteria for identifying the buildings with the non-ductile column issues are not comprehensive and are just an initial filter.”
“It should not be assumed that buildings not fitting within the three criteria of 30 May 2012 won't have a problem. It is worth owners getting a structural engineer to make an assessment of their building for their own peace of mind if they are not sure.”
Hyland said there appeared to be varying method for assessing the issues as there is no codified approach.
For example, the criteria do not cover cases where there is a lack of reinforcing steel in beam-column joints. This was also found to be a possible contributing factor in the collapse of the CTV Building.
Another area for vigilance, suggests Hyland, is the ends of concrete or concrete block walls with one layer of reinforcing steel where non-ductile failure effects can occur.
The Building and Construction Minister has confirmed that there are a further 128 building engineering assessments booked and that councils are following up with the remaining 39 building owners to check when assessments are to be completed.
Two building owners in Auckland who had refused to perform an engineering assessment have now changed their minds.
“This is very pleasing as the review is being done for reasons of public safety,” said Willamson.
“I need to stress that just because a building has non-ductile columns it does not mean it is unsafe. If such buildings are balanced out by other design features they pose no greater danger than other buildings. It’s important to reiterate the CTV building failed catastrophically due to many more issues than just non-ductile columns, including a flawed design.”