By Ally Mullord and 3 News online staff
A report into the Canterbury Television building collapse has found the building did not meet building standards for the year it was constructed.
The Department of Building and Housing has released its findings following a Government-ordered technical investigation, and says the ductility and strength of the building’s columns did not meet 1986 building standards.
The report found the below-standard columns were likely contributors to the CTV building’s collapse during the Christchurch quake on February 22 last year.
A number of possible collapse scenarios were identified by the investigation, but the high number of factors involved has made it difficult to identify a specific collapse scenario. One hundred and fifteen people were killed in the building collapse.
Police held a media conference this afternoon following the release of the Department of Building and Housing report.
Assistant Police Commissioner Malcolm Burgess said police are to assess whether there is potential for criminal culpability over the CTV collapse, and if so an official investigation will take place.
He says it is a very complex situation and difficult to determine whether criminal nuisance or manslaughter can be established.
Mr Burgess says it would be wrong to suggest charges will naturally follow the assessment. But if criminal charges are laid, it will be an “unprecedented case”.
The report, carried out by Hyland Consultants and StructureSmith, identified three critical factors leading to the building’s collapse.
1. Intense ground shaking.
As well as intense horizontal shaking, the CTV building was also subject to one of the highest levels of vertical acceleration recorded in any urban environment.
2. Non-ductile columns
A lack of ductility (being able to change shape without breaking) in the columns made them brittle in the earthquake, and more likely to break. All of the possible collapse scenarios identified by the panel involved the failure of one or more of the columns on the east side of the building, which would have greatly increased the load on the remaining columns and forced the collapse; this is consistent with eyewitness accounts from the day of the quake. Testing on the columns following the building collapse also found they were significantly weaker than expected.
3. Asymmetrical layout of shear walls
The asymmetrical building layout meant the building could twist during the earthquake, contributing to the strain placed on the already brittle columns
The CTV building was constructed in 1986 – however the ductility and strength of the columns, and the asymmetrical layout, were found not to have met 1986 building standards.
Other contributing factors may have included:
- low concrete strength in critical columns
- Low concrete strengths in some of the critical columns.
- Exceptionally high vertical ground movement.
- Possible interaction of columns and concrete spandrel panels (on the external face of the building), making the columns less flexible.
- Separation of floor slabs from the north core of the building.
- Structural influence of the concrete masonry walls, making lower floors more rigid than upper floors, which placed additional stress on the upper columns during the earthquake.
The expert panel drew several conclusions from the investigation into the CTV building failure, the majority of which focused around the need for increased assessment of pre-1995 buildings and, where required, retrospective retrofitting.
Department of Building and Housing Chief Executive Katrina Bach says the Department has already taken action on some of the Expert Panel’s recommendations, and will work with the building and construction sectors and local government to implement the remaining recommendations over time.
She says the findings of the investigation “will make a difference to the way the buildings are designed and constructed in the future – both in New Zealand and internationally”.
The investigations were carried out by a group of leading engineering consultants and referred to eye witness accounts, photographs, site examinations, sampling and testing of materials, structural analysis and testing of various hypotheses using established engineering models.
The investigation will inform the Canterbury Earthquakes Royal Commission of Inquiry.
3 News