Media release – Department of Building and Housing

9 February 2012

Experts identify critical factors in CTV collapse

Intense ground shaking, non-ductile columns and the asymmetrical layout of shear walls were the critical factors contributing to the collapse of the CTV building during the 22 February 2011 Christchurch earthquake, a Department of Building and Housing technical investigation has found.

The Government ordered the investigation in March 2011, along with investigations into the failure of the Pyne Gould Corporation, Forsyth Barr, and Hotel Grand Chancellor buildings, following the 22 February 2011 6.3 magnitude earthquake, which claimed the lives of 184 people, including 115 in the CTV building.

The Department of Building and Housing established a group of leading engineering consultants to conduct the investigations, which were peer reviewed by an expert review panel, chaired by construction law expert Sherwyn Williams.

The comprehensive investigations included eye witness accounts, photographs, site examinations, sampling and testing of materials, structural analysis and testing of various hypotheses using established engineering models.

The investigation into the 1986 CTV building was conducted by Hyland Consultants and StructureSmith.

Three critical factors were found that contributed to the building’s collapse:
1. Intense horizontal ground shaking.
2. Lack of ductility in the columns, making them brittle.
3. Asymmetrical layout of the shear walls, making the building twist during the earthquake, placing extra strain on the columns.
4.
The ductility of the columns (and strength) and the asymmetrical layout of the shear walls were found to have not met the building standards of the day (1986).

Other factors that may have contributed to the CTV collapse included:
• 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
Although it is not possible to be definitive on the sequence of the building’s collapse, the common denominator in all collapse scenarios identified by the Expert Panel was the failure of one or more columns on the east face of the building. This is consistent with eye-witness accounts of the building during the earthquake.

Current building requirements are more stringent now than in the 1980s when the CTV building was constructed. Standards have progressively improved over time as more is understood about how buildings respond in earthquakes.

Department of Building and Housing Chief Executive, Katrina Bach, said the Department has already taken action on some of the Expert Panel’s recommendations, and will implement the others working with the building and construction sector and local government over the coming months and years.

“The findings of the investigations and the learnings from 22 February will make a difference to the way the buildings are designed and constructed in the future – both in New Zealand and internationally.”

Ms Bach said the technical investigation would inform the Canterbury Earthquakes Royal Commission of Inquiry.

“Copies of the Expert Panel report have been provided to the Police and the Institution of Professional Engineers New Zealand for their consideration and action as appropriate.”

Ms Bach said she expected Territorial Authorities (councils) to take close notice of the reports as they developed there own programmes of work to address earthquake risks.

She also encouraged property owners and building users to seek information about the standard of their buildings.

ENDS

To view the final reports visit http://www.dbh.govt.nz/canterbury-earthquake-technical-investigation

[Scoop copy: Executive Summary: Structural performance of Christchurch CBD buildings in the 22 February 2011 earthquake (PDF)]

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