Brittle columns led to CTV building deaths

Non-ductile columns and the asymmetrical layout of shear walls of the CTV building in Christchurch were unable to withstand the February 22, 2011 earthquake.

This was the main finding of a government-commissioned Department of Building and Housing technical investigation.

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

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

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.

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.

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

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

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,” according to Department of Building and Housing CEO Katrina Bach.