Structural problems as well as intense ground shaking contributed to the collapse of the CTV Building in Christchurch last February and the deaths of 115 people, a new investigation has found.
Results of a technical investigation by an expert panel established by the Department of Building and Housing into the building’s collapse during the 2011 Christchurch earthquake have now been released. They indicate that along with intense ground shaking, problems such as non-ductile columns and the asymmetrical layout of shear walls were critical factors in the building’s collapse.
The investigation, along with other investigations into collapses of the Pyne Gould Corporation, Forsyth Barr and Hotel Grand Chancellor buildings, was ordered by the government in March following the February 22 earthquake which claimed the lives of 184 people, including 115 in the CTV building.
Conducted by Hyland Consultants and StructureSmith, it included eyewitness accounts, photographs, site examinations, sampling and testing of materials, structural analysis and testing of various hypotheses using established engineering models.
The investigation found that three critical factors contributed to the building’s collapse. They include:
- Intense horizontal ground shaking
- Lack of ductility in the columns, making them brittle
- Asymmetrical layout of the shear walls, making them twist during the earthquake and placing strain on the columns.
Crucially, the report says that the ductility of the columns (and strength) and the asymmetrical layout of the shear walls were found not to have met the building standards of the day.
Other factors which the report said contributed to the collapse include 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; and 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 the report specifies that it is not possible to be definitive about the sequence of the building’s collapse, it says that failure of one or more columns on the east face of the building was the common denominator in all possible scenarios.
Department of Building and Housing Chief Executive, Katrina Bach, says that the department has taken action on some of the panel’s recommendations and will work with local government and the industry to implement others in the future.
“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” Bach says.
The department says that building standards have improved over time in response to better understanding about how buildings respond to earthquakes. It also says current building requirements are more stringent now than what they were in the 1980s when the CTV building was constructed.