IAIN MCGREGOR/Fairfax NZ
ENGINEER: William Holmes.
Interior columns in the Canterbury Television building were "more susceptible'' to failure than the exterior ones, contrary to the findings of a report on the building's collapse, an inquiry has heard.
Structural engineering professor Nigel Priestley today gave evidence during week three of the inquiry into the CTV building's collapse during the February 2011 quake.
The collapse claimed 115 lives.
Priestley was deputy chairman of a panel of engineers commissioned by the Department of Building and Housing to investigate the failure of modern buildings in the central city during the quake.
The CTV building report, released in January, found the building did not meet the design standards of the day when it was built in 1986.
The most likely causes of its collapse were brittle columns, intense horizontal ground shaking and the asymmetrical layout of structural walls, causing the building to twist and place extra strain on the columns.
Priestley told the royal commission that he agreed with the general findings of the report, but there were some aspects that he did not agree with.
The failure of the interior columns was more significant than the exterior columns, he said.
If an interior column failed, it would pull the others towards it, he said.
Witnesses of the collapse described the building falling mostly into its own footprint.
"If we imagine we have an interior column which has failed, if it fails, the beam does not have enough strength to support the load it carries. It will start to sag very significantly,'' he said.
"This would place vertical and horizontal actions on to the next form of support - the next column.
"The interior columns were significantly more susceptible to failure than the exterior ones.''
Priestley said if investigators had used a technique called a non-linear analysis, it would have produced more accurate results.
However, this technique was halted in favour of another method, he said.
Engineers' differing opinions on CTV reinforcement
More reinforcement in the Canterbury Television building's columns would have made no difference to whether it collapsed, a United States engineer has told a royal commission.
William Holmes, a structural engineer from California who peer-reviewed a Department of Building and Housing report into the CTV building collapse, opened evidence at a royal commission inquiry today.
The report also found the building did not meet the standards of the day when it was built in 1986.An expert panel that investigated the collapse for the department found it was "almost certainly" initiated by the failure of one or more columns on the east wall, facing Madras St, during the February 2011 earthquake.
Panel member Rob Jury, a structural engineer consultant, said yesterday that the building's columns might have withstood the failure if they had been reinforced by a type of steel known as confinement.
Holmes said the beam column joints were more important.
If the column joints had been reinforced, the collapse may have been partial or localised even if the columns were the same, he said.
The commission has adjourned until 2.15pm, when it will hear from the expert panel's deputy, Nigel Priestley, a former professor of structural engineering at the University of California and former senior lecturer at Canterbury University.
Priestley defended the DBH report as "a very thorough piece of work" after it came under attack from the designers when it was released in January.