Interior columns in the Canterbury Television (CTV) building were "more susceptible'' to failure than the exterior ones - contrary to the findings of a report on its collapse, a royal commission inquiry has heard.

Structural engineering professor Nigel Priestley today gave evidence during week three of an inquiry into the CTV building's collapse during the deadly February 2011 quake. The collapse claimed 115 lives.

Priestley was deputy chairman of an expert panel of engineers commissioned by the Department of Building and Housing (DBH) to investigate the failure of modern buildings in the central city during the quake, including CTV. 

The CTV report, released in January and signed off by the panel, 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.

Yesterday, Priestley told the royal commission that while he agreed with the general findings of the report, there were some aspects that he personally did not agree with.

Priestley said the failure of the interior columns was more significant than the exterior columns.

If an interior column failed, it would pull the others toward 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 onto 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.

Priestley was a former Professor of Structural Engineering at the University of California and former senior lecturer at Canterbury University.

Earlier today, the royal commission heard from a US engineer who said that more reinforcement in the CTV building's columns would have made no difference to whether it collapsed.

William Holmes, a structural engineer from California who peer reviewed the DBH report into the CTV collapse,  opened evidence at the inquiry this morning.

The expert panel which investigated the CTV collapse for the DBH found the building's collapse 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.

However, Holmes took the opposite view. He 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 themselves were the same, he said.

- © Fairfax NZ News