A report into the Canterbury Television building collapse failed to fully consider earthquake damage caused before February 2011, an inquiry has heard.
Professor John Mander, a Cantabrian now working in the Department of Civil Engineering at Texas A&M University, today told the royal commission that the September 2011 quake produced close to the full forces and ground acceleration the CTV building was designed to resist.
"By design, significant damage would be expected from such a level of ground shaking," he said.
"The fact the CTV building survived [the September quake] with only minor visually observable damage is a testament to the efficiency of a design that met the aims and objectives of the design codes.
"For any structure to survive such a high level of shaking is a bonus. It was certainly not the requirement at the time the CTV building was designed and constructed in the late 1980s."
A Department of Building and Housing report, released in January, found design and construction flaws in the building.
The report neglected the cumulative effects of the earlier quakes, Mander said.
"While much higher than expected ground motions were observed during the Christchurch earthquake, focusing the discussion on this disregards the fact that the CTV building, and indeed all structures in the Christchurch area, suffered varying degrees of damage [in September 2010]," he said.
Mander earlier told the hearing that Christchurch buildings should have been treated as "guilty until proven innocent" after the September 2010 quake.
Mander said the CTV building should have been red-stickered before the fatal collapse in February last year.
He was called by counsel for the building's designer, Alan Reay Consultants.
The September quake caused "exceptionally high" ground forces that reached the capacity the CTV building was designed to withstand, Mander said.
The damage sustained meant it was "ill-prepared" for a second quake exceeding forces intended in 1980s design standards.
More caution was needed when assessing buildings after September 2010, he said.
"We're all guilty as engineers, in the sense that we didn't realise the severity of what was lurking,'' he said.
"From what I can tell, people went ahead in good faith and made inspections very quickly, and if they saw nothing, then nothing was wrong."
Buildings were inanimate objects and "you didn't have to be worried about offending them", Mander said.
"I believe we should work and operate under the adage that these buildings are guilty until proven innocent."
A person "walking on the street" could have determined column failure was the cause, Mander said.He dismissed conclusions in the Department of Building and Housing report into the collapse as "too vague to be meaningful".
The royal commission resumed today after being halted last week because of commissioner Ron Carter being ill.
The inquiry into the CTV building collapse is now in its fifth week.
More than 80 witnesses will be called during the eight-week inquiry, which will cover the initial building consent issued by the Christchurch City Council, the construction and design, identification of a structural weakness in 1990, and the assessment after the September 4 and Boxing Day quakes in 2010.
The commission has until November 12 to complete its work.