The New Zealand engineering community needs to clarify how earthquake-hit buildings are assessed, in the wake of the fatal February 22 earthquake in Christchurch which killed 182 people.
A top earthquake expert told the Royal Commission hearings into the Canterbury earthquakes today that there is public confusion over how buildings are inspected by engineers post-earthquakes.
Rob Jury, structural engineer at Beca, said: "There has obviously been a mis-match between what the engineering profession believes they are doing and what the public thought they were doing.
"That's not necessarily solely the engineering profession's making - I know there have been a number of us for a number of years trying to explain what it is we could be doing once an earthquake does occur and in the aftermath of an earthquake.''
The admission came after several days of evidence from engineers who inspected the Pyne Gould Corporation (PGC) building in Christchurch city centre before it collapsed during the fatal February earthquake. Eighteen people died in the building.
Structural engineers from Holmes Consulting Group (HCG) Ltd inspected the building four times after the magnitude 7.1 earthquake of September 4 and concluded it was "safe to occupy'' - despite fears being raised from workers and tenants inside the five-storey Cambridge Terrace building.
However, Mr Jury said: "Safety is a very relative term. I don't think that anyone has explained by what we think 'safe to occupy' means.
"I would not deliberately use the word 'safe' because it means different things to different people.
"No building - even modern buildings - are absolutely safe from earthquake shaking.
"If you get an earthquake like February, it's not beyond the realms of possibility that a real modern building could find itself under stress.''
But he also alluded to the fact that Christchurch business owners were desperate to enter their buildings as soon as they could after the shake.
He added: "From my own observations, I can say that after September, a lot of people wanted inside their buildings very quickly to get their personal belongings out.
"If buildings had been closed at that point, it would really have affected the way the city became operational again.''
Beca produced a report for the Department of Building and Housing on the PGC building's collapse, which ruled it came down after the central core wall failed on the eastern side of the first floor.
The report concluded its collapse came as a result of intense shaking which the building was not designed to cope with, rather than from damage sustained in earlier quakes, the reports says.
HCG director John Hare earlier gave evidence supporting the conclusions of his structural engineers Mark Whiteside and Alistair Boys who inspected the building a total of four times between September 7 last year and February this year, and concluded each time that it was "safe to occupy''.
They were questioned by commission lawyer Marcus Elliott on why they ignored previous HCG reports that deemed the building as having "severe weakness seismically'' and being "earthquake prone''.
The pair said they were instructed to carry out basic, Level Two assessments, which were a quick, visual inspection of the building to determine if it had been significantly weakened by quake damage.
Mr Hare, president of Structural Engineering Society New Zealand and who is currently seconded to Canterbury Earthquake Recovery Authority (Cera) as its acting principal engineer and adviser, backed his engineers' conclusions, and said he would have done the same thing.
He said that referring to old reports would simply have been "irrelevant'' to their task.
However, he did accept that "with hindsight'', a detailed assessment - which included a more invasive investigation of the building and its history - is what should have been instructed by the building owner.
Mr Jury produced a dramatic computer graphic which depicted how the building reacted to the violent ground shaking of the February event.
The 'time history analysis' footage showed the building swaying and bending before the magnitude 6.3 earthquake peaked in intensity and a "very large lurch'' resulted in cracks in the columns around its perimeter and one of the main walls began to fail.
The latest phase of the Royal Commission hearings into the Canterbury earthquakes, which is focusing solely on the collapse of the PGC building in the centre of Christchurch, continues.
The hearing is due to conclude tomorrow with an expert panel discussion.
