Council officer feared CTV risk
Christchurch Earthquake 2011
A city council building officer was so concerned by the Canterbury Television building he thought it was not a matter of if but when something would go wrong.
Graeme Tapper, who is now dead, signed off the CTV design in 1986.
His widow, Pat, told the royal commission today that her husband never talked about work at home, but the CTV building was "the one exception".
While it was not called the CTV building at the time, she knew it was the same building because of where it was.
"Graeme went on and on about the CTV building," she said.
"His view was that there were earthquake risks."
Tapper said her husband had not wanted to sign off the building but was under "huge pressure" from his boss, Bryan Bluck, and was worried about his job.
A structural engineer earlier told the hearing he was "concerned" to learn that his calculations for a high rise were used as a guide for the Canterbury Television building.
John Henry said the calculations for Landsborough House were not detailed enough for an inexperienced engineer to understand without guidance.
Henry did the detailed design of Landsborough House, on the corner of Durham and Gloucester streets, while working for Alan Reay Consultants in 1985.
He left the company and was replaced by engineer David Harding, who used Landsborough House as a template for the CTV design.
Henry told the commission that he and Harding spoke at an engineers' event late last year, and Harding told him he had done this.
Henry said he was surprised and concerned because he knew Harding was inexperienced with high-rise buildings at the time he designed the CTV building.
Henry never wrote up his calculations in a way that someone could use as a template, so it was unlikely they were sufficiently detailed for a first-time designer to understand.
"My calculations were clear to an experienced designer," he said.
Harding would have needed mentoring above what he could glean from the Landsborough House calculations.
"I would never expect [someone] to write a set of calculations for first time ... without any help," he said.
''What was missing was someone to guide him through it.''
Harding said in his evidence that he did not feel confident taking on the job on his own.
He trusted his employer, Alan Reay, to check his work, but Reay said there was never such a process in place.
Reay said he had considered Harding competent to do it and that he never asked for help.
Henry today described the key structural differences between the CTV building and the high rise the CTV building was modelled on.
Landsborough House and the CTV building were "substantially mismatched in strength and stiffness", he said.
Using models, Henry showed how connecting the corners of a building was crucial to the strength of a building and its ability to withstand a quake.
In Landsborough House, the corners were joined, which effectively cancelled out vertical focus.
A model representing the CTV building showed how there was effectively no support on one side.
It had a stiff wall on the north side, and on the south side was a flexible wall and a coupled shear wall, which Harding had recommended to increase its strength.
Henry said even a coupled shear wall was "not enough".
His Landsborough House model stood up to twisting, but the CTV model twisted extensively.
"That shows the importance of joining the corners," Henry said.
Henry outlined how the ''vertical north core'', the main support in the building, was inside the frame of Landsborough House.
However, in the CTV design, the north core was on the outside of the main frame, making it more vulnerable to torsional effects.
Henry used a computer modelling programme called Etabs to test his design.
Harding did the same, using Henry's calculations as a guide.
However, he did not do calculations at the corners of the CTV design as he did not realise that he needed to.
The Etabs output in those days gave deflections at the centre of mass only.
"If you didn't know that, you would be on the wrong path without realising it," Henry said.
Landsborough House stood up in the February 2011 quake but is cordoned off and listed for demolition.
- © Fairfax NZ News
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