The Canterbury Television building would not be built today because the construction methods would be unacceptable.

But, in 1986, such techniques were common. Many other buildings in Christchurch, some still standing, were built the same way.

The mid-80s was a heady time in Christchurch. Office blocks were built quickly and cheaply, with an emphasis on maximising floor space. New techniques for multistorey structures emerged. Aesthetics were not top priority. If a building did not need a certain detail, it did not get it.

Born into this environment, the CTV building was designed by engineer David Harding, who had rejoined Alan Reay Consulting Engineer (later Alan Reay Consultants Ltd - ARCL) to gain experience designing multi-storey buildings.

Harding put the building's key support wall on the exterior, not unusual for the time, but the overall design was one that several engineers described as "eccentric".

Most modern office buildings have the shear core in the centre, with floors built around it. The CTV method increased lettable floor space.

Harding and ARCL principal Alan Reay agree on little in the design process.

Reay has since conceded Harding was not qualified for the CTV project: "The situation arose because of the trust I placed in what I understood to be a competent and appropriately experienced registered engineer."

Harding admitted the design had "significant weaknesses" but argued these did not cause its collapse.

The Christchurch City Council issued the permit for CTV in September 1986. It was not a straightforward process.

Council consents officer Graeme Tapper had a "long list of concerns". His widow, Pat Tapper, told the commission her husband was under pressure from his boss, Bryan Bluck, to issue the consent, and the two would have "extreme" arguments about this ARCL design and others.

Tapper issued the permit, despite his misgivings, and Williams Construction began work in October but, like the design and consent processes, construction was troubled.

Williams' parent company was in financial trouble and wanted to offload it. This did not make for a healthy work environment, managing director Michael Brooks said.

He, construction manager Gerald Shirtcliff and quantity surveyor Tony Scott formed Union Construction - which took on the CTV contract when Williams folded. The turmoil meant construction slowed and council inspections were, by the authority's own admission, "light" for a building of CTV's size.

Shirtcliff, a convicted fraudster, said he visited the site monthly, and was not responsible for supervising construction. Brooks, surprised by the admissions, declared Shirtcliff "clearly not up to the job".

The building, finished in February 1988, remained largely empty for two years.

In early 1990, when Canterbury Regional Council considered buying it, a pre-purchase engineering inspection found the floors were not properly connected to the north shear wall, a serious building-code violation and one of Graeme Tapper's concerns four years earlier.

ARCL fixed the problem, but not until late 1991, after the building had been sold to Madras Equities (Prime West went into receivership) and a new tenant was about to move in.

After the earthquake on September 4, 2010, the council did two basic assessments on the building and found it safe to occupy, issuing a green placard. But it advised the owners to get a more detailed inspection quickly.

This was done in late September by engineer David Coatsworth, who, despite asking for and not receiving structural drawings from building manager John Drew, concluded there was no significant structural damage. CTV remained open.

Californian engineer Brian Kehoe endorsed Coatsworth's approach, saying that, while he could have inspected some parts more closely, it may not have changed his findings.

The Boxing Day aftershock prompted a similar response from the authorities. A council inspection resulted in another green placard with no need for a detailed follow-up.

However, witnesses who worked in the building testifed to extra "bounciness" in the floors, more visible cracks and more vigorous shaking during aftershocks or nearby demolition work.

On February 22, 2011, the building succumbed to a magnitude-6.3 earthquake and 115 people died in the collapse and subsequent fire.

The cause of the collapse had two focus points: the strength of the building's concrete columns and connections between the floors and the north shear core.

Were the columns strong enough? Experts agree they were not, but dispute whether this was because they were below code or were damaged by earlier quakes and the shaking on February 22 far exceeded the force they were supposed to withstand.

Engineer Rob Jury said the columns needed more steel reinforcement "that maybe they should have had by the codes of the day".

John Mander, an engineer called by ARCL's counsel, said the column construction was fine. Hidden, cumulative damage from earlier quakes and the violent vertical acceleration on February 22 triggered the collapse.

The beam-column joints ensured forces such as earthquake shaking were transferred from the floors to the shear wall, which was designed to absorb such pressure. Clearly they were not strong enough and again expert opinion is divided: earlier damage combined with unprecedented force, or just inadequate to begin with?

A Building and Housing Department report from February found the building had serious design and construction flaws. Report co-author Ashley Smith said disagreements among the expert panel that compiled it were only on the extent of non-compliance. Everyone agreed it was below code, even when taking the "most lenient" interpretation of it.

The story of the CTV building is a series of unfortunate events, and a mass of contradictions and unknowns. Now it is the commissioners' job to find out why it collapsed.

- © Fairfax NZ News

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