CTV collapse has ripple effect

Photo / File

Catastrophe triggers closer look at 350 similar buildings in big centres and push by property owners for checks

The catastrophic collapse of the CTV building a year ago has prompted an investigation into 350 similar buildings, and also widespread reassessment of commercial offices by companies nationwide.

A combination of building defects meant the central Christchurch building crumbled during the February 22 earthquake, killing 115 people.

The CTV building was constructed after the 1976 watershed when building codes were strengthened, but it contained major defects.

Engineers now say its columns were brittle, lacked flexibility and had not enough steel components, and this led to their failure.

The Department of Building and Housing, which produced a damning report on the tower's collapse this week, said yesterday that it was looking at 352 buildings in Auckland, Wellington and Christchurch to identify which ones had non-ductile columns.

These buildings were all constructed between 1982 and 1995, when non-ductile columns were permitted in building codes.

Department spokeswoman Susan Owens said the survey of buildings was precautionary. It estimated that of the 352 on the list, 130 are at greater risk..

"It may not be an issue. The CTV building had a range of factors that made it collapse, so it's quite unlikely that you'd find that in many other buildings in New Zealand."

The department's report also found that the CTV building's walls were laid out asymmetrically, which meant the six-storey structure twisted during the quake and put more pressure on the columns.

Civil engineers told the Weekend Herald non-ductile columns were still permitted in building codes in the 1980s and 1990s because they were intended to be only a secondary column.

The problems associated with inflexible columns were recognised only little by little, so the building code did not warn fully against their use until 1995.

The CTV collapse has rattled a lot of commercial building owners. Engineering firms and insurance companies have been inundated since last February with companies wanting risk assessment on their own offices.

Beca's technical director of earthquake engineering, Richard Sharpe, said: "Every major portfolio owner is looking at their portfolio and trying to come up with how they will address the different levels of seismic resilience of their buildings and what their policies should be."

Asked whether this reassessment was only in at-risk areas in New Zealand, he said: "No, it's everywhere.

"In the period after the stock exchange crash [in 1986] people wanted them built as leanly and quickly as possible ... and certainly clients were not considering that codes were minimum codes, and you could design above them.

"I think there's a sea change now, the public has finally realised."

The Auckland Council has given some indication of the number of Auckland buildings which might partially collapse in an earthquake, but has refused to release this information to the public.

The council's register of Auckland buildings which could collapse in a moderate earthquake totals 4300.