Bid to reinforce buildings

Owners of Dunedin buildings have been urged to begin strengthening these against damage from potential earthquakes as soon as possible.

The request was backed by a promise of more support from the Dunedin City Council.

The message was delivered to about 120 people, many of them owners of commercial buildings, at a council workshop in Dunedin this week.

The workshop was held in the council's municipal chambers, which has just had about 20 steel reinforcing beams added to strengthen against damage from possible quakes, as part of a $5 million refurbishment this year.

However, Associate Prof Jason Ingham, of the University of Auckland's faculty of engineering, said relatively simple steps could dramatically reduce the hazard posed by unreinforced masonry buildings.

Key among them was using anchor plates or other measures to secure parapets, chimneys and ornamental parts of older buildings, he said.

Evidence from the Christchurch earthquakes showed almost every unsecured parapet had fallen during the city's shaking, killing people below.

About 40 people died in unreinforced masonry buildings.

About 200 of the buildings were later demolished, he said.

The Christchurch earthquakes had been "short", lasting just seconds, while the earthquake that struck Japan on March 11 lasted up to three minutes.

Similar shaking and subsequently more damage could be expected in New Zealand if a major quake occurred along the South Island's Alpine Fault, he said.

"If the Alpine Fault goes, then the expectation is it's going to be one to two minutes, rather than 20 seconds."

The most common damage to occur in unreinforced buildings was diagonal splitting or cracked spandrels, or was from neighbouring buildings "whacking into each other", he said.

Owners should work through a checklist to protect their buildings, beginning by identifying any falling hazards, such as loose parapets, and increasing wall strength, possibly by installing steel ribs or rods to pull buildings together.

"Most of this stuff is not particularly technically demanding ... it would be nice to think more of this work gets done," he said.

Structural engineer Lou Robinson, a principal at civil and structural engineers firm Hadley and Robinson, said it was possible some early Dunedin buildings had "critical structural weaknesses".

The city faced less risk from earthquakes than centres further north, but had not been immune to damage caused by the Christchurch quakes.

"Believe it or not, there was a lot of damage here. Some buildings that subsequently failed ... are probably attributable to that earthquake event."

However, evidence from Christchurch was that masonry buildings could survive shaking if materials were in good condition, making it important to maintain buildings as well as undertake strengthening work.

Council heritage policy planner Glen Hazelton said the council's policy for earthquake-unstable buildings had been adopted earlier this year, and would mean owners of these buildings, where commercial, would be sent requests for information on them by July next year.

They would then have two years to provide initial assessments of the condition of their buildings, which would be used to determine how earthquake-unstable these buildings were.

Owners would then have between 15 and 30 years to strengthen their buildings, or be required to do work sooner if undertaking major alterations or a change of use, he said.

Owners would have to bring their buildings up to at least 34% of new building strength standards, but the council hoped more would opt for a 67% compliance.

However, more help could be on hand for owners doing the work, with additional assistance expected to be unveiled by the council early next year.

That would be on top of help from the Dunedin Heritage Fund, as well as rates relief, partial consent fee waivers and advice offered by the council.

This week's workshop was the second organised by the council and would be repeated each year.

- chris.morris@odt.co.nz