Pacific Tower to be studied by engineers

Still standing: An expert says the Pacific Tower's ability to withstand earthquakes is testament to its design.
Still standing: An expert says the Pacific Tower's ability to withstand earthquakes is testament to its design.

Four quake-damaged links from the steel structure of the Pacific Tower are being removed and will be studied by university engineers over the next few weeks.

The links will be replaced and the repair work is expected to take about a month, says the building's owner, Ernest Duval.

He had planned to open the 22-storey tower in Gloucester St, behind the cordon and home to Rendezvous Hotel, two months ago in time for the Ellerslie Flower Show but the Canterbury Earthquake Recovery Authority (Cera) asked for further engineering checks.

One of the links had fractured in the February quake and was due for replacement, and a further three weakened links will be replaced after those checks.

Duval said all damage to the links was due to the February quake and data on other links was being worked through but, at this stage, they should be fine.

A report on the seismic performance of Christchurch's steel buildings, including the Pacific Tower, was given to the Canterbury earthquakes royal commission in November. The authors included University of Canterbury structural engineering associate professor Greg MacRae and University of Auckland civil engineering associate professor Charles Clifton.

Their initial evaluation of the tower found a fractured eccentrically braced frame (EBF) link in the northwest corner but no others needing replacement.

"This type of failure has not been reported in either EBFs tested in the laboratory or from damage reports from other earthquakes; the reasons for this link fracture are not currently clear and it is to be the subject of a detailed metallurgical and structural evaluation once removed," the report says.

That link, and another EBF link in a city parking garage, were the first EBF fractures reported worldwide, the report says.

Clifton said the links would be removed and intensively tested at Canterbury and Auckland universities' engineering departments over the next few weeks.

The testing would provide invaluable information on how the links performed during the quake and why the fractured link failed, he said.

The area of the fractured link was braced and was to be replaced in October. However, Duval said, when Cera asked for a detailed structural assessment that month, the replacement was deferred.

The December quakes caused further delays and it was decided best to wait until after the summer holidays to make repairs, he said.

His engineers had proposed replacing the links, which were braced, while the hotel was open but Cera asked for this to be done before reopening, he said.

The work was covered by insurance and was fairly expensive but insignificant compared to the replacement cost of the building, he said.

It was a testament to the tower's design that it survived the intense shaking with minimal damage, he said.

"Once these links are done we'll need a further discussion with Cera and . . . they will have to be satisfied the building is safe."

The links acted like a fuse, dissipating the seismic force and keeping essential structural components that could not be replaced from being damaged, he said.

The Press