New quake tech behind revamp of prominent office block

Monday, 13 May 2024

It appears inconspicuous to passers-by, but on a central Wellington building site one of the city’s most extensive earthquake strengthening projects is taking place.

The distinctive teal-coloured Telecom House on Manners St, designed by prominent architect Sir Ian Athfield and now owned by Eyal Aharoni’s Prime Property Group, is having 90 viscous dampers installed. The dampers are shock absorbers which can take on the force of the earthquake and protect the building.

The project is one of the most extensive viscous damper project in New Zealand, possibly the world.

Engineers from around the world had come to the site to see what the team was doing and learn how the dampers were being used, Keyway Construction director John Fletcher said.

A model constructed by the engineers shows the difference before and after strengthening with the dampers: the model on the left swings side to side at an increasingly alarming angle, while the building on the right barely moves at all.

The building with its pre-cast concrete floors and concrete columns was at risk of similar problems to the floor collapse in Statistics House during the 2016 Kaikōura earthquake. Part of the job included connecting the pre-cast concrete floor slabs to each other and tying them to brackets so they stay in place.

Fletcher said there was a focus throughout on preserving the aesthetics of the distinctive Athfield design.

“We want this to be a revitalised beautiful building and we’re doing our best to strengthen it to the highest level we could.”

But installing the dampers had been a challenging job and required trial and error, project manager Paulo Hernan Valdivia Vera said.

The dampers have to be perfectly in place in order to do their job in an earthquake. “If something moves before the damper, the damper is not going to work.”

That meant reinforcing the concrete columns which provide structural support during an earthquake. Steel jackets had to be installed around the buildings columns to hold them in place in the event of an earthquake, requiring about 40,000L of grout to hold the steel in place.

“That was a challenge,” Vera said.

All parts of the frame for the dampers had to be strong enough to support the damper’s weight, too – all up the damper and supporting beam weighs one tonne.

The dampers, which weigh 500kg, are being hoisted piece by piece through the side of the building. Each one can resist 200 tonnes of force, meaning the building overall will be able to resist an earthquake with 18,000 tonnes of force.

The crux of the whole job was building a perfect frame for each damper, said Fletcher – if any part of the frame is slightly off, the damper won’t absorb the shock of an earthquake.

Once complete, the strengthening will bring the building’s NBS rating to 130%. That high level of strengthening means the structure could withstand a one-in-one-thousand year earthquake.

The seismic strengthening and refurbishment will cost $50 million.

The project is on track for completion by the end of 2025. When reopened the building will host a mix of retail, offices, a cafe or restaurant, and five apartments.

The dampers will be visible from the outside of the building as diagonal bars through the windows.

Similar technology was used in the new builds at Bowen Campus, where the two new builds each had 64 viscous dampers.