Auckland's skyline will get a touch of Manhattan when its first major structural steel-framed high-rise commercial tower rises on the ex-Downtown site.
Instead of the block-like construction technique Aucklanders are used to, giant steel beams will be trucked into the city, then bolted and welded together using the same techniques which created many of the buildings on New York's skyline.
Scott Pritchard, chief executive of Precinct Properties which is developing the 39-level 100-shop Auckland waterfront block, said construction materials and techniques to be used would be unique but also necessary to protect Auckland Transport's new City Rail Link tunnels from the gigantic new tower's weight.
"This is the first major Auckland structural steel high-rise," he said.
A diagrid structural steel frame will form the new PwC building's skeleton, rather than reinforced concrete, common in other major Auckland towers, Pritchard said.
"The benefits for the occupants is they're in a really strong building. It's slightly more expensive to build but faster," he said, estimating a 10 per cent time saving on more traditional construction.
Structural steel is far more common in American high-rise construction, particularly in New York and that's not where the similarities with Commercial Bay end, he said.
"The steel is coming from Herrick in the US, working with Culham Engineering in New Zealand. They're joint providers of the steel which Herrick is manufacturing in the US and Thailand," he said.
The project will take about 36 months. Some tenants in the vicinity - particularly in the Tower building on Queen St/Customs St corner - have complained of noise and vibrations.
Shops, restaurants and bars are due to open around October 2018 and offices by June, 2019. A Lower Albert St air bridge between the existing PwC building at 188 Quay St and the new tower will be refurbished.
The podium of the HSBC tower on the Lower Albert St/Quay St corner will be demolished later next year.
"We don't need the site yet," Pritchard said.
Precinct will next month begin digging the CRL tunnels, joining underground routes from Britomart to those to be built beneath Albert St. Those tunnels will take a gradual loop from Queen Elizabeth Square near Britomart up towards Albert St.
Floors in the $850 million Commercial Bay will rise in groups of about three: first the steel frame, then the concrete in-situ floors, then the glass curtain wall facade, Pritchard said.
The tower on reclaimed land will be built to 180 per cent of new building standard - nearly twice as strong as that required to meet building rules.
Precinct is spending $681m on the project but has an independent projected valuation of $853m for the end result.
Fletcher Construction is the head contractor with Richard Coupe and Donnal Lynch in charge on the site. The perimeter is now being protected by sheet piles, driven into bedrock, up to 20m to 25m underground. A diaphragm wall has been built on the seaward side, Pritchard said.
"The diaphragm walls will replace the sheet piles so we secure the whole site and that stops water getting in and gives structural intent to the site - the walls won't fall in when we start digging," Pritchard said.
"The big dig will start in early January, down three basement levels," he said.
Plunge piles will be driven into the ground: "These are the main structural elements which support the building above. About 800 people will be working on the site about this time next year through to early 2018."
Early next year, one gigantic column will be trucked to the site from Whangarei. This is a crucial element of the building, Pritchard said.
"It's the significant column between the CRL tunnels. All the design pins around that key structural steel column," Pritchard said.