Steel’s part in NZ’s most sophisticated office tower

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The $200 million Deloitte Centre at 80 Queen Street Auckland will open in October 2009.
It is a brilliant junction between old and new, blending modern architecture with the historic 1930s street frontage of the Jean Batten Building.

The scale of the 21-level tower, its sophisticated green technology and ingenious use of steel beam construction make it a New Zealand first.
The Deloitte Centre is a great example of how steel offers significant benefits in modern construction, particularly in city sites. The use of steel beams solved time and site constraints, and was the flexible choice in achieving the architectural vision — creatively, technically and practically.

Nick Clements of Steltech Structural Ltd explains: “With steel you can produce a much slimmer structure than concrete columns and beams, so it allows more floor space and a lighter feel to the whole structure.

“It also reduces the overall mass of the building, which reduces the size and cost of the foundations required. It is faster to erect, as there is no requirement for formwork or the time to cure concrete.
“Much of the steel fabrication is done off site so it reduces the manpower and time on site, making for a safer, smoother flowing work site.”

A major construction issue was the need to ensure the building fitted with the facade of the historical Jean Batten Building. The old building’s stud height remains 2.7m yet sophisticated ceiling services have been installed through custom-made welded steel beams.

Modern multi-storey buildings tend to have greater heights between floors due to the need for installing air conditioning and other services. With traditional construction methods the services would have to pass under the floor beams, but with welded steel beams the designer can pass services through the beam webs, saving this height.

Significant use of cut-outs in the beam webs meant all the services tucked neatly in the ceiling space with large ducts going right through big beams.
Steltech worked closely with the fabricators, D&H Steel Construction.

“The fabricator supplied us with electronic files for each different beam design that we fed through to our CNC profile-cutting machine to cut the holes,” Mr Clements says.
“Designers can now push how they use steel by thinking outside the square on how welded beams can be made to almost any shape or size, and with holes pretty much wherever they want them.”

Possibly the most powerful first impression to all who enter The Deloitte Centre is a result of the dramatic steel cantilever in the foyer. The long spanning capability of steel enables the creation of large and graceful areas of unobstructed space in multi-storey buildings.

Here the effect is extraordinary. The architects, local firm Warren & Mahoney and international company Wood Bagot, have achieved their goal of a stunning urban frontage.
“The glazed canopy on Queen Street not only provides shelter to the footpath along the building boundary, but is also a striking element at the main entrance. The primary structure consists of a 900mm deep steel box beam, which is 42 metres long.

“At the main entrance the dramatic box beam cantilevers a total of 12 metres. The glazing is supported off 14 large polished stainless steel arms which, in turn, hold the canopy’s stainless steel spider fixings,” according to Warren & Mahoney architect Richard Voss.

The whole building is based on pushing design boundaries from conventional to very modern, with the lowest possible environmental impact.
As a result, The Deloitte Centre is a smart and efficient building worthy of its 5 Star Green Star rating from the Green Building Council.

The double ventilated façade on Queen Street is part of the project’s “Green” objectives. As Mr Voss explains, it reduces the solar gain on the west-facing façade by virtue of the stack effect. The warm air rises in the 600mm-wide glazed cavity to outlets at high level.

Computational Fluid Dynamic (CFD) modelling was undertaken to predict the air movement speeds and heat patterns within the double ventilated façade. It will efficiently keep the tower warmer in winter and cooler in summer.

Another green feature is the harvesting of rain water from the building. This will be used to flush the toilets. Also, upper level interiors have 2.9m studs, reducing the need for artificial lighting.

Overall, The Deloitte Centre shows how steel construction offers new solutions and opportunities for architects to cost-effectively expand their artistic expression and meet today’s challenges for inspiring, smart, efficient, safe buildings.

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