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Golden Square

A semi-transparent cladding and futuristic car park will ensure Birmingham’s new multi-use Cube building stands out from the crowd.

The opening of the Mailbox development, a conversion of an old sorting office into shops, hotels and canal restaurants in 2000, has given new life to the formerly rundown Ladywood area of Birmingham. Now there’s a new kid on the block – the gold-clad Cube building.

Click here for a cross section of the Cube

The Cube is a 23-storey mixedused development, located on the canal side, next to the Mailbox development. Architect Make and consultant Buro Happold are responsible for coming up with the dazzling scheme for client Birmingham Development Company.

The building will have a concrete frame, supporting five floors of offices with a ninestorey residential space and two-storey hotel above. On top of all this will sit a two-storey glass clad steel structure which will house a restaurant with breathtaking views of Britain’s second largest city.

All of this will sit on a four-storey podium of restaurants and retail space and a basement car park. “It is the last piece of land owned by the Mailbox [that had not been developed] and it wanted a landmark to complete the estate,” says Make project architect for the scheme Frances Gannon, adding: “The Mailbox has been a catalyst for residential development in the area.”

In the centre of the Cube is an atrium that will allow light to flood down into the lower levels. Further up in the residential levels, the floor area of the atrium increases and the O-shaped floor plate gives way to a U-shaped floor, opening up one side of the building and letting light flood into the apartments. “There’s office environment around the courtyard, but then the front face starts disappearing at level 15 to get light into peoples apartments,” says Gannon.

The 53m3 building façade is a gold powder coated aluminium. Where the building steps back on one side at the higher levels, the façade – a semi-transparent screen – goes straight across. “The fourth side had to look solid but still be transparent enough to get light through,” says Buro Happold associate director Stuart Brumpton.

The screen is effectively a net spanning both ways made from a series of 40mm2 steel box sections, which are connected together to form a series of interlocking shapes. However, the façade is not a simple perforated screen. Make wanted it to look as random as possible with no continuous horizontal or vertical lines.

This made supporting the screen more challenging. “On the other sides of the building, because of floor plates and windows, there is some nonrandom element,” says Brumpton. “The screen was the chance to make it completely random. We looked at a number of options involving combinations of horizontal and vertical trusses, cables and steel posts, but they were too regular.”

A three-dimensional truss spans 50m along the top of the screen, helping to take the horizontal wind loads. Vertical loads are transmitted down the screen to where it sits on the concrete floor slabs. The random screen was a compromise between the total chaos wanted by the architect and giving the engineer enough structure to make it work. “Make produced a wish sketch of what it wanted the screen to look like and we analysed it to see where the stresses were,” says Brumpton. “We then asked the architect to tweak the screen to improve its performance. We then reanalysed the tweaked version. We went through two or three iterations.” The screen will come in sections that can be lifted by a crane and bolted on site. Scaffolding will stabilise the screen until it is complete.

The futuristic looking cladding is complemented by futuristic technology in the car park basement. Instead of parking the car, people will simply drive their cars down a short slope to a lift and leave it. The lift takes the car down to the basement and onto a 5m wide conveyor belt. The conveyor belt has three levels of shelves either side of it, where the cars are stored.

As drivers do not need to get in or out of their cars, three can be stored side by side in a parking bay just 6.5m wide as oppose to the 7.2m that would be needed for three conventional parking spaces. The head height for the parking spaces varies between 1.7m and 2.2m – providing a glove-like fit for a range of cars. The system software knows which spaces are empty and pushes the car into the space. “It’s warehouse technology,” says Brumpton. “People don’t need to go down there so you don’t need so much space. The technology is simple and the software makes sure the right car is in the right place.”

By using this technology 300 cars will fit on three levels. To ensure that the maximum usable area for car parking was achieved, the structural supports in the basement took the form of 500mm thick walls forming partitions between the parking bays. The walls contributed to the stability system, acting as shear walls.

Piling for the basement started in November 2007. The 20m deep basement wall was constructed from 900mm diameter contiguous piles with a sprayed concrete liner. Due to site constraints, the basement was one of the most difficult aspects of the project. “The building footprint is as large as it could be on the footprint of the site,” says Brumpton. “The site is bordered by existing buildings to the east and west, the canal to the north and an access road to the south. The basement was a real challenge.”

The ground conditions feature 3m of made ground overlying 4m of sand, 12m of sandstone then mudstone. “There was an ambition to do an open pit excavation,” says Brumpton. “In the end, we did a full contiguous wall around the perimeter with 900mm diameter piles.” As you would expect from a perfectly square building, the 7.5m x 2.5m concrete structural grid is fairly regular. However, as Brumpton says “there’s always an odd one”, and at ground level, some of the above ground columns miss the basement shear wall, leading to a number of 1.5m deep transfer beams.

The upper floors of the development are post-tensioned. By choosing to use a post-tensioned floor system which was slimmer than a traditional concrete slab, the developers could put an extra storey in the building which is due to open in 2010.

BUILDING UP BUSINESS
The client Birmingham Development Company decided to form its own contracting arm – Buildability – to carry out the Cube development.

“When we started the project two years ago, everything was against us,” says Birmingham Development Company director Neil Edginton. “The construction market was really busy and it’s a £76M project on a tight site. Contractors were put off and were pricing high. “It was never our intention to be the contractor but we decided to set up Buildability. We found good staff and provided them with incentives – 60% of the shares are with the staff.” According to Edginton, Buildability is not a one project pony. There are future plans for further developments in the Birmingham area. “We want to find other unwanted bits of land. It’s more than building a building, it’s creating an area,” he says.

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