Abu Dhabi makes Pisa sit up straight

ABU DHABI // Italy's Leaning Tower of Pisa may tilt necks, but Abu Dhabi's Capital Gate puts a new slant on edgy architecture. Guinness World Records officials this week named the 160-metre-tall UAE landmark as the "World's Furthest Leaning Manmade Tower", certifying it as nearly five times more inclined than the freestanding Italian bell tower.

Capital Gate has an 18-degree westward slope, whereas the Tower of Pisa has an incline of less than four degrees. The recognition from Guinness judges helped to distinguish Capital Gate, built next to the Abu Dhabi National Exhibition Centre (Adnec), as "among the world's great buildings," said Sheikh Sultan bin Tahnoon Al Nahyan, the chairman of Adnec. "It's a signature building which speaks to the foresight of the emirate," he said in a statement yesterday.

Although the architects with the RMJM firm, which designed the 35-storey tower, expected long ago that it would become the world's most leaning tower, achieving official recognition took nearly half a year. Tony Archibold, associate director of RMJM and the project leader on Capital Gate, said his team applied for certification in January. "We have been on tenterhooks for a while because we were very sure, but the applications and process for records does take some time," he said.

The design team submitted a dossier verifying their claims, as well as a separate independent study to support the evaluation. "So there's two layers of due diligence," he said. "It's great because we're doing something by pushing the frontiers of structural design." The building, which is to open at the end of the year and house 20,000 sq m of office space as well as the UAE's first Hyatt hotel, was constructed on floor plates stacked vertically until the 12th story. From that point onwards, the floors are staggered by between 30cm and 140cm to create the angle.

The structure of Capital Gate was based on a diagrid system, whereby a steel mesh frame of diagonal support beams distributed the building's load into the edges and skin of the tower, Mr Archibold explained. "It leaves the floor space clearer, so it doesn't use internal columns and also uses a lot less steel," he said. London's Swiss Re Building, also known as the Gherkin, also uses a diagrid system.

But while that building is symmetrical, the angle of Capital Gate would complicate its construction, according to Adrian Welch, the editor of the international architecture news site e-architect.co.uk. "Something like the Swiss Re is not inclined and was probably fairly straightforward, but with the Capital Gate, because it's inclined, you put extra stress on the members," Mr Welch said. "If that happens every few degrees, it's probably phenomenally complicated, and the engineers would be running a lot of computer models to see where the strains would be coming from."

He described the building as "elegant", adding that the diagrid system was necessary for relieving tension. "It's probably impossible to do otherwise," he said. "You can't really cast cones diagonally. And if you cast a core at an angle like that, the whole thing would probably fall over." Mr Welch, himself an architect, said he had been following the progress of Capital Gate for months. "Anybody that does anything different is going to get noticed," he said. "There's a lot of different buildings now in Dubai and Abu Dhabi. They sort of put their heads above the parapet."

Capital Gate is part of Adnec's Dh8 billion (US$2.1bn) Capital Centre, with more than 20 mixed-use buildings. @Email:mkwong@thenational.ae