Nearly a third of the world's tallest building is a spire nobody can use.
The Burj Khalifa in Dubai rises 828 metres. But its top 244 metres is a steel spire with almost no usable space, which one study said could be a skyscraper on its own. Without it, the tower would be 585 metres. Engineers call this 'vanity height', and it is still a remarkable feat.
The Burj Khalifa was designed by the Chicago firm Skidmore, Owings & Merrill, with Adrian Smith as chief architect and Bill Baker as a chief structural engineer. The same firm had designed the Sears Tower, an earlier record-holder. Construction began in January 2004 and the tower opened in January 2010, taking the title of world's tallest building from Taipei 101.
The real engineering challenge at that height is wind. The tower's Y-shaped floor plan is built around a buttressed central core, and as it rises it steps back 27 times in a spiral. Those setbacks shrink its cross-section and are arranged to disrupt the swirling vortices that wind creates around tall buildings, which would otherwise make it vibrate. Even so, the top sways about 1.5 metres. It uses a tubular structural system descended from the ideas of engineer Fazlur Rahman Khan.
The spire, made from more than 4,000 tonnes of steel, houses communications equipment, but otherwise adds height rather than space. A study by the Council on Tall Buildings and Urban Habitat singled it out in a report on vanity height, the part of a skyscraper that rises above its highest usable floor.
The building has plenty of other records and oddities. Concrete for it was pumped a record 606 metres up. Its double-deck elevators travel at up to 10 metres per second. The air at the top is thought to be about 6°C cooler than at the base. And its air-conditioning system collects so much condensed water from the humid air that it helps irrigate the park at its foot.
Source: Wikipedia — Burj Khalifa · Text summarised from Wikipedia (CC BY-SA 4.0)
