What is the world’s tallest structure? The Khalifa Tower in Dubai you might reply. It’s the tallest building at 828 m, but not the tallest structure. The top of the drifting rig of the Ursa tension-leg platform, a floating oil production facility operated by Shell in the Gulf of Mexico, is 1 306m above the ocean floor. The platform is connected to the sea-floor by oil pipelines and four massive steel tethers at each corner, with a total weight of approximately 16 000 tonnes.
The 20th century saw skyscrapers dominate city skylines. By 1980 more that 80% of the world’s buildings over 150m were in North America. Today, however, Asia and the Middle East are the pre-eminent builders of super-tall structures. Every building now sits in the shadow of the Khalifa Tower, the glittering glass-and-steel trophy that opened in Dubai, UAE, in 2010. But for how long?
Wind loading is a major factor in the design of tall buildings. The top of a skyscraper can sway 1m in high winds. Typically, a tall building is designed to sway by no more than 1/500th of its height. Large objects called “mass dampers” help to shift a building’s weight, to balance the pressure of the wind. There is a 660-tonne mass damper, housed-in full public view – near the top of the 508-m-tall skyscraper Taipei 101 in Taiwan.
Moving large numbers if people rapidly to a great height is a challenge. The higher you build, the more lifts you need, but every extra bank of lifts reduces the available floor space to rent. Express lifts also have a speed limit, beyond which passengers begin to feel queasy – the upper limit is around 64km/h. Using double storey lifts to serve two floors at once help efficiency.
In theory, a building’s height is limited only by an architect’s imagination. But a skyscraper is a complex creation, involving engineering, architecture, economics and even politics, with each having its own set of limitations. Location matters, too: tall buildings may topple in earthquake-prone regions and existing building materials can only withstand a certain amount of structural pressure and movement.
All these factors may explain why the Kingdom Tower proposed for Jeddah in Saudi Arabia is the only building with a projected height of around 1 000 m to have been given the go-ahead recently.
Guinness World Records (GWR) uses the definition of tall and super-tall buildings as specified by the Council on Tall Buildings and Urban Habitat (CTBUH). The CTBUH defines “super-tall” as taller than 300m.
How do you measure a tall building? GWR only recognises buildings measured to their “architectural top”, which is defined by the CTBUH as the height “including spires, but not including antennae, signage, flag poles or other functional-technical equipment”. A distinction is made between buildings, towers and structures. GWR defines a “tower” as a building in which usable floor space occupies less than 50% of its height.
There are many pipe dreams on the drawing boards, like the Vertical City proposed for Dubai, which may soar to a mind-boggling 2 400m. But it’s the Kingdom Tower which seems to be the best contender for the next world’s tallest building.
Adapted from Guinness World Records 2013
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