On the evening of 4 January 2010, Dubai switched on the fireworks for the opening of the world's tallest building — and, in the same breath, changed its name. For six years of construction it had been the Burj Dubai; guests at the ceremony learned they were standing beneath the Burj Khalifa, renamed for Sheikh Khalifa, the ruler of neighbouring Abu Dhabi, whose emirate had just rescued debt-laden Dubai with billions in emergency support during the financial crisis. It was a fitting christening for a tower that had spent years defying gravity and finished by acknowledging it.
The numbers still read like a misprint. At 828 metres, the Burj Khalifa did not merely edge past the previous record-holder, Taipei 101, which stands 508 metres; it beat it by more than 300 metres, an increase of over 60 per cent. Skyscraper records are usually broken by a few dozen metres at a time. Nothing in the history of tall buildings had ever jumped so far in a single bound, and no building since has reached 800 metres.
The buttressed core
The problem with going that high is not chiefly weight but wind. The tower was designed by architect Adrian Smith and structural engineer Bill Baker, both then of the American firm Skidmore, Owings & Merrill, and their answer was a system Baker called the buttressed core. In plan the tower is a Y: three wings radiate from a hexagonal concrete core, each wing bracing the others like walkers standing back to back. The shape is often likened to the Hymenocallis, a tropical spider lily with long radiating petals. As the tower rises, the wings step back in a spiral of setbacks, so the building's profile keeps changing. That is not decoration: a constant profile lets wind spill around a tower in rhythmic swirls — vortex shedding — that can set the whole structure rocking. By changing shape every few floors, the Burj Khalifa scrambles the rhythm. Its designers, after long campaigns of wind-tunnel testing, described the trick simply as confusing the wind.
Building it stretched concrete technology to its limits. There is no bedrock beneath Dubai worth the name, so the tower stands on a raft supported by nearly 200 friction piles driven roughly 50 metres into the weak sandstone, held up by grip rather than by anything solid underneath. In the Gulf's heat, concrete was poured mostly at night, chilled with ice, so it would not set too fast. And it was pumped vertically to 606 metres — a world record at the time, achieved with some of the most powerful concrete pumps ever built. Above roughly the 156th floor, even that gave out: the topmost section and the spire are steel, assembled high in the desert sky.
Life at the top
The finished tower has 163 occupiable floors, with an observation deck at level 124 and a higher one later opened at level 148. A large fraction of its height, though, is home to no one: the spire accounts for roughly 200 metres that cannot be occupied, a figure that gave rise to the industry's mischievous term for such summits — vanity height. And the top does move. In strong winds the summit sways gently, by somewhere in the region of a metre and a half to two metres, a motion so slow that occupants rarely perceive it. Engineers regard this flexibility as a virtue: a supertall tower that refused to bend would simply have to be impossibly strong. The building even harvests its own microclimate, collecting millions of litres of condensation a year from its cooling systems for irrigation.
The Burj Khalifa collected records the way other towers collect tenants: tallest building, tallest freestanding structure, most storeys, highest occupied floor. It surpassed not just Taipei 101 but every mast and chimney humans had ever raised. Its construction reportedly cost about 1.5 billion dollars — modest for what it delivers in image, which was always the point. Tom Cruise scaled its glass face in Mission: Impossible — Ghost Protocol in 2011, the tower playing itself. More than a decade after opening, its record still stands, waiting on the long-delayed towers that promise to pass the kilometre mark. Until one of them does, the age of 800 metres has a population of one.
Quiz nuggets
- The Burj Khalifa is 828 metres tall and opened on 4 January 2010, beating previous record-holder Taipei 101 (508 metres) by more than 300 metres.
- It was called the Burj Dubai during construction and was renamed at opening for Sheikh Khalifa of Abu Dhabi, whose emirate had bailed out Dubai.
- Its Y-shaped 'buttressed core' structure, engineered by Bill Baker of Skidmore, Owings & Merrill, is often likened to the Hymenocallis, a tropical spider lily.
- Concrete for the tower was pumped to 606 metres, a world record at the time; above about the 156th floor the structure is steel.
- Tom Cruise climbed the tower's exterior in Mission: Impossible — Ghost Protocol (2011).