The tallest ever

The 2,716.5-foot-tall Burj is not merely “the world’s tallest building”; it’s taller than any other building by more than 1,000 feet. In structure, scale and sheer weight, the pride of Dubai is “a different animal,” says Skidmore Owings & Merrill engineer Bill Baker, who designed the beast with architect Adrian Smith. The engineering has the potential to transform the world’s skylines.

Where the puny Willis (formerly Sears) Tower, for example, has a traditional relationship between height and girth (to make it taller, the footprint would have had to be to an unmanageable size), the Burj Khalifa can, because of its layout and core shape, rise without growing wider throughout its height. The tower’s floors wind upward in a series of setbacks around a central hexagonal core. That core is supported by one of three “legs” that form a sort of flattened tripod. The Burj is stronger for being heavier-the spire alone weighs 4,000 tons-and all that downward pressure helps keep it in place, while reinforced concrete maintains the structure’s stability.

Not that the architects didn’t have to windproof the thing. They put models in a wind tunnel to measure vibrations from the powerful gusts that blow past the building’s upper floors and compensated as they went. It took a while. “Our first shape was not so good,” Baker says, “but like a musical instrument, you tune it.”