ENGINEERING NEWS

Bill Baker on the World's Tallest Building

At 2,717 feet tall, it's the tallest building in the world by more than 1,000 feet — but it didn't start out with such grand ambition.

The first design of Burj Khalifa in Dubai was only 1,700 feet — only 10 meters taller than what was then the world's tallest building, Taipei 101. But as time went on, the market grew, and the developers asked architecture firm Skidmore, Owings, and Merrill to build it bigger. When the building finally opened in January of this year, it was more than a half-mile tall.

"It exists for Dubai to plant their flag on the world's stage," said Bill Baker, the project's lead structural engineer. Baker spoke about Burj Khalifa on May 5 as part of the Dean's Seminar Series at the McCormick School of Engineering.

The building represented a paradigm shift in skyscraper design. Baker and his colleagues developed a new system called a buttressed core, which is a large hexagonal core reinforced by the three buttresses that form a Y shape. This shape allows the building to support itself laterally while keeping it from twisting.

The group modified the design after wind tunnel tests: Wind is the most important factor in tall building design, he said, and their first wind tests showed their initial design would not work.

"You don't accept the wind as a given," he said. "It's part of the design process...We kept reshaping the building."

The building has 54 elevators — the longest elevator trip only takes about two minutes —and has specialized window-washing track systems on floors 40, 73, and 109. Engineers had to test concrete mixes in order to find one that would work in the hot desert sun, and they used a new kind of concrete pump — called the Putzmeister — to pump concrete up as the building grew.

It's mostly residential but houses a hotel at the bottom and office space at the top. Baker said they were mystified as to why the developers would want prime, smaller space for offices, which in the United States generally have large, open floor plans. Baker soon learned that businesspeople wanted a prestigious address to meet with colleagues in the city that acts as the Switzerland of the Middle East.

There are stairs for emergency exit, and Baker said he did walk once from top to bottom. It took him 45 minutes, and, he said, "My calves hurt the next day."

Baker says he doesn't think a building will surpass Burj Khalifa as the world's tallest within the next six years but says he has seen plans for kilometer-tall buildings.

"There is really no structural limit," he says.