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The Engineering Tricks Behind the World's Super Tall and Super Slender Skyscrapers

Our tallest buildings elicit all manner of flowery descriptions and grandiose statement, owing to both their scale and symbolism. In the entryway to Dubai's Burj Khalifa, currently the world's highest, quotes such as "the word impossible is not in the leaders' dictionaries" are prominently displayed, a series of Successories for skyscrapers. But it's numbers, not words, that make these structures so inspiring, specifically complicated engineering calculations. While it's dizzying to think of what's required to construct these massive buildings, for many new construction projects, the math has gotten a even more complicated. Consider New York's Empire State Building, a model of classic skyscraper construction from the early 20th century, and 432 Park Avenue, a recently built, slender 96-story luxury tower overlooking Central Park. It's not surprising the newer building is more than 100 feet taller. What's arguably more impressive is the relative footprints at ground level; at its widest point, the Empire State building stretches 424 feet across. 432 Park Avenue was constructed on a 90-foot square lot.

According to Bill Baker, the structural engineer for Skidmore, Owings & Merrill responsible for the Burj Khalifa, the trend towards taller, thinner buildings has presented new spins on old engineering challenges. When the ratio between the height and width of a building goes beyond 8 :1 or 9:1, it becomes increasingly more expensive to construct, since it requires thicker walls and more sophisticated technology to reduce the amount of swaying and shaking caused by the wind (Baker compared today's thinner supertalls to a fishing rod, and making one stand up straight requires much more reinforcement). The height-to-width ratio for 432 Park Avenue is 15:1; to put that in perspective, if you place a standard ruler on its end, it has a ratio of 12:1.

How do engineers continue to make more with less, and build up while also moving in? >>