How High Will They Build?

Which raises the question, how tall can buildings go? Answer: No structural limit is in sight. Modern buildings are basically thin curtains draped on skeletons of high-stress steel or concrete materials. Columns shift weight to underground substructures in what are, despite their massive appearance, relatively low-density structures. According to Craig Gibbons, director of the Hong Kong office of Arup, a global structural engineering firm, "we could build a kilometer-tall building right now, no question about it. Two hundred, even 300 stories tall, is possible because we can take advantage of lighter, high-stress materials." Wind load challenges require technology, but "making a building stand up, whatever the height, is relatively straightforward."



One challenge not yet solved is getting bigger, heavier construction materials to the height required for a supertall building. Current crane and construction-elevator technology, Gibbons says, is not up to the job. "We're talking columns that would be 4 by 4 meters in girth, like the size of a small room. And many stories in length. As you look at lifting those big pieces, then fitting them together, we'd need an advance in lift technology and in cranes."



Klemencic echoes the common wisdom about supertall towers: "The limitations are more financial and practical, how to move people up and down those great heights. Above 80 stories, the area you need to devote to vertical lift, like elevators, versus rentable space, just is not viable."



But it's not a fixed equation. Advances in materials and elevators make tall buildings more efficient. Shanghai's Jin Mao, topped by the world's highest hotel, uses high-speed elevators that race along at about 30 feet per second; faster elevators reduce the need for more elevator shafts. Double-decker elevators can be employed, stacked on the same shaft, with improvement in floor space efficiency. Meanwhile, materials have grown stronger and lighter.