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| By clustering steel columns and beams in the skyscraper's core, engineers create a stiff backbone that can resist tremendous wind forces. The inner core is used as an elevator shaft, and the design allows lots of open space on each floor. |
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| In newer skyscrapers, like the Sears Tower in Chicago, engineers moved the columns and beams from the core to the perimeter, creating a hollow, rigid tube as strong as the core design, but weighing much, much less. |
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 There's even more to explore at the BUILDING BIG web site, check it out at www.pbs.org/buildingbig.
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