Chicago, the birthplace of the skyscraper, ranks high in the modern skyscraper era, too.
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Chicago’s Willis Tower, completed in 1974, reigned as the world’s tallest for 24 years. Designed by Chicago-based Skidmore Owings & Merrill, the 110-story high-rise “set the standard for supertall skyscrapers worldwide,” employing a “first-of-its-kind bundled-tube structure” that has been replicated in many skyscrapers built since, according to the CTBUH website.
Completed in 1969, the former Hancock Center also represented an important step forward in supertall construction with its braced-tube structural system.
"It introduced a new, recognizable vocabulary of structural expression that continues today,” the council says. “Its exterior bracing allowed the building to consume the same amount of steel as that of a conventional building half its height."