Samuel Wilson
Structural Engineer
Skidmore, Owings & Merrill, New York City

The skyscraper was invented in Chicago in the late 19th century. Internal steel or cast-iron frames, technological innovations in foundation systems and vertical transportation, and great demand for commercial space led to the construction of the first wave of tall buildings. In 1932 the culmination of this first wave, the Empire State Building, became the tallest in the world at 1,250 feet.

The tall buildings of the early 20th century represented incremental improvements on the same idea, through innovation in construction planning, materials science, and geotechnical engineering. The lateral systems of these tall buildings comprised of rows of steel portal frames or interior bracing systems, both of which carry a significant premium for height—the material for a tall building required above and beyond what is required to resist the gravity load alone.

In the 1960s, Fazlur Khan upended this paradigm with the design of the Dewitt Chestnut Apartments tower. The tower’s resistance to lateral forces relies purely on a perimeter frame utilizing closely-spaced columns and deep spandrel beams. Khan’s innovation was to conceive of and design the skyscraper as a single cantilevered tube rather than a stack of planar, rigid frames: this way of thinking ushered in a new age of tower design and construction of which the Dewitt Chestnut Apartments tower was the first. The next three towers to surpass the Empire State, one of which (the Sears Tower) was also designed by Khan, all utilized the same tubular concept and design philosophy.