21000 Mrakodrap Willis Tower

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Facts

  • Architect: Skidmore, Owings and Merrill LLP
  • Classification: Supertall
  • Construction Type: Steel Frame and Curtain Wall
  • Cost: $175 million (1970)
  • Elevators: 104
  • Floor Area: 409,000 m2 (4,400,000 sq. ft.)
  • Footprint: 68 x 68 m (225 x 225 ft.)
  • Height: 442 m (1,458 ft.)
  • Location: 233 S. Wacker Drive, Chicago, Illinois, United States
  • Materials: Aluminum, Concrete, Glass and Steel
  • Pinnacle Type: East Antenna 521 m (1,720 ft.), West Antenna 527 m (1,740 ft.)
  • Stories: 110
  • Year: 1970 – 1974
  • Zoned: Commercial: Office, Communication, Retail & Observation

History

The Willis Tower,located in the heart of Chicago, is an “international style” design consisting of square tubes in a 3 by 3 tube arrangement, with each tube having a footprint of 23 meters (75 ft.) by 23 meters (75 ft.), in essence creating a unified bundle of nine tubes. The Willis Tower was the first building for which this type of “bundled- tubular” construction was used. This design provides stability against high winds and also allows for future upward growth if so desired.

The building is supported by 114 rock caissons secured into bedrock. The foundation and the floor slabs combine to equal 2 million cubic feet of concrete. 76,000 tons of prefabricated steel frame sections measuring 15x25 ft. were put in place. The Willis Tower has more than 16,000 bronze-tinted windows and 28 acres of black aluminum cladding or “skin”.

As the building climbs upward, the tubes begin to drop off giving the Willis Tower its characteristic setback or “step-back”. This geometry of the 110-story tower was developed in response to the original interior space requirements of Sears, Roebuck & Company.

Architect

Designed by the architectural firm Skidmore, Owings & Merrill for Sears, Roebuck & Company, the world’s largest retailer at the time. The tower was completed on May 3, 1973, and is one of the most recognizable landmarks in the Chicago skyline

A revolutionary vertical transportation system was instrumental in the Willis Tower soaring to new heights never previously achieved. 16 Double-decker express elevators travel from the first two floors to “sky-lobbies” located at floors 33/34 and 66/67, where passengers transfer to single local elevators serving all other individual floors.