Willis Tower

(formerly Sears Tower)

Willis
Willis

Project Facts
  • Status Construction Complete
  • Completion Year 1974
  • Design Finish Year 1971
  • Size Site Area: 3 acres Building Height: 1,450 feet Number of Stories: 110 Building Gross Area: 4,455,844
  • Rentable Area 3810000
  • Awards
    1976, Distinguished Building Award, AIA – Chicago Chapter 1975, Best Engineering in High Rise Construction, American Iron and Steel Institute 1975, Award of Excellence, American Institute Of Steel Construction 2015, 50 Significant Structures in 50 Years, Structural Engineers Association Of Illinois
  • Collaborators
    Weidlinger Associates Inc. - New York American Bridge Division Of U.S. Steel Boundary Layer Wind Tunnel Laboratory / Alan G. Davenport Wind Engineering Group Jaros, Baum & Bolles Saphier Lerner Schindler Inc. Cdc Alexander Calder Johnson Controls, Inc. Richard Rush Studio Rothman, Ammann & Whitney The John Buck Company Destafano And Partners Cushman & Wakefield, Inc.
Project Facts
  • Status Construction Complete
  • Completion Year 1974
  • Design Finish Year 1971
  • Size Site Area: 3 acres Building Height: 1,450 feet Number of Stories: 110 Building Gross Area: 4,455,844
  • Rentable Area 3810000
  • Awards
    1976, Distinguished Building Award, AIA – Chicago Chapter 1975, Best Engineering in High Rise Construction, American Iron and Steel Institute 1975, Award of Excellence, American Institute Of Steel Construction 2015, 50 Significant Structures in 50 Years, Structural Engineers Association Of Illinois
  • Collaborators
    Weidlinger Associates Inc. - New York American Bridge Division Of U.S. Steel Boundary Layer Wind Tunnel Laboratory / Alan G. Davenport Wind Engineering Group Jaros, Baum & Bolles Saphier Lerner Schindler Inc. Cdc Alexander Calder Johnson Controls, Inc. Richard Rush Studio Rothman, Ammann & Whitney The John Buck Company Destafano And Partners Cushman & Wakefield, Inc.

An enduring Chicago landmark

For decades the tallest building in the world, the 110-story Willis Tower (formerly Sears Tower) marked a major step in exemplifying and defining SOM’s belief that a building’s structure should inform its exterior profile. The 4.5-million-square-foot tower was the headquarters for Sears, Roebuck & Co. from the time of its completion in 1973 until 1995, when the merchandiser relocated to suburban Chicago. The building’s design, flexible floor plan, and iconic stature have made it a premier address for a host of companies. Today, the tower is well-maintained and remains a center of activity in Chicago’s Loop.

Willis
© Ezra Stoller | Esto
Willis
© Hedrich Blessing

Pragmatic engineering

The iconic setback design of the structure was conceived in response to the original client’s space requirements: Sears wanted a building that incorporated not only large office floors, necessary for the company’s operations, but also a variety of smaller floors for tenants requiring less floor area.

Willis
© Dave Burk | SOM

Pioneering the use of bundled tube construction, the basic structure consists of nine 75-foot-by-75-foot column-free square tubes at the base, forming a cellular-tube frame. The nine bundled structural tubes, each rigid within itself without internal supports, rest on reinforced concrete caissons that go down to bedrock. The tubes are bundled together as a closed square up to the first 50 stories, and then terminate at varying heights to create the tower’s distinctive, multi-tiered form.

Willis
© McShane Fleming Studios

The structural steel frame was pre-assembled in sections and then bolted into place on site. The lightweight building skin, a black aluminum and bronze-tinted glare-reducing glass, serves as an insulator between the interior and exterior structure in order to maintain a relatively constant temperature, which minimizes the expansion and contraction of the frame.

Willis
© McShane Feming Studios

Above the clouds

In 2009, the Ledge at Willis Tower was created to enhance the building with an innovative new observation deck on the 103rd floor. In 2021, SOM continued its 50-year stewardship of Willis Tower with a transformative renovation of the Ledge. Interior enhancements, improved lighting, building technology upgrades and a new exhibition space further immerse visitors in Chicago’s historic skyline.

Above the clouds

Stepping out for a staggering view

The Ledge at Willis Tower is a series of glass-enclosed balconies that offer visitors the opportunity to experience Chicago from 103 stories above ground, seemingly floating above the city. The Ledge foregrounds the iconic views, while showcasing the tower’s pioneering structural design through a minimal design approach and subtle finishes.

© Dave Burk | SOM

The five-sided glass balconies provide views in all directions, approximating the experience of being suspended in the air. The ledges are approximately 4 feet deep, 10 feet high, and 10 feet wide, and made of 1.5 inch laminated glass panels hung from a steel frame. The frames can be retracted into the building on rails for cleaning and maintenance.

Willis
© Dave Burk | SOM
Scott Duncan

We wanted to create a quiet backdrop for people to be fully immersed in the city’s skyline and allow the view to speak for itself.

Scott Duncan

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