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3 Things You Must Know About The Willis Tower In Chicago

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3 Things You Must Know About The Willis Tower In Chicago

Located at 233 South Wacker Drive in Chicago, the Willis Tower was the tallest building in the world until 1996, when it was surpassed by the 1,483-foot (452-meter) Petronas Twin Towers in Kuala Lumpur, Malaysia.

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Located at 233 South Wacker Drive in Chicago, the Willis Tower was the tallest building in the world until 1996, when it was surpassed by the 1,483-foot (452-meter) Petronas Twin Towers in Kuala Lumpur, Malaysia.

Historical Background

Originally named the Sears Tower, the building began welcoming occupants in 1973 and was fully completed the following year. Constructed as the headquarters for Sears, Roebuck and Company, the tower rises 1,451 feet (442 meters) to its rooftop, spanning 108 stories—a measurement that does not include its broadcast antennas. The structure offers over 3.8 million square feet (353,000 square meters) of leasable area for office and commercial use. The global architecture and engineering firm Skidmore, Owings & Merrill (SOM) was responsible for its design and construction, with Bruce Graham as the lead architect and Fazlur Khan as the structural engineer.
By 1969, Sears, Roebuck and Company was the largest retailer globally, with about 350,000 employees. To bring its dispersed workforce together and allow for future expansion, the company commissioned SOM to design a 3-million-square-foot (278,700-square-meter) office high-rise. The site was strategically chosen for its easy access to highways and commuter rail lines, primarily for the convenience of Sears staff. Ultimately, the tower’s location also greatly benefited the city, injecting new vitality into a previously underdeveloped area of the West Loop.
This history is why many Chicago residents still fondly call the building Sears Tower, even though it was officially renamed. In 2009, London-based insurance broker Willis Group Holdings (later Willis Towers Watson) leased over 140,000 square feet across three floors. The agreement included naming rights for 15 years, and on July 16, 2009, the building was formally renamed Willis Tower.

Design and Engineering

The tower’s structural system consists of bundled steel tubes welded into a rigid frame. These interconnected vertical tubes provide mutual support, offering the stiffness required to resist wind-induced sway. The varying heights of the tubes also help disrupt wind currents, reducing structural stress. This efficient design minimized the amount of steel needed for a building of such scale. Most of the steel was prefabricated and welded off-site, with bolted connections completed during erection.
The design concept was reportedly inspired by the irregular arrangement of cigarettes partially pushed out of a pack. The floor plan is modular, composed of nine 75-foot (7-meter) square, column-free units that form a 225-foot (21-meter) square base. The building’s signature stepped profile comes from sets of tubes terminating at different heights: two diagonal units end at the 50th floor, the other two diagonal units stop at the 66th floor, and three more units conclude at the 90th floor, leaving a 20-story upper section.

Architectural Features and Renovations

The exterior is clad in black aluminum and bronze-tinted glass. Black bands encircle the building at the 30th–31st, 48th–49th, 64th–65th, and 106th–108th floors, concealing mechanical louvers. The lobby features Universe, a large-scale motorized mural by American sculptor Alexander Calder, which he described as a “wallmobile.” The Skydeck observation area on the 103rd floor was significantly upgraded in the early 21st century with the addition of The Ledge—four transparent glass boxes that project 4.3 feet (1.3 meters) from the building, providing thrilling, unobstructed views of the city and beyond upon their opening in 2009.
In 2015, alternative asset manager Blackstone acquired the Willis Tower and initiated a $500 million renovation from 2017 to 2022. The project aimed to transform the tower from a purely office-oriented building into a vibrant mixed-use destination. New features include a five-story retail and dining pavilion and accessible rooftop gardens, all designed to attract businesses and encourage public interaction. A notable addition to the exterior is Atmospheric Wave Wall (2020), a public art installation by Danish artist Olafur Eliasson. Composed of curved blue, green, and white tiles that evoke Chicago’s Lake Michigan and Chicago River, the piece dynamically changes appearance with variations in sunlight, weather, and the movement of passersby.

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