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110- story, 1,451-foot (442.3 m)
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- The Willis Tower, originally and still commonly referred to as the Sears Tower, is a 110- story, 1,451-foot (442.3 m) skyscraper in the Loop community area of Chicago in Illinois, United States.
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Willis Tower, formerly Sears Tower, is a 110-story, 1,451-foot (442.3 m) skyscraper in Chicago, Illinois, that opened in 1973 as the world's tallest building. Learn about its design, construction, tenants, observation deck, and name change from Sears to Willis.
- Overview
- History
- Construction
Willis Tower, skyscraper office building in Chicago, Illinois, located at 233 South Wacker Drive, that is one of the world’s tallest buildings. The Sears Tower opened to tenants in 1973, though construction was not actually completed until 1974. Built for Sears, Roebuck and Company, the structure reaches 110 floors and a height of 1,450 feet (442 m...
In 1969 Sears, Roebuck and Company was the world’s largest retailer, employing approximately 350,000 people. In order to consolidate current staff and accommodate anticipated growth, the company hired SOM to design a three-million-square-foot office tower. The location of the tower was strategically selected for its proximity to expressways and commuter rail lines to benefit Sears employees. But in the end, the tower’s location proved to be advantageous for the city as well. The inhabitants of the bustling office building generated new energy in a formerly stagnant West Loop neighbourhood.
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This history explains why many Chicagoans still nostalgically refer to the building as the Sears Tower, although it has not technically been the Sears Tower for years. In 2009 the London-based insurance broker Willis Group Holdings (later called Willis Towers Watson) leased more than 140,000 square feet of office space on three floors of the Sears Tower. The contract included naming rights for 15 years. On July 16, 2009, the name of the building was officially changed to Willis Tower.
Welded steel frames form vertical tubes that support one another to provide the rigidity needed to limit the lateral sway from wind forces. Variations in the height of each individual tube also disrupt air currents, which reduces the stress of the wind on the structure. This system minimizes the amount of structural steel required for a building of its great height. The steel was prefabricated, with nearly all welding done off the erection site and bolt connections made at the site. The innovative vertical-tube design was inspired by the uneven arrangement cigarettes make when they are pushed out of a pack. (See also building construction.)
The building is modular in plan, with nine 75-foot-square, column-free units. These nine square units compose a 225-foot-square base. At the 50th floor two diagonally opposite units stop, forming the first step back. The second step back is at the 66th floor with the other two diagonal units stopping, and the last at the 90th floor with three units stopping, leaving an upper tower of 20 stories.
The exterior is sheathed in black aluminum and bronze-tinted glass. Black bands appear around the building at the 30th–31st, 48th–49th, 64th–65th, and 106th–108th floors, at which points louvers clad the areas devoted to mechanical operations of the building. In the lobby is a major work by the American sculptor Alexander Calder, an enormous motorized mural named Universe, which he called a “wallmobile.” The tower’s observation deck, the Skydeck, is located on the 103rd floor. In the early 21st century the Skydeck underwent a major renovation that included addition of The Ledge, four glass boxes that extend 4.3 feet (1.3 metres) from the building; The Ledge opened in 2009, offering unobstructed views of Chicago and the outlying area.
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The Sears Tower was the world’s tallest building until 1996, when it was surpassed by the Petronas Twin Towers (1,483 feet [451.9 metres]) in Kuala Lumpur, Malaysia. (See Researcher’s Note: Heights of Buildings.)
Learn about the history and design of Sears Tower, the world's tallest building from 1974 to 1997. The tower is 1,454 feet (443.0 meters) high and has 110 stories of office space and a tourist attraction.
Learn about the history, design and structure of the Sears Tower, now Willis Tower, the second tallest building in the world with 527.3m of height. See photos, plans and facts about its construction, floors, elevators and Skydeck.
- Chicago, Illinois, United States
Standing 110 stories tall, its black aluminum and bronze-tinted glass exterior has become emblematic of Chicago, a city crazy about its architecture. Although its record-breaking height has been surpassed several times over, its innovative structural design remains noteworthy.
Willis Tower, formerly Sears Tower, is a 1,450-foot (442.1 m) skyscraper in Chicago, Illinois. It was the tallest building in the world from 1973 to 1998 and is now the third-tallest in the US and the Western hemisphere.
Willis Tower, formerly known as the Sears Tower, is the tallest skyscraper in Chicago and a landmark of the city since 1973. Learn about its evolution, transformation and amenities, from the Skydeck to the broadcast antennae.
