The Willis Tower rises high above Chicago in May of 2016
American Landmarks is an irregular feature focusing on buildings, sites, objects, and structures that have not been officially designated as any of the four landmark types covered on this site but have still been deemed by me to be important icons of America.
The Willis (formerly Sears) Tower in Chicago is a defining work of American architecture and one of the nation's most iconic skyscrapers.
America's fifth-oldest supertall (more than 300 meters high) skyscraper, the Willis Tower followed in the footsteps of the groundbreaking Chrysler and Empire State Buildings of New York and its Chicago colleagues, the John Hancock and Aon Centers, by reaching new heights. At 1,451 feet to its roofline and 1,729 feet to the tip of its antennae, the then Sears Tower outpaced the former World Trade Center as the tallest building in the world upon completion in 1974, a title it would hold until Malaysia's Petronas Towers were completed in 1998. It remained the tallest building in the United States from 1974 to the completion of the current One World Trade Center in 2014.
The Willis Tower was commissioned by its original namesake, the Sears-Roebuck Company, which sought a centralized location for its employees and world headquarters. Legendary architectural firm Skidmore, Owings, and Merrill (SOM) was charged with developing a design. Their plan, devised by SOM architect Fazlur R. Kahn, is said to have been inspired by the stacking of cigarette cartons and consists of 9 bundled tubes, with two rising only to the 50th story, two stopping at 66, three more rising 91 stories, and the final two reaching to the 109th floor where they are topped by a one-story penthouse structure that holds window washing machines, bringing the total height to 110 floors.
Khan had already designed the John Hancock Center in Chicago and was among the world's leading designers of skyscrapers. The bundled tube design allowed for different square footage in different areas of the tower, presenting potential tenants with a range of options suitable to the size of their firm. Structurally, it significantly lightened the building and ensured the tower could resist the increased winds blowing at its exceptional height. In fact, the building is designed to shift up to six inches in the wind.
The massive structure came into being through some big numbers. Three years of construction, 2000 construction workers, $175 million (over $1 billion today) in construction costs, a foundation hole dug 100 feet deep, 2.5 million cubic feet of concrete, 76,000 tons of steel, 25,000 miles of electrical cable, 25,000 miles of plumbing, and 43,000 miles of telephone cable support a 4.5 million square foot, 222,500-ton building which hosts over 12,000 employees and an additional 25,000 visitors on any given day. The Pentagon, headquarters of the United States Department of Defense in Arlington, Virginia, is thought to be the only larger single office building on earth.
Architecturally, the Willis Tower is considered the last great supertall skyscraper of the International Style era, which occupied the middle of the 20th century. The flat roof, geometric design, and full curtain wall of black aluminum and bronze tinted glass are all signature elements of this style. The loss of the original World Trade Center towers in 2001 further cemented the status of the Willis Tower as one of America's most valuable and important tall buildings.
Close-up of Willis Tower. Note the tapered nature of the bundled tube design.
Sears-Roebuck was the largest retailer in the world at the time of the tower's construction and expected a massive need for their corporate offices and significant future growth. However, increased competition from other firms and the advent of the internet created a very different reality, and in 1988 the company sold the tower and moved to a new headquarters in the Chicago suburbs, leaving only its name behind. In 2009, that last vestige was removed when insurance broker Willis Group Holdings moved into the building and signed a 15-year naming rights deal.
Concerns about potential terrorist attacks and a glut of office space in the Chicago market have contributed to varying occupancy rates in the tower. A current renovation project has added several amenities and drawn new tenants to the tower, including United Continental Holdings, the parent company of United Airlines, which is headquartered here.
Despite shifts in occupancy, one feature of the tower which has been successful since the start is the Skydeck observation deck, which is the highest in the nation. On a clear day, visitors can see four states: Illinois, Wisconsin, Indiana, and Michigan. In 2009, a new feature was added to the attraction: four 1.5-inch-thick glass boxes protruding out more than 4 feet from the side of the tower on the 103rd floor known as "The Ledge."
Side View of Willis Tower with "The Ledge" boxes
By lying across the floor of one of the Ledge boxes, visitors have an unobstructed view of the Wacker Drive entrance 103 stories below. They are reminded of the extreme height of the tower by the dozens of rooftops visible beneath them.
View through the floor of a "Ledge" box
With its groundbreaking height, simple but striking design, and firm place in the built tradition of one of the nation's premiere architectural cities, the Willis Tower will remain an American Landmark for centuries to come. Even as new towers rise to record-breaking heights from points all around the world, this Chicago classic will be remembered as a definitive work in the history of the skyscraper and a model for supertall buildings worldwide.
For Further Information:
Skydeck Teacher's Guide with excellent facts and figures on the tower