Willis Tower

Willis Tower
  1. About the Willis Tower in Chicago
  2. Architect and team
  3. Architectureal style
  4. Spaces and uses
  5. Structure and materials

The Willis Tower is an International Style skyscraper designed by Skidmore, Owings & Merrill, with Bruce Graham as lead architect, and built between 1970 and 1974, for a reported $175 million dollars, in Chicago, IL.

Willis Tower is not the only name you might know this building by though. It is common for companies to want to attach their names to iconic buildings when they move in, or for the general public to come up with nicknames, and this one is no exception. The building has changed names several times over the years, and is also known as:

  • Sears Tower between 1974 and 2009.
  • Willis Tower from 2009 until this day.

Its precise street address is 233 S. Wacker Drive, Chicago, IL. You can also find it on the map here.

Architect Bruce Graham and engineer Fazlur Khan used an innovative structural system to address wind loads on a building of this height. The structural steel frame was pre-assembled in sections and then bolted into place. The structure is made up of 9 square steel tubes, each 23 x 23 meters wide, interconnected to act as a single unit, with no columns between the core and the perimeter. Two of the tubes are 50 stories high, two are 66 stories, three are 90 stories, and two are 108 stories.

Some people say the building has 110 floors instead of 108. That is including the elevator shaft and its roof, which are not normally counted as floors.

When it was completed in 1974 it was the tallest building in the world, a title it held until either (and this depends on how building heights are measured, which was not standardized at the time) 1998, when the Petronas Towers in Kuala Lumpur were completed, or 2004, when the Taipei 101 was..

The building has been restored 3 times over the years to ensure its conservation and adaptation to the pass of time. The main restoration works happened in 1980, 2009 and 2019.

Building's timeline

Construction begins
Sears Tower
years ago
  1. 1980 - An entrance pavilion was added on the west side and a small atrium inside the east entrance.
  2. 2008 to 2009 - Four glass capsules were installed on the 103rd floor. Completely retractable, they extend outward to create the illusion of walking on air. The architect in charge was Skidmore, Owings & Merrill.
  3. 2016 to 2019 - This has been the largest restoration of the building so far. The lobby was transformed into an open space with multiple levels and areas for dining, entertainment, and shops. A public park of 2787m2 was added on one of the podiums. The architect in charge was Gensler, SkB Architects, OLIN.

Architect and team

Skidmore, Owings & Merrill, with Bruce Graham as the lead architect, was the architecture firm in charge of the architectural design.

Commonly known as SOM, the firm was founded in Chicago in 1936 and has grown to be one of the largest architecture firms in the world.

Even long after its founders passed away, SOM has remained at the top of worldwide architectural excellence by attracting visionary architects. Amongst their most notorious partners we find names such as Gordon Bunshaft, Bruce Graham, Walter Netsch, Adrian Smith, Myron Goldsmith or David Childs.

SOM has also managed to grow and evolve to tackle the architectural challenges of each time, whatever those might be, and today is committed to aspects as important as efficiency and sustainability, as core values of their designs.

With a legacy spanning decades, SOM continues to shape the skylines of cities around the world, and is a usual contestant in any competition or selection process to design large-scale or iconic buildings and structures.

Skidmore Owings Merrill

Skidmore, Owings & Merrill was in charge of the architectural design, however, architecture is a complex discipline, which usually involves many professionals from different fields, without whom this building would have not been possible. We will surely be leaving out a lot of names here, but here is a list of the people we do know also played their part in making the Willis Tower a reality:

  • Fazlur R. Khan, Srinivasa Iyengar in charge of Structural Engineering
  • Morse Diesel International as the Main Contractor
  • Enclos Corp in charge of Facade Consultancy
  • Westinghouse, Schindler Group and Otis as the company in charge of the elevators system
  • Sears, Roebuck & Company as the Main Developer
  • Jaros, Baum & Bolles in charge of MEP Engineering

Architectural Style

The Willis Tower can be categorized as an International Style building.

The international style originated in Europe in the early 20th century, and made its way to the US a couple of decades later when the rise of the Nazi regime forced figures such as Walter Gropius, Marcel Breuer, or Mies van der Rohe to flee Europe.

The International Style emerged as a response to the prevailing historicism and ornate architecture styles of the late 19th century, which according to a younger generation of architects didn't represent the new materials and construction techniques that were on the rise at the time.

Architecture in the early 20th century US was marked by the adoption of steel structures, modern construction techniques, and the rise of the skyscraper. As it turns out, this combination of circumstances created the perfect ecosystem for the International Style to flourish, becoming the to-go style for skyscraper designs during the mid-20th century, when American cities were growing fast.

The International Style’s legacy can not only be found in numerous iconic buildings across all major American cities, but also incorporated in contemporary architecture, which still puts a big emphasis on functionality and minimalism.

Spaces & Uses

The Willis Tower reaches an architectural height of 1450ft (442m), 1729ft (527m) if you count the antenna, with the last accesible floor being 1355ft (413m) off the gorund. It has a total of 112 floors, 108 above ground and 4 basements, served by 104 elevators.

If you want to get a nice view of Chicago the Willis Tower offers an observatory deck. You can plan your visit to the The Ledge, Skydeck by visiting its website here.

Ever since opening its doors to the public in 1974, the Willis Tower has mainly been used as Commercial space.

1729ft (527m)
1450ft (442m)
1355ft (413m)
4 basements

Materials & Structure

The Willis Tower uses a frame structure made of steel columns and concrete slabs.

A frame structure uses a combination of beams and columns to sustain the building's weight. The walls in this case are non-load bearing, which allows for more flexibility when distributing the interior spaces.

The facade is non-load bearing either, as it is common in frame structure type buildings.

From an aesthetic point of view, the facade features a curtain wall made of black anodized aluminum with vertically running bronze-tinted glass panels, accentuated by black lines emphasizing the tubes. Large windows maximize natural light and views, while the tinted glass reduces reflections and serves, to some degree, as an insulator to maintain a relatively constant temperature, minimizing the expansion and contraction of the framework.

The vertical evolution of the building is also defined by the structural tubes we talked about previously. As some of these tubes are lower than others, the tower draws an asymmetric stepped-back silhouette that has become recognizable not only within the Chicago skyline, but as one of the greatest skyscrapers of all times.

Another material found at the Willis Tower is metal tiles , used in the lobby floor with a stylezed design based on a bundled tube structure.