Chicago natives now affectionately call the Willis Tower ‘Big Willie’, (Figure 1) to go with ‘Big John’, the John Hancock Center, and ‘Big Stan’, the former Standard Oil Building, a sign that the city may finally be accepting the building’s new name. In 2010, the building was renamed the Willis Tower after Willis Group Holdings, a London insurance broker and currently the largest tenant of the tower. The name change will stand for the duration of their ten year lease. Originally, the Willis Tower was called the Sears Tower, after Sears, Roebuck & Company. This company, who commissioned the building as their new headquarters in the early 1970s, played an integral role to the final form and size of the Tower.
Sears, Roebuck and Company was incorporated in 1893 by Richard Warren Sears and Alvah Curtis Roebuck. In the years that followed, thesmall company grew tremendously, becoming the largest mail order business in the world by 1906.1 In the mid-1920s, Sears transitioned from the mail order business into regional stores. By 1969, Sears was the largest retailer in the nation, and looking to update their outdated headquarters.2 With a net income of $441 million that year, the company could financially support the development of an impressive modern building.3 However, Sears needed Chicago’s support in order to make their move to the city center at South Wacker Drive. The company found support from Chicago’s mayor, Richard Daley. He was keen on the commerce that Sears’ headquarters would bring to the Chicago Loop area, which was partly undeveloped land.4 Daley also lifted the height restriction on buildings through a zoning ordinance revision in 1955; the ordinance changed the maximum building height to sixteen times the area of the lot.5 The only remaining obstacle to build higher was the Federal Aviation Administration, which set the maximum building height for Chicago at 2000 ft. above sea level, or 1450 ft above ground.6 However, height did not initially concernSears, as the original Tower design differed greatly from the final design.
It was only after Skidmore, Owings and Merrill (SOM), a structural engineering and architecture firm based in Chicago, got involved that the building took its final form. Sears performed several studies about the company’s project growth and current business practices and concluded that their current and future space requirements were 2 and 4 million square ft, respectively7, with a floor area of 110,000 square ft per department. Also looking for a cost-effective solution, Sears pictured a large 40-story cube. Instead, SOM determined by performing its own studies that departments could save significant amounts of time by stacking two 55,000 square ft stories on top of one another.8 This would change the building into an 80-story tower, but only if SOM could make it cost-effective.
Fazlur Khan, the engineer selected to work on the project, came up with the structural system that defined the Sears Tower. This bundled tube system gave the building its physical strength while saving Sears $10 million as compared to pre-existing structural systems.9 Khan had already worked on another Chicago project, the John Hancock Center, with architect Bruce Graham. In that building, he had used another innovative structural system, the braced tube, which tapered towards the top to provide for various tenant requirements. As the building contained an excess 2 million square ft compared to the initial space demand, Sears needed to consider various tenant requirements, and the shape of the John Hancock Center was similar to what they needed. However, Sears and Graham both wanted something distinctive, not another ‘Big John’. This required a new structural system.