The Willis Tower, built as and still commonly referred to as Sears Tower, is a 108-story, 1,450-foot (442.1 m) skyscraper in Chicago. At completion in 1973, it surpassed the World Trade Center towers in New York to become the tallest building in the world, a title it held for nearly 25 years. The Willis Tower is the second-tallest building in the United States and the 14th-tallest in the world. More than one million people visit its observation deck each year, making it one of Chicago’s most popular tourist destinations. The structure was renamed in 2009 by the Willis Group as part of its lease on a portion of the tower’s space. The building’s official address is 233 South Wacker Drive, Chicago, Illinois 60606. In 1969, Sears, Roebuck & Co. was the largest retailer in the world, with about 350,000 employees. Sears executives decided to consolidate the thousands of employees in offices distributed throughout the Chicago area into one building on the western edge of Chicago’s Loop. Sears asked its outside counsel, Arnstein, Gluck, Weitzenfeld & Minow (now known as Arnstein & Lehr, LLP) to suggest a location. The firm consulted with local and federal authorities and the applicable law, then offered Sears two options: an area known as Goose Island and a two-block area bounded by Franklin Street on the east, Jackson Boulevard on the south, Wacker Drive on the west and Adams Street on the north, with Quincy Street running through the middle from east to west. Sears, which needed 3,000,000 square feet (280,000 m2) of office space for its planned consolidation and predicted that growth would require yet more, commissioned architects Skidmore, Owings & Merrill (SOM) to produce a structure to be one of the largest office buildings in the world. Their team of architect Bruce Graham and structural engineer Fazlur Rahman Khan designed the building as nine square “tubes” (each essentially a separate building), clustered in a 3×3 matrix forming a square base with 225-foot (69 m) sides. All nine tubes would rise up to the 50th floor of the building. At the 50th floor, the northwest and southeast tubes end, and the remaining seven continue up. At the 66th floor, the northeast and the southwest tubes end. At the 90th floor, the north, east, and south tubes end. The remaining west and center tubes continue up to the 108th floor. Black bands appear on the tower around the 29th–32nd, 64th–65th, 88th–89th, and 104th–108th floors. These are louvres that allow ventilation for service equipment and obscure the structure’s belt trusses. Even though regulations did not require a fire sprinkler system, the building was equipped with one from the beginning. There are around 40,000 sprinkler heads in the building, installed at a cost of $4 million. read more…
