Willis Tower Spire in Chicago, Illinois

myminifactory

The Willis Tower stands as a 108-story skyscraper in Chicago, Illinois. Completed in 1973, it surpassed the World Trade Center towers in New York to become the world's tallest building for nearly 25 years. The tower is the second-tallest building in the United States and the 13th-tallest globally. Over one million people visit its observation deck annually, making it a top tourist destination in Chicago. In 2009, the Willis Group renamed the structure as part of its lease on a portion of the tower's space. As of December 2013, the largest tenant is United Airlines, which occupies around 20 floors with its headquarters and operations center. In 1969, Sears, Roebuck & Co. was the world's largest retailer, employing about 350,000 people. To consolidate employees in offices scattered throughout Chicago, Sears executives decided to build a single building on the western edge of the city's Loop. They asked their 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 offered Sears two options: 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. The latter site was chosen, and preliminary inquiries determined that necessary permits could be obtained and Quincy Street vacated. The next step was to acquire the property; a team of attorneys from the Arnstein law firm headed by Andrew Adsit began buying the property parcel by parcel. Sears purchased 15 old buildings from 100 owners and paid $2.7 million to the City of Chicago for the portion of Quincy Street that divided the property. Sears commissioned architects Skidmore, Owings & Merrill (SOM) to design a structure that would be one of the largest office buildings in the world. The tower's distinctive look was achieved through a series of setbacks, which gave it a unique appearance. As Sears continued to project optimistic growth, the tower's proposed floor count increased rapidly, surpassing the height of New York's unfinished World Trade Center. The construction cost about $150 million at the time, equivalent to around $800 million in 2015 dollars. By comparison, Taipei 101, built in 2004 in Taiwan, cost around the equivalent of US$2.14 billion in 2014 dollars. Black bands appear on the tower around the 29th-32nd, 64th-65th, 88th-89th, and 104th-108th floors, which 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. In February 1982, two television antennas were added to the structure, increasing its total height to 1,707 feet (520 m). The western antenna was later extended, bringing the overall height to 1,730 feet (527 m) on June 5, 2000, to improve reception of local NBC station WMAQ-TV.