At the time the Willis tower was constructed in 1974, it was the world’s tallest building, eclipsing New York‘s twin-towered World Trade Center by 25 meters (83 ft). It would keep the title of tallest building in the world until the Petronas twin towers in Kuala Lumpur, Malaysia were constructed in 1997.
There was much discussion on whether the Petronas Towers are actually taller than what was at the time known as the Sears Tower as the height of the antennas on the Petronas Towers are included in the total height, while the height of the antennas are not included in the height calculation of the Willis Tower as they are not considered an actual part of the building.
With the construction of the 508 meters tall Taipei 101 in 2004 this discussion became irrelevant. However, when in November 2013 New York’s One WTC was officially declared taller than the Willis Tower – grabbing the coveted title of the tallest building in the US, the issue was brought up once again: one WTC’s rather pathetic spire was included in the calculation of its height, so that even though the Willis Tower’s roof is a substantial 25 meters (83 feet) higher than One WTC‘s, the latter is now officially 99 meters (325 ft) taller.
In any case, the Willis tower is still the tallest Chicago skyscraper, exceeding the height of the number two, the Trump International Hotel and Tower by 27 meters (89 ft) and The Residences by 79 meters (253 ft).
The building consists of nine framed tubes, which are actually nine skyscrapers on themselves taken together into one building. Originally, the plan included no less than fifteen tubes, but when the planned hotel was
taken out of the project, only nine tubes were used in the final designs. The nine tubes all reach forty-nine stories. At that point, two tubes end. The other rise up to the sixty-fifth floor. From the sixty-sixth to the ninetieth floor, the tower has the shape of a crucifix. Two tubes, creating a rectangular, reach the full height of 442 meters (1451ft).
The result is an interesting tower, which looks different from all angles. The construction, designed by Fazlur Kahn (1929-82), has other advantages : the construction with separate tubes provides lateral strengths to withstand the strong Chicago wind loads, as each tube only needs to take a part of the pressure.
The Willis Tower’s observation deck – known as the skydeck – is one of Chicago’s most popular attractions. At 1,353 ft or 412 m, it’s Chicago’s highest observatory, besting the John Hancock Center’s by 323 ft (98m).
The most spectacular attraction at the skydeck is ‘the ledge’, a glass balcony extending 4.3 ft where you can look straight down. It will make most people feel uneasy at first but the balconies offer spectacular views over Wacker Drive and the Chicago River. More info about the skydeck can be found on this website: www.theskydeck.com
The tower was originally named after Sears, Roebuck and Co., an American chain of Department Stores which was headquartered here. Sears sold the building in 1993 after moving to the suburbs. The building’s name was left unchanged until Juli 16, 2009, when it was renamed Willis Tower for one of the skyscraper’s tenants, a British insurance firm. The move was met with local opposition however, and some even started online petitions to protest the name change.