At the time Chicago's Sears tower was constructed in 1974, it was the world's tallest building, a title it lost when the Petronas twin towers in Kuala Lumpur, Malaysia, were constructed (1997). [Note:The height of the antennas on the Petronas towers are included in the total height, while it is not included in the height calculation of the Sears tower. With the construction of the 508m-high Taipei 101 tower in 2004, this discussion became irrelevant(*1)].

In July 2009 the Sears Tower was renamed to Willis Tower*(2), but many refuse to accept the name change of Chicago's most iconic skyscraper, with some even starting a petition against the change. Sears is short for Sears & Roebuck, one of the world’s greatest clothing companies till 2005 when it joined Kmart..

 The Structure

The building consists of nine framed tubes*(3), which are actually nine skyscrapers on themselves taken together into one building. 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 meter (1451ft).

Wind Load

The tower looks different from all angles. The construction, designed by Fazlur Kahn (1929-82), has another advantage: the separate tubes provide lateral strengths to withstand the strong Chicago wind loads*(4), as each tube takes only a part of the pressure.

The most spectacular attraction at the skydeck is 'the ledge', a glass balcony extending 4.3 ft where you can look straight down. (see < www.theskydeck.com >.

[This article is abridged from the following website < http://www.aviewoncities.com/chicago/searstower.htm >]

Vocabulary: *1: irrelevant : sans intérêt, hors sujet; *2. Renamed to : rebaptisée… : *3. Framed tubes : construction en caisson avec raidisseurs horizontaux supplémentaires. *4 : withstand the load : résister à la charge / à la pression.