This is the Willis Tower, previously known as the Sears Tower.
It is located in Chicago, Illinois, and is one of the most famous skyscrapers in the world, being the tallest building in America. It has 108 stories, and is a total of 1,451 ft. tall at the height of it's roof. With the antennas included in the height, it reaches a total of 1,729 ft. tall! It has a total of 4.56 million sq. ft. of space, of which 3.81 million sq. ft. is rentable. It cost $950,000,000 (in 2005 dollars) to build, which is half as much as Taipei 101!
It was finished in 1973 for Sears and Roebuck; it's purpose was to consolidate the many different locations of Sears and Roebuck in Chicago. It held the record of tallest building in the world till 1998, at which time the Petronas Towers broke the record. In 2009, "Willis Group Holdings", a bank, occupied a large portion of the tower, at which time the tower's name was changed to Willis Tower.
The structure of the building consists of nine square tubes clustered together in a square shape, each of which have a side length of 75 meters. When I say "tube", I mean a structure where the support is on the outside of the tower, not the inside. This gives more space in side the building. When Fazlur Khan designed this tower, it was the first time that tubes had been bundled together. Before, only one tube had been used; Khan decided that if one tube worked really well, why not nine tubes? So he designed the (then) Sears Tower with nine tubes in a square shape of varying heights. Here is an illustration of this:
All the tubes reach the 50th floor. There, two tubes end. The remaining 7 continue up to the 66th floor. There, two more tubes end. The remaining 5 continue up to the 90th floor, where 3 more tubes end. The remaining tubes reach up to the top of the tower. This gives the tower setbacks from the street, and gives it a less imposing look.
This skyscraper is an icon of Chicago, and America.
I think it is very interesting.
