“Officials at Chicago's Willis Tower say the popular tourist attraction is safe, even though a glass ledge jutting from the building's 103rd floor appeared to crack beneath the feet of a visiting family. The see-through glass bays are known as The Ledge and extend about four feet from the building, which was once called the Sears Tower. Officials say the family wasn't in danger when the cracks appeared Wednesday on a glass enclosure. In a statement Thursday, Willis Tower says a protective coating covering the glass surface cracked, not the glass itself. They say the cracks don't affect the "structural integrity" of the ledge, which is designed to occasionally crack. The ledges have proven to be a popular — if a frightening — experience since they opened in 2009 ( “Cracks Appear on Ledge at Chicago's Willis Tower.” (NBC15 RSS. N.P.) About Willis Tower
The Willis tower was formerly named and still commonly called Sears Tower. This building is a 108-story, 1,451-foot skyscraper that was built in 1973. It was formerly the tallest building in the world and it held this rank for almost 25 years. At this point in time, the Willis Tower is currently the second-tallest building in the United States and the eighth-tallest freestanding structure in the world. Over one million people each year visit this enormous skyscraper, which makes it one of the most popular tourist destinations in Chicago. Due to a lease on a portion of the space, Sears Tower was renamed Willis Tower in 2009. Even though it was renamed, people often still refer to it as Sears Tower (Wikimedia Foundation).
How it was built
With about 350,000 employees, Sears, Roebuck & Co. was the largest retailer in the world in 1969. Sears executives agreed they wanted to consolidate all of their employees that had offices all throughout the Chicago area into one building; Sears Tower. Sears wasn't sure where to put it, so they asked an outside council to suggest a location. After the firm met with authorities and the applicable law, Sears was advised that the proposed structure could be built in an area known as Goose Island (Wikimedia Foundation).
After the site was decided upon, the preliminary inquiries determined that the necessary permits would be able to be obtained. The next thing that needed to be done in this process was to gain the property and a team of attorneys from the Arnstein law firm headed by Andrew Adsit. The attorneys began buying the property parcel by parcel. Sears bought fifteen buildings with character and paid $2.7 million to the City of Chicago for the part of Quincy Street which divided the property (Wikimedia Foundation).
Demanding 3,000,000 square feet of space, and predictions that they will grow in the future, Sears found amazing architects by the names of Skidmore, Owings & Merrill (SOM) to come up with a structure that was predicted to be one of the largest buildings in the world. SOM’s team of architect, Bruce Graham and Fazlur Rahman Khan, a structural engineer, designed the building as nine square "tubes" squished into a 3×3 matrix producing a square base with 225-foot sides. The nine tubes would go up to the 50th floor of the building. Once the tubes hit the 50th floor, the northwest and southeast tubes end, and the remaining seven continue up. When they reach the 66th floor, the southwest and northeast tubes end. At the 90th floor, the south, east, and north tubes end. Finally, the center and west tubes continue until the 108th floor (Wikimedia Foundation).
The Willis Tower was the very first building to use Khan's tube structure. This amazing design was structurally efficient and economic. It effectively provided more space and became higher than the Empire State Building, although the cost was much less per unit area. This, in turn, highly influenced the skyscraper construction. It is usually used in extremely tall buildings today, including the world's tallest building, the Burj Khalifa. To honor Khan's contributions to the skyscraper, the Structural Engineers Association of Illinois made a sculpture of him for the lobby of the Willis Tower (Wikimedia Foundation).
Sears executives came together and agreed that the space they are going to occupy will be designed to house their Merchandise Group, and that floor space for future growth would be rented out to smaller firms and businesses until Sears could take it back. The latter floor areas had to be drawn up to a smaller plate to be attractive and marketable to prospective lessees. It also had a high window-space to floor-space ratio. On the other hand, smaller floor plates needed to have a taller structure to yield sufficient square footage. Skidmore architects proposed a tower with large floors in the lower part of the building, which would give the Sears Tower its distinctive look (Wikimedia Foundation).
As you can tell just from the reading, the Willis Tower is an extremely extravagant building that took a very long time to build. If you are interested in touring Willis Tower, it is located in Chicago, IL and is very easy to schedule. Even if you are afraid of heights, on the main floor you can learn more about the history and see pictures of the skyscraper dating back to when they were building it.
Work Cited
“Cracks Appear on Ledge at Chicago's Willis Tower." NBC15 RSS. N.p., 29 May 2014. Web. 08 Oct. 2014.
< http://www.nbc15.com/news/headlines/Cracks-appear-on-ledge-at-Chicagos-Willis-Tower-261135771.html>.
"Willis Tower." Wikipedia. Wikimedia Foundation, 13 Oct. 2014. Web. 13 Oct. 2014.
< http://en.wikipedia.org/wiki/Willis_Tower>
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