The Willis Tower, formerly known as the Sears Tower, is a 110-story skyscraper in Chicago, Illinois, and the second tallest building in the United States. It was finished in 1973 and became the tallest building in the world, at 1,451 feet, a rank it held for 25 years. The structure has a unique "bundled tube" design, made by nine separate tubes, with only two of the tubes reaching to the top 108th floor.
10 Years after People: The Sears Tower is slowly deteriorating, and rainwater rots the Sears Tower's roof. Moisture seeps down into the structure and begins rusting the bolts holding the giant glass and aluminum panels on the exterior. Freezing wind, rain and snow off Lake Michigan violently batter the hulking structure. Some of the plates peel off the building and crash into the streets below.
200 Years after People: Corrosion has devastated the Sears Tower, leaving it as a hollowed-out honey-combed husk. The building's 72 elevators all stopping at different floors are now crashing through the building and weakening its floors as the cables holding them break. The elevators' security brakes kick in, but they corrode, too, and stop working. One of the two elevators connecting the ground floor with the observation deck falls nearly 1000 feet to the ground. Flooding from the Chicago River weakens the 114 pilings driven into the bedrock that holds up the structure. Soon, the entire tower collapses and its antennas fall in different directions, destroying everything in close range to it.