Sears Tower, also translated as Willis Group Tower, is a skyscraper located in Chicago, Illinois, United States. It was once the tallest building in North America. The Sears Tower has 110 floors and was once the tallest office building in the world. About 16,500 people come to work here every day. On the 103rd floor there is an observation deck for tourists to overlook the whole city. It is 412 meters above the ground, and on a clear day you can see four American states.
The building consists of a steel frame structure. The whole building is regarded as a cantilevered beam structure. The farther the structure is from the ground, the smaller the shear force will be, and the vibration caused by wind pressure on the top of the building will be significantly reduced. This greatly enhances the building's stiffness and resistance to lateral forces.