The Willis Tower is a 442 m (1,451 ft) tower located in Chicago, Illinois. This building was formally known as the Sears Tower until its name change in July 2009. The Willis Tower was completed in 1973 and at that time it was the tallest building in the world and held that rank for close to 25 years. It is currently the tallest building in the United States and is the seventh tallest freestanding structure in the world. The Willis Tower has 108 floors and 3 basement level floors. It is a popular tourist destination due to its observation deck known as the Skydeck on the 103rd floor, which allows visitors to view the plains of Illinois across Lake Michigan, Indiana, Michigan, and as far as Wisconsin on clear days.
Who designed the Willis Tower?
Construction of the Willis Tower began in 1970 and was completed three years later in 1973. It was constructed to house all of the office employees of Sears, Roebuck & Co. the largest retail company in the world at that time. To house the employees the company needed 3 million square feet of space with room to expand as the company grew. They commissioned the architect company Skidmore, Owings and Merrill to design the largest office building ever seen.
The Willis Tower was designed by architect Bruce Graham and structural engineer Fazlur Khan. These two men designed a building that would consist of nine square tubes. Each tube was a self contained building in its own right and they were clustered together in a 3 x 3 matrix which formed the base of the building. At different points in the building certain tubes would finish whilst others continued to be built upwards resulting in only the centre and west tubes reaching the 108 floor. A building design like this had never been seen before and Khans’ bundled tube structure is still used in designing skyscrapers today.