Burj Khalifa with Smith's attempts to make the crown more slender. The building opened on 4 January 2010. The tower was designed by Skidmore, Owings and Merrill (SOM), which also designed the Willis Tower (formerly the Sears Tower) in Chicago and the One World Trade Center in New York City. Burj Khalifa uses the bundled tube design of the Willis Tower, invented by Fazlur Rahman Khan. Due to its tubular system, proportionally only half the amount of steel was used in the construction, compared to the Empire State Building. Khan's contributions to the design of tall buildings have had a profound impact
Center City Tower (Philadelphia) with Comcast Corporation, Philadelphia's most high-profile corporation, in mind. Such a rumor would have been killed on January 5, 2005, the day Comcast Center was officially launched. Center City Tower (Philadelphia) Center City Tower was the working name of a formerly proposed skyscraper in downtown Philadelphia. Designed and proposed by the firm now known as KlingStubbins (designers of Philadelphia's Penn Center and Bell Atlantic Tower), the building would have risen to a height of 1,050 feet (320 m) and 75 stories, making it the tallest building in The United States outside New York and Chicago, surpassing the height of the