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
Metropolitan Tower (Chicago) White, the Metropolitan Tower was named the Straus Building when completed in 1924. Though it was the first building in Chicago with 30 or more floors, it was never officially designated Chicago's tallest building since the Chicago Temple Building, also completed in 1924, is taller by but has seven fewer floors. The Straus Building and the Chicago Temple Building were the first to take advantage of the 1923 zoning ordinance; before then, no building in Chicago could be taller than . The Metropolitan Tower was at one time called the Continental National Insurance Company Building (later Continental Center I). From