US dollars so that Dubai could pay its debts – Dubai borrowed at least $80 billion for construction projects. In the 2000s, Dubai started diversifying its economy but it suffered from an economic crisis in 2007–2010, leaving large-scale projects already in construction abandoned. Records The Burj Khalifa set several world records, including: Tallest existing structure: (previously KVLY-TV mast – ) Tallest structure ever built: (previously Warsaw radio mast – ) Tallest freestanding structure: (previously CN Tower – ) Tallest skyscraper (to top of spire): (previously Taipei 101 – ) Tallest skyscraper to top of antenna: (previously the Willis (formerly Sears) Tower – ) Building with most floors: 163 (previously World Trade Center – 110) World's highest elevator installation (situated inside a rod at the very top of the building) World's longest travel distance elevators: Highest vertical concrete pumping (for a building): World's tallest structure that includes residential space World's highest installation of an aluminium and glass façade: World's highest nightclub: 144th floor World's highest restaurant (At.mosphere): 122nd floor at (previously 360, at a height of in CN Tower) World's highest New Year display of fireworks. World's largest light and sound show staged on a single building. History of height increases There are unconfirmed reports of several planned height increases since its inception. Originally proposed as a virtual clone of the Grollo Tower proposal for Melbourne, Australia's Docklands waterfront development, the tower was redesigned by Skidmore, Owings and Merrill. Marshall Strabala, a Skidmore, Owings and Merrill architect who worked on the project until 2006, said in late 2008 that Burj Khalifa was designed to be tall. The architect who designed it, Adrian Smith, felt that the uppermost section of the building did not culminate elegantly with the rest of the structure, so he sought and received approval to increase its height. It was stated that this change did not add any floors, which fit with Smith's attempts to make the crown more slender. The building opened on 4 January 2010. Architecture and design 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