Empire State Building. Khan's contributions to the design of tall buildings have had a profound impact on architecture and engineering. It would be difficult to find any worldwide practices in the design of tall buildings that have not been directly or indirectly influenced by his work. The design is reminiscent of Frank Lloyd Wright's vision for The Illinois, a mile-high skyscraper designed for Chicago, as well as Chicago's Lake Point Tower. When Adrian Smith was conceiving the project at SOM, he looked out his office window toward Lake Point Tower's curved three-wing layout and thought, "There's the prototype". According to Strabala, Burj Khalifa was designed based on the 73 floor Tower Palace Three, an all-residential building in Seoul. In its early planning, Burj Khalifa was intended to be entirely residential. After the original design by Skidmore, Owings, and Merrill, Emaar Properties chose Hyder Consulting to be the supervising engineer and NORR Group Consultants International Ltd to supervise the architecture of the project. Hyder was selected for their expertise in structural and MEP (mechanical, electrical and plumbing) engineering. Hyder Consulting's role was to supervise construction, certify the architect's design, and be the engineer and architect of record to the UAE authorities. NORR's role was the supervision of all architectural components including on-site supervision during the construction and design of a 6-story addition to the office annex building for architectural documentation. NORR was also responsible for the architectural integration drawings for the Armani Hotel included in the Tower. Emaar Properties also engaged GHD, an international multidisciplinary consulting firm, to act as an independent verification and testing authority for concrete and steelwork. The design is derived from Islamic architecture. As the tower rises from the flat desert base, there are 27 setbacks in a spiral pattern, decreasing the cross-section of the tower as it rises and creating convenient outdoor terraces. These setbacks are arranged and aligned in a way that minimizes vibration wind loading from eddy currents and vortices. At the top, the central core emerges and is sculpted to form a finishing spire. At its tallest point, the tower sways a total of . The spire of Burj Khalifa is composed of more than of structural steel. The central pinnacle pipe weighs and has a height of . The spire also houses communications equipment. This spire is widely considered vanity height, since very little of its space is usable. Without the spire,