was the first building to use the framed-tube design. He believed that engineers needed a broader perspective on life, saying, "The technical man must not be lost in his own technology; he must be able to appreciate life, and life is art, drama, music, and most importantly, people." Khan's personal papers, most of which were in his office at the time of his death, are held by the Ryerson & Burnham Libraries at the Art Institute of Chicago. The Fazlur Khan Collection includes manuscripts, sketches, audio cassette tapes, slides and other materials regarding his work. Khan's seminal work of developing tall building structural systems are still used today as the starting point when considering design options for tall buildings. Tube structures have since been used in many skyscrapers, including the construction of the World Trade Center, Aon Centre, Petronas Towers, Jin Mao Building, Bank of China Tower and most other buildings in excess of 40 stories constructed since the 1960s. The strong influence of tube structure design is also evident in the world's current tallest skyscraper, the Burj Khalifa in Dubai. According to Stephen Bayley of The Daily Telegraph: Minoru Yamasaki In the United States, Minoru Yamasaki found major independent success in implementing unique engineering solutions to then-complicated problems, including the space that elevator shafts took up on each floor, and dealing with his personal fear of heights. During this period, he created a number of office buildings which led to his innovative design of the towers of the World Trade Center in 1964, which began construction 21 March 1966. The first of the towers was finished in 1970. Many of his buildings feature superficial details inspired by the pointed arches of Gothic architecture, and make use of extremely narrow vertical windows. This narrow-windowed style arose from his own personal fear of heights. One particular design challenge of the World Trade Center's design related to the efficacy of the elevator system, which was unique in the world. Yamasaki integrated the fastest elevators at the time, running at 1,700 feet per minute. Instead of placing a large traditional elevator shaft in the core of each tower, Yamasaki created the Twin Towers' "Skylobby" system. The Skylobby design created three separate, connected elevator systems which would serve different segments of the building, depending on which floor was chosen, saving approximately 70% of the space used for a traditional shaft. The space saved was