Fazlur Rahman Khan (Bengali: ফজলুর রহমান খান, Fazlur Rôhman Khan; 3 April 1929 – 27 March 1982) was a Bangladeshi-American structural engineer and architect who initiated important structural systems for skyscrapers. Considered the "father of tubular designs" for high-rises, Khan was also a pioneer in computer-aided design (CAD). He was the designer of the Sears Tower, since renamed Willis Tower, the tallest building in the world from 1973 until 1998, and the 100-story John Hancock Center.
A partner in the firm Skidmore, Owings & Merrill in Chicago, Khan, more than any other individual, ushered in a renaissance in skyscraper construction during the second half of the 20th century. He has been called the "Einstein of structural engineering" and the "Greatest Structural Engineer of the 20th Century" for his innovative use of structural systems that remain fundamental to modern skyscraper design and construction. In his honor, the Council on Tall Buildings and Urban Habitat established the Fazlur Khan Lifetime Achievement Medal as one of their CTBUH Skyscraper Awards.
Although best known for skyscrapers, Khan was also an active designer of other kinds of structures, including the Hajj airport terminal, the McMath–Pierce solar telescope, and several stadium structures.
Fazlur Rahman Khan was born on 3 April 1929 to a Bengali Muslim family in Dhaka, Bengal Presidency (present-day Bangladesh). He was from and brought up in the Khan Bari of Bhandarikandi in Madaripur, Faridpur District. His father, Khan Bahadur Abdur Rahman Khan, was a high school mathematics teacher and textbook author who eventually became the Director of Public Instruction in Bengal and, after retirement, served as the first principal of Jagannath College. His mother, Khadijah Khatun, was the daughter of Abdul Basit Chowdhury, the Zamindar (aristocratic landowner) of Dulai in Pabna, who traced his ancestry to a migrant from Samarkand in Turkestan. Khan's paternal uncle, Abdul Hakim Khan, was the son-in-law of Syed Abdul Jabbar, a zamindar based in Comilla.
Khan attended Armanitola Government High School in Dhaka. After that, he studied civil engineering at Bengal Engineering and Science University, Shibpur (present day Indian Institute of Engineering Science and Technology, Shibpur), Kolkata, India, and then received his Bachelor of Civil Engineering degree from Ahsanullah Engineering College (now Bangladesh University of Engineering and Technology). He received a Fulbright Scholarship and a government scholarship, which enabled him to travel to the United States in 1952. There he studied at the University of Illinois at Urbana–Champaign. In three years Khan earned two master's degrees – one in structural engineering and one in theoretical and applied mechanics – and a PhD in structural engineering with a thesis titled Analytical Study of Relations Among Various Design Criteria for Rectangular Prestressed Concrete Beams.
His hometown in Dhaka did not have any buildings taller than three stories. He did not view his first skyscraper in person until the age of 21, and he had not stepped inside a mid-rise building until he moved to the United States for graduate school. Despite this, the environment of his hometown in Dhaka later influenced his tube building concept, which was inspired by the bamboo that sprouted around Dhaka. He found that a hollow tube, like the bamboo in Dhaka, lent a high-rise vertical durability.
In 1955, employed by the architectural firm Skidmore, Owings & Merrill (SOM), he began working in Chicago. He was made a partner in 1966. He worked the rest of his life side by side with fellow architect Bruce Graham. Khan introduced design methods and concepts for efficient use of material in building architecture. His first building to employ the tube structure was the Chestnut De-Witt apartment building. During the 1960s and 1970s, he became noted for his designs for Chicago's 100-story John Hancock Center and 110-story Sears Tower, since renamed Willis Tower, the tallest building in the world from 1973 until 1998.
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.
For enjoyment, Khan loved singing Rabindranath Tagore's poetic songs in Bengali. He and his wife, Liselotte, an immigrant from Austria, had one daughter who was born in 1960. In 1967, he elected to become a United States citizen. Khan was a Muslim at the time when he died.
Khan discovered that the rigid steel frame structure that had long dominated tall building design was not the only system fitting for tall buildings, marking the start of a new era of skyscraper construction.
Khan's central innovation in skyscraper design and construction was the idea of the "tube" structural system for tall buildings, including the framed tube, trussed tube, and bundled tube variants. His "tube concept", using all the exterior wall perimeter structure of a building to simulate a thin-walled tube, revolutionized tall building design. Most buildings over 40 stories constructed since the 1960s now use a tube design derived from Khan's structural engineering principles.
Lateral loads (horizontal forces) such as wind forces, seismic forces, etc., begin to dominate the structural system and take on increasing importance in the overall building system as the building height increases. Wind forces become very substantial, and forces caused by earthquakes, etc., are important as well. The tubular designs resist such forces for tall buildings. Tube structures are stiff and have significant advantages over other framing systems. They not only make the buildings structurally stronger and more efficient, but also significantly reduce the structural material requirements. The reduction of material makes the buildings economically more efficient and reduces environmental impact. The tubular designs enable buildings to reach even greater heights. Tubular systems allow greater interior space and further enable buildings to take on various shapes, offering added freedom to architects. These new designs opened an economic door for contractors, engineers, architects, and investors, providing vast amounts of real estate space on minimal plots of land. Khan was among a group of engineers who encouraged a rebirth in skyscraper construction after a hiatus of over thirty years.
The tubular systems have yet to reach their limit when it comes to height. Another important feature of the tubular systems is that buildings can be constructed using steel or reinforced concrete, or a composite of the two, to reach greater heights. Khan pioneered the use of lightweight concrete for high-rise buildings, at a time when reinforced concrete was used for mostly low-rise construction of only a few stories in height. Most of Khan's designs were conceived considering pre-fabrication and repetition of components so projects could be quickly built with minimal errors.
The population explosion, starting with the baby boom of the 1950s, created widespread concern about the amount of available living space, which Khan solved by building upward. More than any other 20th-century engineer, Fazlur Rahman Khan made it possible for people to live and work in "cities in the sky". Mark Sarkisian (Director of Structural and Seismic Engineering at Skidmore, Owings & Merrill) said, "Khan was a visionary who transformed skyscrapers into sky cities while staying firmly grounded in the fundamentals of engineering."
Since 1963, the new structural system of framed tubes has become highly influential in skyscraper design and construction. Khan defined the framed tube structure as "a three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation." Closely spaced interconnected exterior columns form the tube. Horizontal loads, for example from wind and earthquakes, are supported by the structure as a whole. About half the exterior surface is available for windows. Framed tubes allow fewer interior columns, and so create more usable floor space. The bundled tube structure is more efficient for tall buildings, lessening the penalty for height. The structural system also allows the interior columns to be smaller and the core of the building to be free of braced frames or shear walls that use valuable floor space. Where larger openings like garage doors are required, the tube frame must be interrupted, with transfer girders used to maintain structural integrity.