Fazlur Rahman Khan (April 3, 1929 - March 27, 1982) was a Bangladeshi structural engineer and architect, who initiated structural systems that form the basis of tall building construction today. Considered the Father of tubular designs for high-rises, Khan became an icon in both architecture and structural engineering. He is the designer of Willis Tower – the tallest building in the United States (and tallest in the world for many years) and John Hancock Centre, a 100-story tall building.
He also designed structures that are not high rises such as the Hajj Terminal and helped in initiating the widespread usage of computers for structural engineering. Khan, more than any other individual, ushered in a renaissance in skyscraper construction during the second half of the twentieth century and made it possible for people to live and work in "cities in the sky".
Khan in his short life created a legacy of innovations that is without peer and left an unprecedented and lasting influence on the profession, both nationally and internationally. 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 construction. CTBUH named an award after him called Fazlur Khan Lifetime Achievement Medal. Khan's seminal work of developing tall building structural systems are still used today as starting point when considering design options for tall buildings.
Khan received his matriculation from Armanitola Government High School, in Dhaka. He received his Bachelor of Civil Engineering degree from Ahsanullah Engineering College, University of Dhaka, (now Bangladesh University of Engineering and Technology). He received a Fulbright Scholarship and a Pakistan government scholarship enabled him to travel to the United States in 1952 where he pursued advanced studies 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.
In a career marked by innovation in structural engineering and collaboration between engineering and architecture, Khan introduced design methods and concepts that set new standards for efficient use of material and suggested new possibilities for building architecture. In 1955, employed by Skidmore, Owings and Merrill, he began working in Chicago, Illinois. He was made a partner in 1966 and became a naturalized American citizen in 1967. During the 1960s and 1970s, he became noted for his designs for Chicago’s 100-story John Hancock Center and 108-story Sears Tower, the tallest building in the world in its time, topping out the Empire State Building (1931), and still the tallest in the United States since its completion in 1974. He is also responsible for designing notable buildings in Bangladesh, Australia and Saudi Arabia.
Fazlur Khan had a unique understanding of forces, materials, behavior, as well as art, literature and architecture. Fazlur Khan was not only a creative structural engineer, he was also a philosopher, visionary, educator and humanitarian. He said, "Think logically and find the relationships which exist in every system, because it will help you understand nature itself, making living more meaningful and exciting." According to John Zils, senior engineer and associate partner with Skidmore, Owings & Merrill (SOM), "It was his unique ability to bridge the gap between architectural design and structural engineering that truly set Faz apart from other structural engineers." Because of that, Khan became an icon in both architecture and structural engineering. Khan 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."
Fazlur Khan's personal papers, the majority of which were found 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 realized that the rigid steel frame structure that had dominated tall building design and construction so long was not the only system fitting for tall buildings, marking the beginning of a new era of skyscraper revolution in terms of multiple structural systems.
Tube structural systems
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" variations. 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-storeys constructed since the 1960s now use a tube design derived from Khan’s structural engineering principles.
The tubular designs are for resisting lateral loads (horizontal forces) such as wind forces, seismic forces, etc. The primary important role of structural system for tall Buildings is to resist lateral loads. The lateral loads begin to dominate the structural system and take on increasing importance in the overall building system when the building height increases. Forces of winds become very substantial and forces of earthquake etc. are very important as well. It is the tubular designs that are used for tall buildings to resist such forces.
Tube structures are very stiff and have numerous significant advantages over other framing systems. They not only make the buildings structurally stronger and more efficient, they significantly reduce the usage of materials while simultaneously allowing buildings to reach even greater heights. The reduction of material makes the buildings economically much more efficient and reduces environmental issues as it results in the least carbon emission impact on the environment. Tubular systems allow greater interior space and further enable buildings to take on various shapes, offering unprecedented 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 more than any other individual brought in a rebirth in skyscrapers construction after a hiatus for over thirty years.
Khan's tubular designs have dominated skyscraper construction design since the 1960s. The tubular systems have yet to reach their limit when it comes to height. The beauty of Khan’s tubular systems is that buildings can be constructed using steel or concrete, or a composite of the two to reach lofty heights. His clear approaches to structural systems have often led to expressive structures.
The population explosion, beginning with the baby boom of the 1950s, created widespread concern about the amount of available living space. Khan had the solution — building up. 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."
Khan's initial projects were the 43 stories DeWitt-Chestnut (1964) and 35 stories Brunswick Building (1965). He then did the John Hancock Center (1969), a 100 stories tall building and would later go on to America's tallest building the iconic Willis Tower (formerly called Sears Tower).
Since 1963, the new structural system of framed tubes became 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.
The first building to apply the tube-frame construction was the DeWitt-Chestnut Apartments building that Khan designed and was completed in Chicago in 1963. This laid the foundations for the framed tube structure used in the construction of the World Trade Center.
Trussed tube and X-bracing
Khan pioneered several other variations of the tube structure design. One of these was the concept of X-bracing, or the "trussed tube", first employed for the John Hancock Center. This concept reduced the lateral load on the building by transferring the load into the exterior columns. This allows for a reduced need for interior columns thus creating more floor space. This concept can be seen in the John Hancock Center, designed in 1965 and completed in 1969. One of the most famous buildings of the structural expressionist style, the skyscraper's distinctive X-bracing exterior is actually a hint that the structure's skin is indeed part of its 'tubular system'. This idea is one of the architectural techniques the building used to climb to record heights (the tubular system is essentially the spine that helps the building stand upright during wind and earthquake loads). This X-bracing allows for both higher performance from tall structures and the ability to open up the inside floorplan (and usable floor space) if the architect desires. Original features such as the skin, pioneered by Fazlur Khan, have made the John Hancock Center an architectural icon.
In contrast to earlier steel-frame structures, such as the Empire State Building (1931), which required about 206 kilograms of steel per square metre and Chase Manhattan Bank Building (1961), which required around 275 kilograms of steel per square metre, the John Hancock Center was far more efficient, requiring only 145 kilograms of steel per square metre. The trussed tube concept was applied to many later skyscrapers, including the Onterie Center, Citigroup Center and Bank of China Tower.
Sears Tower (now Willis Tower), engineered by Khan and designed by Bruce Graham, was the tallest building in the world for over two decades. The design for this 1450-foot-tall tower introduced the bundled tube structural system, as well as a new vocabulary in architectural form.
One of Khan's most important variations of the tube structure concept was the "bundled tube," which he used for the Sears Tower and One Magnificent Mile. The bundle tube design was not only the most efficient in economic terms, but it was also "innovative in its potential for versatile formulation of architectural space. Efficient towers no longer had to be box-like; the tube-units could take on various shapes and could be bundled together in different sorts of groupings."
Concrete tube structures
The last major buildings engineered by Khan were the One Magnificent Mile and Onterie Center in Chicago, which employed his bundled tube and trussed tube system designs respectively. In contrast to his earlier buildings, which were mainly steel, his last two buildings were concrete. His earlier DeWitt-Chestnut Apartments building, built in 1963 in Chicago, was also a concrete building with a tube structure. The Brunswick Building, a 35 stories tall building built in 1965 also used this structural system.
Khan's seminal work of developing tall building structural systems in structural steel and reinforced concrete based on building height are still used today as 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:
Khan invented a new way of building tall. [...] So Fazlur Khan created the unconventional skyscraper. Reversing the logic of the steel frame, he decided that the building's external envelope could – given enough trussing, framing and bracing – be the structure itself. This made buildings even lighter. The "bundled tube" meant buildings no longer need be boxlike in appearance: they could become sculpture. Khan's amazing insight – he was name-checked by Obama in his Cairo University speech last year – changed both the economics and the morphology of supertall buildings. And it made Burj Khalifa possible: proportionately, Burj employs perhaps half the steel that conservatively supports the Empire State Building. [...] Burj Khalifa is the ultimate expression of his audacious, lightweight design philosophy.
These pioneering structural systems shaped skyline of cities around the world. Khan is the foremost structural engineer of the 20th century whose contributions to the design of tall buildings have had a profound impact on the profession of architecture and engineering. In his short life, Khan re-shaped the concept of super-tall buildings and man’s ability to live and work in the sky. His developments are among today’s “conventional” systems for skyscraper design. Khan never acquired a household name, but a quarter-century after his death, his legacy lives on in the lives and work of a new generation of structural engineers.
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