Fazlur Rahman Khan Tube structural systems What was the tube structural system? His "tube concept", using all the exterior wall perimeter structure of a building to simulate a thin-walled tube, revolutionized tall building design.
Did this system do well?
Did  the tube structural system do well?
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." CANNOTANSWER
Most buildings over 40 stories constructed since the 1960s now use a tube design derived from Khan's structural engineering principles.
Fazlur Rahman Khan (, Fozlur 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.

Biography
Fazlur Rahman Khan  was born on 3 April 1929 in the Bengal Presidency of British India,  now Bangladesh. He was brought up in the village of Bhandarikandii, in the Faridpur District near Dhaka. His father Abdur Rahman Khan was a high school mathematics teacher and textbook author. He eventually became the Director of Public Instruction in the region of Bengal and after retirement served as Principal of Jagannath College, Dhaka.

Khan attended Armanitola Government High School, in Dhaka. After that, he studied Civil Engineering in 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 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 also did not see his first skyscraper in person until the age of 21 years old, 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.

Career

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.

Personal life
For enjoyment, Khan loved singing Rabindranath Tagore's poetic songs in Bengali. He and his wife, Liselotte, who immigrated from Austria, had one daughter who was born in 1960. In 1967, he elected to become a United States citizen.

Innovations
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.

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 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."

Framed tube
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 Apartment Building, since renamed Plaza on DeWitt, building that Bruce Graham designed and Khan did the engineering for 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 variants of the tube structure design. One of these was the concept of applying X-bracing to the exterior of the tube to form a trussed tube. X-bracing reduces the lateral load on a building by transferring the load into the exterior columns, and the reduced need for interior columns provides a greater usable floor space. Khan first employed exterior X-bracing on his engineering of the John Hancock Center in 1965, and this can be clearly seen on the building's exterior, making it 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 meter and One Chase Manhattan Plaza (1961), which required around 275 kilograms of steel per square meter, the John Hancock Center was far more efficient, requiring only 145 kilograms of steel per square meter. The trussed tube concept was applied to many later skyscrapers, including the Onterie Center, Citigroup Center and Bank of China Tower.

Bundle tube
One of Khan's most important variants of the tube structure concept was the bundled tube, which was used for the Willis Tower and One Magnificent Mile. The bundled 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."

Tube in tube
Tube-in-tube system takes advantage of core shear wall tubes in addition to exterior tubes. The inner tube and outer tube work together to resist gravity loads and lateral loads and to provide additional rigidity to the structure to prevent significant deflections at the top. This design was first used in One Shell Plaza. Later buildings to use this structural system include the Petronas Towers.

Outrigger and belt truss
The outrigger and belt truss system is a lateral load resisting system in which the tube structure is connected to the central core wall with very stiff outriggers and belt trusses at one or more levels. BHP House was the first building to use this structural system followed by the First Wisconsin Center, since renamed U.S. Bank Center, in Milwaukee. The center rises 601 feet, with three belt trusses at the bottom, middle and top of the building. The exposed belt trusses serve aesthetic and structural purposes. Later buildings to use this include Shanghai World Financial Center.

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. Trump Tower in New York City is also another example that adapted this system.

Shear wall frame interaction system
Khan developed the shear wall frame interaction system for mid high-rise buildings. This structural system uses combinations of shear walls and frames designed to resist lateral forces. The first building to use this structural system was the 35-stories Brunswick Building. The Brunswick building was completed in 1965 and became the tallest reinforced concrete structure of its time. The structural system of Brunswick Building consists of a concrete shear wall core surrounded by an outer concrete frame of columns and spandrels. Apartment buildings up to 70 stories high have successfully used this concept.

Legacy
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 Center, 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:

Life cycle civil engineering
Khan and Mark Fintel conceived ideas of shock absorbing soft-stories, for protecting structures from abnormal loading, particularly strong earthquakes, over a long period of time. This concept was a precursor to modern seismic isolation systems. The structures are designed to behave naturally during earthquakes where traditional concepts of material ductility are replaced by mechanisms that allow for movement during ground shaking while protecting material elasticity.

The IALCCE established the Fazlur R. Khan Life-Cycle Civil Engineering Medal.

Other architectural work

Khan designed several notable structures that are not skyscrapers. Examples include the Hajj terminal of King Abdulaziz International Airport, completed in 1981, which consists of tent-like roofs that are folded up when not in use. The project received several awards, including the Aga Khan Award for Architecture, which described it as an "outstanding contribution to architecture for Muslims". The tent-like tensile structures advanced the theory and technology of fabric as a structural material and led the way to its use for other types of terminals and large spaces.

Khan also designed the King Abdulaziz University, the United States Air Force Academy in Colorado Springs and the Hubert H. Humphrey Metrodome in Minneapolis. With Bruce Graham, Khan developed a cable-stayed roof system for the Baxter Travenol Laboratories in Deerfield, Illinois.

Computers for structural engineering and architecture
In the 1970s, engineers were just starting to use computer structural analysis on a large scale. SOM was at the center of these new developments, with undeniable contributions from Khan. Graham and Khan lobbied SOM partners to purchase a mainframe computer, a risky investment at a time, when new technologies were just starting to form. The partners agreed, and Khan began programming the system to calculate structural engineering equations, and later, to develop architectural drawings.

Professional milestones

List of buildings
Buildings on which Khan was structural engineer include:

 McMath–Pierce solar telescope, Kitt Peak National Observatory, Arizona, 1962
 DeWitt-Chestnut Apartments, Chicago, 1963
 Brunswick Building, Chicago, 1965
 John Hancock Center, Chicago, 1965–1969
 One Shell Square, New Orleans, Louisiana, 1972
 140 William Street (formerly BHP House), Melbourne, 1972
 Sears Tower, renamed Willis Tower, Chicago, 1970–1973
 First Wisconsin Center, renamed U.S. Bank Center, Milwaukee, 1973
 Hajj Terminal, King Abdulaziz International Airport, Jeddah, 1974–1980
 King Abdulaziz University, Jeddah, 1977–1978
 Hubert H. Humphrey Metrodome, Minneapolis, Minnesota, 1982
 One Magnificent Mile, Chicago, completed 1983
 Onterie Center, Chicago, completed 1986
 United States Air Force Academy, Colorado Springs, Colorado

Awards and chair

Among Khan's other accomplishments, he received the Wason Medal (1971) and Alfred Lindau Award (1973) from the American Concrete Institute (ACI); the Thomas Middlebrooks Award (1972) and the Ernest Howard Award (1977) from ASCE; the Kimbrough Medal (1973) from the American Institute of Steel Construction; the Oscar Faber medal (1973) from the Institution of Structural Engineers, London; the International Award of Merit in Structural Engineering (1983) from the International Association for Bridge and Structural Engineering IABSE; the AIA Institute Honor for Distinguished Achievement (1983) from the American Institute of Architects; and the John Parmer Award (1987) from Structural Engineers Association of Illinois and Illinois Engineering Hall of Fame from Illinois Engineering Council (2006).

Khan was cited five times by Engineering News-Record as among those who served the best interests of the construction industry, and in 1972 he was honored with ENR Man of the Year award. In 1973 he was elected to the National Academy of Engineering. He received honorary doctorates from Northwestern University, Lehigh University, and the Swiss Federal Institute of Technology Zürich (ETH Zurich).

The Council on Tall Buildings and Urban Habitat named one of their CTBUH Skyscraper Awards the Fazlur Khan Lifetime Achievement Medal after him, and other awards have been established in his honor, along with a chair at Lehigh University. Promoting educational activities and research, the Fazlur Rahman Khan Endowed Chair of Structural Engineering and Architecture honors Khan's legacy of engineering advancement and architectural sensibility. Dan Frangopol is the first holder of the chair.

Khan was mentioned by President Obama in 2009 in his speech in Cairo, Egypt when he cited the achievements of America's Muslim citizens.

Khan was the subject of the Google Doodle on 3 April 2017, marking what would have been his 88th birthday.

Documentary film
In 2021, director Laila Kazmi began production on a feature-length documentary film to be called Reaching New Heights: Fazlur Rahman Khan and the Skyscraper on the life and legacy of Khan. The film is produced by Kazmi's production company Kazbar Media, with development support from ITVS, which provides co-production support to independent documentaries on PBS. The film is helmed by director and producer Laila Kazmi, with associate producer Arnila Guha, and New York-based art director Begoña Lopez. It is fiscally sponsored by Film Independent.

Charity
In 1971 the Bangladesh Liberation War broke out. Khan was heavily involved with creating public opinion and garnering emergency funding for Bengali people during the war. He created the Chicago-based Bangladesh Emergency Welfare Appeal organization.

Death
Khan died of a heart attack on 27 March 1982 while on a trip in Jeddah, Saudi Arabia, at the age of 52. He was a general partner in SOM. His body was returned to the United States and was buried in Graceland Cemetery in Chicago.

See also
 Chicago school
 Engineering Legends, a 2005 book
 List of Bangladeshi architects

Notes and references

Notes

References
 
  Ali, Mir M. (2001). Art of the Skyscraper: The Genius of Fazlur Khan. Rizzoli International Publications, Inc., New York, NY,

External links
 
 Fazlur Rahman Khan Collection in the South Asian American Digital Archive (SAADA)
 Fazlur Rahman Khan Documentary Project
 Fazlur Khan Lifetime Achievement Medal
 Letter from Bill Clinton

 Exhibition at Princeton University

1929 births
1982 deaths
20th-century American architects
American Muslims
Bangladeshi diaspora
American people of Bangladeshi descent
Bangladesh University of Engineering and Technology alumni
20th-century Bengalis
Burials at Graceland Cemetery (Chicago)
Civil engineers
Pakistani emigrants to the United States
Recipients of the Independence Day Award
Structural engineers
University of Dhaka alumni
Grainger College of Engineering alumni
20th-century engineers
Skidmore, Owings & Merrill people
The 1999 Southern Brazil blackout was a widespread power outage (the largest ever at the time) that occurred in Brazil on March 11 to June 22, 1999. 

The blackout involved São Paulo, Rio de Janeiro, Minas Gerais, Goiás, Mato Grosso, Mato Grosso do Sul and Rio Grande do Sul, affecting an estimated 75 to 97 million people. A chain reaction was started when a lightning strike occurred at 22h 16m at an electricity substation in Bauru, São Paulo State causing most of the 440kV circuits at the substation to trip. Brazil was undergoing a severe investment crisis during 1999, which limited spending on maintenance and expansion of the power grid. With few routes for the power to flow from the generating stations via the 440kV system (a very important system to São Paulo state, carrying electricity generated by the Paraná river) a lot of generators automatically shut down because they did not have any load. The world's biggest power plant at the time, Itaipu, tried to support the load that was no longer being supplied by the 440kV power plants, but the 750kV AC lines and the 600kV DC lines that connected the plant to the rest of the system could not take the load and tripped too.

South of São Paulo the consumers experienced an overfrequency, caused because they had more generation than load, mostly because Itaipu was now connected only to this sub-system, but that problem was automatically solved by all generators in the area, that reduced their loads.

The rest of the system experienced a much bigger problem, an underfrequency, since the system had a lot of load and not enough generation capacity. Some generators tripped because of the overfrequency, which aggravated the problem, and after an automatic rejection of 35% of the sub-system load the underfrequency did not go away. This caused the system to break in many pieces, São Paulo and Rio de Janeiro states were split with a few areas remaining online. Most of the Minas Gerais system remained online, and powered Brazil's capital, Brasília, as well as the state of Goias and some of Espirito Santo.

In Rio, the military police placed 1,200 men in the streets to avoid looting. In São Paulo, traffic authorities announced they closed the city's tunnels to prevent robberies. More than 60,000 people were on Rio's subway when lights went out.

At midnight, power began returning to some areas.

See also
 List of major power outages
 Energy policy of Brazil

References

Brazil, 1999
Disasters in Brazil
Southern Brazil blackout
March 1999 events in South America This One's for You is the sixth album by R&B crooner Teddy Pendergrass. It was released just after a bad car accident Pendergrass was involved in, which left him paralyzed from the waist down due to a spinal cord injury. The album did not do as well as his previous albums did on the Billboard 200, peaking at only #59, but it did do well on the R&B album chart, reaching #6. Only one single was released, "I Can't Win for Losing", which peaked at only #32 on the R&B charts.

Track listing
 "I Can't Win for Losing" 4:16 (Victor Carstarphen, Gene McFadden, John Whitehead)
 "This One's for You" 6:18 (Barry Manilow, Marty Panzer)
 "Loving You Was Good" 3:35 (LeRoy Bell, Casey James)
 "This Gift of Life" 4:27 (Kenny Gamble, Leon Huff)
 "Now Tell Me That You Love Me" 5:15 (Gamble, Huff)
 "It's Up to You (What You Do With Your Life)" 5:37 (Gamble, Huff)
 "Don't Leave Me out Along the Road" 3:34 (Richard Roebuck)
 "Only to You" 3:53 (Nickolas Ashford, Valerie Simpson)

References

1982 albums
Teddy Pendergrass albums
Albums produced by Kenneth Gamble
Albums produced by Leon Huff
Albums produced by Thom Bell
Albums produced by Ashford & Simpson
Albums arranged by Bobby Martin
Albums recorded at Sigma Sound Studios
Philadelphia International Records albums