page_title: Fazlur Rahman Khan
section_title: Trussed tube and X-bracing
hierarchical_section_title: Fazlur Rahman Khan / Innovations / Trussed tube and X-bracing
caption_attribution_description: English: John Hancock Center, Chicago
context_page_description: Fazlur Rahman Khan 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. 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.
context_section_description: 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.
caption: In 1960, buildings over 20 stories were still newsworthy. Apartments in the John Hancock Center in Chicago – shown here with its distinctive exterior X-bracing – are located as high as the 90th floor.
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