Tube (structure)

In structural engineering, the tube is a system where, to resist lateral loads (wind, seismic, impact), a building is designed to act like a hollow cylinder, cantilevered perpendicular to the ground.

This system was introduced by Fazlur Rahman Khan while at the architectural firm Skidmore, Owings & Merrill (SOM), in their Chicago office.

[1] The first example of the tube's use is the 43-story Khan-designed DeWitt-Chestnut Apartment Building, since renamed Plaza on DeWitt, in Chicago, Illinois, finished in 1966.

In the simplest incarnation of the tube, the perimeter of the exterior consists of closely spaced columns that are tied together with deep spandrel beams through moment connections.

This assembly of columns and beams forms a rigid frame that amounts to a dense and strong structural wall along the exterior of the building.

Where larger openings like garage doors are needed, the tube frame must be interrupted, with transfer girders used to maintain structural integrity.

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.

[6] This laid the foundations for the tube structural design of many later skyscrapers, including his own John Hancock Center and Sears Tower, and the construction of the World Trade Center, the Petronas Towers, the Jin Mao Building, and most other tall skyscrapers since the 1960s, including the world's tallest building as of 2020[update], the Burj Khalifa.

It can appear in a variety of floor plan shapes, including square, rectangular, circular, and freeform.

Beside being efficient structurally and economically, the bundled tube was "innovative in its potential for versatile formulation of architectural space.

John Hancock Center in Chicago , designed in 1965 and finished in 1969, is an example of the trussed tube structural design
The World Trade Center's Twin Towers were some of the first structures to use a framed tube design. The many columns of the tube can be seen around the exterior of this horizontal cross section. The towers had a core for services, seen in the center. The design was not tube-in-tube since the core had 47 columns spaced relatively evenly, rather than around the edge of the core.
Breakdown of the bundled tube structure of the Willis Tower with simplified floor plans.
Willis Tower , finished in 1973, introduced the bundled tube structural design and was the world's tallest building until 1998
Evolution of skyscraper structural systems
Evolution of skyscraper structural systems