Tube (structure)

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John Hancock Center in Chicago, designed in 1965 and finished in 1969, is an example of the trussed tube structural design John Hancock Center2.jpg
John Hancock Center in Chicago, designed in 1965 and finished in 1969, is an example of the trussed tube structural design

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. [2]

Structural engineering

Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man made structures. Structural engineers need to understand and calculate the stability, strength and rigidity of built structures for buildings and nonbuilding structures. The structural designs are integrated with those of other designers such as architects and building services engineer and often supervise the construction of projects by contractors on site. They can also be involved in the design of machinery, medical equipment, and vehicles where structural integrity affects functioning and safety. See glossary of structural engineering.

Cantilever beam anchored at only one end

A cantilever is a rigid structural element, such as a beam or a plate, anchored at one end to a support from which it protrudes; this connection could also be perpendicular to a flat, vertical surface such as a wall. Cantilevers can also be constructed with trusses or slabs. When subjected to a structural load, the cantilever carries the load to the support where it is forced against by a moment and shear stress.

Fazlur Rahman Khan Bangladeshi architect

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 (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.


The system can be built using steel, concrete, or composite construction (the discrete use of both steel and concrete). It can be used for office, apartment, and mixed-use buildings. Most buildings of over 40 stories built since the 1960s are of this structural type.

Steel alloy made by combining iron and other elements

Steel is an alloy of iron and carbon, and sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.

Concrete Composite construction material

Concrete, usually Portland cement concrete, is a composite material composed of fine and coarse aggregate bonded together with a fluid cement that hardens over time—most frequently a lime-based cement binder, such as Portland cement, but sometimes with other hydraulic cements, such as a calcium aluminate cement. It is distinguished from other, non-cementitious types of concrete all binding some form of aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces, and polymer concretes that use polymers as a binder.

Mixed-use development Type of urban development strategy

Mixed-use development or often simply Live-work space is a type of urban development strategy for living spaces (housing) that blends residential, commercial, cultural, institutional, or entertainment uses, where those functions are physically and functionally integrated, and that provides pedestrian connections. Mixed-use development can take the form of a single building, a city block, or entire neighbourhoods. The term may also be used more specifically to refer to a mixed-use real estate development project—a building, complex of buildings, or district of a town or city that is developed for mixed-use by a private developer, (quasi-) governmental agency, or a combination thereof.


The tube system concept is based on the idea that a building can be designed to resist lateral loads by designing it as a hollow cantilever perpendicular to the ground. 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. [3]

Spandrel The space between a curved figure and a rectangular boundary

A spandrel is a triangular space, usually found in pairs, between the top of an arch and a rectangular frame; between the tops of two adjacent arches or one of the four spaces between a circle within a square. They are frequently filled with decorative elements.

This exterior framing is designed sufficiently strong to resist all lateral loads on the building, thereby allowing the interior of the building to be simply framed for gravity loads. Interior columns are comparatively few and located at the core. The distance between the exterior and the core frames is spanned with beams or trusses and can be column-free. This maximizes the effectiveness of the perimeter tube by transferring some of the gravity loads within the structure to it, and increases its ability to resist overturning via lateral loads.

Truss structure that consists of two-force members only

In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object". A "two-force member" is a structural component where force is applied to only two points. Although this rigorous definition allows the members to have any shape connected in any stable configuration, trusses typically comprise five or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes.


By 1963, a new structural system of framed tubes had appeared in skyscraper design and construction. Fazlur Rahman 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." [4] Closely spaced interconnected exterior columns form the tube. Lateral or horizontal loads (wind, seismic, impact) 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 allow more usable floor space. Where larger openings like garage doors are needed, the tube frame must be interrupted, with transfer girders used to maintain structural integrity.

Skyscraper design and construction

The design and construction of skyscrapers involves creating safe, habitable spaces in very high buildings. The buildings must support their weight, resist wind and earthquakes, and protect occupants from fire. Yet they must also be conveniently accessible, even on the upper floors, and provide utilities and a comfortable climate for the occupants. The problems posed in skyscraper design are considered among the most complex encountered given the balances required between economics, engineering, and construction management.

The first building to apply the tube-frame construction was the DeWitt-Chestnut Apartment Building which Khan designed and which was finished in Chicago by 1963. [5] This laid the foundations for the tube structural design of many later skyscrapers, including his own John Hancock Center and Willis Tower, and the construction of the World Trade Center, Petronas Towers, Jin Mao Building, and most other supertall skyscrapers since the 1960s, including the world's tallest building as of 2017, the Burj Khalifa. [6]

Chicago City in Illinois, United States

Chicago, officially the City of Chicago, is the most populous city in Illinois and the third most populous city in the United States. With an estimated population of 2,716,450 (2017), it is the most populous city in the Midwestern United States. Chicago is the county seat of Cook County, the second most populous county in the United States, and the principal city of the Chicago metropolitan area, which is often referred to as "Chicagoland." The Chicago metropolitan area, at nearly 10 million people, is the third-largest in the United States; the fifth largest in North America ; and the third largest metropolitan area in the world by land area.

John Hancock Center skyscraper in Chicago, Illinois, United States

875 North Michigan Avenue, built as and still commonly referred to as the John Hancock Center, is a 100-story, 1,128-foot supertall skyscraper located in Chicago, Illinois. Located in the Magnificent Mile district, its name was changed to 875 North Michigan Avenue on February 12, 2018.

Willis Tower Skyscraper in Chicago, Illinois

The Willis Tower, built as and still commonly referred to as the Sears Tower, is a 110-story, 1,450-foot (442.1 m) skyscraper in Chicago, Illinois. At completion in 1973, it surpassed the World Trade Center in New York to become the tallest building in the world, a title it held for nearly 25 years; it remained the tallest building in the Western Hemisphere until the completion of a new building at the rebuilt World Trade Center site in 2014. The building is considered a seminal achievement for architect Fazlur Rahman Khan. The Willis Tower is currently the second-tallest building in the United States and the Western hemisphere – and the 16th-tallest in the world. More than one million people visit its observation deck each year, making it one of Chicago's most popular tourist destinations. The structure was renamed in 2009 by the Willis Group as a term of its lease.


From its conception, the tube has been varied to suit different structural needs.

Framed tube

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. Nistncstar1-1-fig2-4.png
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.

This is the simplest incarnation of the tube. It can appear in a variety of floor plan shapes, including square, rectangular, circular, and freeform. This design was first used in Chicago's DeWitt-Chestnut Apartment Building, designed by Khan and finished in 1965, but the most notable examples are the Aon Center and the original World Trade Center towers.

Trussed or braced tube

The trussed tube, also termed braced tube, is similar to the simple tube but with comparatively fewer and farther-spaced exterior columns. Steel bracings or concrete shear walls are introduced along the exterior walls to compensate for the fewer columns by tying them together. The most notable examples incorporating steel bracing are the John Hancock Center, the Citigroup Center, and the Bank of China Tower.

Tube in tube

Also known as hull and core, these structures have a core tube inside the structure, holding the elevator and other services, and another tube around the exterior. Most of the gravity and lateral loads are normally taken by the outer tube because of its greater strength. The 780 Third Avenue 50-story concrete frame office building in Manhattan uses concrete shear walls for bracing and an off-center core to allow column-free interiors. [7]

Bundled tube

Breakdown of the bundled tube structure of the Willis Tower with simplified floor plans. Willis Tower tube structure.svg
Breakdown of the bundled tube structure of the Willis Tower with simplified floor plans.

Instead of one tube, a building consists of several tubes tied together to resist lateral forces. Such buildings have interior columns along the perimeters of the tubes when they fall within the building envelope. Notable examples include Willis Tower, One Magnificent Mile, and the Newport Tower.

Willis Tower, finished in 1973, introduced the bundled tube structural design and was the world's tallest building until 1998 Sears Tower ss.jpg
Willis Tower, finished in 1973, introduced the bundled tube structural design and was the world's tallest building until 1998

Beside being efficient structurally and economically, the bundled tube was "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." [8] The bundled tube structure meant that "buildings no longer need be boxlike in appearance: they could become sculpture." [9]


Hybrids include a varied category of structures where the basic concept of tube is used, and supplemented by other structural support(s). This method is used where a building is so thin that one system cannot provide adequate strength or stiffness.

Other uses

Some lattice towers consist of steel tube elements. They can be used for guyed and for free-standing lattice structures. An example for the first type was Warsaw Radio Mast, an example for latter one are the Russian 3803 KM-towers.


Design usage Skyscraper structure.png
Design usage

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