Exploring the Architecture of Tension

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What is Tensile Architecture?

Tensile Membrane Architecture, Denver Airport 1995, Colorado
Tensile Membrane Architecture, Denver Airport 1995, Colorado. Photo by Education Images/UIG/Universal Images Group Collection/Getty Images

Tensile architecture is a structural system that predominantly uses tension instead of compression. Tensile and tension are often used interchangeably. Other names include tension membrane architecture, fabric architecture, tension structures, and lightweight tension structures. Let's explore this modern yet ancient technique of building.

Pulling and Pushing:

Tension and compression are two forces you hear a lot about when you study architecture. Most structures we build are in compression—brick on brick, board on board, pushing and squeezing downward to the ground, where the weight of the building is balanced by the solid earth. Tension, on the other hand, is thought of as the opposite of compression. Tension pulls and stretches construction materials.

Definition of Tensile Structure:

"A structure that is characterized by a tensioning of the fabric or pliable material system (typically with wire or cable) to provide the critical structural support to the structure."—Fabric Structures Association (FSA)

Tension and Compression Building:

Thinking back at human-kind's first man-made structures (outside the cave), we think of Laugier's Primitive Hut (structures mainly in compression) and, even earlier, tent-like structures—fabric (e.g., animal hide) pulled tight (tension) around a timber or bone frame. Tensile design was fine for nomadic tents and small teepees, but not for the Pyramids of Egypt. Even the Greeks and Romans determined that large coliseums made from stone were a trademark of longevity and civility, and we call them Classical. Throughout the centuries, tension architecture was relegated to circus tents, suspension bridges (e.g., Brooklyn Bridge), and small-scale temporary pavilions.

For his entire life, German architect and Pritzker Laureate Frei Otto studied the possibilities of lightweight, tensile architecture—painstakingly calculating the height of poles, the suspension of cables, the cable netting, and the membrane materials that could be used to create large-scale tent-like structures. His design for the German Pavilion at Expo '67 in Montreal, Canada would have been much easier to construct if he had CAD software. But, it was this 1967 pavilion that paved the way for other architects to consider the possibilities of tension construction.

How to Create and Use Tension:

The most common models for creating tension are the balloon model and the tent model. In the balloon model, interior air pneumatically creates the tension on membrane walls and roof by pushing air into the stretchy material, like a balloon. In the tent model, cables attached to a fixed column pull the membrane walls and roof, much like an umbrella works.

Typical elements for the more common tent model include (1) the "mast" or fixed pole or sets of poles for support; (2) Suspension cables, the idea brought to America by German-born John Roebling; and (3) a "membrane" in the form of fabric (e.g., ETFE) or cable netting.

The most typical uses for this type of architecture include roofing, outdoor pavilions, sports arenas, transportation hubs, and semi-permanent post-disaster housing.

Source: Fabric Structures Association (FSA) at www.fabricstructuresassociation.org/what-are-lightweight-structures/tensile

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Inside Denver International Airport

Interior of Denver International Airport, 1995 in Denver, Colorado
Interior of Denver International Airport, 1995 in Denver, Colorado. Photo by altrendo images/Altrendo Collection/Getty Images

Denver International Airport is a fine example of tensile architecture. The stretched membrane roof of the 1994 terminal can withstand temperatures from minus 100°F (below zero) to plus 450°F. The fiberglass material reflects the sun's heat, yet allows natural light to filter into interior spaces. The design idea is to reflect the environment of mountain peaks, as the airport is near the Rocky Mountains in Denver, Colorado.

About the Denver International Airport:

Architect: C. W. Fentress J. H. Bradburn Associates, Denver, CO
Completed: 1994
Specialty Contractor: Birdair, Inc.
Design Idea: Similar to Frei Otto's peaked structure situated near the Munich Alps, Fentress chose a tensile membrane roofing system that emulated Colorado's Rocky Mountain peaks
Size: 1,200 x 240 feet
Number of Interior Columns: 34
Amount of Steel Cable 10 miles
Membrane Type: PTFE Fiberglass, a Teflon®-coated woven fiberglass
Amount of Fabric: 375,000 square feet for roof of Jeppesen Terminal; 75,000 square feet additional curbside protection

Source: Denver International Airport and PTFE Fiberglass at Birdair, Inc. [accessed March 15, 2015]

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Three Basic Shapes Typical of Tensile Architecture

Roof of the 1972 Olympic Stadium in Munich, Bavaria, Germany
Roof of the 1972 Olympic Stadium in Munich, Bavaria, Germany. Photo by Holger Thalmann/STOCK4B/Stock4B Collection/Getty Images

Inspired by the German Alps, this structure in Munich, Germany may remind you of Denver's 1994 International Airport. However, the Munich building was constructed twenty years earlier.

In 1967, German architect Günther Behnisch (1922-2010) won a competition to transform a Munich rubbish dump into an international landscape to host the XX Summer Olympic Games in 1972. Behnisch & Partner created models in sand to describe the natural peaks they wanted for the Olympic village. Then they enlisted German architect Frei Otto to help figure out the details of the design.

Without the use of CAD software, the architects and engineers designed these peaks in Munich to showcase not only the Olympic athletes, but also German ingenuity and the German Alps.

Did the architect of the Denver International Airport steal Munich's design? Maybe, but the South African company Tension Structures points out that all tension designs are derivatives of three basic forms:

  • "Conical – A cone shape, characterized by a central peak"
  • "Barrel Vault – An arched shape, usually characterized by a curved arch design"
  • "Hypar – A twisted freeform shape"

Sources: Competitions, Behnisch & Partner 1952-2005; Technical Information, Tension Structures [accessed March 15, 2015]

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Large in Scale, Light in Weight: Olympic Village, 1972

Aerial view of Olympic Village in Munich, Germany, 1972
Aerial view of Olympic Village in Munich, Germany, 1972. Photo by Design Pics/Michael Interisano/Perspectives Collection/Getty Images

Günther Behnisch and Frei Otto collaborated to enclose most of the 1972 Olympic Village in Munich, Germany, one of the first large-scale tension structure projects. Olympic Stadium in Munich, Germany was just one of the venues using tensile architecture.

Proposed to be larger and more grand than Otto's Expo '67 fabric Pavilion, the Munich structure was an intricate cable-net membrane. The architects chose 4 mm thick acrylic panels to complete the membrane. Rigid acrylic does not stretch like fabric, so the panels were "flexibly connected" to the cable netting. The result was a sculpted lightness and softness throughout the Olympic Village.

The lifespan of a tensile membrane structure is variable, depending on the type of membrane chosen. Today's advanced manufacturing techniques have increased the life of these structures from less than one year to many decades. Early structures, like the 1972 Olympic Park in Munich, were really experimental and require maintenance. In 2009, the German company Hightex was enlisted to install a new suspended membrane roof over Olympic Hall.

Source: Olympic Games 1972 (Munich): Olympic stadium, TensiNet.com [accessed March 15, 2015]

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Detail of Frei Otto's Tensile Structure in Munich, 1972

Frei Otto-Designed Olympic Roof Structure, 1972, Munich, Germany
Frei Otto-Designed Olympic Roof Structure, 1972, Munich, Germany. Photo by LatitudeStock-Nadia Mackenzie/Gallo Images Collection/Getty Images

Today's architect has an array of fabric membrane choices from which to select—many more "miracle fabrics" than the architects who designed the 1972 Olympic Village roofing.

In 1980, author Mario Salvadori explained tensile architecture this way:

"Once a network of cables is suspended from suitable points of support, the miracle fabrics can be hung from it and stretched across the relatively small distance between the cables of the network. The German architect Frei Otto has pioneered this type of roof, in which a net of thin cables hangs from heavy boundary cables supported by long steel or aluminum poles. Following the erection of the tent for the West German pavilion at Expo '67 in Montreal, he succeeded in covering the stands of the Munich Olympic Stadium...in 1972 with a tent that shelters eighteen acres, supported by nine compressive masts as high as 260 feet and by boundary prestressing cables of up to 5,000 tons capacity. (The spider, by the way, is not easy to imitate—this roof required 40,000 hours of engineering calculations and drawings.)"

Source: Why Buildings Stand Up by Mario Salvadori, McGraw-Hill Paperback Edition, 1982, pp. 263-264

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German Pavilion at Expo '67, Montreal, Canada

The German Pavilion at Expo 67, 1967, Montreal, Canada
The German Pavilion at Expo 67, 1967, Montreal, Canada. Photo © Atelier Frei Otto Warmbronn via PritzkerPrize.com

Often called the first large-scale lightweight tensile structure, the 1967 German Pavilion of Expo '67—prefabricated in Germany and shipped to Canada for onsite assembly—covered only 8,000 square meters. This experiment in tensile architecture, taking only 14 months to plan and build, became a prototype, and whet the appetite of German architects, including its designer, the future Pritzker Laureate Frei Otto.

That same year of 1967, German architect Günther Behnisch won the commission for the 1972 Munich Olympic venues. His tensile roof structure took five years to plan and build and covered a surface of 74,800 square meters—a far cry from its predecessor in Montreal, Canada.

Learn More About Tensile Architecture:

  • Light Structures - Structures of Light: The Art and Engineering of Tensile Architecture Illustrated by the Work of Horst Berger by Horst Berger, 2005
  • Tensile Surface Structures: A Practical Guide to Cable and Membrane Construction by Michael Seidel, 2009
  • Tensile Membrane Structures : ASCE/SEI 55-10, Asce Standard by the American Society of Civil Engineers, 2010

Sources: Olympic Games 1972 (Munich): Olympic stadium and Expo 1967 (Montreal): German Pavilion, Project Database of TensiNet.com [accessed March 15, 2015]