Tensegrity

Skylon by George Morrow

Tensegrity [ten-seg-ri-tee], tensional integrity or floating compression is a structural principle based on a system of isolated components under compression inside a network of continuous tension, and arranged in such a way that the compressed members (usually bars or struts) do not touch each other while the prestressed tensioned members (usually cables or tendons) delineate the system spatially.

The term was coined by inventor Buckminster Fuller in the 1960s as a portmanteau of ‘tensional integrity.’ The other denomination of tensegrity, floating compression, was used mainly by the constructivist artist Kenneth Snelson. Shorter columns or struts in compression are stronger than longer ones. This in turn led Fuller to make claims that tensegrity structures could be scaled up to cover whole cities.

Tensegrity structures are based on the combination of a few simple design patterns: Members loaded in either pure compression or pure tension, which means that the structure will only fail if the cables yield or the rods buckle. This enables the material properties of each member to be optimized to the particular load it carries. Preload or tensional prestress allows cables to be rigid in tension and maintains structural integrity. Mechanical stability allows the members to remain in tension/compression as stress on the structure increases. The structure also becomes stronger as it is loaded.

Because of these patterns, no structural member experiences a bending moment and there are no shear stresses within the system. This can produce exceptionally strong and rigid structures for their mass and for the cross section of the components. The Skylon was a futuristic-looking, cigar-shaped tensegrity structure built in 1951 for the Festival of Britain. A popular joke of the period was that, like the British economy of 1951, ‘It had no visible means of support.’ Six cables, three at each end, hold the tower in position. The three cables connected to the bottom ‘define’ its location. The other three cables are simply keeping it vertical.

In 2009, the Kurilpa Bridge opened across the Brisbane River in Queensland, Australia. A multiple-mast, cable-stay structure based on the principles of tensegrity, it is currently the world’s largest such structure.

In the 1980s, engineer David Geiger designed the Seoul Olympic Gymnastics Arena for the 1988 Summer Olympics using tensegrity principles. The Georgia Dome, which was used for the 1996 Summer Olympics, was a large tensegrity structure of similar design to the aforementioned Gymnastics Hall. Tropicana Field, home of the Tampa Bay Rays major league baseball team, has a dome roof supported by a large tensegrity structure.

Biotensegrity, a term coined by Dr. Stephen Levin, is the application of tensegrity principles to biologic structures. Biological structures such as muscles, bones, fascia, ligaments and tendons, or rigid and elastic cell membranes, are made strong by the unison of tensioned and compressed parts. The muscular-skeletal system is a synergy of muscle and bone. The muscles and connective tissues provide continuous pull and the bones present the discontinuous compression. Even the human spine, which seems at first glance like a stack of vertebrae resting on each other, is actually a tensegrity structure.

A theory of tensegrity in molecular biology to explain cellular structure has been developed by Harvard physician and scientist Donald E. Ingber. For instance, the expressed shapes of cells, whether it be their reactions to applied pressure, interactions with substrates, etc., all can be mathematically modeled if a tensegrity model is used for the cell’s cytoskeleton. Furthermore, the geometric patterns found throughout nature (the helix of DNA, the geodesic dome of a volvox, Buckminsterfullerene, and more) may also be understood based on applying the principles of tensegrity to the spontaneous self-assembly of compounds, proteins, and even organs. This view is supported by how the tension-compression interactions of tensegrity minimize material needed, add structural resiliency, and constitute the most efficient possible use of space. Therefore, natural selection pressures would strongly favor biological systems organized in a tensegrity manner.

As Ingber explains: ‘The tension-bearing members in these structures — whether Fuller’s domes or Snelson’s sculptures — map out the shortest paths between adjacent members (and are therefore, by definition, arranged geodesically) Tensional forces naturally transmit themselves over the shortest distance between two points, so the members of a tensegrity structure are precisely positioned to best withstand stress. For this reason, tensegrity structures offer a maximum amount of strength.’

The origins of tensegrity are controversial. Many traditional structures, such as skin-on-frame kayaks and shoji (Japanese lattice framed doors), use tension and compression elements in a similar fashion. In 1948, artist Kenneth Snelson produced his innovative ‘X-Piece’ after artistic explorations at Black Mountain College (where Buckminster Fuller was lecturing) and elsewhere. Some years later, the term ‘tensegrity’ was coined by Fuller, who is best known for his geodesic domes. Throughout his career, Fuller had experimented with incorporating tensile components in his work, such as in the framing of his dymaxion houses.

Snelson’s 1948 innovation spurred Fuller to immediately commission a mast from him. In 1949, Fuller developed a tensegrity-icosahedron based on the technology, and he and his students quickly developed further structures and applied the technology to building domes. After a hiatus, Snelson also went on to produce a plethora of sculptures based on tensegrity concepts. His main body of work began in 1959 when a pivotal exhibition at the Museum of Modern Art took place. At the MOMA exhibition, Fuller had shown the mast and some of his other work. At this exhibition, Snelson, after a discussion with Fuller and the exhibition organizers regarding credit for the mast, also displayed some work in a vitrine.

Russian artist Viatcheslav Koleichuk claimed that the idea of tensegrity was invented first by Karlis Johansons, a Soviet avant-garde artist of Latvian descent, who contributed some works to the main exhibition of Russian constructivism in 1921. Koleichuk’s claim was backed up by art historian Maria Gough for one of the works at the 1921 constructivist exhibition. Snelson has acknowledged the constructivists as an influence for his work.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.