Tensegrity

For the movement system created by Carlos Castaneda, see Tensegrity (Castaneda)

Needle Tower by Kenneth Snelson (1968)

Tensegrity is a portmanteau of tensional integrity. It refers to the integrity of structures as being based in a synergy between balanced tension and compression components.

The term "tensegrity" was first explored by artist Kenneth Snelson to produce sculptures such as his 18 meter high Needle Tower in 1968. The term 'tensegrity' was coined for Snelson by Buckminster Fuller. Fuller is best known for his geodesic domes, which he developed based on concepts explained and demonstrated by Snelson through sculptures. The term "synergetics" may refer more abstractly to synergetic systems of contrasting forces.

Concept

The Skylon tower at the Festival of Britain, 1951

The simplest tensegrity structure. Each of three compression members is symmetric with the other three and end to end. Each end is connected to three cables which provide compression and which precisely define the position of that end in the same way as the three cables in the Skylon tower define the bottom end of that pillar.

A similar structure but with four compression members.

Tensegrity structures are structures based on the combination of a few simple but subtle and deep design patterns:

loading members only in pure compression or pure tension, meaning the structure will only fail if the cables yield or the rods buckle (the rods would have to be an exceptionally weak material with a very large diameter to yield before they buckle or the cables yield)
preload, which allows cables to be rigid in compression
exact constraint, which reduces stress localization
mechanical stability, which allows the members to remain in tension/compression as stress on the structure increases

Because of these patterns, no members experiencing bending moment. This produces exceptionally rigid structures for their mass and for their cross section.

A conceptual building block of tensegrity is seen in the 1951 Skylon tower. The long tower is held in place at one end by only three cables. Considering only at the bottom end, exactly three cables are needed to fully determine the position of the bottom end of the spire so long as the spire is loaded in compression. Two cables would be unstable, like a person on a slackrope; one cable is just the limit case of two cables when the two cables are anchored in the same place.

A simple three-rod tensegrity structure (shown) builds on this: locally, each end of each rod looks like the bottom of the Skylon tower. As long as the angle between any two cables is less than 180° as seen looking along the rod, the position of the rod is well defined. What may not be immediately obvious is that because this is true for all six rod ends, the structure as a whole is stable. Variations such as Needle Tower involve more than three cables meeting at the end of a rod, but these can be thought of as three cables defining the position of that rod end with the additional cables simply attached to that well-defined point in space.

Metaphorical tensegrity

It should be noted that Webster's dictionary has simplified the collective meaning as "all things working together". And, while this may be seen as an "over-simplification" in lieu of the technical underpinnings that accompany this concept, the phrase is legitimate in the sense of this concept's universal applicability. The phrase aptly covers the "spirit" of the two words used in the creation of this neologism, in that the breadth & depth in its inherent meaning (semantic carriage) is extensive and multi-disciplinary.

For example, the formation of functioning architectures in one particular area of cybernetics research - sometimes referred to as "systems intellect" (the paradigmatic landscapes of the meta-cognitive level), makes use of octahedral matrices for the creation of focuses. The simplest form of tensegrity is that of the octahedron (first discovered by Theodore Pope). These matrices help to expeditiously capture the ever-changing/dynamic "contextual backdrop". So, the formation of these functioning architectures which, theoretically, allows for a kind of "auto-epistemological" approach to the creation of "sentience" in the cybernetic environment, is then dependent upon conceptually-based "primitives" held in tension - compression or complementary relationships. These architectures also allow for the ready implementation of any acquired acumen that has been "codified" as an "expert system" (the algorithmic & heuristic content found therein) relative to the perceived contextual backdrop. This would imply then that even human thought & reconnoitering dialogs have "tensegrital (adj)" underpinnings.

Applications

The idea was adopted into architecture in the 1980s when David Geiger designed the first significant structure - Seoul Olympic Gymnastics Arena for the 1988 Summer Olympics. The Georgia Dome, which was used for the 1996 Summer Olympics is a large tensegrity structure of similar design to the aforementioned Gymnastics Hall.

Theoretically, there is no limitation to the size of a tensegrity. Cities could be covered with geodesic domes. Planets and stars (Dyson sphere) could be contained within them.

"Tensegrity is a contraction of tensional integrity structuring. All geodesic domes are tensegrity structures, whether the tension-islanded compression differentiations are visible to the observer or not. Tensegrity geodesic spheres do what they do because they have the properties of hydraulically or pneumatically inflated structures."

As Harvard physician and scientist Donald 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."

In 2009, the Kurilpa Bridge will open across the Brisbane River in Queensland, Australia. The new greenbridge will be a multiple-mast, cable-stay structure based on the principles of tensegrity.

Biology

The concept has applications in biology. Biological structures such as muscles and bones, 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 muscle provides continuous pull, the bones discontinuous push. Tensegrity has been theorized by Rick Barrett to have implications in Taijiquan and athletics in general. He claims that high level athletes and Taijiquan players enter into "the zone", and have access to the tensegrity of their connective tissue system. This would explain greater levels of integration, strength, and faster reactions in elite athletes.

Russian claims

Russian artist Viatcheslav Koleichuk claimed that the idea of tensegrity was invented first by Karl Ioganson, Russian artist of Latvian descent, who contributed some works based on this principle to the main exhibition of Russian constructivism in 1921 [1]. This claim was backed by Maria Gough in her paper "In the Laboratory of Constructivism: Karl Ioganson's Cold Structures" (October, Vol. 84, Spring, 1998, pp. 90-117). Kenneth Snelson however denied this claim insisting that Ioganson's works were much further than one step from his own concept of tensegrity [2].

Bibliography

Gomez Jauregui, Valentin, Tensegridad. Estructuras Tensegríticas en Ciencia y Arte, Universidad de Cantabria, Santander, 2007, 200 pp.
Donald E. Ingber, The Architecture of Life, Scientific American Magazine, January 1998
Buckminster Fuller, SYNERGETICS—Explorations in the Geometry of Thinking, Volumes I & II, New York, Macmillan Publishing Co, 1975, 1979
Morgan, G.J. (2003). "Historical Review: Viruses, Crystals and Geodesic Domes". Trends in Biochemical Sciences. 28: 86–90. doi:10.1016/S0968-0004(02)00007-5.
Seeking the Gift Tensegrity Dr. Timothy Wilken TrustMark 2001
Amy Edmondson, A Fuller Explanation, EmergentWorld LLC, 2007, 339 pp.
Anthony Pugh, An Introduction to Tensegrity, University of California Press, Berkeley and Log Angeles California, 1976, ISBN: 0520030559
Rick Barrett, Taijiquan: Through the Western Gate, blue snake books, 2006

External links

Valentin Gomez Jauregui's site Very interesting web page (in Spanish) showing images, references and explanations about tensegrity.
Valentin Gomez Jauregui's thesis Very interesting thesis (in English) showing Tensegrity Structures and their application to architecture, with images, references and explanations about tensegrity.
Kenneth Snelson's site with an excellent article on the theory and development of tensegrity as well as pictures of his sculptures from desk top pieces to 90 foot towers.
Tensegrity in a Cell -- This interactive feature allows you to control a cell's internal structural elements. From Donald Ingber and the research department of Children's Hospital Boston.
Stephen Levin's Biotensegrity site Several papers on the tensegrity mechanics of biologic structures from viruses to vertebrates by an Orthopedic Surgeon.
Dynamic Template site: an excellent article by Dr. Lofthouse that demonstrates how spatially-organised flows of aminophospholipids in the red blood cell membrane convert the cell surface into a 'Dynamic Template' for its cortical Spectrin cytoskeleton. This is the only model to date that provides biological cells with a mechanism capable of pre-stressing flexible, membrane-associated protein networks, which is absent from Glanz & Ingbers' exclusively protein based models of cellular 'Tensegrity' structures.
[3] a french article of Tensegrity and spinal manipulations
3D models of tensegrity structures A nice interactive Java applet by Dr. Achim Luhn simulating the dynamics of a couple of regular tensegrity structures