Tensegrity

Left frame
Animation The simplest tensegrity structure. Each of three compression members (green) is symmetric with the other two, and symmetric from end to end. Each end is connected to three cables (red) 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 its tapered pillar.

Left frame
Animation The simplest tensegrity structure. Each of three compression members (green) is symmetric with the other two, and symmetric from end to end. Each end is connected to three cables (red) 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 its tapered pillar.

Tensegrity, tensional integrity or floating compression, is a structural principle based on the use of isolated components in compression inside a net of continuous tension, in such a way that the compressed members (usually bars or struts) do not touch each other and the prestressed tensioned members (usually cables or tendons) delineate the system spatially.[1]

The term tensegrity was coined by Buckminster Fuller in the 1960s as a portmanteau of "tensional integrity".[2] The other denomination of tensegrity, floating compression, was used mainly by Kenneth Snelson. Tensegrity as "The Architecture of Life" is an idea developed by Donald E. Ingber, explained in a January 1998 article in Scientific American.[3]

Concept

Left frame
Animation A similar structure but with four compression members.

Tensegrity structures are structures based on the combination of a few simple 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
• preload or tensional prestress, which allows cables to be rigid in tension
• mechanical stability, which allows the members to remain in tension/compression as stress on the structure increases

Because of these patterns, no structural member experiences a bending moment. This can produce exceptionally rigid structures for their mass and for the cross section of the components.

A conceptual building block of tensegrity is seen in the 1951 Skylon tower. 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.

A three-rod tensegrity structure (shown) builds on this: the ends of each rod look like the bottom of the Skylon tower. As long as the angle between any two cables is smaller than 180°, the position of the rod is well defined. There are also three connection points defining the position the rod tops. This makes the overall structure 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.

Eleanor Hartley points out visual transparency as an important aesthetic quality of these structures.[4] Korkmaz et al.[5][6] put forward that the concept of tensegrity is suitable for adaptive architecture thanks to lightweight characteristics.

Applications

A 12m high tensegrity structure exhibit at the Science City, Kolkata.

The idea was adopted into architecture in the 1960s when Maciej Gintowt and Maciej Krasiński, architects of Spodek, a venue in Katowice, Poland, designed it as one of the first major structures to employ the principle of tensegrity. The roof uses an inclined surface held in check by a system of cables holding up its circumference.

In the 1980s David Geiger designed 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.

Shorter columns or struts in compression are stronger than longer ones. This in turn led some, namely Fuller, to make claims that tensegrity structures could be scaled up to cover whole cities.

As Harvard physician and scientist Donald E. 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.[citation needed]

On 4 October 2009, the Kurilpa Bridge opened across the Brisbane River in Queensland, Australia. The bridge is a multiple-mast, cable-stay structure based on the principles of tensegrity. It is also the largest tensegrity structure in existence.

Biology

Biotensegrity, a term coined by Dr. Stephen Levin, is the application of tensegrity principles to biologic structures.[7] 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[8] and the bones present the discontinuous compression.

A theory of tensegrity in molecular biology to explain cellular structure has been developed by Donald Ingber.[3] 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.[9]

History

Kenneth Snelson's 1948 X-Module Design as embodied in a two-module column[10]

The origins of tensegrity are controversial.[11] 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 incorporating tensile components in his work, such as in the framing of his dymaxion houses.[12]

Snelson's 1948 innovation spurred Fuller to immediately commission a mast from Snelson. In 1949, Fuller developed an 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. Snelson's 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.[13] 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.[14]

Snelson's best known piece is his 18-meter-high Needle Tower of 1968.

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 to the main exhibition of Russian constructivism in 1921.[15] Koleichuk's claim was backed up by Maria Gough for one of the works at the 1921 constructivist exhibition.[16] Snelson has acknowledged the constructivists as an influence for his work.[17] French engineer David Georges Emmerich has also noted how Ioganson's work seemed to foresee tensegrity concepts.[18]

Mathematical explanation

Mathematical model of the tensegrity icosahedron
Different shapes of tensegrity icosahedra, depending on the ratio between the lengths of the tendons and the struts.

The following is a mathematical model for figures related to the tensegrity icosahedron, which explains why the tensegrity icosahedron is a stable construction, albeit with infinitesimal mobility.[19]

Consider a cube of side length 2d, centered at the origin. Place a strut of length 2l on each face of the cube, so that each strut is parallel to one edge of the face and meets the center of the face. Moreover, each strut should be parallel to the strut on the opposite face of the cube, but orthogonal to all other struts. The coordinates of one vertex of the struts are (0,d,l), the coordinates of the other vertices can be obtained by either cyclicly rotating the coordinates (0,d,l)→(d,l,0)→(l,0,d) (rotational symmetry in the main diagonal of the cube) or by changing the sign of the coordinates (0,d,l)→(0,-d,l)→(0,-d,-l)→(0,d,-l) (mirror symmetries in the coordinate planes). The distance s between two neighbouring vertices can be obtained from the following relation

$s^2 = (d-l)^2 + d^2 + l^2 = 2(d-\frac 1 2 \,l)^2 + \frac 3 2 \,l^2$

Now imagine, this figure is built from struts of length 2l and tendons of length s connecting neighbouring endpoints. The relation tells us, that for $s > \sqrt{3 / 2}\,l$ there are two possible values for d: one is realized by pushing the struts together, the other by pulling them apart. For example for $s=\sqrt 2 \,l$ the minimal figure (d=0) is a regular octahedron and the maximal figure (d=l) is a quasiregular cubeoctahedron. When $s =\frac {1} {2} (\sqrt 5 - 1)$ then s = 2d, so the convex hull of the maximal figure is a regular icosahedron.

In the case $s = \sqrt{3/2}\,l$ the two extremes $d=\frac 1 2 \,l$ coincide, therefore the figure is the stable tensegrity icosahedron.

Since the tensegrity icosahedron represents an extremal point of the above relation, it has infinitesimal mobility: a small change in the length s of the tendon (e.g. by stretching the tendons) results in a much larger change of the distance 2d of the struts.

References

1. ^ Gómez-Jáuregui, V (2010). Tensegrity Structures and their Application to Architecture. Servicio de Publicaciones Universidad de Cantabria, p.19. ISBN 8481025755.
2. ^ Swanson, RL (2013). "Biotensegrity: a unifying theory of biological architecture with applications to osteopathic practice, education, and research-a review and analysis". The Journal of the American Osteopathic Association 113 (1): 34–52. PMID 23329804.
3. ^ a b Ingber (January 1998)
4. ^ Eleanor Hartley, "Ken Snelson and the Aesthetics of Structure," in the Marlborough Gallery catalogue for Kenneth Snelson: Selected Work: 1948 - 2009, exhibited February 19 through March 21, 2009.
5. ^ Korkmaz, et al. (June 2011)
6. ^ Korkmaz, et. al (2011)
7. ^ Levin, Stephen, "Tensegrity, The New Biomechanics"; Hutson, M & Ellis, R (Eds.), Textbook of Musculoskeletal Medicine. Oxford: Oxford University Press. 2006
8. ^ Musculoskeletal Prestress, "[1]", Journal of Biomechanics, October 2009.
9. ^ Ingber, Donald (January 1998). Scientific American.
10. ^ Maria Gough, "In the Laboratory of Constructivism: Karl Ioganson's Cold Structures" October, Vol. 84 (Spring, 1998), p. 109.
11. ^ Gómez-Jáuregui, V. (2009). "Controversial Origins of Tensegrity". International Association of Spatial Structures IASS Symposium 2009, Valencia.
12. ^ Dymaxion World of Buckminster Fuller, chapter on Tensegrity.
13. ^ See photo of Fuller's work at this exhibition in his 1961 article on tensegrity for the Portfolio and Art News Annual (No.4).
14. ^ Lalvani (1996), p. 47.
15. ^ Droitcour, Brian (2006-08-18). "Building Blocks". The Moscow Times. Archived from the original on 2008-10-07. Retrieved 2011-03-28. "With an unusual mix of art and science, Vyacheslav Koleichuk resurrected a legendary 1921 exhibition of Constructivist art."
16. ^ Gough (1998), pp. 90-117.
17. ^ In Snelson's article for Lalvani, 1996, I believe.
18. ^ David Georges Emmerich, Structures Tendues et Autotendantes, Paris: Ecole d'Architecture de Paris la Villette, 1988, pp. 30-31.
19. ^ "Tensegrity Figuren". Universität Regensburg. Retrieved 2 April 2013.

Gallery

1. ^ Gómez-Jáuregui (2010), Fig. 2.1, p. 28.
2. ^ Fuller and Marks (1960), Fig. 270.
3. ^ Fuller and Marks (1960), Fig. 268.
4. ^ Lalvani (1996), p. 47

Bibliography

• Fuller, Buckminster. SYNERGETICS—Explorations in the Geometry of Thinking, Volumes I & II, New York, Macmillan Publishing Co, 1975, 1979.
• Fuller, Buckminster. "Tensegrity," Portfolio and Art News Annual, No. 4 (1961), pp. 112–127, 144, 148.
• Fuller, R. Buckminster; Marks, Robert. The Dymaxion World of Buckminster Fuller, Garden City, New York: Anchor Books, 1973 (originally published in 1960 by So. Ill. Univ. Press), Figs. 261-280. A good overview on the scope of tensegrity from Fuller's point of view, and an interesting overview of early structures with careful attributions most of the time.
• Gómez-Jáuregui, Valentin (2007). Tensegridad. Estructuras Tensegríticas en Ciencia y Arte. Santander: Universidad de Cantabria. ISBN 978-84-8102-437-1. (Spanish)
• Gómez-Jáuregui, Valentín (2010). Tensegrity Structures and their Application to Architecture. Santander: Servicio de Publicaciones de la Universidad de Cantabria. isbn=978-84-8102-575-0.
• Ingber, Donald E. (January 1998). "The Architecture of Life". Scientific American.
• Korkmaz, Sinan; Bel Hadj Ali, Nizar, Smith, Ian F.C. (2011). "Configuration of Control System for Damage Tolerance of a Tensegrity Bridge". Advanced Engineering Informatics 26: 145. doi:10.1016/j.aei.2011.10.002.
• Korkmaz, Sinan; Bel Hadj Ali, Nizar, Smith, Ian F.C. (June 2011). "Determining Control Strategies for Damage Tolerance of an Active Tensegrity Structure". Engineering Structures 33 (6): 1930–1939. doi:10.1016/j.engstruct.2011.02.031.
• Lalvani, Haresh (ed.) (1996). "Origins of Tensegrity: Views of Emmerich, Fuller and Snelson". International Journal of Space Structures 11 (1, 2). pp. 27–55.
• Juan, S. J.; Tur, J M (July 2008), "Tensegrity frameworks: Static analysis review", Mechanism and Machine Theory, 43, 7: 859–881, doi:10.1016/j.mechmachtheory.2007.06.010, retrieved 2 April 2013

• Di Carlo, Biagio. "STRUTTURE TENSEGRALI". Quaderni di Geometria Sinergetica, Pescara 2004. http://www.biagiodicarlo.com
• Edmondson, Amy. A Fuller Explanation, EmergentWorld LLC, 2007. Earlier version available online at http://www.angelfire.com/mt/marksomers/40.html
• Forbes, Peter. The Gecko's Foot: How Scientists are Taking a Leaf from Nature's Book, Harper Perennial, 2006, pp. 197–230.
• Hanaor, Ariel, "Tensegrity: Theory and Application," Chapter 13 (pp. 385–408) in J. François Gabriel, Beyond the Cube: The Architecture of Space Frames and Polyhedra, New York: John Wiley & Sons, Inc., 1997.
• Kenner, Hugh. Geodesic Math and How to Use It, Berkeley, California: University of California Press, 1976. Now back in print. This is a good starting place for learning about the mathematics of tensegrity and building models.
• Masic, Milenko, Robert E. Skelton and Philip E. Gill, "Algebraic tensegrity form-finding," International Journal of Solids and Structures, Vol. 42, Nos. 16-17 (Aug 2005), pp. 4833–4858. They present the remarkable result that any linear transformation of a tensegrity is also a tensegrity.
• Morgan, G.J. (2003). "Historical Review: Viruses, Crystals and Geodesic Domes". Trends in Biochemical Sciences 28 (2): 86–90. doi:10.1016/S0968-0004(02)00007-5. PMID 12575996.
• Motro, R., "Tensegrity Systems: The State of the Art," International Journal of Space Structures, Vol. 7 (1992), No. 2, pp. 75–84.
• Pugh, Anthony. An Introduction to Tensegrity, University of California Press, Berkeley and Los Angeles California, 1976, ISBN 0-520-03055-9
• Snelson, Kenneth. Letter to R. Motro, International Journal of Space Structures, November 1990.
• Souza, et al., "Prestress revealed by passive co-tension at the ankle joint", Journal of Biomechanics, October 2009.
• Vilnay, Oren, Cable Nets and Tensegric Shells: Analysis and Design Applications, New York: Ellis Horwood Ltd., 1990.
• Wang, Bin-Bing, "Cable-strut systems: Part I - Tensegrity," Journal of Constructional Steel Research, Vol. 45 (1998), No. 3, pp. 281–289.
• Wilken, Timothy. Seeking the Gift Tensegrity, TrustMark, 2001.