Tensegrity: Encyclopedia - Tensegrity

Tensegrity

In mechanics and biomechanics, tensegrity or tensional integrity is a property of objects with components that use tension and compression in a combination that yields strength and resilience beyond the sum of their components.

Animals and other biological structures are made strong by their tensioned and compressed parts. Muscles and bones act in unison to strengthen the other. This kind of strength exists also at the cellular level, and it is a somewhat new understanding of biological structures.

Tensegrity - Principles

Tensegrity is the pattern that results when push and pull have a win-win relationship with each other. The pull is continuous and the push is discontinuous. The continuous pull is balanced by the discontinuous push producing an integrity of tension and compression.

Buckminster Fuller explained that these fundamental phenomena were not opposites, but complements that could always be found together. Tensegrity is the name for a synergy between a co-existing pairs of fundamental physical laws; of push and pull, and compression and tension, or repulsion and attraction.

If one pushes a ping-pong ball on a smooth table with the point of a sharp pencil, the ball would always roll away from the direction of the push, first rolling one way then the other. Push is divergent.

On the other hand if attaching a string to the ping pong ball with tape, and pulling it creates convergence. No matter how other forces might influence the ball to roll away from you, the string would always bring it to you more and more directly. Pull is convergent.

Another example from common experience occurs when pulling a trailer with a car. When driving uphill, one is pulling against gravity, and a trailer will converge toward the same course behind the car. If the trailer begins to sway, increasing pull by increasing acceleration can dampen the swaying motion.

Driving downhill, however, the trailer may begin to push, and the trailer will begin to sway from side to side.

Tensegrity - The human organism

Two tensegrities are easily recognizeable in systems of the human body. The muscular-skeletal system is a tensegrity of muscle and bone, the muscle provides continuous pull, the bones discontinuous push.

This forms the basis for all human physical mobility. The central nervous system can also be understood as using the analogy of tensegrity where motor neurons and sensor neurons, complement the other in a balance.

A more common example of a tensegrity is in a child's balloon. When examined as a system, the rubber skin of the balloon can be seen as continuously pulling (against the air inside) while the individual molecules of air are discontinuously pushing against the inside of the balloon keeping it inflated. All external forces striking the external surface are immediately and continuously distributed over the entire system, meaning the balloon is very strong despite its thin material.

The automobile tire works the same way. It is the tensional integrity in the tire that yields a low failure rate despite the wear of high speeds and long miles.

This is, perhaps, also the reason why a thin PVC plastic membrane - like in plastic carry bags, is stronger when loaded - it tears easily in an unloaded state, but if the carry bag is full, breaking its structural integrety (i.e. tearing it) is not easy.

A tensegrity then is any balanced system composed of two elements – a continuous pull balanced by discontinuous push. When these two forces are in balance a stabilized system results that is maximally strong.

Tensegrity - Larger structures

Tensegrity also refers to a means of creating structures.

Tensegrity was first explored by artist Kenneth Snelson to produce sculptures such as his 18 metre high Needle Tower (1968). The idea was adopted into architecture in the 1980s with David Geiger designing the first significant structure - a competition hall for the Summer Olympics of 1988. The Georgia Dome, which was used for the 1996 Olympics is a large tensegrity structure of similar design to the aforementioned competition hall.

The term 'tensegrity' was coined for Snelson by Buckminster Fuller from tensional integrity. His famous geodesic domes are themselves tensegrities.

"The great structural systems of Universe are accomplished by islanded compression and omnicontinuous tension. 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."

The larger the tensegrity the stronger it is. The geodesic dome at Disney World in Florida is an example. 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.

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".

Tensegrity was a term used by Carlos Castaneda to refer to the modernized version of some movements called magical passes (a series of meditative stretches, stances and movements) developed by Native American shamans who lived in Mexico in times prior to the Spanish conquest. Castaneda borrowed the term tensegrity from architecture because the magical passes combine tension and relaxation of the muscles, joints and ligaments in a way that yields a stronger, more flexible, and more "aware" physical body. 'Tensegrity' also refers to the flow of energy between people who are practicing the Tensegrity exercises together, according to Nyei Murez, one of the current teachers of Tensegrity.

See also

• Tensile architecture

Adapted from the Wikipedia article "Tensegrity", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki