TENSEGRITY

A tensegrity well-known

The most well-known tensegrity is probably this icosahedron-tensegrity which is made by many enthousiastic tensegrity builders throughout the world. Here only a few pictures, just to show the variations in material and construction methods.

The icosahedron-tensegrity has very typical and unique characteristics that tensegrities normally never have: The struts are exactly parallel or in straight angle to eachother. This is very rare for a tensegrity which can be distinguished by its twisted form. But it may be these straight angles that make this tensegrity so popular. Wherever we humans changed the world we used straight angles, and allthough it may not be a natural form, for us a straight angle is restful and feels normal. I guess one could say that this icosahedron is the nearest tensegrity compared to conventional construction. But it is still a tensegrity with all it's typical properties and qualities.

The tensegrity shown below is a children's toy called skwish and is invented by Tom Flemons. Tom calls himself a geometer and has made tensegrities for over 25 years. He is one of the few persons that actually makes tensegrities for a living (and for pleasure). Tom chose vivid colours, bold ends and the thick wires for obvious reasons, but his invention is that he saw that the real attraction of this toy is the way the tensegrity reacts when you push it or pull it.

The skwish by Tom Flemons

Biotensegrity
Untill now, tensegrities might not have much practical value in architecture, which might be a disappointment for some of us, but in the meantime it has gained a lot of interest from an entirely different science: biology. There are quite a few doctors and biologists that are convinced that "life" is made out of tensegrities. For instance doctor Donald Ingber has written an article "The Architecture of Life" with the following introduction:
"For the past several decades, biologists have attempted to advance our understanding of how the human body works by defining the properties of life's critical materials and molecules, such as DNA, the stuff of genes. Indeed, biologists are now striving to identify every gene in the complete set, known as the genome, that every human being carries. Because genes are the "blueprints" for the key molecules of life, such as proteins, this Holy Grail of molecular biology will lead in the near future to a catalogue of essentially all the molecules from which a human is created. Understanding what the parts of a complex machine are made of, however, does little to explain how the whole system works, regardless of whether the complex system is a combustion engine or a cell. In other words, identifying and describing the molecular puzzle pieces will do little if we do not understand the rules for their assembly."
Ingber is a doctor in a children hospital in Boston, who discovered that the way life is formed has less to do with chemistry and more with architecture.
Just another small paragraph from his article: "From Skeleton to Cytoskeleton: What does tensegrity have to do with the human body? The principles of tensegrity apply at essentially every detectable size scale in the body. At the macroscopic level, the 206 bones that constitute our skeleton are pulled up against the force of gravity and stabilized in a vertical form by the pull of tensile muscles, tendons and ligaments (similar to the cables in Snelson's sculptures). In other words, in the complex tensegrity structure inside every one of us, bones are compression struts, and muscles, tendons and ligaments are the tension bearing members. At the other end of the scale, proteins and other key molecules in the body also stabilize themselves through the principles of tensegrity. My own interest lies in between these two extremes, at the cellular level."
So, according to Ingber, not only the skeleton is a tensegrity, but every cell in your body. He is doing research in this field since the mid '70's so he has produced quite a few articles and can be seen on a few movies on youtube as well.
Observating biological cells, Ingber has seen reactions and movements that can not be explained presuming a cell is just "a bag filled with fluid", but can be explained if it contains a tensegrity structure inside the membrane.

In this article he describes the tensegrity itself as "a system that stabilizes itself mechanically because of the way in which tensional and compressive forces are distributed and balanced within the structure".

One other icon in the biotensegrity science is doctor Stephem Levin. He is mentioned in this website several times, but on this particular page it should be said that Levin is convinced that the icosahedron tensegrity is the building block, the "brick" of nature.

This tensegrity is made by Mitch. On his website http://unityplural.blogspot.comhe illustrates a large-scale design principle on a small scale.

Tensegrity icosahedron: three pairs at straight angles


From a different angle: every end of every strut has four strings


"Het Ding" is made by seven students at the University of Twente (Holland) on a single night in 1974. The compression parts are telephone poles. When people woke up the next morning they couldn't describe what they saw and that is why they called it "The Thing". One could say the Dutch are not very creative with inventing names, but on the other hand one could say the name "The Thing" emphasizes the amazing and mystical part of a tensegrity perfectly.

My Dutch tensegrity collegueJan Marcusmade this one. He uses aluminium tubes and fishingline. The tubes are thicker than mine and the strings are thinner. This makes the compression parts float even better.

Personal note
Somewhere in November 2007 my mother called me to tell me that her brother was dying. "Please go and visit him," she said. "Don't wait till the funeral. Skip the funeral if you like, but go and visit him now." So I went to see my uncle Paul and there we sat at the coffee table. "Come, let's go outside," he said and I had to escort him to his own garden because he was blind and very weak on his feet. He waved a little with his hand trying to show me something and there I saw the first tensegrity in my life. It was just an icosahedron like the one on the this page. Made of steel, a bit rusty and I guess it was one meter high. One week later, he died and I have been making tensegrities ever since.

Practice
For an icosahedron tensegrity (some call it an expanded octahedron tensegrity, but what's in a name?) you need 6 struts and 24 strings. The length of each string should be 0,612 * the length of a strut.

It is probably the most popular tensegrity not only because of it's form, but also because it is the most easy tensegrity to figure out. People with experience with the formula of Pythagoras should be able to unravel the puzzle on rainy Sunday afternoon. I may add that it is much easier to work the other way around. Start by making an icosahedron tensegrity first and then, with the model on the table, try to calculate the string-strut ratio.

Pythagoras: a² + b² = c²

It's called an icosahedron because if you add strings between the ends of every parallel struts, you get 20 nearly equal triangles (the icosahedron).