The fragility of efficiency: Tensegrity lights by Michal Maciej Bartosik

The fragility of efficiency: Tensegrity lights by Michal Maciej Bartosik

The fragility of efficiency: Tensegrity lights by Michal Maciej Bartosik

A few years ago, I came across a photo of a lighting system designed by Michal Maciej Bartosik, although I didn’t know it at the time because the photo was uncredited. “Who did this?” I didn’t figure it out then, but the smart use of fluorescent tubes as structural components in a glowing dome stuck with me. Years later, I’m happy to have figured out who made it, and just how talented he is. Michal Maciej Bartosik studied architecture (and now lives) in Canada. A newer light sculpture/structure of his employs a structural principle popularized by Buckminster Fuller: Tensegrity.

Tensegrity has always made me a little nervous. It’s a very efficient way to hold something up, but there’s no redundancy: every member of the structure is critical to keep the structure standing. If a single cable snaps, it can cause the whole structure to collapse. So while I think these light sculptures are amazing, I have a hard time figuring out what happens when one of the tubes burns out.

3 Comments The fragility of efficiency: Tensegrity lights by Michal Maciej Bartosik

  1. Phil Earnhardt January 30, 2012 at 7:31 AM

    Describing tensegrity as fragile structures sounds incorrect. What Fuller meant by “nonredundant” in his book “Synergetics” is that all tensile elements are participating in the structure — they are at tension. If you want redundant elements then you can add cables. Or look at SInan Korkmaz’s (@sinan_korkmaz twitter stream has references) designs for a tensegrity bridge that adapts to failure of component parts.

    The elements in typical compression-loaded structure are also non-redundant. If you go to your local cathedral and remove a flying buttress or two, bad things will happen to the structure. Don’t even think about removing some central column in those great buildings. The layout of the supporting compression elements in an office building are clear; if you remove one of those elements, you won’t meet code (or have a robust building).

    Nature builds with tensegrity because it’s the most material-efficient and energy-efficient way to create structure. Nature’s lines of tension do have redundancy.

    Your question of how to create a tensegrity-light that can be disassembled by the user (for bulb replacement, moving, or storage) is a good one. One approach that can be used is to have turnbuckles on 2-3 of the lines. Relieving tension on those lines will make disassembly of the whole structure easy. For re-assembly, all the parts are put in place and then the turnbuckles are re-tensioned. A second approach is to have turnbuckles on 1 or 2 of the struts. To disassemble, the struts are contracted a bit, which lowers the tension in all of the lines. While turnbuckles are typically used under tension in structure, there’s no reason that they can’t be used in compression.

    Thanks for blogging about these pieces.

  2. Lefteris February 4, 2012 at 9:27 PM

    For the record when WWII bombing removed flying buttresses from Cathedrals in Europe the structures did not fall because they were so over-designed the buttresses really functioned as decoration.

    Also Fuller did not only popularize tensegrities but soon after Snelson who invented the tensegrities in 1949, taught Fuller how to build them Fuller design the 6-strut icosahedral tensegrity shown here as an ingenious light fixture.

    Also I do not buy the material-efficient and energy-efficient arguments about nature building are repeated so often. Nature uses many non tensegral structures to build with. It is living forms that are tensegrities because tensegrities are useful for organic growth and movement. Living forms have many many functions that are sometimes more important than energy use or using little material for big strength. Just one example is that acceleration to eat or to avoid being eaten is more important than energy efficiency or material use. Engineers tend to look for one dimensional simplicity where appreciating complexity and balancing many functions served by the same form is more appropriate. Nature chooses complexity over simplicity almost always.

    Redundancy mentioned above is more important than “efficiency” so I buy the second half of that paragraph.

  3. Phil Earnhardt February 6, 2012 at 9:57 AM

    Thank you for your reply, Lefteris. The record is clear that Snelson invented tensegrity (he called them floating compression structures, but Fuller’s invented word took hold). Fuller’s analysis of the stress-strain response of his tensegrity icosahedron (or just six-strut tensegrity for those who like simple names) is truly remarkable. I made a YouTube video showing this behavior a couple of years ago: search on “how a tensegrity behaves under stress” to find it. Fuller’s commentary about fractal tensegrity structures (section 740.21 in “Synergetics”) is also remarkable, especially when one realizes that our understanding of fractals was very limited at the time that “Synergetics” was published. Snelson’s contribution was essential; Fuller’s recognition and analysis of these structures was his unique contribution. “Synergetics” without tensegrity would be unthinkable. I recommend Amy Edmondson’s “A Fuller Explanation” (freely readable on Google Books at http://bit.ly/AFEonGB ) as an introduction to Fuller’s wonderful text.

    Fuller’s description of the “evolution” of wheels from compression loaded artillery wheels to tendons of a tensegrity is particularly instructive. It shows the fundamental advantage of a tension-loaded structure over one that is primarily loaded with compression. This distinction is covered well in Edmondson’s book.

    Nature does even better than bicycle wheels. You noted that we’re able so sprint to hunt prey and avoid being eaten ourselves. During those times, we crank up our pre-stress to help us move as fast as possible. The other 95% of the time, we’re able to lower the pre-stress in our structure. Besides moving slower, our relaxed movements (e.g., the lope of an experienced hiker) are far more energy-efficient than a sprint. Sinan Korkmaz is on the tip of this vast iceberg with his papers about tension-adjusting tensegrity bridges.

    Another dimension of the efficiencies is that the tensile elements are also used for information. If you fetch newer published papers by Harvard Biologist Donald Ingber, you’ll see the concept of mechanotransduction. Cells are a tensegrity (actually, a nested tensegrity); the tensile elements are used to signal the expression of genes in the cell. This idea includes morphogenesis: the differentiation and specialization of cells in the developing embryo.

    We haven’t even touched on the remarkable flexibility/fluidity of humans, their adaptability (strength development, aerobic capacity, balance/proprioception, etc.), the ability to do both precision and high-strength activities, or that our structures are self-supporting (i.e., no scaffolding) from conception throughout our lives. It’s not only a question of efficiencies; it’s a question about how such things would even be possible without a fractal tensegrity structure. I don’t know what it would take to have you “buy” these ideas; I’d be interested in seeing what alternatives you are offering instead. I am personally grateful for the field of biomimicry and the folks who are trying to reverse-engineer all of the fiendishly elegant and efficient mechanisms that the blind watchmaker has established over the millennia. You will find some excellent published papers if you search places like sciencedirect.com on biomimetic and tensegrity.

    Flying buttresses are an essential component for Cathedrals to deal with shearing forces. They are not there as ornamental window dressing. Locals were lucky that those buildings did not collapse, and I’m certain the buttresses have long since been replaced.

    Nature’s designs are indeed highly complex, but it is a fallacy to conclude there is a simpler solution. Do you have an alternative in mind? Have you reviewed the design requirements? I cannot imagine a way to meet the requirements of life without tensegrity; perhaps your imagination is better than mine. If you disagree, I would love to hear the specifics how you think this could be done.

    Thanks for your message. I fetched my copy of J E Gordon’s book to check a couple of things. Any day reading a bit of Gordon is a good day.

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