Seperating the ferro- from the -cement
June 23, 2008 at 2:21 pm #630
I just spent time reading about the concept of tensegrity, and this method of geodesically designing structures that give out the most strength from their materials makes sense to me. It makes use of two different materials, one for compression and the other for tension, and arranges them so they both only work in their preferred way. So I’m wondering if there could be some way to make this work for seastead design. What about trading the long spars between flotation and platform for some tensegrity towers ? Make the compression struts from cement, steel or fiberglass or carbon fiber cables for tension elements… this could resist hurricanes. Cover the platform in a geodesic dome or some tensegrity tent. The same technique could also be used for tieing together multiple seasteads with a robust but flexible bridge that could accomodate heaving yet keep them all in their relative place.
If a bulky approach (thick walls, heavy rebar and clubbing mechanical stresses with sheer mass) does not work out economically, maybe a more spidery, ethereal approach could ?June 23, 2008 at 3:15 pm #3321
In my “Tension circle house” the outside ring is in compression and the ropes/cables like the spokes on a bicycle tire are in tension. This seems like what you are asking for.June 23, 2008 at 3:25 pm #3322
It’s not exactly what I’m considering: this design still uses massive bulk pieces for the ring and the central attachment spar. What I mean is switching the “full” blocks for webby networks of struts and cables. Have a look at these example structures. Or maybe this outdoor structure to get a good sense.June 23, 2008 at 10:46 pm #3323
Has anyone ever built something like your examples that served a functional purpose? Those are cool structures for art, but is it practical and used for anything more than art? Have they ever been the most cost effective way to get something real done?
If you just want a larger scale, then my “Tension Circle Marina” is pbobably good for 1000 feet or more in diameter:June 24, 2008 at 3:30 pm #3340
Geodesic domes are an example of this sort of construction, with the distinction that the struts work both in tension and compression (the cable and strut halves are fused). They react very strangely to mechanical stresses (for example, running a truck into one such big dome caused no damage except popping some struts… on the opposite side) because the loads are spread and transmitted all around in ways difficult to predict. And they become more and more robust with their size instead of the opposite.June 24, 2008 at 4:16 pm #3341
I found a nice example of tensegrity building of a waterborne structure here. This was built in Switzerland in 2002 on the lake Neuchatel for an expo, and I think you can still visit it and wander inside. It has four pillars resting on the lakebed.
This sort of design allows tremendous saving on total mass, the buildings can be made like spiderwebs: very light and almost transparent to wind and waves passing through it so it experiences reduced stresses, yet is very robust.June 24, 2008 at 4:57 pm #3342
If people count a dome as a tensegrity structure then my tension circle should count too. It really has more in common with the toys and art tensegrity stuff than a dome does.June 25, 2008 at 11:07 am #3355
The tension circle bears torque stresses, so it is not really a tensegrity concept, sorry. The idea is that there only are compression and tension efforts, and zero shearing/torque. It does not mean that I don't like your concept or that it is less valid for a seastead, of course.
Wait, scratch that, the only torque efforts on the tension circle design are upon individual pieces or the whole thing, and not between its elements, so it indeed counts as a tensegrity concept. You were right.April 3, 2010 at 10:49 pm #9970
Tensegrity structures generally require a ridgid foundation (or else a complete spherical structure). Maybe this would make a good way to anchor a seastead in deep water – provided you have a way to set the anchors in the seafloor.April 4, 2010 at 6:17 am #9971
Tensegrity uses tension to hold it together. That has nothing to do with a foundation.
If you can’t swim with the big fish, stick to the reefMay 5, 2010 at 4:15 pm #10106
I helped my parents build their geodesic dome. Such domes are great structures for resisting earthquakes and extreme weather (tornadoes and hurricanes). The only real tricks to these structures is to attach all the pieces together solidly, and anchor the whole structure down to prevent it from being blown about by high winds. Neither of these requires any great feat of engineering. Geodesic domes make far safer structures than square or rectangular buildings. They are a great choice for seastead structures.
If the major concern, however, is the survivability. Then I would suggest that the seastead be built away from where you find the vast majority of hurricans, which is outside of the equitorial belt between the tropics of Capricorn and Cancer. Without the need to build so robustly, the need for heavy construction material are eliminated and costs are lower.
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