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Geodesic cylinder?

topic posted Wed, May 21, 2008 - 6:03 PM by  Landon
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Is there anyone who has any info on strut length ratio and layout, for building a structural column/ cylinder capable of supporting weight up to maybe 1000 lbs. My par diameter is 13 feet. The project is for a raised platform.
posted by:
Landon
Oregon
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  • Re: Geodesic cylinder?

    Thu, May 22, 2008 - 12:12 AM
    Well, a cylinder isn't rigid, so right off the bat you have a bit of a problem. The top and bottom edges will fold under load.

    I think 1000 lbs is more than this can handle, but you could consider a dome deck on an optimal 2v dome: www.timefold.com/domedeck

    It will definitely hold 600 lbs.

    If you build the 2v from 1" EMT instead of 3/4" EMT it will definitely hold 1000lbs, in my opinion. 1" EMT is 4 times as strong as 3/4" EMT, and I have experimentally determined that a 3/4" EMT optimal dome with a dome deck will support 600 lbs. So, I think it is more than safe enough to assume that 1000 lbs is within reach of an optimal 2v with 1" EMT.

    If what you need is 13' platform, your dome deck would have to be larger. You could easily design a flat platform that took advantage of the vertexes one level down from the top pentagon. You'd want diagonals from each vertex to an adjacent dome outer dome deck vertex, to ensure that the deck was rigid. If you are interested in moving in this direction, I'd be happy to describe the technique further.
    • Re: Geodesic cylinder?

      Thu, May 22, 2008 - 3:48 PM
      I actually have a 2v 1"EMT dome but heres the thing, I want to built a sphere and put it on top of a cylinder to make a giant gum ball machine
      • Re: Geodesic cylinder?

        Tue, May 27, 2008 - 8:44 AM
        Ahh, ok. So, you need something that looks like a cylinder. That could be accomplished with something that is structurally rigid with a cylindrical exterior shape. For example, you could build a dome and extend the sides upward with additional struts to give the appearance of a cylinder, even though the majority of the strength comes from the dome itself. The domedeck design uses vertical risers from the top pentagon of a 2v. You could do that and also have vertical risers from the bottom vertexes of the dome. You could extend the "deck" out to the tops of those verticals with additional triangles. The dome "inside" the cylinder would be providing all the strength. If you made the outermost vertical risers *taller* than the bottom dome, the deck would end up being concave, so the sphere on top would appear to be sitting inside it.

        www.timefold.com/domedeck

        I think though, that if you were going to put a sphere on top, a cylinder would be *more* rigid than if it was supposed to stand alone. But, the amount of weight you are going to have with a sphere on top is going to demand a pretty strong base. Will people be allowed to climb on it? Or, rather, how will you prevent people from climbing on it? People weight a lot... and could easily crush the understructure... The sphere would have to be attached so securely that it could not fall off and roll, obviously. I'm sure you've already thought of all this.

        So, will there be gumballs?
        • Re: Geodesic cylinder?

          Wed, May 28, 2008 - 2:23 PM
          the structure will be an observation deck and an optical marker for my camp. I figured that the gum balls would be yoga balls to lounge on for a small number of people. An elevator has been thought of as well using a portable winch called a pullzall, running off the 2000 watt inverter in my panel van. then building an attachment the van and winch can also be used as a crane to lift the structure.
          • Re: Geodesic cylinder?

            Thu, May 29, 2008 - 2:50 PM
            I think I'd be tempted to insert added struts to form a 3-D triangular structure so that it is truly rigid and can sustain a lot of weight. I'd make it from 1" EMT and have lots of redundant triangles. Essentially, when you have enough triangles in 3 dimensions the structure is rigid. It can be a bit of a trick to get everything the right size, but once you do it will be strong and rigid.

            I built a 3-d geodesic nose (the Desert Nose) www.timefold.com/nose and it was strong and rigid. I made it from 3/4" emt and there were about 320 struts. It was a symmetrical structure, so there were pairs of identical struts on both sides, but aside from a few unique struts there were about 150 different lengths. I wrote software to analyze the structure, determine the lengths of struts and lay them out into 10' lengths with minimum waste. I would be happy to share the software with you (written in perl). It is designed for any symmetrical structure. It even produces labels to attach to struts so you can keep them straight. I'm not sure if this is right for your project, but if you decide to create something custom this is one way to go, and it has worked before. First you create a model (e.g by soldering together copper wire) and then you label the vertexes and struts. Then you measure the X-Y-Z position of each vertex. You create a text file with the XYZ for each vertex and another that identifies which strut falls between which pair of vertexes. The software does all the rest, including generating color images of the structure from various angles, using color to show depth.
            • Re: Geodesic cylinder?

              Fri, May 30, 2008 - 12:39 AM
              I would love this software
              • Re: Geodesic cylinder?

                Fri, May 30, 2008 - 5:01 PM
                I'm sorry for the delay. I thought the files were on my web site, but they weren't. So, I fixed that and now they are. The page you want is here:

                www.timefold.com/guests/ho...age26.html

                About 7 paragraphs under Bucky Fuller's picture is a link to the program:
                www.timefold.com/guests/ho.../vert2.txt

                There are some instructions there that explain how you will have to rename the file to vert2.pl and make it executable. I also put up a makefile with lots of examples of how I used the program in the desert nose project. If you are not familiar with makefiles, you can still look at it to get some ideas of command lines. The vert2 program is a comand line program -- you run it from a shell (Terminal if you are on a mac). If you're on a PC, I think this will be difficult (but not impossible) to use. You'll have to get and install perl. If you are used to Unix computers or are familiar with the Mac Terminal program, this is pretty straightforward.

                You can contact me at hoco@timefold.com if you have questions. I'll answer them if I can, time permitting. Read the above page first (you can skip the history stuff -- not relevant to using vert2.pl). However, you'll need to come up with the data files (vertex XYZ info and struts connected by vertexes info) and you'll probably need to create a physical model for that, unless you are *really* good at math. I'm not. That is why I made a model, measured it and wrote this program.
  • Re: Geodesic cylinder?

    Fri, July 4, 2008 - 11:43 PM
    Hey there,

    Sorry about the long delay in reply.

    There is an simple, strong, excellent cylindrical design if you have a bunch of dome struts lying around, but it is not a geodesic, which is, after all, based on emulating a sphere, not a cylinder.

    Imagine laying out a flat pentagon. From each vertex send up 2 struts which then form a triangle with their neighbor strut which comes up from the next vertex over. At these points make another flat pentagon. This will be rotated from the first pentagon. Repeat.

    There is a name for this shape, but I don't remember what it is and my literature is about an hour and a half drive away.

    A couple of guys from colorado put three of these columns up using struts from their two domes at burning man in, hmmm, 2003. They put catwalks between the columns, and supported all sorts of stuff up there. They said they had an engineer do stress simulations and it was all good.

    I'm sure it's been done other times too.
    • Re: Geodesic cylinder?

      Thu, July 10, 2008 - 8:18 PM
      The name of the thing (I just went in to the attic and dug out my reference material) is a pentagonal antipyramid column. I just did a search on google and there are no images for it. If you search on pentagonal column you get some text-- it's a crystal structure of some compounds.

      I have an image for it, and pics from the one I saw at burning man. I will see if I have time to scan them for you.
      • Re: Geodesic cylinder?

        Thu, July 10, 2008 - 10:01 PM
        Well, after I did a search and couldn't find a single image on the web for a pentagonal antipyramid column, how could I resist being the first person to get that content on to the internet?

        picasaweb.google.com/bruce.s...idColumn

        Be sure to mouse over the captions for the full description.

        The photos are from High Risk Camp, burning man 2003. A bunch of guys from colorado, you can probably track them down through the apogaia community.

        I'd like to point out that these things were very solid. They've got two of them up, with wood planks in between, and I saw people walking on the planks and climbing up the sides of the towers. They invited me to climb one, but I'm not that good a climber and I forewent the pleasure.

        Also note the drum kit at the top of one of these columns. SOLID! My recollection is that they had an engineer friend run load calculations on the structures before they put them up and the numbers came out good. They made these columns by pooling the struts from two conduit domes.

        The drawings come from the instruction manual from a Tensegritoy set. I highly recommend this toy to people interested in geodesics and tensegrity. Be sure to order an extra bag of struts.

        I included some other drawings from the manual that showed other structures besides the pentagonal antipyramid columns that might also be useful for cylindrical structures. Note that the tetrahelix (one of my personal favorites, I've made some with 8 foot struts) does not stand straight up from its base, but at an angle.
    • Re: Geodesic cylinder?

      Sun, July 13, 2008 - 12:41 PM
      The basic element is a pentagonal antiPRISM. which is just repeated every two cells.
      • Antiprism, was: Geodesic cylinder?

        Sun, July 13, 2008 - 12:42 PM
        ... and you could start with a regular polygon of an odd number of sides, if you want
        to approach a circular cross section.
        • Re: Antiprism, was: Geodesic cylinder?

          Mon, July 14, 2008 - 8:54 AM
          So it doesn't really mater how many sides (5,7,9,11ect) past 5? It is just a repetitious pattern in two cells. do you know anything about the strut factors?
          • Re: Antiprism, was: Geodesic cylinder?

            Mon, July 14, 2008 - 9:10 AM
            I SEE!!!!!! All it is is a bunch of frequency 1 geos going topless, all stacked up into a column!!! so there wouldn't be a strut factor to deal with. everything would be the same length
            • Re: Antiprism, was: Geodesic cylinder?

              Mon, July 14, 2008 - 6:23 PM
              Yes, all struts the same length.

              Though I reckon you could vary the lengths between the vertical and horizontal members a bit and it would be OK. For instance, the strut lengths for two of the three kinds of struts in a 3 frequency dome are pretty close, so if you had a 3 frequency dome you wanted to repurpose as a somewhat cylindrical column, I think you could use one length for horizontals and the other for verticals, and use most of your dome up?

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