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Shear Strength of an Erected Pipe

  1. Jul 31, 2008 #1
    Does anyone know how to determine what size/type of pipe/tubing would be necessary to withstand given wind speeds?

    Specifically, I'm wanting to build a "megatree", an outdoor Christmas tree made simply by stringing lights from the top to the bottom in a conical shape. I'd like a 20' + tree, but I don't know what size pipe/tube I'd need as the mast.

    My initial plan is to bury a 2'-3' pipe in reinforced concrete in the ground to serve as a sleeve for the main pipe (no more than about 1/8" inch play) which would be guy-wired. I want to be able to remove the main pipe after Christmas and cap off the sleeve at ground level.

    The lights (and star on top) will add about 200 pounds, spread evenly in all directions around the main pipe, if that makes a difference.

    I prefer to use galvanized steel (no PVC). I was considering 1.5", but didn't know if wall thickness would matter in my application. Does anybody have any suggestions on what to go with to ensure winds (short of a hurricane) won't bring it down? Winds in my area will gust from time to time in the 40 mph range. Rare to see 50+ mph sustained winds.
  2. jcsd
  3. Aug 10, 2008 #2


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    For a pipe mast height of 6.10 m above the ground surface, and assuming the guy wires are not pretensioned, I'm currently getting a required steel pipe outside diameter of 60.33 mm, with a wall thickness of 3.91 mm.
  4. Aug 10, 2008 #3


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    It currently appears a 6.10 m steel pipe having an outside diameter of 48.26 mm and a wall thickness of 3.68 mm might also be adequate.
  5. Aug 10, 2008 #4
    Why not tie three of the wires to earth as guy strands? The forces applied to your tree by the winds will increase as you add lights on multiple strands. Calculation of the withstand rating for the free-standing pipe will not be sufficient for determining its ability to withstand windgusts when lights are attached. I am surprised that the previous answers did not include that factor.
    Last edited: Aug 10, 2008
  6. Aug 13, 2008 #5
    re the winds
    you'd be looking at "flow induced vibrations" which have scuppered many a structure.
    you'll need to figure out the natural frequency of the structure (dont ask me how)
    then i think your looking for the strouhal number, you'll get it from the dimensions of the pipe (lenght and diameter),
    lol, get someone who's good at fluid mechanincs

    on the other hand you could chance your arm
    best of luck
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