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How much weight can .75 sq tube tripod handle

  1. May 20, 2013 #1
    How much weight can .75" sq tube tripod handle

    I would like to build a tripod 12' high to lift and permanently hold approx. 150lbs.
    It will be lifting an 18" dia. drum as high as the tripod will allow. I thought of using a triangle shaped plate at the top to enlarge the upper diameter of the tripod. Will .75" 16 gauge sq. tubing handle this without a lot of cross bracing? The feet will be stuck in the dirt. If this won't work, what is the min. size tubing needed?
    This is my first posting, so if the pic didn't come through, please advise.


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  2. jcsd
  3. May 20, 2013 #2


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    The material that you choose will make a huge difference in the answer.
    ABS tubing won't stand up as well as high-carbon steel.
  4. May 21, 2013 #3
    I don't know what ABS tubing is. I will be using the standard sq. tubing that I buy at the steel yard, I guess its mild steel.
  5. May 22, 2013 #4
    Will it support the weight? Possibly. Will it SAFELY support the weight? Not likely.
    Your sketch does not provide sufficient detail to make any kind of meaningful determination.
  6. May 22, 2013 #5


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    Sorry, that was meant to be an exaggerated example. ABS is similar to PCV, ie: a plastic compound that is used to make pipes, eaves troughs, patio furniture, etc..
  7. May 24, 2013 #6


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    I meant PVC; man, that's embarrassing. Too late to edit it now.
  8. May 24, 2013 #7

    jim mcnamara

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    150 lbs of metal falling 6 feet can kill a human. Please. You need to think about, not just structural strength, but safety in general - meaning permanently keeping kids and dogs far away, for example. You need to consider rigging.

    If this is temporary you might want to consider renting some type of lift. For longterm you can also buy lifts meant for large engine installation in vehicles, at reasonable cost from places like Harbor Freight (US only). I mean reasonable in terms of a few hundred US dollars versus losing your house in a lawsuit.

    What I'm saying is your plan sounds, um, "underinformed". This may be unfair of me.

    This is a gantry:

  9. May 24, 2013 #8
    Thanks for your opinions.
    My mistake, I thought that this was a forum where qualified persons would answer the question using practical engineering standards as a basis.
    My post also included, "If this won't work, what is the min. size tubing needed?".
    I know that I could build this tripod out of 2", 11 gauge mild steel tubing and have an adequate safety factor built in, but that wasn't my question.
    If you are qualified to answer the original post, please do so, if not, please don't respond.

  10. May 25, 2013 #9
    This isn't simply a matter of "minimum tubing size". You want to hang a 150 pound drum 12 feet in the air. Among other things, I rather doubt the drum is just going to forever hang motionless and untouched, so there are quite a few variables to consider.

    You're basically asking for a structural engineer to design your project for free.
  11. May 25, 2013 #10


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    Being incredibly rude and ungracious is not likely to win you any friends here.
    And as Pantaz mentioned, we don't appreciate being insulted for not giving you exactly the free advice that you want.
  12. May 27, 2013 #11
    This is more a mechanical engineering problem than materials. quite a range of materials would do, but practically speaking that's not what you want to know about.

    I suggest you do a bit of reading on truss's to get an idea of the forces involved


    Essentially though, your design lacks cross members to counter balance the bending moments at the cap. Without cross members the bending moment (I forget the real name for this force) will be huge.
  13. May 27, 2013 #12


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    vothsr: I think your basic configuration with one cross brace per side is probably stable, although I have not tested it. If not, also add one slanted cross brace per side.

    Moving on to the strength, the global strength appears to be governed by the buckling strength of each leg. And 19.05 x 1.651 mm mild steel square tubing is inadequate. Also, you cannot just design it for the axial compressive load in each leg, because, sooner or later, you know someone will apply a bump load (side load) to the leg. The side load makes a difference in the analysis. I have assumed a bump load of V = 180 N.

    Therefore, it currently appears you would need to use 31.75 x 1.651 mm mild steel square tubing. Or, alternately, 25.4 x 3.048 mm mild steel square tubing.
  14. May 28, 2013 #13


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    By the bye, the socially acceptable plural of "person" is "people"; "persons" is just gaseous, best saved for politicians and lawyers.
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