How much weight can .75 sq tube tripod handle

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Discussion Overview

The discussion revolves around the structural integrity and safety of a tripod made from .75" square tubing intended to support approximately 150 lbs at a height of 12 feet. Participants explore material choices, design considerations, and safety implications related to the construction of the tripod.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • vothsr inquires about the weight capacity of .75" square tubing for a tripod design intended to lift a drum.
  • Some participants suggest that the choice of material, such as high-carbon steel versus mild steel, significantly impacts the tripod's strength.
  • Concerns are raised about the safety of supporting 150 lbs at a height of 12 feet, with one participant emphasizing the potential dangers of falling weights.
  • Participants discuss the need for cross bracing to counteract bending moments and improve stability, with varying opinions on the adequacy of the proposed design.
  • One participant estimates that the current design may be inadequate and suggests larger tubing sizes for safety, while another emphasizes the complexity of the forces involved in the structure.
  • There is a disagreement regarding the appropriateness of the original inquiry, with some participants feeling that the request for specific engineering advice is unreasonable without sufficient detail.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the adequacy of the .75" square tubing for the intended purpose. Multiple competing views exist regarding material choice, design safety, and the necessity of additional structural supports.

Contextual Notes

The discussion highlights limitations in the provided design details, assumptions about load conditions, and the need for a more thorough analysis of structural forces involved.

vothsr
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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.

Thanks
vothsr
 

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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.
 
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.
 
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.
 
vothsr said:
I don't know what ABS tubing is.
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..
 
I meant PVC; man, that's embarrassing. Too late to edit it now.
 
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:

http://www.harborfreight.com/1-ton-telescoping-gantry-crane-41188.html
 
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.

Thanks
 
vothsr said:
...
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.
...

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.
 
  • #10
vothsr said:
If you are qualified to answer the original post, please do so, if not, please don't respond.

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.
 
  • #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

https://en.wikipedia.org/wiki/Truss

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.
 
  • #12
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.
 
  • #13
vothsr said:
I thought that this was a forum where qualified persons

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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