Shear Strength of an Erected Pipe

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Discussion Overview

The discussion centers around determining the appropriate size and type of pipe or tubing needed to support a tall outdoor Christmas tree structure, specifically in relation to wind resistance. The focus includes considerations of structural integrity, material choice, and the impact of additional weight from decorations.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the necessary specifications for a pipe mast to withstand wind speeds, mentioning a height of over 20 feet and a weight of approximately 200 pounds from lights.
  • Another participant calculates a required steel pipe outside diameter of 60.33 mm with a wall thickness of 3.91 mm for a height of 6.10 m, assuming no pretensioning of guy wires.
  • A different participant suggests that a 6.10 m steel pipe with an outside diameter of 48.26 mm and a wall thickness of 3.68 mm might also be sufficient.
  • One participant raises a concern about the adequacy of calculations by emphasizing the need to consider the forces from wind gusts when additional weight from lights is added, suggesting that guy wires should be anchored to the ground.
  • Another participant introduces the concept of "flow induced vibrations" and mentions the importance of understanding the natural frequency of the structure and the Strouhal number, indicating a need for fluid mechanics expertise.

Areas of Agreement / Disagreement

Participants express differing views on the necessary specifications for the pipe, with multiple calculations and suggestions presented. There is no consensus on the best approach to ensure stability against wind forces, and concerns about additional factors like vibrations and anchoring are raised.

Contextual Notes

Limitations include assumptions about wind conditions, the impact of additional weight from decorations, and the need for further calculations regarding vibrations and structural dynamics.

blackcomb
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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.
 
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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.
 
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.
 
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:
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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