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Anonymous Poster #1

Scaffold Buckling

08/07/2017 8:55 AM

I have a horizontal beam to which a number of support members are anchored using supplied fittings, the support members are at an angle of 52.3 degrees to the horizontal. I know the following information about the GS Pipe:

Outer Diameter(Do)=48.3 mm, Inner Diameter(Di)=45.05 mm, thickness(t)=3.25 mm, Tensile Strength = 290 N/mm2, Yeild Strength=185 N/mm2.

How would I work out the max force applied through the support members before the horizontal scaffold pipe buckled? Please just point me in the direction for the right equations and methods used. Thank You.

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#1

Re: Scaffold Buckling

08/07/2017 9:10 AM

One initial observation:

If the inner diameter is 45.05 and the outer 48.3: then the thickness is 1.625mm. Half of what you worked out.

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#2
In reply to #1

Re: Scaffold Buckling

08/07/2017 9:16 AM

Appologies, you are correct Di = 41.8mm

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#3

Re: Scaffold Buckling

08/07/2017 9:23 AM

The best method would be to carry out practical testing in a laboratory.

After all, the age of the <...pipe...>, its corrosion condition, its materials-of-construction and the number of holes in it are among the things not known (otherwise these things would be stated among the <...following information...> in the original post).

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#4

Re: Scaffold Buckling

08/07/2017 9:41 AM

Are you actually a consultant for a portable amusement ride manufacturer?

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Anonymous Poster #1
#5
In reply to #4

Re: Scaffold Buckling

08/07/2017 9:49 AM

I'm afraid not, this is for a personal project. Though that looks like a terrible accident.

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#9
In reply to #4

Re: Scaffold Buckling

08/07/2017 10:19 AM

Apparently, a support beam was rusted out from the inside. I wonder how many more are out there...

https://twitter.com/Aly10TV/status/894258324354605057/photo/1

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#11
In reply to #9

Re: Scaffold Buckling

08/07/2017 10:56 AM

I've always considered it a joke when people say that if it weren't for the paint holding "it" together there would be nothing there at all..

Structural paint job indeed.

The dim bulbs who have given theses rides a clean bill of health over and over need to learn how to do their job. .. lesson learned for the casual observer. A few new cotter pins do not a safe ride make.

I can't believe these safety officers were not trained to look for catastrophic rust. Truckers are held liable if a rusted chunk flies off.

Seriously wrong.

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#15
In reply to #11

Re: Scaffold Buckling

08/07/2017 11:13 AM

Absolutely true, a cursory inspection of incidental hardware is useless when structural integrity fails.

There is one ironic aspect this memo and report does bring to light. This ride and the fatality were both the same age. It may become necessary for amusement rides older than some mark (10 years?) to get a periodic (2 year?) structural x-ray to determine how much corrosion exists.

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#6

Re: Scaffold Buckling

08/07/2017 9:50 AM

You left out the most important information, the distance between supports. Also, a drawing would convey a lot more than words...

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Anonymous Poster #1
#8
In reply to #6

Re: Scaffold Buckling

08/07/2017 10:15 AM

Here is a rough idea of what I have. Please forgive the drawing ability

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#13
In reply to #8

Re: Scaffold Buckling

08/07/2017 10:58 AM

With the forces applied, there is a bending moment that is maximum at the force points. The tube will fail when it buckles under compression. Try it with a soda straw.

Here are the formulas for calculating stress and deflection from bending a pipe:

http://www.atcpublications.com/Sample_pages_from_FDG.pdf

Here is an online calculator that might help in calculating strength:

https://www.roguefab.com/tube-calculator/

Be safe, leave a good safety factor.

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Anonymous Poster #1
#14
In reply to #13

Re: Scaffold Buckling

08/07/2017 11:06 AM

That's great I will start there, thanks for the help.

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#7

Re: Scaffold Buckling

08/07/2017 9:51 AM

That's like saying I have a car, how fast will it go with the gas pedal depressed halfway....There are so many underlying factors and variables it's impossible to say...for all we know it may collapse under it's own weight...

Why don't you just tell us what you're trying to do? Build a support structure for a solar array? It won't pass code without certification of some sort...

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#10

Re: Scaffold Buckling

08/07/2017 10:33 AM

Any <...equation...> is only ever a mathematical abstract of observed reality.

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#12
In reply to #10

Re: Scaffold Buckling

08/07/2017 10:56 AM

I still love George Box's quote:

All models are wrong; some models are useful.

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#16

Re: Scaffold Buckling

08/07/2017 11:19 AM

an off topic comment, be it deals with scaffolding.

China uses Bamboo Scaffolding quite effectively.

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#17
In reply to #16

Re: Scaffold Buckling

08/07/2017 11:33 AM

The reflection of the cone threw me off for a second.. And I'm still trying to decide what they might be working on?

..I can't say it doesn't look like a rigging I wouldn't come up with myself. I do love me some bamboo

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#19
In reply to #17

Re: Scaffold Buckling

08/07/2017 1:17 PM

That's one way of being high on grass!

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#18

Re: Scaffold Buckling

08/07/2017 12:30 PM

First, to what specific purpose is the structure to be put ?...

Second, is it to be an exterior, or an interior, structure ?...

Third, is this to be for a permanent, or a temporary, structure ?...

Fourth, where is this project to be geographically located, and subject to what loading, weather, geotechnical, seismic, etc. conditions, extremes, etc., year-round ?...

Do you have a Strength-of-Materials (or similar) textbook handy ?...

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#20

Re: Scaffold Buckling

08/08/2017 9:13 AM

There's more to it than just bending stress. Buckling is a stability issue. Check code requirements for lateral bracing and spacing as even tho' you may satisfy allowable stress, the deflections (i.e. sidesway) can induce instability.

The simple beam equations don't directly expose this potential effect. Look for key phrases like Euler buckling and P-Delta effects in your research.

AISC have a steel design code book that covers most of this.

Manufacturing imperfections and variability in material properties are covered by the code stress utilization factors however "used" material needs be inspected and integrity verified when making these assumptions.

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#21
In reply to #20

Re: Scaffold Buckling

08/08/2017 9:17 AM

Add "lateral torsional buckling" to that list of search topics...

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