Pipe Stiffness

When you talk about a soda can gaining stiffness, I think you're referring to resistance against buckling; that would be due to being filled with a relatively incompressible liquid more than the pressure of the fizz.

So, give us some more details about the application.

Yes, your wording is the correct one. I want to reduce the floppyness and the chance of buckling of a vertical pipe by pressurizing it. I observed that even the thin walled water bottle is stiff as long as there is considerable CO2 pressure left.

The application is an elevated antenna measuring setup, where a metallic tower would distort the measurements. Hence the choice of a pipe. But as soon as there is a significant size antenna on top, it sways significantly in any breeze. Guying is a pain, and have to be disconnected for every hoisting anyhow. So the idea of pressurizing it to the rated value. I know, that long and slender objects tend to sway and then fail by buckling. What I don't know, by what factor I am better off by pressurizing it?

Or there is no quick estimate, just trying it?

Pressurising it with what?

What other examples of this particular application can be observed?

Is this an application that could be solved by using a balloon with a lighter-than-air gas inside it (Helium, for example)?

http://en.wikipedia.org/wiki/Moored_balloon

I missed that it is non-metallic. You just couldn't put much pressure in something like that. Think about thinning the walls, using square tubing, and bigger.

We have done comparable jobs by injection of (non metal containing-) epoxy into the pipe.

Make sure no air is introduced or left at the top by proper de-airation.

Any air left would give a 'week point' in the pipe.

Think of the way (metal) pipes were bended in the past by filling it with sand, closed at both ends and then bend it, the required forces to do so are much higher.

Epoxy will not move (like sand) and adhere to the inside of the wall.

Tests showed an improvement against buckling of ca 2.5 - 3 time the present strength.

regards, Tom

Thank you for your guidance, mainly for nick name, rhabe, and tom hoekstra for their meaningful guidance. I start to understand, what it takes to professionally approach and solve the problem. BUT, my real problem (preceding the other one) is that I deal with electronics. Euler is familiar from 50 years (or a few hundreds years) ago. Calculating is a quite different order of magnitude problem for me. Ask me about digital, an RF filter, low noise preamplifiers (you get the drift) I am fine. But, I did not do mechanics since 1960s.

So - while greatly appreciating all the guidance I am getting - my original question is, even if in a rule of thumb, rough estimate, a multiplex of the basic buckling limit is: if I pressurize a plastic pipe, say, 1/2 of the rated value (by the way that is for burial, with bending and stone pushing agains it in this standard in a fashion I cannot translate from practical testing circumstances), how much do I gain in stiffness (as a multiple) and buckling resistance in the Euler sense (a multiple again, if some sensible formula can be found or pointed out). All I am asking is for your professional judgment or assessment, nothing else.

I already devised a horizontal arrangement for testing the results, and will publish it here if / when I succeed or fail.

Ok then you should give a couple of data and it is possible to give you an indication as a pressure:

- weight on top

- side area of top load subject to wind effect (transverse wind load).

- which is the maximal wind speed you expect to still work with.

- tube dimensions

- material of tube.

- height of the load when tube vertical

- what Rahbe wrote on the side cables is correct and you should consider this solution in your approach.

If you want to test in an horizontal position you should never the less generate a force as the weight may be using a real weight and cables and pulleys.

The fixture should introduce the loads without any stiffness since if it has a stiffness this will modify the behaviour and your results on the fixture will not be any more valid for the true vertical position.

I changed my mind : I prepared a detailed sheet so that you can make all computations by your self and make if necessary changes in order to optimize.

So that you do not need any more to send the values listed in my previous comment but only send you e-mail address either on the general page or using the personal mail. The sheet is in word so that you can read it without any difficulty.

Nick, I appreciate it very much.

My address is: levelesLL@msn. com

Have you got the sheet? does it help you?

Yes, I got it, and I am just digesting it. Once I fully get it, there is time for numerical what ifs. Right now the the inertia moments D^4 dependence is particularly intriguing. A few graphs later I will see the relationships better.

thanks.