Scott,

https://m.youtube.com/watch?v=GpWv0S7m1cI

Finding the strength of a tube

Shemaya and David W, this only shows that there is more than one way of doing things.
The shown formula ( in posting # 7817591) is the standard way over here of finding the bending strength of a tube. Other, similar formulas handles rectangular tubes, I-beams and wotnot. The lovely thing with a round tube is that it is equally strong in all directions.

There is also a set of similar formulas which deals with the stiffness of tubes and beams, but I haven't bothered with them (except, sometimes, comparing their numbers  -  higher value of Inertia means stiffer tube)

Frankly, although 'my' formula may look intimidating at first, it is quite straightforward in use. A spreadsheet would speed up the use of it, if one needs to do these calculations frequently.

Shemaya, to raise a number to the power of 4 is one thing. When calculating SA/Disp, one has to raise to the power of 2/3 (or 0.6667)!

Good luck!
Arne

PS:
David W’s formula only involves multiplications. That method has probably been developed for use with slide rules. These were at their best for multiplications (..we used them on my first year of technical school, but switched to calculators the second year, in 1974..).

Thanks David W. Which units do you use, to make this work?

Arne, thanks also to you for the earlier clarification. I've actually succeeded in getting some sensible numbers. Miraculous. Turns out there are several online scientific calculators, and this one worked out great. This was especially helpful because working through the formula turned out numbers that were bigger than my household calculator could manage. The online one was also perfectly happy to do x^4. That was fun!

Shemaya

Arne,

the factor represents the distance between the center of area of each of the curved sections of the pipe that make up the imagined I beam, expressed as a fraction of the outside diameter of the pipe. The 0.88 factor more accurately represents the actual distance but I generally use the 0.8 factor as it builds in a little extra safety factor in the calculations.

Anonymous wrote:

Robert wrote:

David wrote:

I compute the weight of a parallel tube 24' x 7" x ⅛" to be 33.8 kg or 74.4lbs.

Hmmm--This chart from a metals vendor (see attached pdf) puts the weight per foot of 7" x 1/8" at 2.099 pounds per foot, times 24 ft is 50.3 lbs.

rself

PS--The weights in Reply # 7816554 on 7815815 are shipping weights. These poles are cone-tapered such that the bottom half or so are straight wall (see ECXA25 pdf attached). So using the standard tube sizes.pdf you can estimate the weight of the pole alone . I got an estimate of 70 lbs weight for the ECXA25 which is 5" x 5/32" x 33 ft, 6063-T6.

The table is clearly wrong, Robert. Look at the line above. 0.08 wall thickness and a weight of  3.143 lbs? That's also wrong. I've checked my working, and will stand by it.

In an earlier post I wrote that a 6” x 1/8” 24 ft tube of 6061t6 would weigh about 64 lbs. That was based a Speedy Metals listing of .22 lbs / inch or 63.4 lbs. By Speedy Metals specs a 7” tube of the same thickness should weigh 74 lbs.