**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..).