Is square tubing more, less, or just the same resistant to flex across its diagonal (like this <> ) than in a "normal" orientation (like this [] )?

Given the poorly worded question, here's another shot at it: If a 3' length of square tubing suspended at each end can hold X pounds at the center when two sides are vertical and two are horizontal, would it hold X*k, X/k, or X pounds if rotated 45 degrees along its lengthwise center axis?

[Edited on 30/8/04 by carcentric]

something tells me that the tube should be stronger like this <> but not sure why

is any good :

http://mnhpva.org/tech/frame_tubes.html

Less strength as the tube will deform flat easier. The loads should be placed square to the tube.

<> is much weaker than []

Mick

A square tube is equal stiff in bending at any angel, at least in theory.
I 'm repeating my self ain't I?

Cheers!

yup, you are! and so will i! in my opinion, the <> is weaker cos it will collapse first. I think everyone will agree with this. [] there is no obvious place for a fail to start, so it will last longer. with <> it will simply press flat and then go west.

In which case it will collapse first is more a mater of how the load is applied and thats another story.
If the load is correctly applied the tub will be equally strong in all directions.
But true, it is a little easier to make the <>-case unstable but that is not a weakness in the tube but a weakness in the design where the tube is used.

I wasn't asking about tub construction - I have a length of square tubing that I want to use as a crossbeam from which I can hoist drivetrains out of donor cars.

Sounds like it'll be safer to use the tubing in the [] orientation. Now to find some bedframe rails for the uprights!

Thanks for the info.

Call me a spoilsport, but here's a page of useful free software including a structural sections calculator which will take a lot of the guesswork and bull5hit out of comparing round to square tube.
Link.