HMS Beagle wrote:
There is no mystery to the engineering of steel tube, round, square, or otherwise. Both shapes resist torsion and bending. And a square tube will resist both more bending, and more torsion (and more compression while we are at it) than a round tube of the same dimensions. This is very well worn and reliable science that can be found in any properties of materials textbook.
I think these myths stem from the fact that using a given amount of material, you can make a round tube that is slightly stronger than a square one. In other words, the same amount of material used to make a 2" square tube could have been used to make a 2.5" round tube, and the round tube will be stronger. But at the same dimensions - 2" tube to 2" tube - the square tube is stronger.
I was thinking more specifically to point loading in the classic square vs a circle stress format.
Happijacs have notoriously buckled from side loads at the point where the outer tube is applying sidewall pressure to the inner jack tube, where as similar round tube jacks have bowed and deformed, but not completely buckled in on themselves (they've taken on a curve, like bending a roll cage).
They haven't been known on this forum as "crappijacs" for nearly two decades for nothing, between their tube wall weaknesses and the sheer pin problem that would literally cause the camper to plummet to earth, and all of this BEFORE Lippert got ahold of the company, a company notorious for poor quality steel trailer frames.