Rigidity of tubing VS solid bar

[isuzunut]

Ok, I searched.
And I need some one to confirm what is more rigid. If you have a 1 inch solid steel bar and a 1 inch, say... 1/4 inch wall pipe, what is easier to bend the rod or the hollow tube?

 

[Danger]

Welcome to PF, Isuzunut.
I'm not actually sure about the diameter, but tubing is definitely more rigid on a by-weight basis. If you look at things like car frames, roll cages, fence posts, aircraft landing gear, etc., you'll notice that it's all tubular. For the same reason, I-beams and H-beams are used in building construction. All that I can tell you is that it's because of the way compression, tension, and torsional forces are distributed. Someone else will have to give you the straight facts.

 

[AlephZero]

The rigidity in bending is proportional to the moment of area of the cross section.

So ignoring any other considerations, for the same mass of material, increasing the diameter and decreasing the wall thickness gives more rigidity. A solid bar is the worst (most flexible) case.

Obviously there ARE other considerations, if the walls of the tube are very thin.