Hollow circular tube versus hollow rectangular shaft

[daniel wood]

Sportnut:
If I am using exact same aluminum material, with exact same thickness of gauge and I construct a 4ft long hollow circular tube that is 1" diameter, and I also construct a 4ft long hollow rectangular shaft that is 1" square, which would be more resistant to bending?

 

[Bill_K]

Hard to say, but the circular pipe would resist bending equally in all directions. Whereas the square pipe would be great in horizontal and vertical directions but would quickly fail if you tried to bend it along a diagonal (making it diamond-shaped)

 

[daniel wood]

Thanks Bill. I appreciate your response.

 

[AlephZero]

The square tube would be stiffer because more of the material is further from the centerline.

The stiffness ratio (from the second moments of area) is (1/12) / (pi/64) = about 1.7

Post #2 is wrong. The square tube is also equally stiff for bending in any direction, though this is not so "obvious" as it is for a circular tube.