08/04/2015
The best beam shape is an I or better yet, an I
When a beam bends under loading, the top shortens (is compressed) and the bottom is stretched (tension). Compressive and tensilestresses are respectively greatest at the very top and bottom of the beam, and they decrease towards the middle, where stresses are zero at the neutral axis
A rectangular beam used in a vertical orientation (B) is more efficient than the same beam used horizontally (A) because a greater percentage of its material is located where stresses are greatest - away from the neutral axis. This puts most of the material where most of the work needs to be done. For the same reason, an I-shaped beam (C) is even more effiecient.