
An I beam is the most efficient in one direction load bearing, if the I beam is bent side to side it functions as an H beam and is much less efficient. The most efficient shape for both directions in 2D is a box however the most efficient shape for bending in any direction is a cylindrical shell or tube. But, for unidirectional bending, the I or wide flange structural beam is superior. A H beam has a thicker center web which sometimes is misinterpreted as stronger but in reality, just has different applications.