Quote:
Originally Posted by Schumi
Bending stress is calculated as My/I where M is the moment at the cross section, y is the distance to the neutral axis, and I is the section inertia. All else equal, the section inertia is all that sets the two apart.
The lower the stress the better. Since Inertia is on the bottom of this equation, the greater the inertia, the lower the stresses, the better the beam is in bending.
I'm not going to calculate the inertias but but looking at them they are going to be very close.
If they are some sort of standard steel beam, there are lookup tables for inertias for standard stuff. Or it's easy to calculate section inertia of something simple like that.
I want to actually say the 8x8 has a higher inertia.
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That was my gut reaction too, but a quick FEA run on both indicates otherwise.