todd wrote:

We're in luck. I'm a mechanical engineer who specialized in
materials engineering.

I have a couple questions for you then. Something I always wondered.

Imagine a torsion box, well made with 1/4" ply top and bottom and 1-
1/2" thick. Let's say it's for a shelf 6ft long and 11-1/4" wide. Now
imagine a solid plank, 2x12 construction lumber (not fir). Would you
think the torsion box would be stiffer or would the solid plank be
stiffer?

I would imagine that if one used oak instead of spf, the oak plank
would be stronger than both.

Also, would I be correct in thinking that 2 pieces of 1x12 laminated
together would be stiffer than a solid 2x12? If so, why? (other than
minimizing and spreading out defects, which is pretty obvious)

I know I could probably do some homework and look this stuff up... but
you're here, right?