"blueman" wrote in message

Also, does anybody know the "typical" Modulus of Elasticity (in N/mm^2
or PSI) and density (in Kg/m^3 or lb/ft^3) for:
Baltic Birch plywood (assume 13 ply for 3/4" thickness)
Birch plywood with Poplar core (assume 7 ply for 3/4" thickness)

I don't have a clue. What I do know is that the design and construction have
much more to do with performance than pushing the pencil or slide rule with
all the stuff you are asking about. Rather than do all of that math, add
stiffness with construction. I couple of simple support under the shelf, or
on the front edge will do more than adding thickness of shelving. Just take
a look at bridge design.