blueman writes:
"Jim" writes:
The modulus of elasticity would be about 2,000,000 psi. Sorry to say, my
manuals only cover hardwoods such as oak, hickory, and maple; thus I cannot
give you a better answer than this.. However, the construction of the
plywood has no influence on the modulus of elasticity. But the construction
certainly affects the moment of inertia, and therefore, the maximum stress
and the maximum deflection.
Jim

Based upon looking at some calculators and skimming the analytical
paper cited in another response, it seems like Baltic Birch plywood
would have an MOE of 1/2 to 2/3 that of the Baltic hardwood number
that you quoted.

Also, if I am understanding you correctly, then I think you are
incorrect in saying that the construction of the plywood doesn't
effect the MOE -- in fact, per the article mentioned in another
response, the transvers-oriented plys contribute only minimally to the
stiffness. So much so that when there are only a small number of plys
there is a significant difference in MOE between plywoods with the
face grains oriented parallel vs. orthogonal.

Even if I assume that the plywood has only 50% of the MOE of pure
hardwood, then using the equation for deflection of a shelf with
uniformly distributed load and supported ends (like adjustable
shelving), I get that the shelf could support about 280lbs and still
deflect only 1/32 inch per foot which is reportedly the approximate
limit for being noticeable to the average human eye. If I assume that
the MOE is more like 2/3 of the hardwood equivalent, then I get a
maximum support without visible deflection of about 380 lbs.

Given that I need to only generously support 200 lbs (and probably
more like 150), I should be OK, even taking the worst case and
allowing for additional sagging with age.