Try this for some Baltic birch properties. Be careful to distinguish
between the terms 'modulus of elasticity' and 'section modulus'.
http://w3.upm-kymmene.com/upm/internet/cms/upmmma.nsf/lupgraphics/WISAFormbirchEN.pdf/$file/WISAFormbirchEN.pdf

from a Google search on 'plywood birch "modulus of elasticity"'

http://www.google.com/search?hl=en&q...=Google+Search

Incidentally, glues have low elastic modulus also and, like the cross plies,
contribute very little to the overall stiffness, most of which comes from
the contribution of the surface plies. For an extreme example of this
behavior try a search on "sandwich panel" wherein a relatively thin surface
skin is bonded to a foam or honeycomb core, as in hollow core interior
doors.

The practical solution to your shelf application is to bond a solid wood
strip (wider than the plywood thickness) to the front of your plywood shelf
where it will serve the dual purpose of stiffening the shelf and of hiding
the cut edge of the plywood. Perhaps add a mid-span support (cleat, clip,
pin) under the back of the shelf. Or, use a solid wood shelf. Note that
minimal initial deflection, while important, is not the whole story. Highly
stressed wood will take a set over time (engineers call this 'creep') which
shows up as a sag in the shelf. Either build a shelf stiff enough to resist
this or plan to turn the shelf upside-down occasionally. I have to do the
latter every few years on a commercial bookcase with 3-foot shelves of teak
veneer over particle board -- heavily loaded with my wife's collection of
Southern Living annual cookbooks.

David Merrill

"blueman" wrote in message
...
Snip...

While somewhat intuitive, I would have thought with all the glues and
resins that you would get some benefit that would make the stiffness
more than just 50% of the equivalent pure hardwood.
snip...

In any case, it still would be good to get some general specs on the
typical MOE for Birch plywood.

Thanks