Duane Bozarth wrote:

mike hide wrote:
....
Basically only the strata that are in one direction are actually
contributing to the bending strength. So in terms of solid wood consider it
as a sheet of wood half the thicness of the plywood . In practice support
stringers of solid wood are always a good the deeper the better....mjh

That's not actually quite right--the glued laminations add significantly
more resistance to bending owing to the glue than if they were not
present entirely (as your model suggests).

Actually, I found that

http://www.fpl.fs.fed.us/documnts/fplrn/fplrn059a.pdf

shows you're a lot more nearly right than I thought, Mike...

Their test data shows neglecting the transverse plies gets pretty close
to the right answer than I thought--although it's a long report and I
haven't had time to read it thoroughly, there's one apparent
inconsistency I don't quite see how follows because it also seems to say
is essentially same as solid lumber of same dimension but seemed to
refer to nominal dimension unless I somehow missed the nomenclature...