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RE: Timber Beam Deflection

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-----Original Message-----
From: Roger Turk   Wood is the poor cousin
of structural material, its been used so long it gets no respect.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Well said Roger - Rodney Dangerfield should have been the spokesperson. I
wasn't trying to be argumentative, but was interested to find out if you had
any technical information to support your theory.
I think the most important thing to remember is that wood, unlike concrete
and steel was a living organism and therefore was comprised of a large
percentage of water. I would go farther to assume that the cellular
structure is nowhere near as compact as that of concrete or steel and
because of this I would assume there is room for physical changes in the
shape of the cell to occur due to fiber tensile stresses.
I would also think that it would be difficult to try and create a strict
definition of it's behaviour since each piece is virtually unique. The
number of variables including moisture content, the location in the trunk
that the sample was taken (tighter grain closer to the core or looser grain
as you approach the outer ring, damage from bacterial and viral strains
occuring at some point in the wood's hundred or so year life span, knots,
checks, warps, twists and a whole bunch of other variables associated with
this unique material.
The only way this comes close to predictable is when dealing with
manufactured products that are controled in growth and taken from young
growth. Microwaving the "splines" in glues makes it dimensionally
predictable. For this reason, I don't think that structural lumber like
Parallams experience the same type of creep problem as sawn lumber.
But, Roger, I agree with - wood is a truly wonderful material that just
"aint got no respect" from most of the structural community. Personally, I
prefer it to any other material to design with.