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WOOD - Engineered Lumber vs. Sawn Lumber

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Dennis Wish Wrote:
The contractor verified that the beam was a DF #1 as specified and that
there was no visible defect to it. Being the case and re-checking all
numbers, I came to the opinion that the beam was received with a "crown" and
that the framer placed the beam with the "crown" side down. I see no other
explanation (the beam was a 6x12 DF #1 which had to fit in a space between a
9' garage door and a 10' plate height).


Dennis, if you don't mind I would like to start a new topic from something
you stated in you previous email.  BTW, I'm behind you also, I think you
documented yourself well and had this been for a larger fee, would have been
able to justify it in court.

Now, my question is, why would you not use engineered lumber for such a large
span, like a Microlam beam?  It is stronger, stiffer and straighter.  Would
the cost have been much different?

DF #1
	Ix=697 in.^4
	Sx=121 in.^3
	E=1,600,000 psi
	Fb=1,350 psi (I am not sure which of the many species of DF you use in the
NDS)
	Fv=85 psi

	Max Moment = 13,613 ft.-lbs.
     
            E * Ix = 1.1152E9

Microlam 1-3/4 x 11-7/8
	Ix=245 in^4
	E=2,000,000 psi
	Fb=2,925 psi (depending on the species available in your area)
	Fv=285 psi

	Max Moment = 10,060 ft.-lbs per ply

	E * Ix = 4.9E8 per ply

Therefore 2.3 plies (actually 3) of Microlam are needed to equal the
stiffness of DF#1, but if stiffness didn't control then Microlam blows DF#1
out of the water based on moment and shear.  Maybe 2 plies would have worked.
 Would 2 plies of Microlam cost significantly more than a single 6X12 beam? 
Does most of the profession use sawn lumber or engineered lumber in these
conditions?
__________________________________________________

Richard Lewis, P.E.
Missionary TECH Team
rlewis(--nospam--at)techteam.org

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.