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Re: WOOD - Engineered Lumber vs. Sawn Lumber

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-----Original Message-----
From: Richard Lewis <rlewis(--nospam--at)techteam.org>
To: seaoc(--nospam--at)seaoc.org <seaoc(--nospam--at)seaoc.org>
Date: Monday, September 08, 1997 9:17 AM
Subject: WOOD - Engineered Lumber vs. Sawn Lumber



>>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
>

No question about it - an I am licensed to TJ for their TJ-Beam program. I
guess at the time I found that a 6x10 worked with, what I considered to be
acceptable deflection limits for this span. The other decision was that the
wall was actually a double 2x6 wall constructed to satisfy and architectural
detail and to provide the thick Adobe look.
In retrospect,  a Parrallam is much more desireable, but it was a decision
made at the time and I felt that the calculated deflections were acceptable.
The measured calculations reflect a problem that I feel was proven to be due
to a "crowning" of the delivered member.

While we are on the subject - Why is it that Trus Joist (or Lousiana Pacific
or the other manufactered wood products companies) do not provide
manufactured beams in conventional depths to sawn lumber. Why not produce a
5 1/2" x 11 1/2" member rather than an 11 7/8" beam. I have had to juggle
details in order to fit a manufactured beam into locations where I could use
a sawn lumber.
Why, too, are Glu-Lam beams not made in conventional widths - ie, 3.5, 5.5.
It would be a lot easier to get a beam in a wall that was 5 1/2" rather than
5.125?
It would be understandable if the posts and studs supported these widths or
depths, but I think it makes detailing more difficult.

Here we go again?
Dennis Wish PE