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RE: Solutions for Wrong Grade Glue-lam?

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Based on testing of full size unbalanced beams in the "flipped direction",
the industry has recently increased the bending values for unbalanced beams
with the compression zone stressed in tension.  FYI, Fb for a 24F-V4 is now
2,400/1,850 for tension zone stressed in tension/compression, respectively.
Although this doesn't answer your question w/r to cutting the beams in half,
the increased stresses might allow you to rethink your options (if you
weren't aware of it!).

Sources:
2001 NDS Supplement
APA's ICBO Evaluation Service Report ER-5714
http://www.icbo.org/ICBO_ES/Evaluation_Reports/pdf/5714.pdf
AITC 117-2001 Design Values/Specifications

HTH,
Tom

-----------------------------------------------------------------------
Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
P.O. Box 11700
Tacoma, WA 98411-0700
ph: 253/565-6600
fx: 253/565-7265
-----------------------------------------------------------------------


> -----Original Message-----
> From: Thor Matteson, SE [mailto:matteson(--nospam--at)yosemite.net]
> Sent: Tuesday, January 14, 2003 7:50
> To: SEAINT
> Subject: Solutions for Wrong Grade Glue-lam?
> 
> 
> I just got word that two glue-lam roof beams in a 3-year-old house I
> designed
> are not the specified grade.  The design is a two-span
> condition--one span is about 18 feet
> and the other is 22 feet.  For one of the beams, the 22-foot 
> span has a
> ridge and other strange
> framing coming into it.  Governing shear and bending stresses 
> occur over the
> center support.
> 
> The beam was very clearly noted on the plan as 24F-V8 grade.  
>  Any grade
> markings on the installed beam were covered up by finish ceiling and
> insulation, so I could not
> verify the grade.  The owner assured me that they ordered 
> what was specified
> on the plans, but the only written information available was 
> their invoice
> from the lumber company and the beam manufacturer's shipping 
> sticker from
> the beam wrapper, which had some numeric codes on it along 
> with beam size
> and date of birth.   The beam mfr's representative recently called to
> tell me that the numeric codes matched a 24F-V4 beam.
> 
> If this is so, the beam is over-stressed by almost double 
> (what kind of
> engineer would I be if I put an additional safety factor of two into
> everything I design?  Unemployed....).
> 
> My initial thought is to turn the continuous beam into two 
> simply supported
> beams by cutting through it directly over the center post.  
> This would cause
> the point of maximum bending stress to move from over the 
> post (negative
> moment) to somewhere close to mid-span (positive moment).  
> Since the beam is
> fabricated for positive moment, everything should now be 
> fine, assuming that
> the beam can carry the positive moment.  Only difference is
> that now the beams could sag more than twice what a 
> continuous beam would
> have, but for a roof without plaster ceiling it is still 
> code-compliant.
> 
> Any thoughts?  Have any of you done this before?   What if 
> the owners do
> nothing?
> (This seems scary to me, as the beam could fail in bending 
> over the center
> support;  this would not be a clean failure like a saw-cut, and
> could
> lead to shear failure, collapse, death, dismemberment, not to 
> mention water
> damage....)
> 
> Thor
> 
> 
> 
> 
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