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Re: GLB Failure

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Could it possibly be that the beam was put in upside down?  In other words,
the compression zone was put on the bottom and consequently stressed in
tension and the tension zone stressed in compression.  As I'm sure you know,
the compression zone allows only half of the tensile flexural stress as
compared to the tension zone.

Just a thought.

-----Original Message-----
From: Parkerres(--nospam--at)aol.com <Parkerres(--nospam--at)aol.com>
To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Date: Friday, September 18, 1998 1:39 PM
Subject: GLB Failure


>To all:
>
>A question regarding possibile causes of the failure of a glulam beam:
>
>At the request of a client, the other day I looked at a glulam beam which
had
>failed in the roof of a one-story building.  (Fortunately, we did not
design
>this.)  The building is about 20 years old, and the beam appears to be
about
>5-1/8" x 24".  The beam is about 42' long supporting a panelized wood roof
>system.  There is nothing of note weight-wise on the roof.
>
>The beam has "broken" at about midspan and is now temporarily shored.  The
>finger joint in the lowest lamination has separated about 3", and there are
4
>or 5 other major cracks in the beam at the failure point.  The cracks are
>primarliy horizontal but are diagonal enough to be extending through the
>laminations not along the glue lines.  The beam has sagged about 6" due to
the
>failure and was probably hanging from the roof until it was shored.  The
beam
>is over a kitchen area.   Reportedly, someone heard a "pop" and noticed the
>ceiling was sagging.  The failure was noticed when the ceiling was opened
to
>inspect the beam.
>
>We are recommending that the beam be removed and replaced from above, which
>the owner is willing to do.
>
>However, I am curious as to possible failure causes.  There is no unusual
>equipment on the roof and the building engineer says they have no ponding
>problems.  Could the failure be related to heat or gases from the kitchen?
>Could it be a latent defect?
>
>Any thoughts and/or similar experiences would be appreciated.
>
>Thanks,
>
>Bruce Resnick, S.E.
>Parker Resnick Str. Eng.
>
>
>
>
>