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RE: GLB Failure

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Bruce,
I could not run a calculation on the beam to verify and imagine you had (you
did not indicate the tributary area or the roof loads). You mention that it
is a panelized wood roof and yet seem to indicate that it is residential
constrution. Is there a ceiling attached or any addiional loads being taken
by the beam that may not have been part of the original design?
Also, could the beam have been sized with a camber, but not installed with
one?
Nothing is impossible, but I have not heard of many GLBs that fail in the
lamination. You mentioned other cracks at midpoint. Are these perpendicular
to the laminations? Were there any concentrated loads applied in the past in
area's that you can not see?

There are companies (although you will have to search for them) that will
evaluate wood failures. They would probably be your best bet to determine
the cause of failure.

Tell us what your preliminary calculations uncovered. What was the required
camber and do you think that the beam was supplied with the camber designed
into it or is it possible that the camber was eliminated or the camber side
was placed down?

Dennis

-----Original Message-----
From: Parkerres(--nospam--at)aol.com [mailto:Parkerres(--nospam--at)aol.com]
Sent: Friday, September 18, 1998 12:31 PM
To: seaint(--nospam--at)seaint.org
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.