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GLB Failure

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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.


Bruce Resnick, S.E.
Parker Resnick Str. Eng.