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Re: Question regarding GLB

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Janelle

The "cracking" that you describe is consistent with a bending type failure
where the bottom lamination fails in tension (the end joint pulled apart)
and the resulting deflection and stress redistribution causes the
"delamination", a diagonal crack(s) and a crack near mid-depth parallel to
the laminations.

Before you decide on a repair, I suggest that you evaluate some of the other
conditions associated with the structure.

1. What is the climate? Is this a high humidity or dry climate? How often is
it exposed to rainfall or snow?
2. Is the existing glb pressure preservatively treated?
3. Does the existing glb have decay areas?
4. What life expectancy is expected for the beam if it is repaired in place?

If you decide on using a repair with steel rods and plates, consider this.

1.  What effect would using exposed steel have on the aesthetics?
2.  Would steel bolts and plates need maintenance (due to exposure to
elements)?
3.  What is the effect of trapping moisture in the wood where steel plates
contact the wood?
4. And what are the economics? (The expense of labor for installing all the
steel bolts can be quite high.)

You may want to consider replacing the glb with a new pressure treated glb.

Bruce Pooley
Timber Design
3448 South Newland Court
Lakewood, CO 80227
303-989-8701

----- Original Message -----
From: JANELLE L. PERRY <jlp(--nospam--at)schneiderassoc.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, December 08, 1999 3:25 PM
Subject: Question regarding GLB


> I have been asked to design a repair for a Glue-Lam beam approx. 20-30
> years old.
>
> The beam seems to have failed in tension at a finger-joint in the bottom
> lamination and delaminated up from the failure 3' and above the failure
> at the center of the beam. (or vice versa, I suppose).
>
> The beam is in an exposed condition, which makes the fix more difficult.
> It is a 5 1/8" x 18" beam spanning 30' with the failure occurring about
> 10' from the face of support.  The beam holds about 15' of tributary
> tile roof, sloped at approx. 4:12.
>
> I would appreciate any help or guidance.
>
> Thanks.
>
> Janelle
>