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Re: Cutting a Glulam Beam

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----- Original Message -----
From: Shafat Qazi <seaint-ad(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, June 29, 1999 11:38 PM
Subject: Cutting a Glulam Beam


> One of my clients wishes to install a garage door to his two car garage.
> The header beam is too low and needs to be reduced in depth by about 4.5
> inches. One of the solutions proposed by the client's contractor is to
> remove the bottom three laminations and add a new post + pad  about
> mid-span. The current Glulam beam is 21 inches deep. It works as a 16.5
> inch beam for the reduced span.
>
> Question: Is there a problem if he cuts 4.5 inches from the bottom of the
> Glulam?
>
> Shafat
>

Bruce Pooley comment: There may be a problem if the bending stress and
stiffness are reduced by cutting so that the design loads cannot be
supported.
If it is a 24F-V4 Douglas Fir beam, the tabular design value for Fbx
(extreme fiber in bending about the x-x axis) is reduced from 2400 psi to
1500 psi, and the Ex (modulus of elasticity about the x-x axis) is reduced
from 1,800,000 psi to 1,700,000 psi. Shear parallel to grain design value,
Fvx,  remains at 240 psi (this value is based on the core laminations).

Another consideration is the spacing of end joints (mostly commonly are
finger joints) that are required to be spaced a minimum of 6 inches between
finger joints in the moment critical zone (central 75% of the span and the
bottom 3 laminations). If the end joints are not properly spaced, I would
reduce the Fbx value by 200 psi. For bearing at supports, the Fcperpx
(compression perpendicular to grain) design value is reduced from 650 psi to
560 psi.

Cutting off laminations is not generally recommended and certainly would
void any warranty. Good Luck!