What about cutting the glulam beam through and supporting on a single post?
This would create two simple spans of smaller length than the original
single span and has the advantages of:
a. peak moment will be smaller than the current condition...meaning
that the compression lams are adequate as they are
b. peak shear will be less...hopefully by enough that the center plies
(which you have by now reduced by 4 ½ ") will be adequate
c. moment at the end will be zero solving the transformed T-section
Of course there is going to be some detailing involved...I assume that you
are going to need some length of the 4 ½ " removal to fit the garage door
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Wednesday, June 30, 1999 10:54 AM
Subject: Cutting a Glulam Beam
As noted by many other responses to this query, the
lamination grades for the
outer laminations are different than the core laminations.
So, cutting off 3
laminations at the bottom of the beam would remove *all* the
laminations. A question that remains is, if you do this,
will the beam still
be structurally adequate?
Since the core laminations may be a different species as
well as grade from
the outer laminations, the E-value would also be different.
you remove the outer laminations, and transform the
remaining section, you
would end up with a T-section, which moves the neutral axis
increases the tension stress in the lower lamination.
Putting a steel plate on the bottom and making it composite,
transformed section neutral axis down, increasing
compression stresses in the
top. Damned if you do; damned if you don't!
As has been pointed out, putting a post in would create
tension in the top,
and unless the beam was fabricated as a "balanced"
the quality of the top laminations for tension stresses is
IIRC, top laminations subjected to compressive stresses are
also permitted to
have butt joints instead of finger joints --- and glued butt
joints have no
reliable tension value.
Good luck. (Why are so many responders wishing you this?)
A. Roger Turk, P.E.(Structural)
>>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
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