From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Wed, 30 Jun 1999 13:54:02 -0400
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 higher quality
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. Therefore, if
you remove the outer laminations, and transform the remaining section, you
would end up with a T-section, which moves the neutral axis up, which
increases the tension stress in the lower lamination.
Putting a steel plate on the bottom and making it composite, moves the
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" lamination combination,
the quality of the top laminations for tension stresses is unknown. Also,
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 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