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glu-lams and termite damage

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Mike,

If the termite damage is restricted to the top of the glue-lam in the middle 
of the span, I think that you might be in luck if you can answer the question 
of how did the termites get to the top of the glue-lam at the middle of the 
span.  (I am assuming subterranean termites, which have to maintain contact 
with the ground to survive.  Dry wood termite damage does not progress 
rapidly and can be very localized.)

Although the GLB is 30 inches deep, remember that it is only the outer two to 
three laminations that are providing flexural resistance and that the inner 
laminations are of a lower grade material.  Also, at the middle of the span, 
absent significant wind uplift, the top of the beam is in compression which 
means that finger joints are not necessary there.

If the damage is localized as you have described, I would consider jacking up 
the GLB in the vicinity of the damage to take the load off the beam, cutting 
out the damaged area and installing new laminations with butt joints 
(staggered, of course).  The lumber for the repairs should be seasoned to the 
moisture content of the GLB before installation.

I would consider the king post alternative very carefully before using it as 
this type of structure is very unstable laterally.  The king post would have 
to be laterally braced to prevent lateral buckling.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Michael Cochran wrote:

. > Can anyone provide guidance in repair of an existing glu-lam beam with 
. > termite damage.
. > 
. > In my particular case I have an existing glu-lam beam,  50 foot backspan 
. > with a 11 foot cantilever that has termite damage at the midspan of the
. > backspan. The roof is a panelized system with 4x16 purlins at 8 foot on 
. > center by 24 feet long. The glu-lam beam is 5-1/8 x 30 and the initial 
. > visable termite
. > damage uncovered so far extends down at least 3 inches from the top of the
. > glu-lam.  The original design was tight, so by subtracting out 4.5 inches 
. > of lumber for a net depth of 25.5 inches, the glu-lam no longer figures 
. > unless the live load gets down to about 10 psf (dead load is 12 psf). The 
. > length of the visible damage along the surface is about 12 inches. We 
. > plan on furthur investigating the extent of damage, but before proceeding 
. > too far, I would like to get the opinions or experiences of others.
. > 
. > The possible options that come to mind are:
. > 
. > 1. Replace the glu-lam  (probably the most expensive)
. > 
. > 2. Cut out the damaged part of the glu-lam and replace with new lumber 
. > (glue and threaded dowels (assuming that the damage does not extend too 
. > deep into the glu-lam).
. > 
. > 3.  Add external reinforcement (king post with tension cable) to change 
. > member to be primarily an axial loaded compression member (again assuming 
. > the damage is not that extensive). 
. > 
. > 4. Add column at this location (not the most desireable, but cheaper than
. > replacing the glu-lam).
. > 
. > There is other termite damage in the building requiring some of the 
. > purlins to be replaced.  The building will be sprayed for termites and 
. > dryrot once all repairs have been made.
. > 
. > Thanks in advance
. > 
. > Michael Cochran
. >