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Re: Fire repairs to Glulam Beams

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Steve,

I assume that you have had the charring removed by a light sand-blasting and 
have measured the reduced cross-section and compared it to the undamaged 
cross-section.  You might find that the damaged section is not damaged as 
great as it may appear.

Charring tends to insulate the underlying wood and prevent it from being 
damaged.

Using the AITC lamination requirements, the remaining cross-section may be 
more than adequate to carry the required loading.  I think that the first 
evaluation that has to be done is loading demand and compare it to the 
section capacity where the damage has been done.

Based on the information that you provided, if the damage is *centered* 12 
feet from the support, it is at about the 1/4 point on the span, and, for a 
uniform load, the moment is 75% of the maximum moment.  A 10 percent 
reduction in section modulus should therefore be adequate.  90 percent of 
the maximum moment would occur at about 1/6 the span (about 7.5-feet) from 
the center of the span.

Hope this helps.

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

Steve Helfrich wrote:

>>Can anyone direct me to information on the pros and cons of various repairs 
that can be done to restore the strength of a fire-damaged glulam beam?  The 
beam that I am evaluating has lost about 10 percent of its section modulus 
over a distance of about 12 feet, about 12 feet from the end.  The beam is a 
6 3/4 by 33, and spans 45 feet between supports.

I have looked into the possibility of using a carbon/epoxy composite 
laminate, and aluminum sandwich core that is bonded to the beam.  We are also 
looking at a post-tension system.  Client wants to evaluate bolting steel 
plates to the GLB, and we are also looking at bolting wood (probably GLB) to 
the existing.

Any thoughts?
  
Thanks for any help you can send.<<

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