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RE: Acceptable Level of Overstress

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Thanks everyone… I guess I better start adjusting my cutoff to 5% if the IBC and NFPA both have the clause. It will get me prepared for whatever code we have 10 years from now.


FYI, the beam was a simple span glulam… so the 24f stresses back then are probably the same as now. Probably should have been more clear. The Cv factor is not the controlling adjustment factor, so it should be the same as original (back in 1973).


Also, I certainly do not exceed 5% overstress (Usually no more than 2% to be honest) on new members, but on existing, I have had bosses/owners to push it to 15% overstress (when I was younger). Now that my stamp is on the drawings, I get a little nervous when I approach 10%. I don’t have a problem up to about 7-8%





-----Original Message-----
From: Seth W. Cutler [mailto:seth(--nospam--at)]
Sent: Thursday, December 04, 2003 8:56 AM
To: seaint(--nospam--at)
Subject: Re: Acceptable Level of Overstress



When we check existing wood beams we use the allowable stresses at the time the building was designed/built.  Our office standard is 5% overstress due to the variability in the material and how likely the member will see the full load.  If it's 6% or higher then we might come in and sister on a member at mid-span to bump up the section.  There are other solutions too if it's exposed.

I'm assuming it is bending stress that is controlling.  Make sure you are using all allowable stress increases.  If it's shear stress then you could use the newer NDS which allows a higher shear stress.  The reason for this was discussed in previous threads.


At 03:22 PM 12/3/2003, you wrote:

What is the general practice on acceptable level of overstress when checking an existing member for capacity?
I have an existing wood beam that is 6% overstressed with new loads. I am prepared to deem that “Acceptable”. I was always taught that 10% or less overstressed is okay. I have a plan checker wanting to cut the limit at 5%. Is this somewhere in the code???
Gerard Madden, SE, PE
California Licensed Structural and Civil Engineer
Madden Engineering
2183 Eaton Drive
Lodi, CA 95242
T: 209.368.9955
F: 209.368.9966