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RE: Acceptable Level of Overstress[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Acceptable Level of Overstress
- From: "Caldwell, Stan" <scaldwell(--nospam--at)halff.com>
- Date: Thu, 4 Dec 2003 14:58:41 -0600
Gerard, and everyone else:
As the years pass, I am increasingly involved as an expert witness defending fellow design professionals. I find that an engineer learns more from failures than from successes, and it is always preferable to learn from the mistakes of others. One thing that I have learned is that some plaintiffs attorneys are very skilled in convincing nontechnical juries of the absolute sanctity of the exact wording in applicable building codes and standards. For example, I know of one current case where a multi-million dollar judgment hinges on a discrepancy of less than 2 psf net roof uplift, even though there is a residual factor of safety in the uplift design of at least 1.25.
Imagine the situation you might find yourself in if one of your projects experiences a failure and it is determined that you intentionally approved a 10% overstress in some member, even if this member is unrelated to the failure. The plaintiffs would have a "field day" at your expense. When I entered the profession in 1970, I was taught that the various codes allowed an overstress of 3%. I have used that value for the past 33+ years. If I can convince myself that IBC and other current codes now allow 5% overstress, I will adjust accordingly. However, I would never consider approving an overstress above this amount. In today's litigious world, such practice would be foolhardy.
Stan R. Caldwell, P.E.
Beat LA!! Beat LA!!
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%
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