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Re: shear wall design; std. of care[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: shear wall design; std. of care
- From: Charles Greenlaw <cgreenlaw(--nospam--at)speedlink.com>
- Date: Wed, 17 Nov 1999 21:59:29 -0800
At 11:41 AM 11/17/99 -0500, you wrote: >Using dead loads to resist uplift between the ends of a plywood shear wall, >by >analysis, creates a higher shear than that of the standard of care for >calculations. I agree that where dead loads act between ends of a plywood shear wall, rather than being concentrated at the ends, then the maximum shear STRESS is indeed higher than the average. And calculating "average" shear wall shear stress, and then using it blindly as the design stress for proportioning the wall's elements, is probably the most common and naive method out there. It is the customary simplest method. But to use the term "standard of care" as an offhand euphemism for "customary simplest method" is absolutely outrageous. "Standard of care" is a legal term of the most serious and grave import. It is defined in BAJI, the state's official jury instructions, and is the basis for jury, judge, or hearing officer to use in weighing evidence, including expert testimony, as to whether an accused person was negligent. Ignorant, careless use of this term by engineers can and does cause blameless engineers to be sued for serious money and to have revocations of their licenses pursued tenaciously by the PE Board. Costs to save one's savings and one's license to practice quickly runs to many tens of thousands of dollars, with no recourse against anyone. All because another engineer didn't know his engineering with enough versatility, and didn't know legal terms at all. Or worse. While on this scolding rant, I ought to observe how badly the practice of structural engineering is degenerating into what they do in a Prussian military school: everyone has to conform and comply and replicate what Herr Headmaster dictates. No initiative, no creativity, no disobedience. Marching in circles like simpletons? No problem; it's the standard of care. Code book read like the Mensa Book of Puzzles? It ought to; we're the elite of all engineers. State of the art? It's artwork where you paint by the numbers-- the Committee's numbers. Know a better way? Forget it; it's not the standard of care. > I have never seen the use of the increase of shear to balance the static >model. That's a candid admission. But what does it imply? That you haven't yet seen everything that other engineers have seen, or that what you haven't seen you presume defective? Hopefully only the former. >Many, like Dennis Wish, recognize the issue and do not use the dead load >resistance that occurs between the ends of the wall. To the contrary, Dennis said he "never really thought about the reasons" for not using dead load out along the wall. Bill Allen however gave the reason that is the most compelling: There isn't enough fee to fool around calculating little increments of dead load to offset overturning uplift. This is the same disincentive I follow, even though I worked out for myself in Jan 1985 the same findings so well expressed by Nels Roselund the other day. But if I expect a calculated need for some hold-down device, I use a plenty strong and stiff one, because it costs little more than a wimpy one, and seismic loads are understated, and gravity has little available overstrength. Do I reckon with increased panel shear stress due to distributed O.T.-resisting dead load? I'll never tell, because it might not resemble some engineer critic's "standard of care". Charles O. Greenlaw, SE Sacramento CA Still on SEAOC Prof. Practice Committee; unsure why or for what good.
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