Beam advice

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On 20-Mar-2006, snipped-for-privacy@ece.villanova.edu wrote:

This is exactly why you should not be taken seriously. You have your equations, but you haven't got a clue.
Mike
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Michael Daly wrote:

But he is a chipper fellow. It doesn't offset his tenuous grasp of logic and engineering - still, it must count for something.
Do you know that TV show NUMB3RS? Nick would be a great "guess" star. While he was running off half-cocked and making stupefying assumptions, the stars of the show could proceed to resolve things in a rational manner. Kind of a Point/Counterpoint thing.
R
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You have my numbers. Where are your numbers? :-)
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Nick, this is not a mental exercise. We're not playing with numbers because we're bored. It's a real guy's house, with a real question about the structure. With out real information about snow loads, earthquake, wind loading, all of that fun stuff you ignore, and which can _easily_ supercede any occupancy or dead load, the numbers are imaginary. They have no meaning. So what's the point in _guessing_ at a solution?
The fact is, you really don't care whether it's a real situation of not - a real house or not. You see no difference because your first love is juggling numbers. To each, his own. But please don't go selling your "solution" as anything other than a mental exercise.
R
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This is Beams 101. I'm surprised anyone would argue about it, unless they don't understand it or just love to argue :-)

And engineering is done with numbers. Or perhaps feeble arm-waving, for the numerically-illiterate :-)

The USENET bestiary also includes those who say "We can't see it from here" and "You must hire an engineer" and "WATCH OUT!!! WHAT YOU ARE DOING COULD BE DANGEROUS!!!" :-)

The OP described a beam and asked if it would be strong enough.
Estimating its strength is a reasonable first step.
Nick
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On 21-Mar-2006, snipped-for-privacy@ece.villanova.edu wrote:

Estimating its strength doesn't answer his question. The bafflegab you post might mislead the naive into believing it is an answer. You're being irrisponsible and can't bring yourself to admit it. Most of the other responses have been of the "you haven't provided enough information" sort, because - he hasn't provided enough information.
Mike
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Like the response below? :-)
Article: 797996 of alt.home.repair From: snipped-for-privacy@ece.villanova.edu Subject: Re: Beam advice Date: 19 Mar 2006 07:55:38 -0500 Organization: Villanova University

Depends on the kind of wood and the load and its distribution.

Like, what's the load on the beam? With bending moment M = WL/8 in-lb and a total uniform load W in pounds and L = 14x12" and S = M/f = bd^2/6 in^3 and f = 1000 psi and d = 11.25" and b = 5" (3x1.5+0.5, if half the plywood grain runs lengthwise), W = 8bd^2f/(6L) = 8x5x11.25^2x1000/(6x14x12) = 5022 pounds. You might make it stronger by substituting some metal for plywood.
Nick
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On 20-Mar-2006, snipped-for-privacy@ece.villanova.edu wrote:

Your numbers are useless in the absence of load information and details on the beam support. There are two sides to the general problem of building a structure, P and R - loads and resistance. You are focussing on only one.
Mike
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RicodJour wrote:

I had a very similar situation where I removed a chimney. I kick and kick and kick myself for not hiring a structural engineer before and DURING the work. Hired one after the fact, engineer thinks the work may be ok but I do not. We have had many rain leaks (even after replacing the roof twice) and now I may have to rebuild a portion of an exterior wall because I think there has been movement. My theory is that the chimney was providing stiffness to the structure, like a column. In our case, the chimney was also supporting wood beams which were difficult to remedy. I think the structure is moving differently and somehow letting water in. Don't be a big dumby like I was. I have spent 5x the cost of the engineer and still have water dripping into my house because of movement. Also, if you hire a structural engineer make sure you have them come to the site and approve the work before it gets covered up!
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On 19-Mar-2006, snipped-for-privacy@ece.villanova.edu wrote:

PE in what? - Electrical? Chemical? Transportation? If he isn't a structural engineer, he isn't likely to know what I've pointed out to you.

Show him the Unistrut manual and ask him to explain the column on the extreme right that lists load reduction factors. Let us know what he has to say.

Plate and shell theory. FEA would be easier.
Mike
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Structural engineering, which he also teaches and writes books about. He's the lead engineer on a $20 million building now. He uses lots of Unistrut in his work.

Local buckling.

We talked about that ("page 61") and I asked where the curve came from.

He said Unistrut has several failure modes. I guessed the curve came from the main twisting one with the open side up, vs the local buckling one for short lengths, with a safety factor. Where do you think it came from?

Perhaps you can answer this question: "Exactly how much perturbation is needed to cause torsional longitudinal failure as a function of load?" You might say "Exactly zero, at full load," or "Exactly zero, at the derated load on page 61," but neither of us would believe that :-)
Then again, from a quantum-mechanical point of view, there is an infinitestimal but finite probability that every molecule in a 10' strut will suddenly decide to be somewhere else for an instant...
Nick
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On 21-Mar-2006, snipped-for-privacy@ece.villanova.edu wrote:

Writes books? - give us his name.
He'd better brush up on his engineering skills...

Guesses are not what you need - you need knowledge.

Tell your idiot friend to look up "lateral-torsional buckling" in a real structural engineering book - e.g. page 203 of "Structural Steel Design". Lambert Tall ed. 2nd edition Ronald Press Company, NY.
Lateral-torsional buckling is critical in slender beams - and a ten foot long unistrut supported only at the ends qualifies. Open channel sections are more sensitive to it than closed sections (as I have already pointed out). To prevent this, you have to either brace the beam along the length or limit the load and that's what the load reduction factors are for. The OP was asking for a closet rod unsupported along its length, hence only the latter approach is appropriate.

You're an blowhard that thinks he know more than he does.
Mike
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To be a PE, don't you have to have knowledge of various fields?
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Yes, esp after the FIT exam, with questions about dam design, crystallography, electronic controls, and so on. In PA, an electrical PE can legally design bridges and skyscrapers. And pediatricians can do brain surgery...
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

What's your point? That there are stupid regulations with lots of loopholes in existence?
Or are you suggesting that since you don't know anything about the specific design requirements of the original question, you can concentrate on Beam Theory 101 to "offset" the lack of information?
Gee, my car's not starting, but I don't know anything about engines. Let me make sure the tires are at the right pressure...
R
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RicodJour wrote:

Just give up on Nick. He's always long on equations but completely lacking in any common sense or practical real world experience. This whole thing is laughable. He tells the guy how much weight a bunch of 2X12's can hold, as if that is the solution to his problem. Like the guy already knows the load that's going to be on the beam, how it's distributed, what structural support there is at the endpoints, etc. Unbelievable.
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snipped-for-privacy@optonline.net wrote:

Laughable, yes, but I do get concerned that someone who doesn't know any better will believe his spiel.
He reminds me of a kid that is _so_ proud of their newfound knowledge, forgetting that with knowledge comes responsibility. He's irresponsible with his knowledge, and careless with his assumptions. Many people on usenet are. Maybe I just expect more from him, I don't know.
R
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Well... Brain Surgery isn't exactly rocket science...
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Steve Barker LT wrote:

After reading your additional information and viewing the photo, I would have to say that I feel all the stronger than an engineer is not optional.
I can't express this in any other way, but to say:
It would be extremely foolish not to pay the cost of an engineer. Keep in mind that if it fails and you did not use an engineer, your home insurance will likely be voided.

--
Joseph Meehan

Dia duit
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On Sun, 19 Mar 2006 19:13:01 GMT, "Joseph Meehan"

First off, I am a structural engineer and second, forget about the insurance costs or voided policy. If the building fails and someone is inside, you may lose lives.
To the OP: Would the cost of an engineering opinion be worth the cost of losing a family member?
I followed most of this thread and while I understand the concepts of engineering design and code, most of the thread is valid. I will say, rather than get stuck on "too" much theory, I'd follow the local building codes for this situation (I didn't look at any pictures tho). And besides the sizing of the beam, the number of fasteners or location in the flitch beam and the ends will also matter (inotherwords, what good is a correct beam size if the connections fail). And I don't think live load reductions will come into play here tho I'm not up on all local codes but I've used the UBC codes some time ago.
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