You haven't defined what you mean by "column" here. If they take it mean a theoretical single column unit then there can, by definition, be no connection to break can there?
Was this your intention?
Richard Gage Blueprint for Truth Rebuttals on YouTube by Chris Mohr
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You haven't defined what you mean by "column" here. If they take it mean a theoretical single column unit then there can, by definition, be no connection to break can there?
Was this your intention?
NoahFence
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I wish someone saw that coming.
An unfair comment I think, Noah. Chris's responder has a long history of neutral engineering answers over there. The reference to a Truther site looks like an unfortunate coincidence.
Depends on the material, depends on the geometry, but it can happen. In fact the "resistance" (strength) of a column can actually go negative, i.e. its own weight can exceed its strength, so it becomes a drag on any redundant members supporting it.
In practice, most columns will fracture before bending this much. We don't usually make columns out of spring steel or thermoplastics... but a plot of stress vs. strain will be continuous right up to the point of fracture. (ETA: Some exotic composites, viscoelastics, and supercooled non-Newtonian fluids excepted, but don't worry about these.)
For all intents and purposes, a real structural column like the ones in WTC 7 will reach their maximum (buckling) strength under load, become somewhat weaker as they are forced to displace further, and then abruptly go to "zero." There can be some minor additional energy absorption in a dynamic situation, viz. Dr. Bazant's plastic hinges, until they actually fracture and then they contribute nothing. But for all intents and purposes they are no longer contributing to strength in the static case once buckled.
What the moment frames are doing is providing fixed end conditions to the columns, which makes them stronger than columns with merely pinned or unfixed ends. The moment frames can buckle as well, and if this happens first, the columns suddenly become much weaker than they were before as their ends are no longer fixed. Hence a buckle in the moment frame can lead to an instantaneous buckling in the columns.
The moment frames can also absorb a little more energy after they buckle, but again, not much and it depends on how they're hit.
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sheeplesnshills
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His comment on the member recovering from buckling if the load was removed is purely theoretical. A loaded column in a building will fail when it buckles as there is no realistic way that the load would be removed. Even if the load is transferred to neighboring columns the initial column will remain at the the bucking point and carry little of the load. Joints are simply where the beam will fail at loadings lower than the theoretical bucking point. Either way the failure would be near instantaneous and total, the only difference being that one would happen before the other did.
The point is that once the column has failed there would be little resistance thereafter.
Clayton Moore
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The emanating force unleashed as the result of the column 79 walk off was a globally destructive juggernaut.
little resistance thereafter You gotta love that explanation.
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NoahFence
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He can complain in FM again. There's that!
chrismohr
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Hi gang,
After this set of replies to my second round of questions I have now spilled the beans. Here are some more answers from the Structural Engineering forum:
1.) Going back to my original question #2, does resistance in a buckling column ever go to zero? Or does it gradually decrease? If a column is loaded just above its critical load, it will start to buckle. In its slightly buckled form, the column will continue to react with a force slightly below its critical load. If the load is caught at that time by external supports, the column will continue to react with the same force.
If buckling is allowed to progress, the axial force will diminish with increasing lateral displacement because some of the strain energy within the column is required to resist bending due to eccentricity.
On a Euler's curve (?) diagram it looked to me like there was a dramatic drop in strength/resistance but not all the way to zero. What Euler's curve? Please provide a reference. There should not be a dramatic drop in resistance at the start of buckling.
Assuming that the "center" hinge point never actually snaps apart, by the time it bends to 90 or 100 degrees, as a very rough estimate, would there still be 5% resistance? 2%? Depends on the properties of the column. Why is that important? The column has already failed.
2.) Would a set of columns with moment frames provide extra strength/resistance as they buckle? I don't understand the question. Perhaps a sketch would help.
As JAE asked, what is your application and why are you interested in post-buckling behavior?
I've answered them now. They were getting justifiably curious. Now they know I'm a 9/11 nut.
After this set of replies to my second round of questions I have now spilled the beans. Here are some more answers from the Structural Engineering forum:
1.) Going back to my original question #2, does resistance in a buckling column ever go to zero? Or does it gradually decrease? If a column is loaded just above its critical load, it will start to buckle. In its slightly buckled form, the column will continue to react with a force slightly below its critical load. If the load is caught at that time by external supports, the column will continue to react with the same force.
If buckling is allowed to progress, the axial force will diminish with increasing lateral displacement because some of the strain energy within the column is required to resist bending due to eccentricity.
On a Euler's curve (?) diagram it looked to me like there was a dramatic drop in strength/resistance but not all the way to zero. What Euler's curve? Please provide a reference. There should not be a dramatic drop in resistance at the start of buckling.
Assuming that the "center" hinge point never actually snaps apart, by the time it bends to 90 or 100 degrees, as a very rough estimate, would there still be 5% resistance? 2%? Depends on the properties of the column. Why is that important? The column has already failed.
2.) Would a set of columns with moment frames provide extra strength/resistance as they buckle? I don't understand the question. Perhaps a sketch would help.
As JAE asked, what is your application and why are you interested in post-buckling behavior?
I've answered them now. They were getting justifiably curious. Now they know I'm a 9/11 nut.
Christopher7
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The columns will provide resistance as they buckle. The more they buckle the less resistance they will provide. This is self evident. The engineer has stated that the loss of resistance would not be a lot at first. The 2% no doubt refers to the fullf formed hinge on the right.
The columns in the NIST collapse simulation are still buckling when the building has descended ~20 feet. That is during the FFA.
Chris,
Will you acknowledge this please?
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chrismohr
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Chris7,
No I do not acknowledge your claim at all. I have repeatedly and directly asserted, along with others who have quoted the NIST Report, that the first two seconds into the collapse, columns were buckling. That was the slower-than-freefall phase which I don't even understand your take on (was it collapsing down or was this an optical illusion?). Certainly after those first two seconds, residual resistance was probably very low. The four designs you showed of the column buckling in the NIST Report don't even take us into the FFA period. They just don't. Read the timings again. This is the fourth or fifth time you've harped on this and I'm not wasting my time yet again going back to re-link the old posts. Finis. 86. Done.
No I do not acknowledge your claim at all. I have repeatedly and directly asserted, along with others who have quoted the NIST Report, that the first two seconds into the collapse, columns were buckling. That was the slower-than-freefall phase which I don't even understand your take on (was it collapsing down or was this an optical illusion?). Certainly after those first two seconds, residual resistance was probably very low. The four designs you showed of the column buckling in the NIST Report don't even take us into the FFA period. They just don't. Read the timings again. This is the fourth or fifth time you've harped on this and I'm not wasting my time yet again going back to re-link the old posts. Finis. 86. Done.
sheeplesnshills
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Its called gravity.
And your problem with it is what? The whole point of them teaching me at college about buckling, Euler, Gunge, Kutta etc was to show that the above was the case.
Try this simple test. Stand on an empty soda can that is standing upright. It will likely support your weight (they will my 200+ pounds). then tap the side of the can.....how much resistance is there after it starts to collapse.....that right, very little. Now why should a column in WTC7 behave any differently once it has passed the point it fails? The loading to complete the bend of the column, or more likely fracture its joints, is tiny compared to its original load bearing ability.
DGM
Skeptic not Atheist
Why are you fixated on the simulation? You seem not to understand this is a tool to understand a complex system. You do know it really doesn't have to exactly mimic reality to be valid?
thedopefishlives
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Why are you fixated on the simulation? You seem not to understand this is a tool to understand a complex system. You do know it really doesn't have to exactly mimic reality to be valid?
Because disproving the simulation means disproving the NIST report means proving CD, don'tcha know.
Christopher7
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I keep repeating and you keep ignoring the distance the building has fallen.
The NIST model has descended about 20 feet in Figure 12-62
I asked you to measure the folding area between floor 7 and 14 and compare that to 7 floors that are not collapsing. This shows a drop of about 20 feet. Why do you persist in ignoring this?
Yes they do!
The last frame shows in the video at 16 seconds. [that's where the video stops] The building has descended much more than the 7 feet in Stage 1. [measure from the top of building to top of screen for comparison and do the math] It is clearly into Stage 2.
And this is the fourth or fifth time you've ignored the FACT that the building had fallen more than 20 feet and therefore it was into the FFA.
The lurkers can see that you are denying this critical fact. Only the fanatically faithful, who deny all evidence of the many NIST frauds, are supporting you.
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LSSBB
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Poll time!
tsig
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Appeal to invisible lurkers fallacy.
chrismohr
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Chris7,
I do not engage in NIST-picking. I know the models don't 100% reflect the video and photo evidence. NIST says so. I have one interest: CD or natural collapse? If a line of thinking relates to that question I pursue it. For example, thermitic materials in the dust? yes or no? Interesting, may lead to something, hire Jim Millette. NIST collapse model one second off? Not interesting. Column buckling and how it relates to resistance> That could lead to something. Others disagree with what I find interesting, but at least I agree that the question is CD vs natural collapse. NIST-picking is both brain-damaging and leads nowhere because all it shows is that model =/= reality. I know that. I think you believe that if you can find a way that a NIST model does not reflect reality, that somehow leads us eventually to the CD conclusion. I completely disagree and won't waste time on that line of thinking.
PS Hi lurkers how are you? Isn't it nice of Chris7 to ask me to perform for you?
I do not engage in NIST-picking. I know the models don't 100% reflect the video and photo evidence. NIST says so. I have one interest: CD or natural collapse? If a line of thinking relates to that question I pursue it. For example, thermitic materials in the dust? yes or no? Interesting, may lead to something, hire Jim Millette. NIST collapse model one second off? Not interesting. Column buckling and how it relates to resistance> That could lead to something. Others disagree with what I find interesting, but at least I agree that the question is CD vs natural collapse. NIST-picking is both brain-damaging and leads nowhere because all it shows is that model =/= reality. I know that. I think you believe that if you can find a way that a NIST model does not reflect reality, that somehow leads us eventually to the CD conclusion. I completely disagree and won't waste time on that line of thinking.
PS Hi lurkers how are you? Isn't it nice of Chris7 to ask me to perform for you?
Miragememories
Banned
The NIST graphic images visually render results concluded by the model's calculations.
If a careful examination of those simulation images reveals a collapse pattern strongly at odds with the reference video, you have to question the very validity of the NIST collapse conclusions.
This is hardly "NIST-picking".
MM
If a careful examination of those simulation images reveals a collapse pattern strongly at odds with the reference video, you have to question the very validity of the NIST collapse conclusions.
This is hardly "NIST-picking".
MM
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