TheRedWorm
I AM the Red Worm!
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Sigh... once again, for the truthers. And I'd love to see this question answered for a change.
How can such a floor...
... stop something like this...
Go ahead, Heiwa.
Moderated Steel structures cannot globally collapse due to gravity alone
- Thread starter Heiwa
- Start date
Go ahead, Heiwa.
leftysergeant
Penultimate Amazing
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So? It can be done. The parts of the towers that failed were , for all intents and purposes, basicly big free-span roofs. Just let enough snow accumulate on a roof, and it is coming down. If there is another identical roof beneath it, that roof is now burdened with not only the debris that made the first roof collapse, but with the weigh of the collapsed roof as well. The next roof will, thus, be burdened with nearly three times the weight needed to collapse it.
Where is the arresting mechanism?
Yes please, Heiwa. I'm not an engineer, therefor I would like you to explain it to me. I can't figure it out by myself.
How can this floor...
[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_11696474df7b2e709f.jpg[/qimg]
... stop this ...
[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_11696474df7bfd686f.jpg[/qimg]
Well - the first picture shows a very thin floor with its trusses bolted to the perimeter columns assembly. The latter consists of vertical steel box columns and horizontal spandrels all around the structure.
The load on the floor is transmitted to the perimeter columns.
Remove the floor ... and no load is transmitted to the perimeter columns.
The perimeter columns assembly is quite strong - it can carry 5 times the load from the floors. Factor of Safety, FoS, is 5.
The second photo shows the South Tower just after a big, non-uniform explosion has taken place inside the structure and the whole upper part has tilted sideways. Debris and smoke are ejected in all directions. The upper part is evidently disconnected from the lower structure, i.e. the perimeter columns have been cut off. Such an event cannot be result of local structural failures due heat + gravity. All described in more detail in my papers.
Furcifer
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And the load from the upper section was greater than 5x the load from the floor alone.
I love how you plug you own website at every chance. Just in case someone who doesn't know any better is reading.
The arresting mechanism is the strain energy built into the lower structure and that the loose loads will take the easiest way down.
In your case the top roof collapses at midlength between the walls, so the snow flows to middle of the floor (not roof!) below that may be overloaded there and the snow (the loose load) continues to flow down, etc. But the walls are not affected by these local failures of roof and floors and will remain standing. Just look where the loose loads are relocated after each failure and you will understand.
In WTC cases there are very little loose loads that are relocated. If you believe the whole upper part suddenly becomes a loose load, maybe you have a loose bolt in your brain. The upper part is always connected to the lower structure - the beauty of steel structures - and cannot drop ... and therefore cannot crush down the lower structure.
ElMondoHummus
0.25 short of being half-witted
Two things:
- As many others have pointed out multiple times, when the floor is removed, the lateral bracing for the perimeter is removed, and structural integrity is compromised. The columns would at that point fail to remain vertical on their own accord, nevermind the fact that the upper section is falling on them.
- Whatever the perimeter columns' load bearing capacity is, it's a capacity for static loads. Not the moving, accelerating load it experienced on 9/11!
Why do you argue around what logic makes so clear?
leftysergeant
Penultimate Amazing
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And what holds it up when the floors are removed by over-loading.
As I have repeatedly pointed out, those floors are exactly comparable to a bunch of free-span roofs which, by your own admission, are fallible when over-loaded. The weight of the debris which fell on them over-loaded them.
Now not only do we have nothing holding them upright, we have debris pushing outward on them. What arrests that?
The sagging floors began pulling the perimeter columns inward. They were, in that distorted condition, no longer capable of supporting weight above that point. That is what caused their failure.
1. Evidently, when you remove a floor and the load it carries to a column, you also remove possible lateral support of the column provided by the floor. Everything changes ... and you have to reanalyse.
2. Structural integrity evidently changes when you remove or disconnect parts. This is normal part of structural damage analysis.
3. The effects of loose parts contacting other parts is also normal part of structural damage analysis.
You may recall that NIST never did any stuctural damage analysis of WTC1/2 and that's the reason why the subject is still being discussed. NIST just suggested without any evidence that potential energy, PE, released (no calculations or explanations) due to gravity alone exceeded the available strain energy, SE, of the structure (no calculations) or PE>SE=global collapse.
I simply suggest that SE > 1000*PE and explain why in my papers. And then we have friction, PE lost by deflections, etc.
What NIST simply suggest is that if you drop something on a steel structure, the latter collapses!
Simple lab tests prove that wrong immediately. Drop anything on anything and see what happens! Or do my demonstrations for children. In most realistic cases the upper part just bounces.
This whole suggestion that a top part of a building suddenly drops is absurd. I have not seen any video of a top part of a building dropping free fall except WTC7 and for that to happen the whole bottom structure must have been removed! NIST agrees that WTC7 top part drops free fall ... and then they make structural analysis of this this!! However, no loads are acting on a free falling structure = all stresses are ZERO!
I really hope Obama will ensure that NIST makes a new attempt to explain its previous, funny findings. The previous attempt under Bush is just an embarrassing failure by Sunder & Clowns at the National Institute of Stupid Technicians, NIST.
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I agree that if you overload something, e.g. a roof or floor, it breaks at its weakest point (local failure).
I doubt very much that a sagging floor will pull a perimeter column inward. First of all there is too little load on the floor. Second, if there is load, the floor truss itself or its bolted connection to the column will fail first (local failures). Easy to prove by FEA or full scale test.
All explained in my papers that nobody has managed to debunk.
Fixed that for you.
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In a previous (and lengthy) exchange on this very subject Heiwa refused to acknowledge that there could ever be a horizontal component generated by debris falling under the influence of gravity. For example when a falling beam struck the corner of a still fixed beam.
It's perfectly clear that Heiwa is either devotedly trolling or unhinged, whether an (ex)"engineer" or not. That a troll would devote the time and energy to constructing such a complex website as his seems unlikely. Trying to engage in discussion with him directly is clearly futile, though onlookers might find some value in seeing his arguments destroyed.
leftysergeant
Penultimate Amazing
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You have assumed too much. You are assuming that the excess load will make the floor sag, and thus fail, only in the middle. You assume that the end connections would be able to hold greater weight than would the trusses themselves.
Those photos I have seen of perimeter columns with the truss seats showing indicated that the seats were forced downward and inward.
This is consistant with the failure of the floors having occurred at the seats on the perimeter columns. This would be consistant with the way the floor slabs in the Bouwkunde collapse failed. You still have not accounted for the effect of that debris which could not fall straight down because of the resistance of lower floors pushing out on the perimeter columns.
It would be absurd to assume that the shell could stand by itself. It is meant to flex in the wind, true enough, but it relies on the rest of the structure to maintain its shape.
You still have it being possible to build a supertanker that will never break up in high seas during a hurricane.
First of all, there was no explosion just before that picture was taken.
Second, this did not answer the question.
How can that floor truss stop the falling upper part of the building?
Sorry, I do not see any sagging floors on the pictures.
funk de fino
Dreaming of unicorns
No-one said you could. What pulled the columns in?
No, debris is just falling vertically due to gravity. No horizontal component there. Drop anything on something using gravity - test yourself.
Evidently if something is slooping 45°, the anything may bounce 90° leaving something intact, which just proves my point re bouncing and PE<SE.
If PE>SE there will be no bounce and something will continue vertically (0°).
Thanks for the kind words re website. Very popular - good feed back from visitors. I also get some good ideas via JREF.
If you find any errors of any kind on web site, pls send e-mail and I'll fix it.
Lennart Hyland
Muse
The lead designer for WTC, Leslie Robertson, agrees with NIST right? Well I think thats enough.