Failure mode in WTC towers

[Newtons Bit]

You don't know your behind from first base about engineering and are obviously not in any position to judge who is right here. The fact that you are willing to go out on a limb and say something like this exposes the fact that your bias has no basis.

He asked you to take one of our statements and de-construct it. Please use diagrams and, if you desire, full context quoted resources - just scan the whole page. Or are you unable? It's a simple question.

You've backed yourself into a corner and said that the beam-column connections can't rotate. This is b.s. on two levels. First the beam-column connections in moment frames can rotate, I've already posted a finite element model that shows that.



Notice how the beam and column are at right angles, and yet they are not level, they've rotated. The second b.s. item that you've just posted is that the core columns are fixed end connections.

It is absolutely incredible that you use the towers swaying in the wind to claim the core columns could rotate due to floor loads when they were fixed end conditions restrained at both ends.

The core columns are not fixed at any end, anywhere. That's a stupid waste of money. The core columns are pinned at their foundation, they are pinned with simple shear connections to the floor slabs and they are FREE at the roof. And don't even start with your moronicy (can I invent a word?) about how the floor slab braces them. There is no positive connection between the floor slab and the core columns as there are no shear studs protruding from the columns to the floor slab. It is also standard practice to block out the floor slab around the column and put in construction joints so as to prevent cracking at the columns. Even then, the floor slab would never be able to generate even a thousandth of the required moment capacity to resist the columns from moving.

And yes, the core columns would rotate, a very small amount, due to eccentric vertical reactions. The perimeter columns would rotate slightly more as they are completely unbalanced.

 

[Max Photon]

Mo Rons? Dat ain't good.

I'm not ashamed to confess that a "Dummies" or "Idiots" introduction to engineering would be most welcome. (I once told a clerk at Border's that I find the "Dummies" books too challenging and the "Idiots" books too simple--was there something written specifically for "Morons"?)

Just for Morons

 

[Max Photon]

Do perimeter columns experience moments?

Is this correct?

Realcddeal is saying that vertically plumb perimeter columns, attached to fully intact, non-sagging floor trusses, experience axial loads, but do not experience significant moments.

The rest of you are saying realcddeal's claim is idiotic, and that in the real case of the WTCs, the perimeter columns do indeed experience significant moments, but the moments are sub-critical to the structure, and are harmlessly distributed via columns splice bolts and truss seat connections (and spandrels?).

Max

 

[Gravy]

Is this correct?

Realcddeal is saying that vertically plumb perimeter columns, attached to fully intact, non-sagging floor trusses, experience axial loads, but do not experience significant moments.

When I first read the last page a while ago, that's also what I thought, but it appears that realcddeal is referring only to the core columns.

 

[Gravy]

Actually, Gravy, that's a non sequiter.
That situation is true, but has nothing to do with the discussion under way.
Realcddeal is thinking local and applying it globally... (if it works for a 2X2 array, it works for an NXN--analysts will understand that one...)

ETA--I see you corrected. Thank you, sir.

I'm a strange editor. I need to actually make a post before it registers that I've made a mistake. It's not enough for me to preview a post. I have to hit the "Enter" key. I had a roommate like that once. Every single workday she would leave the apartment and as soon as she shut the door behind her she'd charge right back in and grab the thing she'd forgotten. Of the several hundred days we lived together, I'd say there were probably 20 in which she didn't have to close the door behind her to remind herself of something. The human brain is marvelous.

Conspiracists can't comprehend the fact that I have spent by FAR the most "debunking time" in debunking myself, because I'm interested in getting things right. They hate the idea that a layman who's not under the influence of an MKULTRA mind-control program would actually want to learn stuff. I debunk myself many times a day. Although I may not show it often, you and others here have taught me SO MUCH about how to think.

 

[gumboot]

I debunk myself many times a day.

Is that healthy? Something might fall off.

 

[Heiwa]

13. Once the upper block gets moving, the dynamic load exceed the carrying capacity of the structure, and total collapse ensues.


ETA: If anyone wants to reword this and repost it, please feel free.

I would reword 13. as follows.

Once the upper block gets moving due to buckled columns (local failures) in the initiation zone below, the upper block moves down a little and comes to rest on the buckled structure still connected to the structure below (and equilibrium is reinstated). Evidently the load carrying capacity of the intact structure below is sufficient to carry the upper block (as it did it before some columns buckled). No total collapse ensues.

 

[Dave Rogers]

I've been rather disengaged from this thread due to illness (nothing major), so I've got a bit of catching up to do. Sorry for the compound post but there are several comments I wanted to reply to.

I for one have not pushed explosive or thermite demolition, but don't be silly. Explosives or thermite can fail any structural component just as well as a "NIST fire".

Explosives can cause point failures, but they can't cause softening and sagging. Arguably, neither can thermite, because it burns too hot; it's either melt the steel or nothing. I have a hard time envisaging any explosive or thermite related mechanism that could cause the perimeter column bowings, and I've yet to see anyone propose a viable one.

First, you are assuming the collapse floor only fell 12 feet in a 2 second time frame during the inward pull of the perimeter columns. That assumption isn't supported anywhere. The 12 foot drop of the antenna by that amount when it was 140 feet further up is not indicitive of the exact fall of the collapse floor and the core columns they were attached while the perimeter columns were being pulled inward.

By the way, the core was 137 x 87 feet and with the 209 foot square building with 14 inch square perimeter columns at each side the floor trusses were 35 and 60 feet long.

Putting aside the truly inconsequential nitpicking, your reference for the prior fall of the antenna is: http://911research.wtc7.net/wtc/evidence/videos/wtc1_close_frames.html
The text on that page reads: "The radio tower descends about 10 feet relative to the facade." The time given is two frames in the sequence rather than two seconds; the actual time spacing is one second, so that was the only error I made. Since your own source gives a 10 foot drop, I could perhaps be forgiven for assuming a greater drop - which favours your hypothesis - in evaluating the conclusions you drew from it.

As for the fall of the antenna not being indicative of the fall of the floors where bowing took place, if that's the case then you require that the core must have been severed at two places at least - one below and one above the region where the perimeter columns bowed inwards - and that for some reason the upper and heavier part of the core fell more slowly than the lower and lighter part. Any ideas why that should have happened?

For your paper on the antenna drop, try not to come up with too high a value, because that'll leave you with a tough choice: do you try and explain away the fact that the perimeter columns didn't bow inwards above the initiation zone, or do you hypothesise that all the floor trusses from the initiation zone to the roof were severed at the beginning of the drop? I'll await your conclusions with mild interest.

I still stand by my rejection of your conclusion that the collapses required assistance. You have made two implicit assumptions in reaching it: firstly, that collapse cannot initiate unless the global safety factor falls below unity, and secondly, that the only relevant property of the columns is the resistance to purely compressive stress. The former amounts to an assumption that (a) the structure redistributes loads perfectly whatever the damage profile, and that (b) progressive failure cannot occur. The latter amounts to an assumption that there are no lateral forces on any columns, and is incidentally incompatible with the former. Since the observed collapse was initiated by a progressive failure begun by lateral forces on the perimeter columns, your line of reasoning therefore reduces to: If we eliminate the entire class of phenomena that includes the actual cause of collapse, then we cannot hypothesise a viable alternative cause of collapse. This is logically defensible but utterly irrelevant.

Thanks Ryan!

Here's the new, improved summary:

1. Jets destroyed perimeter and core columns;
2. Jets dislodged SFRM;
3. Fires heated poorly-protected floor trusses;
4. Heated floor trusses expanded and sagged;
5. Heated core columns experience creep and thermal shortening;
6. Action of hat trusses redistribute load away from the cores to the perimeter columns
7. Sagging floor trusses exerted catenary forces on perimeter columns;
8. Contracting floors after local burnout accentuate pull-in forces, particularly along long-span trusses;
9. Catenary forces caused perimeter columns to bow inward;
10. The eccentricities of inward bowing perimeter columns exceeded the moment capacity of the column splice bolts, causing the bolts to fail;
11. The dominant failure mode for inward bowing columns was to separate and pivoted at the failed splices;
12. However, there were cases of bowing and buckling in less than three-story lengths. (Bowing at initiation, for instance, was spread through many "waffle sections," and since these were staggered, the bowing was sometimes greatest near connections, and sometimes in the middle.)
13. Once the upper block gets moving, the dynamic load exceed the carrying capacity of the structure, and total collapse ensues.

Sounds reasonable enough to me, but I'm not a structural engineer so there may be details I've missed.

Dave

 

[Heiwa]

Do perimeter columns experience moments?

Is this correct?

Realcddeal is saying that vertically plumb perimeter columns, attached to fully intact, non-sagging floor trusses, experience axial loads, but do not experience significant moments.

The rest of you are saying realcddeal's claim is idiotic, and that in the real case of the WTCs, the perimeter columns do indeed experience significant moments, but the moments are sub-critical to the structure, and are harmlessly distributed via columns splice bolts and truss seat connections (and spandrels?).

Max

As the floors are in principle hanging on the columns via a pin joint, no moment is transferred to the column! Just the weight of the floor adjacent to the column is transferred as shear via the pin joint to the column, where it adds to the compressive load in the column.

If the connection of the floor to the column is not a pin joint, i.e. the floor cannot rotate freely at the joint, then evidently a moment is transmitted into the column. But that was not the case in the WTCs. The floors could rotate freely vis-à-vis the columns = no moment was transmitted. So Realcddeal is right.

Quite basic, actually. Any more questions?

 

[pomeroo]

As the floors are in principle hanging on the columns via a pin joint, no moment is transferred to the column! Just the weight of the floor adjacent to the column is transferred as shear via the pin joint to the column, where it adds to the compressive load in the column.

If the connection of the floor to the column is not a pin joint, i.e. the floor cannot rotate freely at the joint, then evidently a moment is transmitted into the column. But that was not the case in the WTCs. The floors could rotate freely vis-à-vis the columns = no moment was transmitted. So Realcddeal is right.

Quite basic, actually. Any more questions?

Why are you incapable of learning anything?

 

[DGM]

As the floors are in principle hanging on the columns via a pin joint, no moment is transferred to the column! Just the weight of the floor adjacent to the column is transferred as shear via the pin joint to the column, where it adds to the compressive load in the column.

If the connection of the floor to the column is not a pin joint, i.e. the floor cannot rotate freely at the joint, then evidently a moment is transmitted into the column. But that was not the case in the WTCs. The floors could rotate freely vis-à-vis the columns = no moment was transmitted. So Realcddeal is right.

Quite basic, actually. Any more questions?

So the exterior of the building would sway independent of the core.

 

[pomeroo]

Just for Morons

Nice try, but Blanchard is still the bright guy and you're, well, not as bright.

 

[funk de fino]

Threads like this are normally the ones I like the most because I learn a lot of stuff from the postings by NB, Dave R, rwguinn, R Mackey, GU, Gravy etc etc

Unfortunately they are generally always have to be spoiled by trolling posters like Heiwa and realdcdeal et al who display an inability to display any level of understanding of what they post about (which is obvious even to the layman)

Is there any way these could be structured so that only the relevant players could be involved that keeps the chaff and flare from the trolls out?

 

[Apollo20]

Funk de fino:

This is a site to debate conspiracy theories. Without conspiracist's posts we would have the converted preaching to the converted. That would belong on a site like Physorg don't you think!

 

[funk de fino]

Funk de fino:

This is a site to debate conspiracy theories. Without conspiracist's posts we would have the converted preaching to the converted. That would belong on a site like Physorg don't you think!

Appollo, I appreciate that, but I do not mind reading threads by Christopher 7, Gregory, Einsteen or even Max Photon etc. It just saddens me to see threads like this that I learn so much from (including threads where you post) spoiled by the incompetants that seem to also inhabit this site.

If this was my thread I would be sure hosed at some of the guff that has been thrown into it by people who do not know better.

Does every thread in this forum have to hijacked by trolls who know nothing?

 

[Newtons Bit]

Why are you incapable of learning anything?

Wow, Heiwa and Mr. Szamboti are crazy. Heiwa says that moment can't be induced in a core column because the reaction is pinned, and Mr. Szamboti says that moment can't be induced because they're fixed connections. I guess you can't ever have moment induced in columns.



Especially not in connections that look like the above, nope never (/sarcasm).

 

[Newtons Bit]

Appollo, I appreciate that, but I do not mind reading threads by Christopher 7, Gregory, Einsteen or even Max Photon etc. It just saddens me to see threads like this that I learn so much from (including threads where you post) spoiled by the incompetants that seem to also inhabit this site.

If this was my thread I would be sure hosed at some of the guff that has been thrown into it by people who do not know better.

Does every thread in this forum have to hijacked by trolls who know nothing?

Oh no, realcddeal actually knows a few things about engineering. He's at least familiar with the terminology, which baffles me since he screws up every concept. I'm of the conclusion that he's doing it intentionally, which of course makes him a troll.

 

[Dave Rogers]

No, I did not, it's standard. But it's quite entertaining.

Are you sure it's a standard fallacy? I googled "unevaluated inequality" and only got a couple of hits, one to the post above and the other (indirectly - I had to dig a bit) to a post of mine in January. To be honest I thought it was a term I'd created myself to describe the standard truther "I don't know what it ought to look like but it shouldn't look like that" argument.

Dave

 

[tsig]

I'm sure you're completely correct, but I remain puzzled. He can pontificate to his heart's content on twoofer sites. He will be addressing the dumbest, most uncritical fools on the planet. Such dunces will swallow anything and he can bask in their adulation, a la David Griffin. Why come here and be slapped down by people who understand that he is a know-nothing? What's in it for him? Can he tell the imbeciles on 911blogger that he invaded the JREF and got crushed again? He can do what they all do and proclaim victory, but what if someone takes the trouble to check?

Answered your own question. When have you ever known twoofers to bother to even click on a link to check a fact much less google.

All he as to do is assert" I went ta JREF and made 'em my punks" and they will believe.

 

[Gravy]

Funk de fino:

This is a site to debate conspiracy theories. Without conspiracist's posts we would have the converted preaching to the converted. That would belong on a site like Physorg don't you think!

I suggest you check who was posting here from March-August, 2006. I have. There were almost no conspiracists participating, yet what a lot of learning was accomplished!