Would the WTC Twin Towers have collapsed from fire alone, without plane impact?

[Mendel]

The energy comes from the kinetic energy you built up as you fell.

Where does the kinetic energy come from?

 

[Mendel]

as far as i know everyone agrees if you drop a box on other cardboard boxes, the other boxes dont completely collapse.

I have had that happen when boxes don't align well. (Books are heavy.)

 

[Mendel]

The question is, How was the system broken? How were the parts singled out? What caused the system to stop working as a whole?

INITIATION vs PROGRESSION

the top block toppled, rotating, misaligned with the lower support structure, because the damage and the heat shifted the load onto elements which eventually gave way under the increased strain = initiation.

the falling top block fell unsupported onto the floor below, functionally removing it from the structure. Then onto the floor below that, etc = progression.

We have talked about this. At length.

 

[Henkka]

ps. you need to stop imagining this. that would be hard to imagine, that is Gage's cardboard box theory. but that is not what happened.

I will now defend Richard Gage's cardboard boxes, so help me God. That demonstration was widely ridiculed, but I think he made an important point, which I think I can illustrate better. See, what everyone found ridiculous about the example was his use of solid cardboard boxes. Obviously the tiny box couldn't accelerate through the larger box. But what if we visualized the problem with the "real thing", rather than cardboard boxes? I captured an image of an accurate 3D model of the core structure from this video:
Source: https://www.youtube.com/watch?v=Wkm0vm6_oTo


No-click policy: It's simply a clip from a documentary of a 3D model of the towers being constructed piece by piece, starting with the core, then the perimeter, and finally the floors.

I then photoshopped it to replicate Gage's cardboard box experiment:



Now, here's what NIST had to say about the collapse time of WTC 1:

31. How could the WTC towers collapse in only 11 seconds (WTC 1) and 9 seconds (WTC 2)—speeds that approximate that of a ball dropped from similar height in a vacuum (with no air resistance)?

And part of the answer goes:

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass."

https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-towers-investigation

So according to NIST, WTC 1 came down in 11 seconds, and was "essentially in free fall". But how long would free fall take exactly? Well, the buildings were about 415 meters tall, and from the website https://www.omnicalculator.com/physics/free-fall I get a fall time of 9.2 seconds from that height. So from that, we know that block A in my illustration would fall to the ground in about 9.2 seconds. But here's the problem... Block B needs to destroy all that stuff below it in 11 seconds, just 1.8 seconds more than it takes block A to fall to the ground. Can it be done?

 

[Thomas B]

INITIATION vs PROGRESSION

the top block toppled, rotating, misaligned with the lower support structure, because the damage and the heat shifted the load onto elements which eventually gave way under the increased strain = initiation.

the falling top block fell unsupported onto the floor below, functionally removing it from the structure. Then onto the floor below that, etc = progression.

We have talked about this. At length.

It's not clear to me how that made the lower section stop working as a system. I've tried to explain (at lenght) how I think the top block could just have been been impaled on the lower section and come to rest.

Not incidentally, however, the same strength would probably have prevented the complete separation of the top section from the lower section.

Where the strength was and how it was lost is a math problem that I'm trying to work out a load path diagram for.

Truthers explain it with pre-planted thermite and RDX.

 

[Mendel]

Block B needs to destroy all that stuff below it in 11 seconds, just 1.8 seconds more than it takes block A to fall to the ground. Can it be done?

a) How much energy is needed to "destroy"?
b) The core was not destroyed by the falling box (see the spire, and Gamolon's photo above).

 

[Mendel]

It's not clear to me how that made the lower section stop working as a system.

The floors transfer lateral forces, and brace the outer wall and the core. Once you destroy the floors one by one in the progression phase, the lower section structure is no longer intact.

 

[Mendel]

how I think the top block could just have been been impaled on the lower section and come to rest.

this requires the floors being impaled to carry the weight of the block, which they can't.

 

[deirdre]

But here's the problem... Block B needs to destroy all that stuff below it in 11 seconds, just 1.8 seconds more than it takes block A to fall to the ground. Can it be done?

no offense but im not going to trust your block A speed, just because i dont get how you figured out air resistance.

just remember that block b increasingly becomes a lot HEAVIER than block A ever will.

 

[deirdre]

this requires the floors being impaled to carry the weight of the block, which they can't.

i imagine by "impaled" he means they got hung up on the columns.

I've tried to explain (at lenght) how I think the top block could just have been been impaled on the lower section and come to rest.

but your top block is staying together in one piece right?

 

[Henkka]

no offense but im not going to trust your block A speed, just because i dont get how you figured out air resistance.

just remember that block b increasingly becomes a lot HEAVIER than block A ever will.

I think the website I used doesn't factor in air resistance... So block A is coming down in about 9.2 seconds in a vacuum. With air resistance, it would be a bit slower, but I have no idea how much. But NIST's recorded time for WTC 1 of 11 seconds was with air resistance obviously. So if both were in a vacuum, A should come down in 9.2 seconds, and B should destroy the structure below it in less than 11 seconds.

As for the second thing, uhh, heavier things don't fall faster than lighter things. Heavier things will certainly crush stuff faster, but A has nothing to crush, so it's already going at the top speed possible for a falling object in Earth's gravity (that isn't being pulled or pushed down by anything other than gravity).

 

[Thomas B]

this requires the floors being impaled to carry the weight of the block, which they can't.

Work this through, step by step, with math and you'll start to see where I'm at. Like I say, I'm working on this and I'll be sure to post my results when I have something interesting.

Basically, ROOSD/NISTFAQ has the entire weight of the top section coming down on only the floor connections of a single floor. I've got at least half of that load shifted onto the columns under the area of the floor pans (after it has shifted and rotated), and therefore shifted onto the floor connections of the floor above. I've then got floor pans piling up on those (lower) columns (in so far as the upper floor connections break) but those columns are of course designed to support that weight.

After about six floors have been sheared off the perimeter and cores this way, you've got a messy stack of "pancakes" impaled on about 280 columns of steel. with a little "hat" of floors on top.

Note: as I've said before, this silly image follows only from allowing that the collapse could even initiate. The same strength that I'm here positing to arrest the collapse after it initiated would, in reality, have prevented the process from starting.

 

[Gamolon]

So according to NIST, WTC 1 came down in 11 seconds, and was "essentially in free fall". But how long would free fall take exactly? Well, the buildings were about 415 meters tall, and from the website https://www.omnicalculator.com/physics/free-fall I get a fall time of 9.2 seconds from that height. So from that, we know that block A in my illustration would fall to the ground in about 9.2 seconds. But here's the problem... Block B needs to destroy all that stuff below it in 11 seconds, just 1.8 seconds more than it takes block A to fall to the ground. Can it be done?

NIST did NOT say WTC1 came down in 11 seconds? How did you get this so wrong?!

NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: (1) precise timing of the initiation of collapse from video evidence, and (2) ground motion (seismic) signals recorded at Palisades, N.Y., that also were precisely time-calibrated for wave transmission times from lower Manhattan (see NIST NCSTAR 1-5A).

From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.

 

[deirdre]

As for the second thing, uhh, heavier things don't fall faster than lighter things.

but its not a heavier object. its an object that gets progressively heavier as it goes. and its air cushion is different. i figured that messes up the acceleration calculations. but you could be right.

 

[Gamolon]

After about six floors have been sheared off the perimeter and cores this way, you've got a messy stack of "pancakes" impaled on about 280 columns of steel. with a little "hat" of floors on top.

Block B needs to destroy all that stuff below it in 11 seconds, just 1.8 seconds more than it takes block A to fall to the ground. Can it be done?

Ok.

Can we stop talking about the "the top block crushing the lower block" and deal in reality? Video evidence and photos show there was no 6 floor top block crushing the lower 98 floor bottom block in 11 seconds.

Explain in your own words what may have caused what we see in the photo below.

 

[Henkka]

NIST did NOT say WTC1 came down in 11 seconds? How did you get this so wrong?!

Well sure, I guess you can get pretty wildly varying times depending on when you determine the collapse "ended". And it's hard to measure exactly, since the dust cloud is in the way. But this is their wording, not mine:

Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass."

But we can bump up the collapse time to 15 or even 20 seconds if you want. I think there's still an intuitive problem there, that it's only a few seconds longer than a block that is literally falling through nothing.

 

[Gamolon]

What do you mean by the "floor", here? The layer of concrete supported by the trusses? The building was already holding up the mass of the top block, so I don't quite understand what you're asking here.

Not really... He said the kinetic energy of the top block would destroy the floor below. But in order to do that, the kinetic energy must decrease, and its equation is E = 1/2 * mass * velocity^2. Since the mass is obviously not decreasing, instead the velocity must decrease. Now, the unsaid thing in this discussion is that we both know the velocity of the top block of WTC 1 did not decrease, it accelerated. So you have to wonder, how did that happen?

You can think about it this way... When you jump into a swimming pool, your body displaces water, right? You push it out of the way as you become submerged. And pushing water requires energy. The energy comes from the kinetic energy you built up as you fell. This makes it so that you slow down, instead of continuing to accelerate to the bottom of the pool and breaking all your bones.

Do you see deceleration here?

 

[Gamolon]

Well sure, I guess you can get pretty wildly varying times depending on when you determine the collapse "ended". And it's hard to measure exactly, since the dust cloud is in the way. But this is their wording, not mine:

No, you got it completely wrong.

They CLEARLY did not say what you say they did. They did not say WTC1 collapsed in 11 seconds and even told you what fell in 11 seconds in the SAME ANSWER, but you ignored it and cherry picked what you wanted.

 

[Gamolon]

But we can bump up the collapse time to 15 or even 20 seconds if you want. I think there's still an intuitive problem there, that it's only a few seconds longer than a block that is literally falling through nothing.

If there was a "solid block" all the way down crushing the lower block like you think, then explain the photo in post #215.

 

[Thomas B]

Can we stop talking about the "the top block crushing the lower block" and deal in reality?

We're on the same page here, to an extent. I think we all feel that the idea of a "top block" crushing the lower section is absurd. It's just (to me) even harder to see how a "mass of falling debris" with no internal structure could do it.

 

[deirdre]

i just realized this is the "fire alone" thread. me thinks you guys are way off topic

 

[Henkka]

Ok.

Can we stop talking about the "the top block crushing the lower block" and deal in reality? Video evidence and photos show there was no 6 floor top block crushing the lower 98 floor bottom block

I agree. Now tell that to Zdenek Bazant, The American Society of Civil Engineers, Journal of Engineering Mechanics, and Wikipedia. The mainstream view is that an intact top block "crushed down" the underlying structure, and then "crushed up" itself.

 

[deirdre]

We're on the same page here, to an extent. I think we all feel that the idea of a "top block" crushing the lower section is absurd. It's just (to me) even harder to see how a "mass of falling debris" with no internal structure could do it.

so if someone dropped a 10' x 10' thousand pound concrete slab on you while you were sleeping, you think you would be crushed more than if they dumped a 1000lbs of broken up concrete on you?

edit: change that to 5000 lbs i just realized 10x10 is only 10lbs per foot.

 

[Gamolon]

We're on the same page here, to an extent. I think we all feel that the idea of a "top block" crushing the lower section is absurd. It's just (to me) even harder to see how a "mass of falling debris" with no internal structure could do it.

You mean to tell me you can't understand how a mass of 6 floors above can overload and shear the floor connections/seats/truss ends, circled in red in the photo below? You think all of these around the perimeter façade should have held up?

 

[Gamolon]

I agree. Now tell that to Zdenek Bazant, The American Society of Civil Engineers, Journal of Engineering Mechanics, and Wikipedia. The mainstream view is that an intact top block "crushed down" the underlying structure, and then "crushed up" itself.

We've already told you we don't agree with everything Bazant says (well some of us anyways). Why do you keep bringing him up?

 

[Henkka]

We've already told you we don't agree with everything Bazant says (well some of us anyways). Why do you keep bringing him up?

Okay, so... Why is the mainstream field of engineering lagging behind some Metabunk posters when it comes to understanding the most historically significant collapses of all time?

 

[Gamolon]

We're on the same page here, to an extent. I think we all feel that the idea of a "top block" crushing the lower section is absurd. It's just (to me) even harder to see how a "mass of falling debris" with no internal structure could do it.

Picture of a sheared/bent floor truss/seat (circled in red).

Does that look like explosives did that or something shearing it as it moved down ward?

 

[Gamolon]

Okay, so... Why is the mainstream field of engineering lagging behind some Metabunk posters when it comes to understanding the most historically significant collapses of all time?

My opinion?

It was explained to many people's satisfaction and many probably don't care for a more in-depth explanation. Most are satisfied that the "buildings came down due to plane impacts and/or unfought fires.

The only people I see debating this are small in number and are in internet forums. I NEVER have anyone bring this up to me outside of the internet forums.

 

[Gamolon]

Okay, so... Why is the mainstream field of engineering lagging behind some Metabunk posters when it comes to understanding the most historically significant collapses of all time?

And who is “the mainstream field of engineering”? Bazant?

Are you expecting the entire engineering field to publish things in order to appease a few laypeople and put what happened in easy to understand terms?

Just to clarify, my above comment was about the general public.

 

[econ41]

Okay, so... Why is the mainstream field of engineering lagging behind some Metabunk posters when it comes to understanding the most historically significant collapses of all time?

Mainstream engineering has addressed the WTC collapses to its satisfaction. In two possibly three strands. And the state of mainstream knowledge is another aspect that would benefit for you to understand if you ever choose to learn. These three strands are:
1) Academic formal discussion where Bazant was attempting to develop a generic model of high rise tower progressive collapse. That led to the dead end trail of Bazant & Verdure's "Crush Down/Crush Up" hypothesis which is not valid for "OOS" structures for reasons I 've already outlined for you.
2) Professional formal analyses by high profile Firms intended to support litigation; AND
3) Othe high rise constructions which have, like WTC in its time, pushed the frontiers of knowledge and practice.

None of those groups have the slightest interest in attempting to overcome the limited understanding or dishonesty of conspiracy theorists. Not all truthers have been conspiracy theorists. In the earlier era when I first became involved in explaining WTC collapse there were many genuine honest 9/11 truthers who simply did not understand the issues - specifically why the plane crash and fires caused Twin Towers to collapse without needing CD help. They were not obsessed CTs on a vendetta to prove the world wrong. They simply were genuine honest people who did not understand. It was a positive experience helping those genuine truthers learn. Most of those truthers - who were truly worthy of the label "truther" - have left the scene and we are left with mostly the conspiracy theorist remnant. Most "Truthers" still active are committed conspiracy theorists.

And there are different levels on the side of sceptics or debunkers. Even here on Metabunk there are differing levels of understanding and preferred styles of explanation....

So do you think traditional skyscrapers with evenly spaced columns can't undergo ROOSD? Only "tube-in-tube" structures?

"ROOSD" == "Runaway Open Office Spce Destruction" Runaway" == unstoppable progressive collapse. "Destruction" == should be obvious. AND "Open Office Space" == tube in tube. And despite your desperate attempts at denial and projection the ONLY ROOSD collapses to date have been the ONLY collapses of tube-in-tube designed buildings. So, at this time in history "ROOSD" means the "way the WTC Twin Towers collapse progressed"

Now to push the front edge of developing understanding I did, about 10 years ago, start a discussion with couple of serious debunkers to see if we could modify Bazant's CD/CU hypothesis which, as it stands is invalid for WTC Twin Towers and ROOSD, to see if the formula could be modified to deal with different column spacings. My colleagues opted out of debate as soon as they realised we were saying Bazant was wrong. Remember most debunkers have a "glass ceiling" - they believe that NIST and Bazant are infallible and the ultimate standards of truth. I don't for reasons I will rigorously support if anyone dares to challenge me.

 

[Gamolon]

So if you dropped the top 55 floors on the bottom 55 floors, they would maybe destroy each other simultaneously.

Explain why your logic above fails when using it to explain what happened in Mick’s video I linked above.

How come Mick’s structure didn’t arrest the downward motion of the dropped 3 floors/levels after destroying 3 floors/levels of the lower structure?

Where’s the deceleration of the upper section?

 

[benthamitemetric]

I mean an actual floor system as described by NIST in the calculation we've been talking about for three days. What would happen if you slowly loaded the mass of one of the upper blocks onto an actual single floor system in either tower?

Took a few hours away to get some work done and I just note that, @Henkka, you did not reply to this after I responded to your request for clarification. So, I repeat: What would happen if you slowly loaded the mass of one of the upper blocks onto an actual single floor system in either tower?

 

[econ41]

Sorry folks but I have an ongoing frustration and we need to get the issue "on the table".

Look at NIST's calculation again.

Why do so many debunkers persist in taking NIST as the ultimate authority when the physics of the collapse stands in its own right? Especially on issues where online debate among qualified debunkers has taken understanding forward from the NIST explanations written over a decade ago?

......and NIST's equations are so conservative because they do not even account for the massive amount of energy from the momentum of the fall...

IF debunkers stopped relying on the "authority" of NIST, Bazant et al and relied on the underlying physics which does not depend on whether or not the "authority" got the explanation correct.

We would bypass the legitimate confusion that this post of @Henkka's reveals:

Wrong answer. At the moment of impact, the kinetic energy of the falling mass was E = 1/2 * mass * velocity^2.

So @Henkka is correct. On both points. The NIST answer is misleading even tho, as NISTophiles we can generously excuse it as "conservatism" BUT why not simply remove the third party distraction? Referring to the NIST-induced confusion does not help move the discussion of @Henkka's concerns forward.

Both Oystein and I have explicitly explained the distinction between static loading, sudden loading and impact loading. And @benthamitemetric's post also explains it. @Henkka clearly understands the aspect of "impact loading" that NIST conspicuously avoided in FAQ #18 et simile explanations.

@Henkka correctly identifies the situation without the fog of excusing NIST's questionable explanation.

If the mass stays the same, what has to decrease in order for that mass to break apart anything below it?

........ and, sadly, once again Henkka avoids the obvious way forward. I may have said it once or twice! "Understand the actual collapse mechanism." "For the WTC Twin Towers". and "Stop derailing into false analogies re-Verinage.

 

[econ41]

Again, you can't just assert that when that's the whole dispute...

Your "whole dispute" is not the topic under discussion

Like a prosecutor telling the judge the defendant is guilty because he's a murderer.

Yet another false analogy.

So do you think traditional skyscrapers with evenly spaced columns can't undergo ROOSD? Only "tube-in-tube" structures?

Of course. It is true "by definition". Despite your attempts to re-define terminology.

And I've already posted a more extensive comment on the state of play wrt extending "ROOSD" to meet Bazant's earlier goal of developing a generic model. The big barrier >> "ROOSD" aka tube-in-tube collapses (both of the ones seen to date) is diametrically opposite to and incompatible with "1D approximation" >> a more complex issue we can discuss in another thread if anyone is seriously interested.

 

[benthamitemetric]

IF debunkers stopped relying on the "authority" of NIST, Bazant et al and relied on the underlying physics which does not depend on whether or not the "authority" got the explanation correct.

I am using NIST's simple calculation (1) because it is accurate on its face and (2) because it does provide a sufficient basis for understanding why the towers were doomed to total collapse given where their initial collapses triggered. And I don't see how that calculation induces any confusion. To the contrary, I think if Henkka and Thomas_B took the time to understand what it was saying as a practical matter, it would alleviate a lot of their confusion. I know you have a hobby horse of not relying on NIST and that's fine, but they did a lot of good work that can be relied on from time to time in the right contexts, and this is one of those contexts. All the calculation is missing is a disclaimer about how conservative it is, but that can be easily explained, as I have been doing.

If you want to go through and crank out a spreadsheet that estimates floor by floor how much energy was lost to breaking the structure versus how much was gained from the fall and the accretion of falling mass, etc., then go ahead. Because Henkka and Thomas_B do not yet understand NIST's simple calculation, I'm pretty sure that's what they are expecting to see if you keep going down that path (and, spoiler alert, they will then just say that you are still performing the calculations at too high a level of generality and abstraction anyway). But I think NIST is right that, if one understands the mass alone would cause the floors to fail even without any momentum, such an exercise is a waste of time as the ultimate conclusion is forgone, so I'm focusing on those first principles.

 

[econ41]

ooops @benthamitemetric You edited the post whilst I was considering whether to further derail the thread. I "liked" - actually "AGREED" your post in the original form even tho it lays out some nuance differences in our preferred approaches to these discussions.

BUT then you edited the post to add this You added this:

If you want to go through and crank out a spreadsheet that estimates floor by floor how much energy was lost to breaking the structure versus how much was gained from the fall and the accretion of falling mass, etc., then go ahead.

I thought you understood me better than that. I would be the last person to ever lay out detailed calculations when the issue in contention depends on more "strategic" or "big picture" issues of principle.

Because Henkka and Thomas_B do not yet understand NIST's simple calculation, I'm pretty sure that's what they are expecting to see if you keep going down that path (and, spoiler alert, they will then just say that you are still performing the calculations at too high a level of generality and abstraction anyway).

I'm not unaware of the behavioural and group dynamics issues.

But I think NIST is right that, if one understands the mass alone would cause the floors to fail even without any momentum, such an exercise is a waste of time as the ultimate conclusion is forgone, so I'm focusing on those first principles.

Actually, we agree on those points. They are not the cause of my concern.

 

[benthamitemetric]

I thought you understood me better than that. I would be the last person to ever lay out detailed calculations when the issue in contention depends on more "strategic" or "big picture" issues of principle.

I guess I'm lost as to how you can better illustrate the bigger principle that the towers were doomed than by showing convincingly that the mass of the top blocks alone would have destroyed the floors following the initial collapse event. At some point, the hypothesis that the collapse could have progressed via floor failures did need to be tested for plausibility against the reality of the building's construction and I think NIST's simple calculation is actually a very elegant way to perform that test. I still don't see any evidence that Thomas_B and Henkka actually understand the point, which is why I've been slow walking them right up to it. Maybe tomorrow they can wake up and realize why there is no "v" in NIST's simple calculation, however.

ooops @benthamitemetric You edited the post whilst I was considering whether to further derail the thread. I "liked" - actually "AGREED" your post in the original form even tho it lays out some nuance differences in our preferred approaches to these discussions.

Sorry, lawyerly force of habit to keep refining if given the chance.

 

[econ41]

I guess I'm lost as to how you can better illustrate the bigger principle that the towers were doomed than by showing convincingly that the mass of the top blocks alone would have destroyed the floors following the initial collapse event.

Without dragging this sideline discussion out too far. The technical fact of the cause of rapid progression is not in dispute. The "falling material missing columns and landing on floors" issue was the biggest misunderstanding that derailed debate for many years - 2001 to about 2009-10 then tapering off as the true explanations became more understood. The confusion affecting "both sides" as the debate polarised into two sides.

The leading cause of confusion was Bazant & Zhou's "Limit Case" paper of 2001-2. Many from "both sides" took the "Top Block" dropping to impact with columns aligned as what literally happened. It didn't. It was about 2009-10 before on-line debunker prevailing wisdom came to grips with that central factor that we - you and I - now in this discussion - are agreed on. The weight of falling material, once the process was established, was sufficient to shear the floor to column connections. Even if placed there as a "suddenly applied load" without the overwhelming effect of dynamic impact.

But that simplistic explanation does not address how the process got started. How the Top Block dis in fact break up at the start and not at the end as asserted by Bazant & Verdure. Or why the collapse progressed at 2/3rds "g" - tho several early researchers has done the momentum calculations. More had identified the "debris missed the columns" but no-one was explicitly putting those separate issues into one coherent explanation. many mo

At some point, the hypothesis that the collapse could have progressed via floor failures did need to be tested for plausibility against the reality of the building's construction and I think NIST's simple calculation is actually a very elegant way to perform that test.

I understand and respect your preferred perspective. The issues of plausibility have been explored in some depth over the past 12 years in several forums.. Sadly much of the expertise not quite up to the level of the challenge. My last serious attempt to reconcile the irreconcilable - the gap between what happened (ROOSD) and Bazant's efforts (CD/CU) - was about 2013. Same issue as we see now - there were objections to me asserting that Bazant was wrong. I've never found an error in NIST's work but I disagree with some of their style choices - as per this occasion. (I would have put in the disclaimer on FAQ #18 - identifying the missing option of impact loading and explicitly explaining why the argument was conservative. At the least it would have saved engineers like me the need to fret and fume about the blatant missing bits every time I read it. ) ( The Bazantophiles could have lynched me when I first identified those couple of Bazantian errors. )

I still don't see any evidence that Thomas_B and Henkka actually understand the point, which is why I've been slow walking them right up to it. Maybe tomorrow they can wake up and realize why there is no "v" in NIST's simple calculation, however.

I think the reality is that they are determined to remain down a rabbit burrow. and will switch rabbit burrows every time someone posts a sound explanation or rebuts one of their claims. (Remember the reason I OPed this thread - to pressure for "on-topic" dioscipline. I was optimistic. that explicitly stated goal didn't survive the first few posts. )

Sorry, lawyerly force of habit to keep refining if given the chance.

No problem. Remember I'm a half trained lawyer myself - got the degree but no practicing certificate and never practiced. My pedantry comes more from my public sector senior bureaucrat roles plus a bit from military experience.

 

[Mendel]

i imagine by "impaled" he means they got hung up on the columns.

yes
and then the connection to the rest of the block break off because it's too heavy
it doesn't really matter which side of the connectors the weight is on, though I do imagine that the performance might well be worse in the opposite direction

if you impale a floor,
that floor now has to hold the whole top block up

but that top block is attached via the floor connectors

and we know from NIST FAQ #18 that they won't hold the weight

which means the floor gets separated, broken, and cascades down

as do the next 6 floors

ROOSD ensues

 

[Thomas B]

You mean to tell me you can't understand how a mass of 6 floors above can overload and shear the floor connections/seats/truss ends, circled in red in the photo below? You think all of these around the perimeter façade should have held up?

In the falling block scenario, I'm imagining 6-12 floors entangled in each other around the collapse zone, after which the process stops.

In the falling debris scenario, I'm imagining the mass dissipating as the individual pieces hit the floor pans without immediately breaking the floor connections, until enough pieces accummulate on each floor to overload it.

Not knowing how to do the math, I can only say I've got a feeling it would take less than 12 floors before there's not enough mass above the next floor to arrest the collapse, especially since the columns would also have a chance to put up a fight against floor pans that are presumably intact above the falling "front" of debris.

(But the fluid behavior of the debris front in the ROOSD model isn't very clear to me. As I understand it, its a region of highly "chaotic" forces.)

In both cases, you'd end up with a tangled mess near the top of a now 100-story building.

Picture of a sheared/bent floor truss/seat (circled in red).

Does that look like explosives did that or something shearing it as it moved down ward?

I don't think anyone would argue that if explosives were involved then there wouldn't also be a lot of mechanical (gravity-induced) damage.