Acceleration of the falling top blocks.

[tsig]

Dave, I fixed your sentence, just like you fixed the two words in one of my posts where a letter was left out inadvertently.

With that aside, let's just say you have one of two legitimate ways forward. Either you go back and include the column resistance, or simply accept that your attempt to explain the constant acceleration as being possible due to natural circumstances didn't work out, and leave it at that.

No harm done unless you continue to claim a fatally flawed explanation, which does not include the most significant resistance, is still viable.

How much resistance does a buckled column have?

 

[ozeco41]

How much resistance does a buckled column have?

Exactly....

The top block was falling in the real world which Chandler et al measured.

So it was way beyond merely "buckled" - for every column.

 

[Oystein]

I thought my version was slightly more subtle.

Let's see if your version is more effective.

I tried subtle, anbd got ignored.
Plus, I was informed that subtle and not so subtle has been tried on Tony many times for long time before, also to no avail.

So maybe this now.

BTW Why do both "sides" of this discussion mix up Bazantian bits with Real World bits???

Because they can

But frankly, who on "our" side mixes up "Bazantian bits with Real World bits" in "this" discussion? I think you need to be careful not to "pour out the baby with the bath".

Tony brings in numbers from Bazant's consideration of column resistance and mixes that bit up with "real world", where columns were largely bypassed. So if he thinks that Bazantian bit informs us about real world with the result that resistance was at least nearly enough to arrest collapse, he is clearly mistaken and has misapplied Bazant.

These numbers, and Bazant's approach, are however good input for an inequality that applies in the real world: IF theoretical, Bazantian, resistance of columns did not exceed that which is necessary to arrest collapse, AND resistance of the structural elements that actually were affected by and yielded to momentum impact was significantly lower than column resistance by at least an order of magnitude, THEN it follows that, in the real world, actual structural resistance was insufficient to arrest collapse and the margin was at least an order of magnitude.

This conclusion can be arrived at by carefully applying Bazant's method and his numbers for the limiting case to observations. It could be derived from Bazant alone, if reasonable assumptions are allowed, but it cannot be derived from visual observations alone.

 

[Dave Rogers]

These numbers, and Bazant's approach, are however good input for an inequality that applies in the real world: IF theoretical, Bazantian, resistance of columns did not exceed that which is necessary to arrest collapse, AND resistance of the structural elements that actually were affected by and yielded to momentum impact was significantly lower than column resistance by at least an order of magnitude, THEN it follows that, in the real world, actual structural resistance was insufficient to arrest collapse and the margin was at least an order of magnitude.

So the conclusion is that we shouldn't criticize Tony so much. He's just fighting against inequality wherever he sees it.

Dave

 

[WTC Dust]

1) Wasn't intended to be a fully detailed explanation.
2) Yes
3) Actually I was describing the overall process. So where it began AND "has already started" are subsets of what I used the term for.

"began" is a confused term to use in that context. The key about those two times is that they are the times at which the collapses entered a stage of "visible in macro to a human observer". Draw up some better words if you don't like those ones.

The guts of the issue is "what event started the obvious to macro observation rapid collapse at those times." Again change the words if they don't convey the meaning.

So to your question "...what, in [my] mind, caused..."

To my mind the cascade failure had been progressing for some time prior to each of those two times. That process had reached the stage where the "last straw" would "break the camels back". OR, slightly less colloquially, the next bit of failure triggered the fall of the top block.

There were three main processes which I have regarded as possibilities as trigger mechanisms:

1) Inwards bowing of perimeter columns as identified by NIST;
2) Core failure which certain researchers on the 911Forum claim occurred before perimeter failure. I find much of the work of those researchers is persuasive as to technical facts. BTW they are generally on this forum regarded as "truthers".

Those two often referred to as "perimeter led initiation" and "core led initiation". I am agnostic on whether I prefer either of those or some other variant which would still become those two categories. Column failure was critical and there were only two groups of columns. Collapse initiation at the observed times you refer to involved failure of both sets of columns. And, to my mind, it matters not which went first.

3) Assistance by some malicious human intervention. I discount this possibility totally for a wide range of reasons - coming down from the strategic level of "Why do it" down through all levels of "How" - and resting on two premises 1) I cannot conceive of any reason or method AND 2) No-one of those claiming nefarious activity have ever, to my knowledge, put forward a comprehensive reasoned and supportable claim.

I have posted fuller explanations of the progress of a cascade failure on other forums - not all now still on line. It is a process which many engineers don't comprehend at much detail in my experience. And there is no way that we can say "Colum234 went first then column567 followed by column789 etc etc"

So, in your theory, what exactly caused all this weakening?

 

[WTC Dust]

An experiment: take several drinking straws, and wedge the end of one into the other until you have an assembly that looks like a yard-long straw.

Take this long straw, and see you long it will stand upright without you providing any support to keep it from tipping over.

That force that makes the straw tip over - the same force that made the "spires" collapse once their lateral supports (the floors) had fallen away - is called

Gravity.

The thing about gravity is that it didn't change significantly over the time period in question. So, at one moment, you have a building standing there. Then, at another moment, you have a building being destroyed. Gravity didn't do this.

 

[WTC Dust]

Your theory only seems to account for a detaching of the floors from the support columns. It doesn't seem to address the destruction of the support columns.

Tony! Argh!

I now not only highlighted but also boldfaced, italicised, underlined, magnified and colored the parts of your post that not just need reconsideration or improvement, but where you are
plain and fatally WRONG!!!

Tony, it is wrong, mistaken, erroneous, stupid to claim that column resistance slowed the collapse front. It didn't! The columns were largely bypassed,and that is easily observable at least in the case of the perimeter columns, which peeled off in large unbuckled sheets as the floors were sheared off on their insides.

The most important structural resistance to the avalanching floors was that of column-to-floor connections, which were orders of magnitude weaker than as-built (laterally fully braced) column strength.

Columns mainly suffered self-buckling subsequent to their loss of lateral bracing. All your values and claims about column resistance are wrong and do not apply.

Open your eyes, man!

 

[twinstead]

Your theory only seems to account for a detaching of the floors from the support columns. It doesn't seem to address the destruction of the support columns.

What exactly do you think should happen once the floors detach from the support columns?

 

[ozeco41]

I tried subtle, anbd got ignored.
Plus, I was informed that subtle and not so subtle has been tried on Tony many times for long time before, also to no avail....

been there done that - see the Column79 walk off thread where I pointed to the key problem back at post 151 and we are now at post 2046 and, despite a couple of acknowledgements of my point, the discussion is still playing within Tony's limitations.

...But frankly, who on "our" side mixes up "Bazantian bits with Real World bits" in "this" discussion? I think you need to be careful not to "pour out the baby with the bath"....

you could be right with the limit of "in "this" discussion?" - I'm so accustomed to all four positions on Bazant getting it wrong.

...Tony brings in numbers from Bazant's consideration of column resistance and mixes that bit up with "real world", where columns were largely bypassed. So if he thinks that Bazantian bit informs us about real world with the result that resistance was at least nearly enough to arrest collapse, he is clearly mistaken and has misapplied Bazant....

No doubt about that.

Not sure how far I go with you on this lot:

...These numbers, and Bazant's approach, are however good input for an inequality that applies in the real world: IF theoretical, Bazantian, resistance of columns did not exceed that which is necessary to arrest collapse, AND resistance of the structural elements that actually were affected by and yielded to momentum impact was significantly lower than column resistance by at least an order of magnitude, THEN it follows that, in the real world, actual structural resistance was insufficient to arrest collapse and the margin was at least an order of magnitude....

...my problem is not that you are wrong - you aren't - but that the finesse of understanding needed to support your line will near certainly be lost in the general run of forum discussion.

...This conclusion can be arrived at by carefully applying Bazant's method and his numbers for the limiting case to observations. It could be derived from Bazant alone, if reasonable assumptions are allowed, but it cannot be derived from visual observations alone.

I remain very nervous about "limiting case" material used in connection with "real world" UNLESS very explicitly stated clarification of the limits within which it is being used.

Preferably repeated four or five times. [/joke with serious point embedded]

 

[ozeco41]

So, in your theory, what exactly caused all this weakening?

Temperature lowering strength of some members>>>>some of those members go into overload and fail>>>>loads redistribute>>>>More members fail>>>>>more loads redistributed>>>>process goes exponential>>>>impact and fire zone weakens below level needed to support top block>>>>top block falls>>>>global collapse is inevitable given unique structure of Twin Towers.

 

[MarkLindeman]

Otherwise we are in "cloud cuckoo land" if that colloquialism is understood.

Is that an actual English phrase? We do have a "Wolkenkuckucksheim" in our language ("home of the cloud cuckoo")

It comes to both English and German -- and, I suppose, other languages -- from Aristophanes in The Birds. So it's a literary reference, like "utopia," but less familiar and more colorful.

By whatever name, many of the arguments about e.g. Bazant and Zhou do feel more like theological debates than scientific discussions. I don't think that is because anyone is predisposed to defend Bazant and Zhou (or the NIST report, etc.) as inerrant in the original manuscripts, but is more a reaction to truthers' obsession with Exposing The Lies In The Official Story. Regardless, it's a regrettable (but probably not very important) dumbing down.

 

[WTC Dust]

What exactly do you think should happen once the floors detach from the support columns?

I don't have a precise answer for your question, because I don't think floors detached from support columns. I'd like to know what YOU think destroyed the support columns after these floors supposedly detached.

 

[Oystein]

The thing about gravity is that it didn't change significantly over the time period in question.

Correct. Gravity didn't change. Something else did. Have you done the experiment?

One long very slender column made up of a number of individiual straws that are not laterally supported.

Vs. a singel straw.

Observe.
​

Then answer this:
What is different about the very long, slender straw column vs. the not so slender, long single straw?
(To help you with this, I left hints by applying some boldfacing)

So, at one moment, you have a building standing there. Then, at another moment, you have a building being destroyed.

And between those moments, there were many moments where a lot of things happened.

For example: Floors got stripped off of the columns. Did that change something important, in your opinion? (Hint: If you correctly identified the bolded parts in my previous reply as relevant to the answer, you might use them again!)

Gravity didn't do this.

Let's suspend judgement on this until after you have figured out successfully what happened to the straws before they buckled, and what may have happened to some columns before they buckled.

 

[twinstead]

I don't have a precise answer for your question, because I don't think floors detached from support columns. I'd like to know what YOU think destroyed the support columns after these floors supposedly detached.

Well, since your PhD isn't in engineering, I'll take your opinion that the floors didn't detach from the support columns with a grain of salt, if you don't mind. But, to answer your question...GRAVITY. I know you don't believe that, but pardon me if I want a second opinion.

 

[Oystein]

Your theory only seems to account for a detaching of the floors from the support columns. It doesn't seem to address the destruction of the support columns.

Yes, that's correct.

That's because destruction of the support columns wasn't a significant collapse mechanism of the main avalanche. Columns mainly buckled subsequently after they lost lateral bracing and with it, disproportionately, resistance to bucklimng. Do you know what happens to the load bearing capacity of a column when its laterally unsupported length, say, triples?

Have you ever observed videos of the collapses, and aerial photos of the rubble pile after the collapses? Have you noticed how very large sheets of perimeter columns never were "destructed" as in "were bent, broken, severed and fractured at every floor", and how they largely just tipped over? Only a few actual breals along their entire lengths. Before they hit the ground.

And have you never seen how a large proportion of the core remained standing for a while after the rest of the collapse had come to completion?

So in light of these observations of columns largely NOT suffering destruction during collapse, do you think my theory should account for columns largely suffering destruction during collapse, or NOT? (This time, I capitalized a couple of words to drop you hints about the correct answer)

 

[WTC Dust]

Temperature lowering strength of some members>>>>some of those members go into overload and fail>>>>loads redistribute>>>>More members fail>>>>>more loads redistributed>>>>process goes exponential>>>>impact and fire zone weakens below level needed to support top block>>>>top block falls>>>>global collapse is inevitable given unique structure of Twin Towers.

That's the official story, yeah. I heard it already, many times.

Thing is, I've done thousands of experiments that required consideration and manipulation of temperature. I know how hot office fires get, which isn't that hot compared to what it takes to weaken steel significantly.

You could have filled the WTC to the top with jet fuel and lit a match, and you'd end up with a horrible fire, but the steel would remain. Steel is a component of jet engines. If jet fuel fires could significantly weaken steel, you couldn't fly a jet engine. The steel parts would get all wonky from the temperatures.

You might move the blocks a bit and say, "Oh, but after ten minutes, any jet fuel would have burned out, so we are talking about an office fire." My response is that office fires don't burn hotter than jet fuel fires, so we are still stuck with a serious temperature deficit.

Then you might respond with, "But the building was also damaged by a plane crash." My response to that is that whatever happened earlier in the day, those buildings were standing tall afterwards.


The official story of fires and lopsided damage doesn't account for the initial moments of structural failure of the buildings.

 

[Oystein]

been there done that - see the Column79 walk off thread where I pointed to the key problem back at post 151 and we are now at post 2046 and, despite a couple of acknowledgements of my point, the discussion is still playing within Tony's limitations.

You don't have your rules for dealing with trolls for no reasons at all, I suppose

you could be right with the limit of "in "this" discussion?" - I'm so accustomed to all four positions on Bazant getting it wrong.

Sure I could

Not sure how far I go with you on this lot: ...my problem is not that you are wrong - you aren't - but that the finesse of understanding needed to support your line will near certainly be lost in the general run of forum discussion.

Well, I am addressing this mainly to Tony now, and since he is a seasdoned debater and experienced engineer, I am sure he is quite capable of getting it.

Eventually.





Ohhh aren't I the uncurable optimist

I remain very nervous about "limiting case" material used in connection with "real world" UNLESS very explicitly stated clarification of the limits within which it is being used.

Hmm since Tony imported Bazant's numbers for column resistance, perhaps he can take a shot at clarifying the limits of their applicability? Tony?

Preferably repeated four or five times. [/joke with serious point embedded]

 

[WTC Dust]

I can barely understand what you're saying. It really seems like an apology from a kid trying to hide what he did wrong.

I've seen the evidence you mention. At some point you might finally understand that I have been studying 9/11 diligently since the events occurred.

Yes, that's correct.

That's because destruction of the support columns wasn't a significant collapse mechanism of the main avalanche. Columns mainly buckled subsequently after they lost lateral bracing and with it, disproportionately, resistance to bucklimng. Do you know what happens to the load bearing capacity of a column when its laterally unsupported length, say, triples?

Have you ever observed videos of the collapses, and aerial photos of the rubble pile after the collapses? Have you noticed how very large sheets of perimeter columns never were "destructed" as in "were bent, broken, severed and fractured at every floor", and how they largely just tipped over? Only a few actual breals along their entire lengths. Before they hit the ground.

And have you never seen how a large proportion of the core remained standing for a while after the rest of the collapse had come to completion?

So in light of these observations of columns largely NOT suffering destruction during collapse, do you think my theory should account for columns largely suffering destruction during collapse, or NOT? (This time, I capitalized a couple of words to drop you hints about the correct answer)

 

[Oystein]

I don't have a precise answer for your question, because I don't think floors detached from support columns.

Why do you think so?

If floors never detached from support columns, then they were still attached on the ground. Is this what you observed?
(Alternatively, you could posit that they were never attached in the first place and levitated somehow...)

If floors did not detach from columns, what else detached from what - or did the whole structure just fold down?

I'd like to know what YOU think destroyed the support columns after these floors supposedly detached.

I don't think the support columns were destroyed. For reasons read my last reply to you.



So in essence, I think you got it all totally wrong, and the opposite of what you believe is true.

 

[ozeco41]

That's the official story, yeah. I heard it already, many times....

Not so. It is my explanation which is what you asked for. Whether or not it aligns with the "official version" is irrelevant to the question you asked and I answered.

The rest of your post is nonsense.