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Old 11th May 2016, 08:45 AM   #81
JSanderO
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Whatever was "colliding" in the twin tower events/collapse when the visible movement began... was structures whose meeting interface was more of less of the same strength... Smash two cereal boxes together... they are equally crushed where the collide.. or two the same cars... and so on.

This is some basic it's amazing that this has become a meme that a PhD in engineering feels merits a research paper. And the internet will discuss it ad infinitum.

Waste of time.
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Old 11th May 2016, 04:42 PM   #82
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Originally Posted by JSanderO View Post
Whatever was "colliding" in the twin tower events/collapse when the visible movement began... was structures whose meeting interface was more of less of the same strength... Smash two cereal boxes together... they are equally crushed where the collide.. or two the same cars... and so on.

This is some basic it's amazing that this has become a meme that a PhD in engineering feels merits a research paper. And the internet will discuss it ad infinitum.

Waste of time.
Agreed like arguments about why you don't load a giant bulldozer into a pickup truck.The Biggest Bulldozer in The World - Komatsu D575A: http://youtu.be/JNjH3FLemIQ
Fast forward to 220.
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Old 11th May 2016, 08:30 PM   #83
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Originally Posted by JSanderO View Post
Whatever was "colliding" in the twin tower events/collapse when the visible movement began... was structures whose meeting interface was more of less of the same strength... Smash two cereal boxes together... they are equally crushed where the collide.. or two the same cars... and so on.

This is some basic it's amazing that this has become a meme that a PhD in engineering feels merits a research paper. And the internet will discuss it ad infinitum.

Waste of time.
I've pointed that out a time or three. Just shows that even skeptics and professional scientists have a vital need to be "right" and win, dammit!
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Old 11th May 2016, 09:38 PM   #84
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Originally Posted by JSanderO View Post
Whatever was "colliding" in the twin tower events/collapse when the visible movement began... was structures whose meeting interface was more of less of the same strength... Smash two cereal boxes together... they are equally crushed where the collide.. or two the same cars... and so on.

This is some basic it's amazing that this has become a meme that a PhD in engineering feels merits a research paper. And the internet will discuss it ad infinitum.

Waste of time.
The "dropping to impact" and therefore "colliding" probably the two most embedded memes.

....and both of secondary importance at best.

Imagine how WTC collapse understanding may have progressed faster if Mr Zhou had not been studying for PhD ...
...and Mr Szamboti had needed to look for another false foundation for his "magnum opus" paper.
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Old 12th May 2016, 02:41 AM   #85
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Originally Posted by JSanderO View Post
Whatever was "colliding" in the twin tower events/collapse when the visible movement began... was structures whose meeting interface was more of less of the same strength... Smash two cereal boxes together... they are equally crushed where the collide.. or two the same cars... and so on.

This is some basic it's amazing that this has become a meme that a PhD in engineering feels merits a research paper. And the internet will discuss it ad infinitum.

Waste of time.
And you're wrong about this, when the collision is vertical & the structure is like the WTC.
And Ozeco is wrong, too.

I'm a little too busy to write up why, but I'll get to it in a couple of days.

A vertical collision bears little resemblance to a horizontal collision.

If you, or Oz, were to bother to re-read my original post, and take a few moments to think about what I wrote, and try to address the points, you might come to figure out for yourself why you're wrong.
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Old 12th May 2016, 02:52 AM   #86
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As every competent engineer has pointed out, many times, not only is the detail of collapse after it started unknown and actually unknowable with current capabilities, it is unimportant, other than to provide fodder for all those pompous folks who obviously are more into being right ( which carries a strong "you're wrong, you unintelligent, incompetent idiot" factor along with it.
Trying to model 3x10^23 simultaneous equations with 3x10^23 +18 variables just us not possible, and one description is just as good as (and probably actually included in) another.
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Old 12th May 2016, 08:36 AM   #87
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Of course as the process evolved after the initial mechanical collisions... a dissociated mass began to grow and it thus growing mass was what raced down through the tower destroying all the floor slabs in its path to the ground. The collisions were no longer that of equal cereal boxes...
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Old 12th May 2016, 09:54 AM   #88
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Originally Posted by JSanderO View Post
Of course as the process evolved after the initial mechanical collisions... a dissociated mass began to grow and it thus growing mass was what raced down through the tower destroying all the floor slabs in its path to the ground. The collisions were no longer that of equal cereal boxes...
The collisions were never like boxes, boxes don't have multiple connections or parts.
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Old 12th May 2016, 10:08 AM   #89
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Originally Posted by Crazy Chainsaw View Post
The collisions were never like boxes, boxes don't have multiple connections or parts.
I was using an analogy... the initial meeting of the top and bottom was of materials and components of similar strength... as the destroyed material moves down... it is of a different nature... a collection of bits and pieces which grows with each floor collision... that is

mass of bits and pieces smashes into neat flat thin slab and destroys slab likity split. Bits and pieces get more ground up with each floor impact... generating finer granule size... Mass is growing... floors remain same 4.5" slabs.
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Old 12th May 2016, 04:34 PM   #90
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Originally Posted by tfk View Post
And you're wrong about this, when the collision is vertical & the structure is like the WTC.
And Ozeco is wrong, too.
Wasn't my claim - I'll leave it to Sander.
Originally Posted by tfk View Post
I'm a little too busy to write up why, but I'll get to it in a couple of days.
I'll await any response from you addressing my reasoned explanation and the facts I identified in support of my assertion re validity of CD/CU. The facts are are the critical aspect - the logic is trivial.
Originally Posted by tfk View Post
A vertical collision bears little resemblance to a horizontal collision.
??? Not my issue.
Originally Posted by tfk View Post
If you, or Oz, were to bother to re-read my original post, and take a few moments to think about what I wrote, and try to address the points, you might come to figure out for yourself why you're wrong.
I read it when first posted and analysed your argument relative to the real event and my explanation of the CD/CU claim I am supporting.

Your alternative claim:
1) Adopts a narrower scope which does not address EITHER the objective of this thread OR my specific claim;
2) You "beg the question" in that your starting scenario assumes the conclusion you want to derive;
3) The level of detail you provide is not relevant for several reasons. One of which is that any maths calculations within an assumed scenario will by definition "prove" the assumption;
4) In logic structure you are making the same error as T Szamboti made with "Missing Jolt" - assuming your conclusion in your starting premise THEN wandering around a circle to "prove" your starting point.
5) Your reasoning and your conclusion directly oppose Bazant's limit case as per B&Z 2002.

And my statement of the relationship of the issues does not fall into that trap. So to falsify my explanation you need to prove that my assertions of fact are wrong OR that my logic linking them is wrong.
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Old 12th May 2016, 04:56 PM   #91
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Originally Posted by rwguinn View Post
As every competent engineer has pointed out, many times, not only is the detail of collapse after it started unknown and actually unknowable with current capabilities,
Fully agreed - that is why I rarely if ever try to "work up from details".
Sadly most truthers and many debunkers are not proficient in arguing from the known bigger picture issues and descending only as deep as is necessary into details. For what should be non-contentious refer to my many posts over about 6 years identifying that common fault with Major_Tom's arguments. (A lack of issue taxonomy amounting to a "flat earth" argument - all issues assumed to be at the same level - ignoring or with M_T denying the reality that some "lower level issues" are part of some "higher level issues".) And - for whatever reasons of history - it is a common limitation seen in engineers and accountants (those who tend to be "left brain" biased) - who do not - cannot think outside the limits of the "nine dots" or the text book routine method or the calculator/FEA
Originally Posted by rwguinn View Post
it is unimportant,
Maybe to you and many other members - those who often refer to "4 planes and 19 terrorists" or similar "high level" picture. True obviously at that level. But there are many who are interested in details - and - of course - this thread arose out of such an interest. A difference of opinion over identification of a collapse mechanism. Bottom line - if you are not interested why play "dog in the manger" to those who are?
Originally Posted by rwguinn View Post
other than to provide fodder for all those pompous folks who obviously are more into being right ( which carries a strong "you're wrong, you unintelligent, incompetent idiot" factor along with it.
My SOP/ROE's for posting for many years - I ignore insults, snide comments and usually ignore lies by innuendo and similar debating tricks when they appear to be intentional. Not simply lack of knowledge or understanding.
Originally Posted by rwguinn View Post
Trying to model 3x10^23 simultaneous equations with 3x10^23 +18 variables just us not possible,
Same issue as first point commented on. I agree - that is why - one of several reasons - why the lead with calculations or FEA "Technician Engineer's Approach" is futile.
Originally Posted by rwguinn View Post
and one description is just as good as (and probably actually included in) another.
Good point. Can I take it that you spotted that tfk's OP "alternate claim" is a narrow subset - "actually included in" (And actually rebutted by) my explanation?
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Old 12th May 2016, 08:46 PM   #92
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Originally Posted by ozeco41 View Post
Fully agreed - that is why I rarely if ever try to "work up from details".
Sadly most truthers and many debunkers are not proficient in arguing from the known bigger picture issues and descending only as deep as is necessary into details. For what should be non-contentious refer to my many posts over about 6 years identifying that common fault with Major_Tom's arguments. (A lack of issue taxonomy amounting to a "flat earth" argument - all issues assumed to be at the same level - ignoring or with M_T denying the reality that some "lower level issues" are part of some "higher level issues".) And - for whatever reasons of history - it is a common limitation seen in engineers and accountants (those who tend to be "left brain" biased) - who do not - cannot think outside the limits of the "nine dots" or the text book routine method or the calculator/FEA
First, a little background--for most of my career i specialized in analysis of structural systems due to dynamic responses and random/transient events. It is ingrained, part of my DNA, if you will, to refuse to look at individual components as stand-alone items until the function of the overall system is resolved. They are all part of a system of some sort. Only when analysis shows where a failure is likely to occur, or when the system is not performing in simulation the way it needs to do I truly delve into the detail
Quote:
Maybe to you and many other members - those who often refer to "4 planes and 19 terrorists" or similar "high level" picture. True obviously at that level. But there are many who are interested in details - and - of course - this thread arose out of such an interest. A difference of opinion over identification of a collapse mechanism. Bottom line - if you are not interested why play "dog in the manger" to those who are?
At one point, I loved "Science Projects",and to a certain extent, still do. But experience has shown to me that some of them are not possible to obtain a singular and definitive solution, and that the idiots will glom on to any perceived discrepancy and restart the whole damn thing all over again, and numerous engineers who should know better will move heaven and earth to "Prove" you/me wrong. Call it my interfering in somebody's troll perpetuation project.

Quote:
My SOP/ROE's for posting for many years - I ignore insults, snide comments and usually ignore lies by innuendo and similar debating tricks when they appear to be intentional. Not simply lack of knowledge or understanding.
I wasn't necessarily referring to you in particular,as there are numerous more blatant offenders out there, and I'm glad you recognized the intent
Quote:
Same issue as first point commented on. I agree - that is why - one of several reasons - why the lead with calculations or FEA "Technician Engineer's Approach" is futile.
Calculations and FEA are wonderful tools, and work well in the hands of someone who understands their limitations. If they cqan get the boundary conditions right, they stand a good chance of getting good, usable answers within those limitations.
Quote:
Good point. Can I take it that you spotted that tfk's OP "alternate claim" is a narrow subset - "actually included in" (And actually rebutted by) my explanation?
I could lie and say yes, but to be perfectly frank, I did not study the claims of wither of you in the kind of detail (by doing the mathematics and modeling myself). But looking at each floor as a system, and the aftermath/ detritus, it is not a stretch to say that every failure mode possible took place in the hell-hole of chaos that each of those buildings became during the collapse. Too many variables, too many degrees of freedom to eliminate anything
As far as the 1d/2d modeling of B&V: We all do it. We have to, lest the model become entirely too big to be useful. But its validity generally ends when linearity disappears from the scene. We can say--"all the columns on this side are "exactly" the same and evenly spaced, so we can combine them, IFF all the other lines of columns are the same and similarly spaced, AND the floors and trusses are homogeneous"
That's where it breaks down, of course, and a 1d/2d model is essentially useless when we get into non-linear geometry combined with non-linear material properties
The other issue I take offense at is not yours: the "weakness of the joints". none of the joints that failed were "weak". They were all capable of handling up to 2 to 5 times the maximum load expected and reasonable. They were weak only in the sense that when hit with hundreds of times the design load, they were incapable of carrying it--and many of those loads came from a totally unexpected, and therefore only marginally considered, direction.
I keep thinking of Mycroft and the Professor's conversation in "The Moon is a Harsh Mistress"
I don't thin we shoul hit that mountain any more"
"Why?"
"It's not there now."
Overkill. Plain and simple
This is long, and probably inaccurate by some accounts, but i've been going 18 hours now, and you still deserved a response.
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Old 12th May 2016, 11:20 PM   #93
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My apologies for not getting back to you as quickly as I ought. I've been up to my eyeballs on another project.

But I've read your other post. And this one. And I will, eventually, address all the points.

But I did feel the need to respond to one point:

Originally Posted by ozeco41 View Post
Your alternative claim:
1) Adopts a narrower scope which does not address EITHER the objective of this thread ...
I gotta ask, Oz.
Who died & made you Royal PooBah Arbiter of the Objective of the Threads??

ONE of the two of us started this thread.
Big hint: it wasn't you.

This thread did not have any objective until one of us (again, not you) GAVE it an objective by starting it.

And the objective that I gave it was NOT to "ignore what I write, because that's not the objective here."

I find it pompous & a little rude for you to state, in the thread that I started, that YOUR casting of the question of asymmetric crush down is the objective of this thread, while MY casting of the same question "does not address the objective of" a thread that only got its objective ... when I started it.
__

That being said ...

This is a democratic gathering. That means that one of its strengths is a certain amount of chaos & rebellion.

I've always found it easy to ignore derails & tangents. And every once in awhile, one of those tangents brings up a surprising, terrific connection between the "proper" topic & some person's leap of logic or illogic.

I've never once objected to anyone (mod or anyone else) about anyone's post being off-topic.
I never intend to.
__

With regard to:

Originally Posted by ozeco41 View Post
Your alternative claim:
1) Adopts a narrower scope which does not address ... my specific claim;
Well, Oz, I have an very symmetry to report...

Despite my asking you to do so several times, someone out there in Aussie land hasn't addressed my specific claims, either.

And is now concocting a bunch of verbose, tortured reasons to explain that he doesn't intend to.

That's not very equitable.

I have asked you & Sander & others to at least address the thoughts that I laid out in the OP, that IMO, go right to the core of the question of "is the crush down asymmetric?"

Thus far, I've seen nobody address those two simple concepts.
__

I have not attempted to stop you from making any argument that you please. As a matter of fact, I specifically invited you to come & present your arguments.

I've not claimed that your arguments are off-topic.

You are free to bring whatever logic you wish to disagree.

And I, and everyone else is perfectly free (& invited) to bring whatever logic they wish to affirm or disagree with your (or my) arguments.

You do NOT have the right to tell anyone that their arguments "don't address the topic of this thread."

[/rant]

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Old 13th May 2016, 01:37 AM   #94
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Originally Posted by rwguinn View Post
First, a little background--for most of my career i specialized in analysis of structural systems due to dynamic responses and random/transient events. It is ingrained, part of my DNA, if you will, to refuse to look at individual components as stand-alone items until the function of the overall system is resolved. They are all part of a system of some sort. Only when analysis shows where a failure is likely to occur, or when the system is not performing in simulation the way it needs to do I truly delve into the detail
Exactly. The confusions arise when "other factors" intrude including the lack of a "systems and subsystems" comprehension.
Originally Posted by rwguinn View Post
At one point, I loved "Science Projects",and to a certain extent, still do. But experience has shown to me that some of them are not possible to obtain a singular and definitive solution, and that the idiots will glom on to any perceived discrepancy and restart the whole damn thing all over again1, and numerous engineers who should know better will move heaven and earth to "Prove" you/me wrong2. Call it my interfering in somebody's troll perpetuation project.
1 - usually the "truther side" proponent.
2 - usually a debunker - often a debunker engineer who cannot tolerate the reality that a "JREF declared truther" gets something right. Major_Tom has adopted a deliberately provocative style of posting. Ironically copying the style of abuse he copped from the "regulars" here - and watch the denials of THAT history even tho the posting evidence is still in full view. BUT he has been - still is - correct on three or four issues which the debunkers historically got wrong and still play denial games over. Cold blooded objective assessment of facts aint all that popular around here.
Originally Posted by rwguinn View Post
I wasn't necessarily referring to you in particular,as there are numerous more blatant offenders out there, and I'm glad you recognized the intent
Sure - "intent" is far harder to prove than "truth" or "falsity". I usually avoid "liar", "lies" and derivatives for that reason. Truth/untruth is relatively easy to discern but "intention to be untruthful" AKA "lying" is harder. I usually refer to Gage and Szamboti as being "professionally dishonest" - the standard of proof for "professionally dishonest" is lower than for "lying".
Originally Posted by rwguinn View Post
Calculations and FEA are wonderful tools, and work well in the hands of someone who understands their limitations. If they can get the boundary conditions right, they stand a good chance of getting good, usable answers within those limitations.
That is a key problem with most of the second rate debunker side arguments. Failure to define the scenario and the claim - somewhat broader than just the "boundary conditions" depending on how wide you define "boundary conditions".
Originally Posted by rwguinn View Post
I could lie and say yes, but to be perfectly frank, I did not study the claims of wither of you in the kind of detail (by doing the mathematics and modeling myself). But looking at each floor as a system, and the aftermath/ detritus, it is not a stretch to say that every failure mode possible took place in the hell-hole of chaos that each of those buildings became during the collapse. Too many variables, too many degrees of freedom to eliminate anything
True at that detailed level. The issues under ongoing contention on this and other forums are not down at that level. Specific to my assertions on this topic the deliberate maintenance of pseudo confusion is between two distinct and mutually exclusive mechanisms of collapse viz: A mechanism which never happened but which was based on crushing (buckling) of ALL columns as an artifice to determine a "worst case' limit. AND the real event mechanism which effectively bypassed the axial strength in compression of the columns.

For a complex of reasons less than truthful members continue to confuse/conflate/mix and match what did not and never could happen with the real event. That in many different guises is the source of confusion which is BOTH (??) artificially maintained AND denied. I kid you not. I do not participate in discussions which sink to that level of dishonesty.
Originally Posted by rwguinn View Post
As far as the 1d/2d modeling of B&V: We all do it. We have to, lest the model become entirely too big to be useful. But its validity generally ends when linearity disappears from the scene. We can say--"all the columns on this side are "exactly" the same and evenly spaced, so we can combine them, IFF all the other lines of columns are the same and similarly spaced, AND the floors and trusses are homogeneous"
That's where it breaks down, of course, and a 1d/2d model is essentially useless when we get into non-linear geometry combined with non-linear material properties
Agreed for "non-linearity". The situation with this topic - whether this thread or the several others - is not linearity per se BUT very simply "Wrong Model". Persons - including engineers who should know better - variously playing mobile goalposts with two 180o opposed models - viz "columns in line resisting collapse" which never happend and never could happen AND "columns bypassed and playing little if any trole inresting collapse" which was the real event.
[quote=rwguinn;11275852]The other issue I take offense at is not yours: the "weakness of the joints". none of the joints that failed were "weak". They were all capable of handling up to 2 to 5 times the maximum load expected and reasonable. They were weak only in the sense that when hit with hundreds of times the design load, they were incapable of carrying it--and many of those loads came from a totally unexpected, and therefore only marginally considered, direction.

Originally Posted by rwguinn View Post
I keep thinking of Mycroft and the Professor's conversation in "The Moon is a Harsh Mistress"
I don't thin we shoul hit that mountain any more"
"Why?"
"It's not there now."
Overkill. Plain and simple
This is long, and probably inaccurate by some accounts, but i've been going 18 hours now, and you still deserved a response.

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Old 13th May 2016, 03:16 AM   #95
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I am not sure what the symmetry you referred to is... or why it would matter? Color me dense.

My conception of the event... let's use 1wtc... is that post plane strike the insides of the building above the strike zone was coming "undone" and as such disengaged from the structural matrix and dropping. If the bit dropped and what it dropped on could support the increase load... it would be a new live load on that region. of floor. I don't see material dropping onto columns... or the axial load system.

The fires continued to cause the structural matrix to "warp" leading to more bits dropping and some column ends mis-aligning. This meant that some column lines below were unloaded... and some of them were uploaded with redistributed loads. The heat likely also weakened some of the remaining column lines... like cooking the middle of a single piece of spaghetti.

The failed columns from the plane strike likely would cause those above to become hangers and fail their connection to the columns above... a bearing situation is very different a hanger/tension system... and the column to column splices were clearing not designed as hanger. So I suspect there was a fair amount of load being moved to the slabs below as bits dropped down when columns to column connections failed.

I also suspect that this process began to "hollow out" the structural 3D matrix and the heat continued to expand the beams as it moved through the core to the regions where floors remained and could support "burning"... leading to more heating of beams and more local column weakening and more column end misalignment and more material dropping and fewer intact column lines to support the mass of the floors above still in a 3D structural matrix.

The hat truss seems to have been a block of heavy mass over the entire foot print largely not impacted by the process I describe above. However that process removed the axial support of the hat truss which caused the remaining columns supporting it to carry increasing loads... turning the truss into a sort of bridge spanning the remaining columns.

The hat truss now a bridge finally failed in the middle and the concentrated load of the 360 ton antenna caused it to break up... and the last columns supporting the mass... mostly floors attached to the facade at the upper floors.... buckled... and the top was pulled off all remaining inline columns and began to drop.

At this point all hell broke loose and there were all manner of dropping bits from the upper section... disengaged and this rapidly evolved into the driving floor slab destroying dynamic load which raced down through the tower.

Was there crush up and crush down? Doubt it. There was a rain of material exceeding the capacity of the slab it fell on... and this process was runaway and progressive and took out every floor one by one with negligible resistance.

Symmetry? What plane/axis and what type of symmetry are you concerned with? And why would it matter? The destruction involved in short order all the area of the floors... but it was likely not a footprint wide uniform dropping mass.... but regions ahead and behind by a small fraction of a second.

That's what it looks like to me based on how the building was initially damaged and then progressively by fire based on the key distinguishing features of the structure.

One a threshold mass drops locally on a slab.. that slab is destroyed locally. If the slab is stronger than the connection to the axial system.. the connection will fail if weaker, the slab will shatter locally. If a elevator motor drops on a slab... the slab loses.. If a slab drops on a slab.. they both lose.
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Old 13th May 2016, 06:19 PM   #96
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Originally Posted by tfk View Post
My apologies for not getting back to you as quickly as I ought. I've been up to my eyeballs on another project.
No problem. The underlying issue of the relevance of CD/CU to the real WTC Twins collapses has been around for years.

Originally Posted by tfk View Post
But I've read your other post. And this one. And I will, eventually, address all the points.
The central need is to address my claim and my already outlined arguments because they encompass your own narrower focussed counter claim.

Originally Posted by tfk View Post
But I did feel the need to respond to one point:
.....
I gotta ask, Oz.
Who died & made you Royal PooBah Arbiter of the Objective of the Threads??

ONE of the two of us started this thread.
........
You do NOT have the right to tell anyone that their arguments "don't address the topic of this thread."

[/rant]
I'm aware of your persistent style of extraneous nit picking abuse. Feel free to exercise it whenever it helps you to feel good.

HOWEVER the trick of ranting on nit picking irrelevances whilst missing the main points of argument will not advance anything.

The full scope of discussion of the topic "Crush down / Crush up" demands consideration of the real event despite your narrowing the focus and avoiding the real event. And despite your false assertions "put it into simple to understand language" and "my description of why Bazant’s 'asymmetric crush down' is an accurate approximation to the actual events".

I agree that "It ain’t perfect" - nor is mine BUT mine is broader than yours - it covers the scope of yours which is a sub-set of mine. And yours commits the error of "begging the question". Two questions actually - you limit the case to presumed 1D column crushing - which wasn't the real event AND you limit it to "crush down" BEFORE "crush up" - which wasn't the real event either.

Neither of us needs to be perfect at first attempt. We should get better if we can discuss. BUT it has to be EITHER the real event put in proper context - my objective OR the arbitrary "limit case" model which you are following.

So real event or fantasy? Your call.

And - don't miss the irony - If you prove that the "real event" was by a column crushing 1D mechanism you will have falsified half of B&Z 2002. One of the risks of trying to defend Bazant at any cost.

Last edited by ozeco41; 13th May 2016 at 06:44 PM.
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Old 14th May 2016, 02:55 PM   #97
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Originally Posted by ozeco41 View Post
I'm aware of your persistent style of extraneous nit picking abuse. Feel free to exercise it whenever it helps you to feel good.
Attempted patronizing noted.
And rejected.

I've never gotten into nit-picking, rather than attempting simple clear discussions, with anyone except femr & the other Truthers, who LOVED to be willfully, intentionally vague & constantly changing with their definitions of words.

I do note that one of us recently admitted to also playing that same game for his amusement.
Originally Posted by ozeco41 View Post
Don't forget the early motion history - and the fun femr2 and I had for months describing it somewhat obscurely so that everyone who wasn't thinking missed the point.
If you are going to “intentionally describe things obscurely” so that you can “have fun”, you’ve lost the right to object when someone nit-picks your comments, to try to get you to state what you mean clearly.

A whole bunch of this post is completely obscure, because you still refuse to state what you mean … clearly.
You frequently refer to things that you’ve stated in the past.

I don’t keep track of all the things that you’ve stated in the past.
I don’t expect you to keep track of all the things I've stated. So I’m perfectly happy to re-state my opinions, clearly, as needed.
Please do the same.

Originally Posted by ozeco41 View Post
HOWEVER the trick of ranting on nit picking irrelevances whilst missing the main points of argument will not advance anything.
You're welcome to call it nit-picking.
I prefer to think of it as "being precise with one's terminology”, or “agreeing on the definitions of words”.

ONE of us is an engineer, and writes like one: clearly & concisely.
ONE of us is a lawyer, and writes like one: not so clearly or concisely.

Originally Posted by ozeco41 View Post
The full scope of discussion of the topic "Crush down / Crush up" demands consideration of the real event despite your narrowing the focus and avoiding the real event.
And where the hell did this nonsense come from?
I AM talking about the real event.
I've never narrowed anything, to avoid talking about the real event.

In my opinion, the REAL event showed asymmetric crush down.

My contention is that, during crush down of the REAL buildings, the crush up into the upper block may have progressed as much as 1 story, and then stopped.

But another KEY part of the discussion is Bazant’s models.
There we are talking about the models, and there is a discussion about how closely they capture the various aspects of the real collapse.

There is no avoiding talking about BOTH the real event & the models, in this discussion.

I will be clear when I’m talking about the REAL collapse.
And when I am talking about Bazant’s models of the collapse.

Please do the same.
Please stop making silly, inaccurate assertions about my "narrowing the focus" or "avoiding talking about the real event".

Originally Posted by ozeco41 View Post
And despite your false assertions "put it into simple to understand language" and "my description of why Bazant’s 'asymmetric crush down' is an accurate approximation to the actual events".
This isn't a complete sentence.
I have no idea what you are trying to say.

Originally Posted by ozeco41 View Post
I agree that "It ain’t perfect" - nor is mine BUT mine is broader than yours - it covers the scope of yours which is a sub-set of mine.
Your WHAT is broader than my WHAT??
My WHAT is a subset of your WHAT??

In what way, precisely please, is my WHAT a subset of your WHAT?

Originally Posted by ozeco41 View Post
And yours commits the error of "begging the question". Two questions actually - you limit the case to presumed 1D column crushing - which wasn't the real event
First, a “1D model” is completely independent of “column crushing”.
One can have a 1D model that involves columns crushing, or does not involve column crushing.
One can have a column crushing model that is 1D, 2D or 3D.

No, I do not limit the discussion to 1D models.
I have asserted that nobody has demonstrated any reason that a 1D model can not accurately capture the important characteristics of the collapse.

I’ve heard you, and the boys at the 911Forum, assert that "a 1D model is a priori inadequate or wrong" repeatedly. I disagree.

I’ve told you, in the past, that in order to go beyond asserting it, you must AT LEAST provide a concise argument about which characteristics of the real event cannot be captured by a 1D model, AND demonstrate that those characteristics significantly change the output of the model.

I’ve stated that the BEST way to demonstrate that a 1D model is inadequate is to generate a valid 2D or 3D model, and to then show the quantified differences in the OUTPUT that result from using the 1D versus the higher dimensional model.

In this particular case, the output of Bazant’s 1D model was crystal clear: “the collapse would not arrest, it would continue to the street level”. That was the primary output of Bazant’s models.

If your 2D or 3D model reaches the conclusion that “the collapse will arrest”, then that IS a VERY significant difference between a 1D & a 2D/3D model. And the 1D model is proven inadequate.

It's fair to say that, in the context of this discussion, the "no crush up during crush down" was also an output of Bazant's model.

If your 2D or 3D model reaches the conclusion that "crush up DOES happen during crush down", then that is also a significant difference, and the 1D model was inadequate to this output.

If your 2D/3D model reaches the same conclusions, that “the collapse does not arrest”, and that "crush up during crush down does not occur", then you have demonstrated no significant difference between your 2D/3D model & the 1D model.

And your statement that “the 1D model is inadequate” is proven wrong.

Simply "asserting that a 1D model is wrong", without providing adequate substantiation, is "truther incompetent".

I do note that this is going to be a serious challenge for you. Because, from everything that I've read, neither you, nor the guys at the911forum, are capable of generating a real, engineering based 2D or 3D model.

Nor, from everything that I've read, of understanding the math details of Bazant's 1D model. Oh, you think you understand the words. (I'm pretty sure that you don't, but that's a different issue.) But you don't understand the math.

Originally Posted by ozeco41 View Post
AND you limit it to "crush down" BEFORE "crush up" - which wasn't the real event either.
There are 2 separate “crush up” phases.
Let's agree on some clarifying terminology.

The first is the “crush up” during the crush down phase.

I assert that this crush up happens minimally during crush down.

I interpret you as saying, “this crush up does happen significantly during the crush down”, although you haven’t quantified the amount of crush up you expect, to my knowledge. Truthers frequently assert that there would be equal crush down & crush up during this crush down phase.

From my perspective, this is the core of this discussion & our disagreement.

The 2nd “crush up” is the phase that happens after the debris pile has reached the ground.
I’ve asked that we set aside discussion of that phase for now.

Originally Posted by ozeco41 View Post
Neither of us needs to be perfect at first attempt. We should get better if we can discuss. BUT it has to be EITHER the real event put in proper context - my objective OR the arbitrary "limit case" model which you are following.
I am talking about the REAL event, in which I believe that the first “crush up” happened minimally (1 story or so).

Separately, I’ve also been talking about Bazant’s MODEL of the crush down phase. In those models, he did use “limit cases” (i.e., column buckling). I’ve tried to make it clear when I’ve been talking about the actual events or the math model.

Originally Posted by ozeco41 View Post
So real event or fantasy? Your call.
The real event.

Then the math models.

And we be clear when we are talking about each.

Originally Posted by ozeco41 View Post
And - don't miss the irony - If you prove that the "real event" was by a column crushing 1D mechanism you will have falsified half of B&Z 2002. One of the risks of trying to defend Bazant at any cost.
Nobody that I know of (including Bazant and me) thinks that column crushing was the real failure mode.
I do believe that a 1D model was adequate for the purpose to which Bazant put it: to prove that collapse arrest would not happen.

I do NOT “defend Bazant at all costs”.
I defend him when I believe that he is correct about some aspect, and I read that you assert that he is wrong.
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Old 14th May 2016, 05:01 PM   #98
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What exactly do you think is "crushing"? up or down?


Full Definition of crush

transitive verb

1 a : to squeeze or force by pressure so as to alter or destroy structure <crush grapes>
b : to squeeze together into a mass

2: hug, embrace

3: to reduce to particles by pounding or grinding <crush rock>

4a : to suppress or overwhelm as if by pressure or weight
b : to oppress or burden grievously <crushed by debt>
c : to subdue completely

5: crowd, push <were crushed into the elevator>

6: archaic : drink

It's not 2, 4b, 4c, 5 or 6... 1a and 3 seem to describe aspects of the event... and perhaps 1b.

Do you make a distinction between the columns (axial system) and the floors and beams which support them?

or

Do you consider the entire matrix of floors, beams and columns the thing which is crushed? The bits or the assembly of bits?
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Old 14th May 2016, 08:29 PM   #99
Seymour Butz
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Originally Posted by JSanderO View Post
What exactly do you think is "crushing"? up or down?


And there's the miscommunication that Tom and Oz are having.

Since Bazant uses the term "crush up/down" to describe what the columns are doing, Oz assumes the same of Tom, even there's no indication of that. Indeed, I believe Tom describes a cushion of debris between the two fronts, which therefore means that in his mind, it is floors and trusses and core floor beams and concrete......

My .02.....
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Old 14th May 2016, 09:37 PM   #100
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Originally Posted by Seymour Butz View Post
And there's the miscommunication that Tom and Oz are having.

Since Bazant uses the term "crush up/down" to describe what the columns are doing, Oz assumes the same of Tom, even there's no indication of that. Indeed, I believe Tom describes a cushion of debris between the two fronts, which therefore means that in his mind, it is floors and trusses and core floor beams and concrete......

My .02.....
Wait. What? How does one consider that a 1D modelling of a complex structure such as the towers is simply a column? I certainly never realized that that was Oz's contention, but if so, I can see why things have gone the way they are.
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Old 14th May 2016, 10:31 PM   #101
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Originally Posted by rwguinn View Post
Wait. What? How does one consider that a 1D modelling of a complex structure such as the towers is simply a column?
I don't know how any informed engineer would make that error - I certainly haven't. Misunderstanding of 1D is only one of the issues of technical confusion I have identified and at least partially explained if ever we can can get the technical arguments addressed.
Originally Posted by rwguinn View Post
I certainly never realized that that was Oz's contention,...
It isn't - so better "unrealise" it Meanwhile - I'll risk the derail - also look at tfk's position. He has the bottom part of the tower explicitly in 2 or 3D - his argument "switches horses" from a column crushing "B&Z limit case model" to a real event "runaway down the office space tube" model (Which I would prefer to call ROOSD driven Three Mechanisms...but....). When the distinction between which mechanism is the central fact of dispute - and he has a bet both ways. Totally at odds with B&Z which is absolutely clear on the distinction between "limit case" and "real event".
Originally Posted by rwguinn View Post
but if so, I can see why things have gone the way they are.
It is not "so" - no need to go further into a confusing side track. I've presented my reasoned technical argument which so far has not been addressed. I've also outlined the main flaws I identify in tfk's counter claim. And my outline of rebuttal has not been addressed either.

I'm considering whether to restate my argument one last time for tfk and also - separately - restate the flaws I identify in tfk's own position.
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Old 14th May 2016, 10:55 PM   #102
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Originally Posted by Seymour Butz View Post
And there's the miscommunication that Tom and Oz are having.

Since Bazant uses the term "crush up/down" to describe what the columns are doing,...
correct - that is one of the premises of my posted and argued explanation.

Originally Posted by Seymour Butz View Post
Oz assumes the same of Tom,...
Au contraire - I find tfk's posts variously wrong or unclear on that very point. It is the central issue. And I have been explicit in asserting that:

(a) Correct application of "1D" means "columns in line" AND
(b) B&V is unambiguous - it is explicitly 1D and therefore has "columns in line".

Originally Posted by B&V 2007
and a dynamic one-dimensional continuum model of progressive collapse is developed
If any one can argue that those two are wrong please go for it.

Originally Posted by Seymour Butz View Post
...even there's no indication of that.
It follows from the partial argument he has presented so far. And it is explicitly spelled out in B&V 2007. In fact the pgimeno argument - supported by Oystein as "pretending" - or some form of Socratic learning - actually supports my argument. Remember I am claiming that B&V does not apply to WTC 9/11 Twin towers progression. pgimeo supported by Oystein say "Bazant knew that for B&V 2007". tfk is not accurately explicit - actually he is ambiguous by conflating or "switching horses" between the two models which are the central issue of contention - hence the confusion and ambiguity.
Originally Posted by Seymour Butz View Post
Indeed, I believe Tom describes a cushion of debris between the two fronts, which therefore means that in his mind, it is floors and trusses and core floor beams and concrete......
Yes - and that is the second core issue of confusion or error. The dominant and deciding mechanism was EITHER column crushing as per B&Z 2002 "limit case" which I claim B&V is based on OR it was mass of material falling down the office space tube stripping floors plus the associated perimeter peel off and core strip down.

AND it is one or the other - not mix and match.

Nor is it "we can modify B&V to make it a good enough approximation" - which may be true tho' I doubt the practicality.

Originally Posted by Seymour Butz View Post
My .02.....
Your comment is worth more than $US 0.02

I'll probably make one more attempt in responding to tfk as soon as I get time.
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Old 15th May 2016, 05:09 AM   #103
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This is hysterical!!!!!!!!!!!!!!!!

Please fellas try to explain the following changes in the building... what was going on inside (structurally) from 8:56am - 10:28am

a) at the strike elevation
b) above the strike elevation
c) below the strike elevation

Visual observations: (approximate times)

7:00 am - static state
8:56 am - plane hits the building floor 94-97
9:15 am - fires spreading
10:20 am - INWARD BOWING east facade south side - SMOKE EJECTIONS
COLLAPSE PHASE
10:28 am - Antenna begins to drop into roof
10:28 am - top appears to drop, antenna tilts
BOTTOM COLLAPSE PHASE (ROOSD)
10:31 am - top has disintegrated bottom begins to disintegrate from top down,facade peels
10:31 am+ remaining core cores fall, buckle, topple

When does crush up or crush down begin? When does it end? how is it expressed in the visual record?

Go for it!
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Old 15th May 2016, 06:52 AM   #104
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Originally Posted by JSanderO View Post
This is hysterical!!!!!!!!!!!!!!!!
There are other words.

Originally Posted by JSanderO View Post
When does crush up or crush down begin? When does it end? how is it expressed in the visual record?

Go for it!
It never was "crush" either way. Disintegrate Down and Disintegrate Up ran concurrently at the start of ROOSD driven progression stage - "ROOSD" was the leading sub-mechanism causing the other two sub-mechanisms of Perimeter Peel Off and Core Strip Down.

Most of "crush up" - which was supposed to wait til near ground level - actually completed as "disintegrate up" in the first few storeys of progression stage. Without any "columns in line" being buckled into failure.

..and "crush down/crush up" isn't in the visual record because it never happened.
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Old 15th May 2016, 08:02 AM   #105
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Originally Posted by ozeco41 View Post
There are other words.

It never was "crush" either way. Disintegrate Down and Disintegrate Up ran concurrently at the start of ROOSD driven progression stage - "ROOSD" was the leading sub-mechanism causing the other two sub-mechanisms of Perimeter Peel Off and Core Strip Down.

Most of "crush up" - which was supposed to wait til near ground level - actually completed as "disintegrate up" in the first few storeys of progression stage. Without any "columns in line" being buckled into failure.

..and "crush down/crush up" isn't in the visual record because it never happened.

there ya go... chaotic disintegration of the building floors and columns over time... progressing down from the plane strike zone.
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Old 15th May 2016, 09:50 AM   #106
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Being pedantic, the B&V model is really 2D -- height and time -- and the only thing it attempts to do is to model the collapse "history" (i.e. the height over time). The essential premise behind the formulation is that the progression rate depends on the energy absorption rate, and I haven't seen any refutation of that thesis.

The model makes (at least) three simplifying assumptions: that on average, the energy absorption rate is constant; that the energy absorption rates of the top and bottom blocks are the same; and that using the energy absorption produced by column buckling is a "close enough" approximation for a simplified model.

The first question that I think should be asked about the model is whether the three differential equations in the model accurately reflect the physics involved, given those assumptions. That's something far beyond my ability to assess, but I haven't yet seen any criticism of the formulas per se (probably because very few people actually understand them). Rather, criticism centers on the column buckling premise as "not real," which is entirely a secondary consideration, IMO. If the model does not accurately predict the collapse time, then that particular simplification is a likely suspect, and the "fix" is to use more realistic energy absorption rates, which would require analyzing all the major energy sinks and estimating the relative contribution of each.

But I still believe that CD/CU is entirely a result of that second assumption -- that the energy absorption rates were the same in the top and bottom block. If the columns in the lower block were being stressed to the buckling point, then there wouldn't have been enough reaction force on the top block columns to also buckle them. However, the same thing would happen if you used any other energy sinks for both the top and bottom blocks: If the bottom block is subject to the weight and inertia of the top block plus the debris layer, it will fail before the reaction forces in the top block reach that same level, because that failure point is the maximum reaction force the bottom block can provide and it's acting to slow the fall of both the debris layer and the top block.

Therefore, if the CD/CU prediction is not an accurate modeling of what happened to the WTC towers, then I think the culprit is fairly obvious, as is the "fix": Figure out what was different about the destruction of the top and bottom blocks. (I am still of the opinion that the tilt was an important factor in this.)

I think this would be an entirely esoteric argument of interest only to structural mechanics theoreticians, except for one thing: "truthers" have a mad hate of Bazant because in B&Z he deprived them of a favorite "truther syllogism": "I don't understand how a gravity-driven total collapse could happen (and I'm very smart), so it must have been impossible," followed by the usual conspiricist's fallacy of "anomaly -> hoax -> conspiracy."

I'm pretty sure that even Major_Tom's pathological obsession with CD/CU began with the notion that disproving CD/CU would invalidate the entirety of Bazant's arguments and veer the discussion back to the controlled demolition hypothesis, which is abject nonsense. If anyone wants to say that the B&V model is irrelevant to the WTC towers, I couldn't care very much less, but then that irrelevancy is also itself irrelevant.
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Old 15th May 2016, 11:24 AM   #107
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Great post, WilliamSeger!

Earlier today, I opened B&V to check out what the assumptions really are, and whether "column crush" is a sine-qua-non for the model. But then I watched all the sunday sport, and forgot to return...

So I am glad you confirm my suspicion that B&V does not depend on the mechanism of column crush and instead would hold true for other failure mechanims as well. That's how I read the abstract.


Now I have a hunch for why B&V still fails to model the real WTC collapses, where, I believe, much of the top part DID disintegrate ("crush up") before "crush-down" was completed:

The several parts of the structure are crushed at different rates - "height over time" is not the same for all parts. In particular, the compacted debris layer moves below the upper ends of both the perimeter walls and the core (lower part). This allows for example the standing walls to shear the falling floors off the perimeter where the falling perimeter passes outside the standing walls.

And all of this is as irrelevant as you say
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Old 15th May 2016, 03:47 PM   #108
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The vast majority of the columns of the building did not see loads exceeding their normal capacity. There were a few at the point of release... the remaining spire columns buckled from Euler forces... because of the absence of bracing making them too slender.

Column crushing is something that did not happen.
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Old 15th May 2016, 03:48 PM   #109
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Originally Posted by JSanderO View Post
What exactly do you think is "crushing"? up or down?
In Bazant’s analysis (THE MODELS) and, I would argue, in the REAL world, it doesn’t matter what is being crushed.

“Crush” is a pure fraction (no units) that just refers to the height ratio between its “current height / fully compacted height”.

Assume that the "compaction ratio" (Bazant's "stretch" parameter in BV, λ) is 0.18. (As he uses in BV.)
A "100% crushed floor" would then be 0.18 * 12’ = 2.2' thick.

In the interests of our clarity...

THE FOLLOWING IS THE MODEL.!

Then:
When the floor stands at 12' tall, it is 0% crushed.
When the floor stands 7.1' tall, it is 50% crushed.
When the floor stands 2.2' tall, it is 100% crushed.
__

Bazant's evolving definition of λ.

In BV, Bazant defines λ as a parameter (a constant that one can choose, but stays constant within each analysis run). In Fig 6 of BV, you can see that he checked out λ at the following values {0, .18, .3, .4}. For the rest of his analyses, he kept λ = 0.18.

In Bazant, Le: “Closure to “Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions” by Bazant & Verdure”, Bazant starts playing with λ as a function of height within the compacted layer λ(z) but finishes this paper by asserting that λ was approximately a constant (λ = 0.2 for the North Tower & λ = 0.205 for the South).

Finally, in BLGB, he allows λ to be a variable (i.e., he assumes a linear function of height within the crush zone).
λ(z) = (1 − κout)μ(z)/μc

By this definition, the “crush zone” is any part of the building where λ ≠ 0.
___

THE FOLLOWING IS REALITY.!

Find the lowest floor ABOVE the crush zone that still stands 12' tall. Call it FloorHi.
Find the highest floor BELOW the crush zone that still stands 12' tall. Call it FloorLow.

The number of floors within the crush zone are therefore:
FloorHi - FloorLow - 1.

e.g., if FloorHi = 98 & FloorLow = 88, then there are 9 floors in the crush zone: 89, 90, 91, 92, 93, 94, 95, 96 & 97.

These floors should take up 9*12’ = 108’ tall.
When fully crushed, they'd take up (108*.18) = 19.4'.

If in reality, the distance between the bottom of FloorHi & the top of FloorLow were 41.6', then the AVERAGE crush in the crush zone would be 75%. (41.6 is 75% of the way from 108 to 19.4.) And, under this condition, λavg = 0.25

Note: The examples above merely constitute the definition that you asked for. It doesn't say anything about what the "correct" λ is.

The fact that nobody can see thru the debris cloud makes it impossible to say what any particular amount of crush applies to any particular floor at any given time.

BACK TO MODEL.
But any particular math model would predict the value of the crush us at any given time & location.
Output accuracy subject to quality of input assumptions.

Last edited by tfk; 15th May 2016 at 03:56 PM.
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Old 15th May 2016, 04:06 PM   #110
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Originally Posted by WilliamSeger View Post
Being pedantic, the B&V model is really 2D -- height and time -- and the only thing it attempts to do is to model the collapse "history" (i.e. the height over time).
I don't know if they've gone & redefined things since I was in college.
(They keep doing that & it pisses me off. For example, I was shocked to learn that, today, the number 1 is NOT considered to be a prime number.!??)

height = F(time)

height = dependent variable.
time = independent variable.

I'd define this as a 1D system.
__

By the definitions I was taught, the dimensionality is the number of variables necessary to characterize the aspect of the system that you're interested in.

First, the engineering definition if a "1D model" is that it needs only one independent variable in order to fully specify the dependent variable about which one wishes the model to provide information.

Most often, the independent variable is "time" and the dependent variable, in the case we are looking at, is the vertical position of some defined point on the building, such as the roof line, the crush front, whatever.

__

As a pertinent aside:
Sometimes, one can reduce the dimensionality of the problem by being clever.

For example, suppose one wants to know the position of a train on some typically convoluted, real, 3D track.

In real 3D space, it would take 3 dimensions to define the train's position, {x, y, z} as a function of t. But two of those coordinates can be eliminated, because the train is constrained to stay on the track (barring disaster).

The topography of the track is fixed. It follows a fixed, unchanging path in 3D space, so the train cannot really occupy any position in 3D space.

So one can eliminate all 3 of the {x, y, z} variables, and define a single one: "distance along the track from some arbitrarily defined start point."

Now you have reduced the 3D model ({x, y, z} position in 3D space) to a 1D model ({r} = distance from start location on track).

One has to simply calculate the acceleration of the train (in the direction of the track) as a function of time, and one can calculate (by single & double integration) the velocity & location of the train in along the track.

And then one can look up the "distance along the track" in a table & derive the true 3D position of the train in 3D space.

Last edited by tfk; 15th May 2016 at 04:08 PM.
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Old 15th May 2016, 04:28 PM   #111
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Originally Posted by ozeco41 View Post
Originally Posted by rwguinn View Post
Wait. What? How does one consider that a 1D modelling of a complex structure such as the towers is simply a column?
I don't know how any informed engineer would make that error - I certainly haven't.
And neither have I. Whether you think I'm "informed" or not.

The dimensionality of the model says NOTHING about the homogeneity of the model. One can have a model, made up of columns, slabs & office furniture, that is still a 1D model, if you can figure out a way to define the interested parameter (in this case the height of the top of the building) using just a single variable (z).

I employ the engineering definition of "dimensionality of a model": the number of variables (excluding any independent variable like "time") required to define the pertinent quantity of any system.

Bazant's model is 1D because there is only one dependent variable that one needs to specify the system: "z" (height of the roof of the building).

If one wanted to know height & lateral displacement (x & z), then one would have to develop equations that allowed both drop & lateral movement. Then that would require a 2D model.

If you want to know motion in all 3 axis, then a 3 dimensional model would be required.

BUT ...

If you were interested only in the ENERGY balance (sources & sinks), even allowing 1D , 2D or 3D motion, one could produce this in a 1D model. Since energy is a scalar, and one can employ CoE considerations to calculate what the kinetic & potential energy values are.

Of course, if you also want to know velocity vectors in each {x, y, z} direction, then you're back to a 3D model.

Originally Posted by ozeco41 View Post
I'm considering whether to restate my argument one last time for tfk and also - separately - restate the flaws I identify in tfk's own position.
You don't need to state it one more time.
Simply point to where you stated it, cogently, the first time.

I've seen you make lots of assertions, like my "something, I have no clue what" is a subset of your "something, I have no clue what".

I've asked you to clarify what you meant.

If I missed your clarification, please simply direct me to it.

But these comments of yours, if you're not going to clarify your terminology (in plain English, please), serve no purpose as "statements of your arguments".

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Old 15th May 2016, 05:46 PM   #112
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Originally Posted by tfk View Post
In Bazant’s analysis (THE MODELS) and, I would argue, in the REAL world, it doesn’t matter what is being crushed.

“Crush” is a pure fraction (no units) that just refers to the height ratio between its “current height / fully compacted height”.

Assume that the "compaction ratio" (Bazant's "stretch" parameter in BV, λ) is 0.18. (As he uses in BV.)
A "100% crushed floor" would then be 0.18 * 12’ = 2.2' thick.

In the interests of our clarity...

THE FOLLOWING IS THE MODEL.!

Then:
When the floor stands at 12' tall, it is 0% crushed.
When the floor stands 7.1' tall, it is 50% crushed.
When the floor stands 2.2' tall, it is 100% crushed.
__

Bazant's evolving definition of λ.

In BV, Bazant defines λ as a parameter (a constant that one can choose, but stays constant within each analysis run). In Fig 6 of BV, you can see that he checked out λ at the following values {0, .18, .3, .4}. For the rest of his analyses, he kept λ = 0.18.

In Bazant, Le: “Closure to “Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions” by Bazant & Verdure”, Bazant starts playing with λ as a function of height within the compacted layer λ(z) but finishes this paper by asserting that λ was approximately a constant (λ = 0.2 for the North Tower & λ = 0.205 for the South).

Finally, in BLGB, he allows λ to be a variable (i.e., he assumes a linear function of height within the crush zone).
λ(z) = (1 − κout)μ(z)/μc

By this definition, the “crush zone” is any part of the building where λ ≠ 0.
___

THE FOLLOWING IS REALITY.!

Find the lowest floor ABOVE the crush zone that still stands 12' tall. Call it FloorHi.
Find the highest floor BELOW the crush zone that still stands 12' tall. Call it FloorLow.

The number of floors within the crush zone are therefore:
FloorHi - FloorLow - 1.

e.g., if FloorHi = 98 & FloorLow = 88, then there are 9 floors in the crush zone: 89, 90, 91, 92, 93, 94, 95, 96 & 97.

These floors should take up 9*12’ = 108’ tall.
When fully crushed, they'd take up (108*.18) = 19.4'.

If in reality, the distance between the bottom of FloorHi & the top of FloorLow were 41.6', then the AVERAGE crush in the crush zone would be 75%. (41.6 is 75% of the way from 108 to 19.4.) And, under this condition, λavg = 0.25

Note: The examples above merely constitute the definition that you asked for. It doesn't say anything about what the "correct" λ is.

The fact that nobody can see thru the debris cloud makes it impossible to say what any particular amount of crush applies to any particular floor at any given time.

BACK TO MODEL.
But any particular math model would predict the value of the crush us at any given time & location.
Output accuracy subject to quality of input assumptions.

All nonsense...

The floor was:

4 1/2" thick of concrete
11' - 7 1/2" of air

REPEAT 31 times between mech floors

Between slabs there were the floor trusses, suspended ceiling, furniture and perhaps some partitions and mechanicals between the slabs. There was very little stuff by volume to crush or compact.

Compaction of air and furniture? Be serious!

Columns crushed? Rubbish... there was only a handful and they buckled / knuckled at release. the rest of the columns pass the columns they were connected to axially.

Real world: buildings are 95% (or more) air!
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Old 15th May 2016, 06:36 PM   #113
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Originally Posted by JSanderO View Post
All nonsense...

The floor was:

4 1/2" thick of concrete
11' - 7 1/2" of air

REPEAT 31 times between mech floors

Between slabs there were the floor trusses, suspended ceiling, furniture and perhaps some partitions and mechanicals between the slabs. There was very little stuff by volume to crush or compact.

Compaction of air and furniture? Be serious!

Columns crushed? Rubbish... there was only a handful and they buckled / knuckled at release. the rest of the columns pass the columns they were connected to axially.

Real world: buildings are 95% (or more) air!
It's about a model.

Real world doesn't strictly apply. The parameters and variables of concern for the model do.

We all know the real world - buildings on fire and damaged by aircraft collapsed.

A researcher is free to model a system any way he wants, as long as he states his asumptions, shows the derivation of his equations and what algorithms he uses, and it all checks. The reader is warned to take all the assumptions, etc. into account before applying the results elsewhere.
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Old 15th May 2016, 06:45 PM   #114
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Originally Posted by LSSBB View Post
It's about a model.

Real world doesn't strictly apply. The parameters and variables of concern for the model do.

We all know the real world - buildings on fire and damaged by aircraft collapsed.

A researcher is free to model a system any way he wants, as long as he states his asumptions, shows the derivation of his equations and what algorithms he uses, and it all checks. The reader is warned to take all the assumptions, etc. into account before applying the results elsewhere.
Goodie Gumdrop...

After the towers fell people were amazed... Perhaps a few physcists and structural engineers weren't.

For whatever reason.... people and institutions came forth to explain why/how the buildings collapsed and so fast and totally etc.

Theoretical math models don't cut it for this purpose... They can stay in Ivory Towers (or Faulty Towers for that matter)

After a few years NIST came out with what was supposed to be a plausible scenario for the towers. It was heavily based on assumptions. This made is NOT a literal description of the collapses... but a possible one.

As this was a progressive collapse... there are several paths to the runaway ROOSD phase in the twins... or whatever you want to call it.

The only really interesting aspect is how the ROOSD phase was initiated. CU / CD has little or nothing to do with that.
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Old 15th May 2016, 07:09 PM   #115
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Originally Posted by JSanderO View Post
Goodie Gumdrop...

After the towers fell people were amazed... Perhaps a few physcists and structural engineers weren't.

For whatever reason.... people and institutions came forth to explain why/how the buildings collapsed and so fast and totally etc.

Theoretical math models don't cut it for this purpose... They can stay in Ivory Towers (or Faulty Towers for that matter)

After a few years NIST came out with what was supposed to be a plausible scenario for the towers. It was heavily based on assumptions. This made is NOT a literal description of the collapses... but a possible one.

As this was a progressive collapse... there are several paths to the runaway ROOSD phase in the twins... or whatever you want to call it.

The only really interesting aspect is how the ROOSD phase was initiated. CU / CD has little or nothing to do with that.
Have you canvassed every academic paper modeling the events of every tragedy before reaching your conclusion?
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Old 15th May 2016, 11:35 PM   #116
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Originally Posted by tfk View Post
...
The dimensionality of the model says NOTHING about the homogeneity of the model. One can have a model, made up of columns, slabs & office furniture, that is still a 1D model, if you can figure out a way to define the interested parameter (in this case the height of the top of the building) using just a single variable (z).
...
Thanks for this well-written post, tfk, I learned and - hopefully - understood a bit more than before
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Old 16th May 2016, 02:48 AM   #117
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Originally Posted by LSSBB View Post
Have you canvassed every academic paper modeling the events of every tragedy before reaching your conclusion?
No, have you? What does that have to do with CU CD? I have looked at the structure and the visuals of the collapse and applied some basic knowledge of structure and materials reactions to fire and reached my own conclusions which ring true.

The so called "ROOSD" process... is one which is derived from observation not calculation. So it is with the pre ROOSD period.

LOOK, STUDY THE STRUCTURE.... THINK.

attached is a section through the column at the upper stories including the plane strike zone up to the roof... thru the columns and through the slabs only. The columns are less than .012% of the floor area foot print at floors 92-99

Not much to CU CD here.
Attached Images
File Type: jpg CU CD.jpg (53.3 KB, 5 views)

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Old 16th May 2016, 08:15 AM   #118
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Originally Posted by JSanderO View Post
No, have you? What does that have to do with CU CD? I have looked at the structure and the visuals of the collapse and applied some basic knowledge of structure and materials reactions to fire and reached my own conclusions which ring true.

The so called "ROOSD" process... is one which is derived from observation not calculation. So it is with the pre ROOSD period.

LOOK, STUDY THE STRUCTURE.... THINK.

attached is a section through the column at the upper stories including the plane strike zone up to the roof... thru the columns and through the slabs only. The columns are less than .012% of the floor area foot print at floors 92-99

Not much to CU CD here.
Don't care. All this is a tempest in a teacup. I am not the one railing about Bazant's paper when it's applicability to any meaningful discussion on this subforum passed many moons ago. It's a limited model.
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Old 16th May 2016, 08:51 AM   #119
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Originally Posted by LSSBB View Post
Don't care. All this is a tempest in a teacup. I am not the one railing about Bazant's paper when it's applicability to any meaningful discussion on this subforum passed many moons ago. It's a limited model.
I don't much care either... CU CD is a waste of time....

A limit model which has no meaning for the collapse of the WTC twin towers and demonstrates nothing.

'nother graphic for the crush guys.
Attached Files
File Type: pdf FF G 2.pdf (71.3 KB, 3 views)

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Old 16th May 2016, 09:06 AM   #120
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Originally Posted by JSanderO View Post
All nonsense...

Originally Posted by JSanderO View Post
What exactly do you think is "crushing"? up or down?
Full Definition of crush
transitive verb
1 a : to squeeze or force by pressure so as to alter or destroy structure <crush grapes>
b : to squeeze together into a mass
etc.
Pretty quick on the "all nonsense" trigger there, cowboy.

No, not nonsense at all.

First off, you asked 2 questions.

First, you asked “what was crushed?”
Second, you asked “what is meant by crush?”

I answered your second question, in the context of the model & the real world.

You’re welcome.

I am working on another project, and grabbing small snippets of time for this. So I didn’t get to your first question.

Originally Posted by JSanderO View Post
The floor was:

4 1/2" thick of concrete
11' - 7 1/2" of air

REPEAT 31 times between mech floors

Between slabs there were the floor trusses, suspended ceiling, furniture and perhaps some partitions and mechanicals between the slabs. There was very little stuff by volume to crush or compact.
Those concrete floors were in their “thinnest” state BEFORE they were crushed. Take any flat steel reinforced concrete, break it up, and it will then take up far more vertical space.

All (nearly all) of the core columns & girders were entrained within the main debris pile (i.e., within the footprint of the towers). They were not stacked neatly & flat within the debris.
These would all have produced random bridges & spaces below those bridges.

Many, many, many other smaller objects would have formed much smaller bridges, with empty pockets below them.

There were several people who survived the crush down in one of the stair wells. There was lots of room, and they could see upwards, thru several stories, to blue sky above them. If everything was as compressed as your suggesting, they never would have survived, much less been able to see thru several stories of debris.

Originally Posted by JSanderO View Post
Compaction of air and furniture? Be serious!
Please. Nobody suggested the “compaction of air”.

And you seem unfamiliar with the concept of “Bulk Modulus”.

First, it is nearly impossible to get any substance, be it liquid or solid, to change its actual volume. Virtually all solids & liquids are “incompressible”. Virtually all substances will expand laterally (the amount it expands is called Poisson’s Ratio, and is ≈ 0.3 for most substances) while you compress it vertically. It’s total volume does NOT change.

Water, for example, is almost completely incompressible. This is exactly why pressurized containers of water are harmless (i.e., not “bombs”), whereas compressed containers of gas ARE bombs. The energy stored in the contents is a product of the pressure x the compression. Even at very, very high pressures, the compression of water is approximately zero, so the amount of energy stored in the water is approximately zero. If the wall of the container ruptures, nothing happens. No energy is released.

If the wall of a gas pressurized container ruptures, then you’ve got a bomb. Or a rocket. For those who have ever watched the scary video of a “bottle of compressed air not tied to the wall, knocked over & the valve broken off. The gas container becomes a rocket which will go thru concrete walls.!

"Incompressible" includes things that we generally think of as “compressible”, such as rubber, elastomers & foams.
Rubbers & elastomers aren’t really compressible, they are “easily deformable”.

A round slug of rubber or elastomer may have a very soft durometer (be very compressible) while unconstrained. But if you constrain them laterally (place a slug of rubber in a close fitting, strong metal tube), suddenly it isn’t compressible at all. In order for it to compress vertically, it MUST expand laterally.

Foams are a very high percent entrapped (closed cell foams), or non-entrapped (open cell foams) air. The solid component of the foams form long, thin easily deformable walls. But again, once the foam is compressed down, such that all the air is removed & it is compressing “thin wall on thin wall”, it becomes nearly incompressible, too.

In order to compress something’s volume, you’ve got to overcome intermolecular repulsion forces. these are orders of magnitude stronger than the shear forces that are responsible for “deformation”.

Gasses are compressible. Not liquids. Not solids.

There was certainly nowhere near the pressure required to produce volumetric compression any of the towers debris. Including desks, fragile ceramic & porcelain fixtures, pipes, tubes or (sadly) humans.

Originally Posted by JSanderO View Post
Columns crushed? Rubbish... there was only a handful and they buckled / knuckled at release. the rest of the columns pass the columns they were connected to axially.
Most of the external columns were ejected out of the footprint. Those were obviously not crushed.
Virtually all of the core columns girders were entrapped in the rubble.

And we have two distinct definitions of “crushed” here.

1. “Structurally crushed”: will they still support the weight that they were designed to? Answer: no.
2. “volumetrically crushed”: do they take up as much volume as they did originally? Answer: yes.

In the discussion here, compaction ratio (λ), the 2nd definition is the meaningful one.

Originally Posted by JSanderO View Post
Real world: buildings are 95% (or more) air!
So, in other words, you think that Bazant’s λ should be ≈ 0.05.

Bazant things it should be ≈ 0.20.
Bazant also accounted for the mass fraction that was ejected, κout ≈ 0.20.

A priori, I’m going with Bazant’s estimate.
Because this is one of his specific fields of study (the compaction of debris in large structural failures).

You are welcome to present your argument for your number.

I’d recommend that you use some algebra.
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