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Old 4th May 2016, 04:30 AM   #41
JSanderO
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Originally Posted by tfk View Post
I beg to differ. Since it was descending at around 0.65G, it was colliding with something that provide an upward force of 0.35W, where W = the weight of the entire upper block.

This is a huge force.

If it were colliding with "nothing", then it's downward acceleration would have been 1.0G.

Which knife splices in the towers?

In the rest of your post, it’s not clear (to me, at least) your sequence of events.
Would you care to list them in order?

But, more pertinent to this thread, would you care to comment on my comments in the OP?

Tom

Perhaps I was inarticulate... I believe that when we can see the top moving downward... it DOES accelerate because it begin from a state of no moving. My point was that when what we see DOES begin to move down... the facade... the inside was already very compromised and much of the structure was mis aligned... with the columns below... almost all of them probably... and much of the slabs inside the core and parts outside the core had already collapsed and were disengaged from the "top" and had fallen onto/into the lower section. This was not a SINGLE pristine block/mass encountering a a single pristine mass below. The upper descending one was probably more disintegrated that the top of the lower... but the lower probably had broken slabs.

But as non significant mass was shed the total top section's mass DID encounter the resistance of the slabs and columns of the lower section. So what?

The fact is that each engaged to the structure bit of the bottom saw mass strike it dynamically and for the slabs this load exceeded their capacity. There was no arrest with material piling up on the top slab of the lower "intact" building... There was a cascading progressive runaway floor destruction underway.

There was likely very few steel to steel impacts. If so they would be column hitting beam/girder and these concentrated point loads would bust through any beam they came down on.

What's to prove here? The forces were formerly contained in the axial system... floor loads framed into the spandrels on the perimeter and the belt girder at the core... the core's floor loads had standard beam and girder framing. Floors buts dropping in the core did the same destruction as the dropping bits outside the core.

The tell tale that this inside the top block destruction was underway BEFORE the motion of the entire top was the movement of the antenna of 1wtc... which preceded the block moving down. the insides below the massive antenna had become undone already.

I suppose many want to treat the collision of the top and bottom as two simple masses. hitting each other. I think this was not the case. It was a collection of multiple parts of the top hitting multiple parts of the bottom section. So you can not reduce this to mass Top interacting with mass Bottom. This is only a "theoretical abstraction" description.

++++

All the rolled sections were connected with "knife" splices to the columns of the core.... The columns has beam stub outlookers and the beams and griders framed to the had splice plates bolted between the outlookers and the beam/girder.

The outside the core trusses were support and bolted DOWN onto angles welded to stand off blocks. This was most likely to facilitate installation.. fitting massive panels within the standard tolerance for construction.. and perhaps allow for some expansion and contraction???? dunno

The other reason for the out lookers for the outside the core floor trusses was that the core columns began as 22x52 bock columns at the base and reduced to as small as 12wf at the top. The floor pans outside the core were all manufactured to the same size... and connected to the facade and so at the top....they didn't reach the core columns AND the were not spaced as the core columns were... so the belt girder was cantilevered off the 24 perimeter core columns... short at the base and up to 32" at the top.

And finally the column to column connections were unrestrained... simply plates welded and or bolting a column to the one above with the appropriate steel space shims for alignment. These connections were not designed as hangers and offered little resistance if the column was being displaced.

When the plane severed core columns the ones above likely dropped down some distance because the columns connections could not carry the load in tension and the bolts and or welds would fail. Long story short... a large section of the upper block had dropped when the plane severed multiple columns.

++++

plane hits
columns severed
facade loads redistributed
portions of slabs around severed columns break free and drop down to the lower section (mutual damage below and above)
fire causes expansion of core beams
expanded core beams push remain aligned in place columns to displace
columns to column connections fail as pushed columns mis align
columns above have their column to column connection turn to tension/hanger connections
tension hanger connections fail column drop pulling down
this process repeats as the fire distorts / expands the beams inside the core
The loss of axial capacity for the remaining attached loads exceeds capacity FOS has dropped locally to below 1
remaining columns buckle
facade splice shear and the top exterior box drops... significantly hollowed out
All of the top mass is not freed from the axial paths and the ROOSD or runaway floor destruction begins largely bypassing all the lower columns.
Lower columns are too unstable without bracing and many topple with the falling floor mass
facade peels away absent lateral support
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Old 4th May 2016, 05:05 PM   #42
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Originally Posted by Oystein View Post
Bazant pretending the model describes the actual WTC buildings and their collapse mechanisms is incorrect.


Tom, do you agree with this statement by Oystein?


Multiple quotes in which both Bazant and David Benson refer to the model within their 2007-2008 papers as describing the actual WTC1 and 2 collapse mechanisms are provided at this link with simple guiding questions that even you should be able to answer.
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Old 4th May 2016, 05:12 PM   #43
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Originally Posted by Major_Tom View Post
Tom, do you agree with this statement by Oystein?


Multiple quotes in which both Bazant and David Benson refer to the model within their 2007-2008 papers as describing the actual WTC1 and 2 collapse mechanisms are provided at this link with simple guiding questions that even you should be able to answer.
It describes the energy values as it was intended to do, but the limited case statement shows that it was not intended to represent the actual collapses.

A Computer model of the actual collapses was impossible to produce, too many variables, to much data too crunch.

Shortcuts had to be taken.
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Old 4th May 2016, 05:12 PM   #44
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Originally Posted by Major_Tom View Post
Tom, do you agree with this statement by Oystein?


Multiple quotes in which both Bazant and David Benson refer to the model within their 2007-2008 papers as describing the actual WTC1 and 2 collapse mechanisms are provided at this link with simple guiding questions that even you should be able to answer.
I'm wondering, After almost 10 years why have you not moved on? Have you documented obsession in your "book"?

Just think, A autobiographical case study for the last chapter.
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Old 4th May 2016, 05:41 PM   #45
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Frankly mathematical models to communicate to the public... or to engineers even.. what was going on in the collapse of the twin towers doesn't cut it. In fact I will go so far as to say it is impossible in a few equations to describe the quantity of mechanical interactions leading to the destruction we saw. They of course completely ignore one of the main factors of WHY the towers collapsed... fire... something I doubt Dr. B bothers with.

His work essentially adds nothing to understanding the collapse and I don't know anyone finds it useful.

By the way what is a limit case? And what does it have to do with an actual event?

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Old 4th May 2016, 05:53 PM   #46
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Originally Posted by JSanderO View Post

By the way what is a limit case? And what does it have to do with an actual event?
It's an upper bound. Useful to study material and design strengths. It might have nothing to do with the reality but, it usually is used the design models.
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Old 4th May 2016, 05:57 PM   #47
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Originally Posted by DGM View Post
It's an upper bound. Useful to study material and design strengths. It might have nothing to do with the reality.
There ya go... it does have nothing to do with reality!
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Old 4th May 2016, 06:01 PM   #48
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Originally Posted by JSanderO View Post
There ya go... it does have nothing to do with reality!
Not true. It's used to design models to build future buildings. Is that not reality?

Bazant was not "debunking".
.
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Old 4th May 2016, 06:10 PM   #49
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Originally Posted by Major_Tom View Post
Tom, do you agree with this statement by Oystein?


Multiple quotes in which both Bazant and David Benson refer to the model within their 2007-2008 papers as describing the actual WTC1 and 2 collapse mechanisms are provided at this link with simple guiding questions that even you should be able to answer.
I already answered them in detail, here:

http://www.internationalskeptics.com...8#post10891238

My answers don't agree with your assessment.
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Old 4th May 2016, 06:13 PM   #50
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Originally Posted by JSanderO View Post
Frankly mathematical models to communicate to the public... or to engineers even.. what was going on in the collapse of the twin towers doesn't cut it. In fact I will go so far as to say it is impossible in a few equations to describe the quantity of mechanical interactions leading to the destruction we saw. They of course completely ignore one of the main factors of WHY the towers collapsed... fire... something I doubt Dr. B bothers with.

His work essentially adds nothing to understanding the collapse and I don't know anyone finds it useful.

By the way what is a limit case? And what does it have to do with an actual event?
Actually it shows that any building with the same energy potential compromised in a similar way will under go a similar collapse.

Limited Case is a hypothetical case to determine a structures reaction to the forces placed upon it.

A building is a set of energy structures, the way the energy travels though the structure determines mode of Collapse.

Banzant's method was Eular buckling combined with floor failures.

He choose to use the strongest possible case to counter Claims By Jones and his idiot cohorts. Who even after he proved them mathematically wrong, continued the nonsense.

Crush Down, Crush up was not even Benzant's Idea, as far as I can recall, it was a result of computer simulations. Mass retention.

It is complicated how everything took place.
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Old 4th May 2016, 06:22 PM   #51
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Originally Posted by DGM View Post
Not true. It's used to design models to build future buildings. Is that not reality?

Bazant was not "debunking".
.
No it's not... engineering load tables are used to design buildings and structures... those load tables were originally derived from empirical testing.
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Old 4th May 2016, 06:23 PM   #52
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Originally Posted by Crazy Chainsaw View Post
Actually it shows that any building with the same energy potential compromised in a similar way will under go a similar collapse.

Limited Case is a hypothetical case to determine a structures reaction to the forces placed upon it.

A building is a set of energy structures, the way the energy travels though the structure determines mode of Collapse.

Banzant's method was Eular buckling combined with floor failures.

He choose to use the strongest possible case to counter Claims By Jones and his idiot cohorts. Who even after he proved them mathematically wrong, continued the nonsense.

Crush Down, Crush up was not even Benzant's Idea, as far as I can recall, it was a result of computer simulations. Mass retention.

It is complicated how everything took place.

The same energy potential? Are you nuts?
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Old 4th May 2016, 06:25 PM   #53
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Originally Posted by JSanderO View Post
No it's not... engineering load tables are used to design buildings and structures... those load tables were originally derived from empirical testing.
His model is based on the tables and then put in motion(not necessarily realistic). The definition of a limiting case.
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Old 4th May 2016, 06:36 PM   #54
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Originally Posted by JSanderO View Post
The same energy potential? Are you nuts?
The energy potentials are determined by Gravitational loading, and strength of the structure.
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Old 4th May 2016, 06:37 PM   #55
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Originally Posted by Crazy Chainsaw View Post
Originally Posted by Major_Tom View Post
....Multiple quotes in which both Bazant and David Benson refer to the model within their 2007-2008 papers as describing the actual WTC1 and 2 collapse mechanisms are provided at this link with simple guiding questions that even you should be able to answer.
It describes the energy values as it was intended to do, but the limited case statement shows that it was not intended to represent the actual collapses.

A Computer model of the actual collapses was impossible to produce, too many variables, to much data too crunch.

Shortcuts had to be taken.
Wrong paper Crazy Chainsaw.

Your comments are true for Bazant & Zhou 2002 which was explicitly NOT what Major_Tom OR Oystein were referring to.

Both Oystein and Major_Tom were explicitly referencing the 2007-8 papers which went off the rails starting with Bazant & Verdure 2007. Those later papers use the crush down crush up hypothesis which is specifically a 1D approximation. AND they assert that the cd/cu 1D approximation applied to the WTC Twin towers events.

Bazant was correct in concept with the limit case of B&Z 2002 - and all your comments are valid for the 2002 paper. Such is not in dispute. The error under discussion arose in the later papers which applies the limit case which never happened in reality mechanism to the WTC Twin Towers where it is not valid.

This thread with its loaded question false global assertion strawman OP is (or should be) about Crush Down/Crush Up ["CD/CU"].

Put simply:
1) CD/CU seems to be a valid starting point for Bazant's stated goal of developing a generic modelling for progressive collapses. BUT in its present stage of development it is emphatically 1D - therefore its validity as proposed so far is limited to those cases where 1D approximation is valid.
2) The "progression" for the twin Towers collapses was by definition at least 2D and the 1D approximation is not valid. So CD/CU does not apply to WTC Twin Towers collapses.

The reasoning is simple and has been explained multiple times.

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Old 4th May 2016, 06:51 PM   #56
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Originally Posted by ozeco41 View Post
AND they assert that the cd/cu 1D approximation applied to the WTC Twin towers events.
You're probably aware that that claim is disputed by some people including me, therefore can you cite where that assertion appears, please?
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Old 4th May 2016, 06:55 PM   #57
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Originally Posted by ozeco41 View Post
Wrong paper Crazy Chainsaw.

Your comments are true for Bazant & Zhou 2002 which was explicitly NOT what Major_Tom OR Oystein were referring to.

Both Oystein and Major_Tom were explicitly referencing the 2007-8 papers which went off the rails starting with Bazant & Verdure 2007. Those later papers use the crush down crush up hypothesis which is specifically a 1D approximation. AND they assert that the cd/cu 1D approximation applied to the WTC Twin towers events.

Bazant was correct in concept with the limit case of B&Z 2002 - and all your comments are valid for the 2002 paper. Such is not in dispute. The error under discussion arose in the later papers which applies the limit case which never happened in reality mechanism to the WTC Twin Towers where it is not valid.

This thread with its loaded question false global assertion strawman OP is (or should be) about Crush Down/Crush Up ["CD/CU"].

Put simply:
1) CD/CU seems to be a valid starting point for Bazant's stated goal of developing a generic modelling for progressive collapses. BUT in its present stage of development it is emphatically 1D - therefore its validity as proposed so far is limited to those cases where 1D approximation is valid.
2) The "progression" for the twin Towers collapses was by definition at least 2D and the 1D approximation is not valid. So CD/CU does not apply to WTC Twin Towers collapses.

The reasoning is simple and has been explained multiple times.
Actually I was referring too the computer program not the abstract of the program, there is a significant difference, between the two.
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Old 5th May 2016, 04:24 AM   #58
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Explain how / why the twin towers columns buckled (the ones that did).
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Old 5th May 2016, 05:03 AM   #59
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Originally Posted by JSanderO View Post
Explain how / why the twin towers columns buckled (the ones that did).
The errection welds in the columns would fail once bracing in the core was damaged enough to allow the columns to walk off center which is what you see when you see the buildings tilting, that requires significantly less energy than in Banzant's original Idea.

In other words the computer program showed the buildings did not have enough strength to even spread the top falling mass.

The claim being made at the time by Cters was the buildings should have toppled, or the mass of the top block should have been lost, ejected.

Crush up crush down was a mathematically proven Idea to put those claims to rest, then Cters simply moved the goal posts with missing jolt.

One rediculous claim countered another invented it never ends, with Cters, Goal post just spout wings and fly.
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Old 5th May 2016, 08:14 AM   #60
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Originally Posted by JSanderO View Post
Explain how / why the twin towers columns buckled (the ones that did).
Off-topic for this thread, but it is due to an A×E/L function, using P and M applied loads, an analysis unknown to all but a few millions of peope who have been exposed to 2nd year engineering studies..
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Old 5th May 2016, 08:43 AM   #61
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Originally Posted by ozeco41 View Post
Wrong paper Crazy Chainsaw.

Your comments are true for Bazant & Zhou 2002 which was explicitly NOT what Major_Tom OR Oystein were referring to.

Both Oystein and Major_Tom were explicitly referencing the 2007-8 papers which went off the rails starting with Bazant & Verdure 2007. Those later papers use the crush down crush up hypothesis which is specifically a 1D approximation. AND they assert that the cd/cu 1D approximation applied to the WTC Twin towers events. ...
My comment was worded quite deliberately when I wrote that Bazant in 2007 "pretends" that the cd/cu 1D approximation applied to the WTC Twin towers events; and that this is "incorrect".
This leaves the door open for an interpretation along the lines of pgimeno's long reply to M_T's set of questions half a year ago: That Bazant was following the detractors (JG and GSz?) by accepting (or ignoring) their hypotheses - that the Bazant model would be applicable to the real WTC, to show then that they are wrong within that incorrect frame (and, implicitly, would be even wronger in a true reference frame).

Another case of "Truthers are wrong on every level of detail - the premises, the big picture, the methods, the numbers and all the other details".

A bit like a truther claiming that that animal over there is a pink unicorn with a couple of antlers.
ozeco points out there is no real animal over there.
Oystein nitpicks that the zoologist may pretend that unicorns exist to strike down some claim about them.
pgimeno finds that an animal with a couple of antlers would not be a unicorn.
tfk defends the eminent zoologists's theory of deer.
Chainsaw experiments with pink dye for fur.
All of us are right, and all for the right reasons, and yet we fight like cats.
M_T complains that all of the above are smart idiots, but he cannot admit that there is not, in fact, a unicorn over there, as he used to claim himself years ago.
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Old 5th May 2016, 10:28 AM   #62
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Originally Posted by rwguinn View Post
Off-topic for this thread, but it is due to an A×E/L function, using P and M applied loads, an analysis unknown to all but a few millions of peope who have been exposed to 2nd year engineering studies..
This is not the correct answer. We know what can cause a column to buckle... too much load exceeding compressive strength.. or too slender...

So the question is:

how did the load increase? (assuming it did)

or

how did the capacity significantly decrease (considering the FOS) (assuming it did)

or a combination of the these two

Or maybe another mode leading to buckling???

Heat will decrease the compressive strength of steel. Was there enough heat to drive the stretch below service load?
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Old 5th May 2016, 11:27 AM   #63
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Originally Posted by JSanderO View Post
This is not the correct answer. We know what can cause a column to buckle... too much load exceeding compressive strength.. or too slender...

So the question is:

how did the load increase? (assuming it did)

or

how did the capacity significantly decrease (considering the FOS) (assuming it did)

or a combination of the these two

Or maybe another mode leading to buckling???

Heat will decrease the compressive strength of steel. Was there enough heat to drive the stretch below service load?
Or weakening of the iron crystals, allowing ductile deformation, the Load remained the same the load path changed.
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Old 5th May 2016, 12:24 PM   #64
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Originally Posted by Crazy Chainsaw View Post
Or weakening of the iron crystals, allowing ductile deformation, the Load remained the same the load path changed.
Why would the iron crystals get weaker?
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Old 5th May 2016, 12:46 PM   #65
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Originally Posted by JSanderO View Post
Why would the iron crystals get weaker?
Heat, Iron crystals loose strength when heated, especially where carbon is absent, as in the free ferites created during welding.
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Old 5th May 2016, 01:14 PM   #66
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Originally Posted by JSanderO View Post
So the question is:

how did the load increase? (assuming it did)

Asymmetrical heating of the columns would cause a load increase. A group of columns exposed to higher temperatures or more exposure (Columns exposed to fire on 5 or 6 floors as opposed to ones 2 or 3 floors of fire) will expand and try and lift the the entire weight of the building above them (through the hat truss) on there own.
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Old 5th May 2016, 02:25 PM   #67
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Originally Posted by waypastvne View Post
Asymmetrical heating of the columns would cause a load increase. A group of columns exposed to higher temperatures or more exposure (Columns exposed to fire on 5 or 6 floors as opposed to ones 2 or 3 floors of fire) will expand and try and lift the the entire weight of the building above them (through the hat truss) on there own.
Can you provide some basic calculations to support this?

One inch of steel will expand 0.00000645 inches for every degree Fahrenheit increase in temperature...

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Old 5th May 2016, 02:33 PM   #68
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Originally Posted by JSanderO View Post
Can you provide some basic calculations to support this?
Are you kidding ? Thermal expansion is well known.
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Old 5th May 2016, 02:57 PM   #69
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I don't dispute steel expands... I am curious as to the amount of heat which would cause the columns to expand and buckle. Which columns do you think this happened to?
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Old 5th May 2016, 04:48 PM   #70
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Originally Posted by waypastvne View Post
Asymmetrical heating of the columns would cause a load increase. A group of columns exposed to higher temperatures or more exposure (Columns exposed to fire on 5 or 6 floors as opposed to ones 2 or 3 floors of fire) will expand and try and lift the the entire weight of the building above them (through the hat truss) on there own.
No Columns expanding under load experience slip and tensile destortion as they weaken do to heating.
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Old 5th May 2016, 05:00 PM   #71
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As far as I could see in debris photos... there were remarkably few core columns which buckled.

Then notable one was the horseshoe column which only could buckle as it did if the bottom and the top were restrained. No?
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Old 5th May 2016, 06:17 PM   #72
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Originally Posted by JSanderO View Post
As far as I could see in debris photos... there were remarkably few core columns which buckled.

Then notable one was the horseshoe column which only could buckle as it did if the bottom and the top were restrained. No?
That Column was a perfect U buckle, it probably was the last one to fail, the others likely failed before they completed S bends.
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Old 6th May 2016, 03:40 AM   #73
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Originally Posted by Crazy Chainsaw View Post
That Column was a perfect U buckle, it probably was the last one to fail, the others likely failed before they completed S bends.
So where are the 80 plus buckled columns? (less the ones severed by the planes)?
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Old 6th May 2016, 03:51 AM   #74
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Originally Posted by JSanderO View Post
So where are the 80 plus buckled columns? (less the ones severed by the planes)?
They were on top of the rubble pile and most likely removed before most of the engineers were on site since, they would not have suffered major distortion, only slight bending inducing walk off, they might have been overlooked in the piles of steel at the recycle centers.
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Old 6th May 2016, 03:34 PM   #75
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Originally Posted by Oystein View Post
My comment was worded quite deliberately when I wrote that Bazant in 2007 "pretends" that the cd/cu 1D approximation applied to the WTC Twin towers events; and that this is "incorrect".
Believe it or not I understand.

Let's you and I get back to basics - set aside for now the multiple layers of confusion affecting other members. We (you and I) are at risk of saying the same thing in different ways and thinking we disagree.

The primary issue for this thread is the validity of the Bazant (B&V 2007) CD/CU hypothesis.

tfk OPed the thread after I repeated - in another thread - some assertions I have made many times - viz "CD/CU" is a valid model where it applies. It is a 1D approximation. It cannot apply validly to WTC "Twin Towers" collapse for reasons posted many times.

The OP issued this "challenge":
Originally Posted by tfk View Post
I'm starting this to discuss with Oz (or anyone else) the assertion that Bazant's asymmetric crush down is false.
Which is not the assertion that I made and AFAIK no other member has made that assertion. It conflates the two parts of my statement - simply stated as "CD/CU is OK BUT it doesn't apply to WTC collapses". I have never said CD/CU is false - merely that it doesn't apply to WTC collapses. So a straw-man by implication misrepresenting my position.


Your assertion Oystein is that Bazant may have been pretending or similar for purposes of encouraging debate. No problem for me tho' I doubt it if we read the full setting.

IF Bazant is "pretending" it means that he knows that the 1D approximation does not fit WTC event and is trying to raise discussion so that others recognise it. He already has one convert - me. Except that I worked it out for myself.

If he is pretending - he is right for what he really believes - and it agrees with me.

If he is NOT pretending - he is wrong. And it should be easy to prove to anyone prepared to stop playing games and enter serious discussion. Starting - step one - define what they are talking about. The REAL 9/11 WTC collapse event.

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Old 6th May 2016, 06:04 PM   #76
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Originally Posted by ozeco41 View Post
Believe it or not I understand.

Let's you and I get back to basics - set aside for now the multiple layers of confusion affecting other members. We (you and I) are at risk of saying the same thing in different ways and thinking we disagree.

The primary issue for this thread is the validity of the Bazant (B&V 2007) CD/CU hypothesis.

tfk OPed the thread after I repeated - in another thread - some assertions I have made many times - viz "CD/CU" is a valid model where it applies. It is a 1D approximation. It cannot apply validly to WTC "Twin Towers" collapse for reasons posted many times.

The OP issued this "challenge":

Which is not the assertion that I made and AFAIK no other member has made that assertion. It conflates the two parts of my statement - simply stated as "CD/CU is OK BUT it doesn't apply to WTC collapses". I have never said CD/CU is false - merely that it doesn't apply to WTC collapses. So a straw-man by implication misrepresenting my position.


Your assertion Oystein is that Bazant may have been pretending or similar for purposes of encouraging debate. No problem for me tho' I doubt it if we read the full setting.

IF Bazant is "pretending" it means that he knows that the 1D approximation does not fit WTC event and is trying to raise discussion so that others recognise it. He already has one convert - me. Except that I worked it out for myself.

If he is pretending - he is right for what he really believes - and it agrees with me.

If he is NOT pretending - he is wrong. And it should be easy to prove to anyone prepared to stop playing games and enter serious discussion. Starting - step one - define what they are talking about. The REAL 9/11 WTC collapse event.
No engineer or physicist could possibly produce the equations which describe the real event. It was millions and millions of mechanical interactions and before collapse there was heat effecting hundreds of materials in hundreds of places over m ore than 1 hr. This is simply impossible to describe with math by humans or computers. Accordingly it is a fool's errand and only any attempt would be grossly inaccurate or just no descriptive.

Bazant was a huge detour to people understanding the collapse... which is probably conceptually not very difficult to understand... The initiation is perhaps more challenging because there are so few visual tell tales... and so it requires more understanding of fire science.., materials science and some basic statics.... knowledge of the actual structure and the ability to imagine 3D events though time. The initiation was a process.

+++++

No.... the buckled columns were not on the top of the pile and removed lickity split... there were very few of them and the were not removed before the photos were taken.

Explain why....
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Old 7th May 2016, 01:18 PM   #77
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Sorry, Oy, I wrote most of this response to you a couple of days ago, but was interrupted before I finished it.

Originally Posted by Oystein View Post
I think oz's point is that the WTC towers were not examples of "some tall, uniform cross-section building", since they didn't have a "uniform cross-section". Therefore, the math model that "CD/CU jumped right out of" cannot be validly applied to the WTC.
I meant “uniform vertically, floor to floor”. Not “uniform horizontally, across the cross sectional area”, or homogeneous.

Further, there was nothing in Bazant’s math that required “homogeneity” of the colliding pieces in order to generate cd/cu.

BTW, I disagree, even about the homogeneity.

During the crush-down (which is the period about which we are talking), the lower surface of the upper block is a giant mass of destroyed, compacted debris. There is nothing more uniform or homogeneous than this.

And non-homogeneity only matters if the non-homogeneous components can provide some significant resistance to the collapse forces.

I believe that the weakness of the connections rendered the entire structure mechanically homogeneous in the collapse process.

Even if it was neither visually homogeneous nor mechanically homogeneous as a static structure.

But, again, cd/cu is tied to NEITHER the 1 dimensional nature of his calculations, nor the homogeneity of the cross-sectional area.

Asymmetric crush down emerges directly from the two factors that I listed in the OP:
1) the amount of damage between any two similar structures is proportional to the impact velocity between them, and
2) in a vertical collapse, as soon as the supports for any structure is removed, that structure begins to fall.

As I think about it, there is a 3rd effect that should be noted, as well:
3) Because the compacted mass has a lot of compliance (i.e., is not a solid), then the peak impact forces generated at the bottom of the compacted layer will be significantly attenuated (thru dissipative friction & by spreading out in time and space) by the time that they are transmitted to the upper debris layer / upper block interface.

These are the only (now 3) factors that need to be correct in order for asymmetric crush down to be correct.
(As I said in the OP, I'll address crush up later.)

This is exactly why I started this thread.

By the way, just for yucks & giggles, could you address the points that I made in the OP & here, please.

Originally Posted by Oystein View Post
Bazant's math done to his model is (probably; I didn't check) correct.
I spot checked (read “labored thru, having to review much math”) several steps.

Just as you'd expect from someone who literally wrote the book on the collapse of large structures, everything I checked (in the math) was correct.

Originally Posted by Oystein View Post
Bazant pretending the model describes the actual WTC buildings and their collapse mechanisms is incorrect.
And this is where I don't get the "recreational iconoclasm".

First off, Bazant is an EXTREMELY serious person. There is little levity in any of his conversations. And if he thinks that anyone is bringing up 9/11 CT, the conversation ends immediately.

So, no, I don't believe for one instant that he has ever "pretended" anything.

You've seen his body of work.
You've seen the accomplishments & honors.
He ain’t a god. He ain’t infallible.
But the guy is a bona fide Structural Engineering Genius.

Do you really think that he is unaware of the sort of objections that have been brought up here??
He had several years between his BZ & BLGB. Do you think that, if he thought that one of these factors invalidated his conclusions, that he wouldn’t have changed his analysis?

Originally Posted by Oystein View Post
Of course I could misunderstand him, or you, or both.
Always a possibility. For all of us.
That's what communication is for.
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Old 7th May 2016, 02:04 PM   #78
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For clarity, whenever I’ve mentioned cd/cu, I’ve been expressly interested in “asymmetry crush down”. This is the only portion of the mechanism that seems to be pertinent to any debates about the collapse.

Whenever I’ve used it, it has been in direct reference to the WTC collapse, and to the collapse of any similar tall structure, where the collapse begins in the vertical middle of the structure.

“Crush up” is, IMO, irrelevant. It is technically correct. I believe that there were some structures that must have remained above the crush zone, and therefore not suffered the same amount of destruction (specifically “crushing”) that the rest of the tower suffered. But those structures were absolutely not a “pristine” upper block, as proven by the temporarily standing core column remnant.

So, in order to be clear, I’ll use ACD (rather than CD/CU) to mean “asymmetric crush down”.

Originally Posted by ozeco41 View Post
tfk OPed the thread after I repeated - in another thread - some assertions I have made many times - viz "CD/CU" is a valid model where it applies. It is a 1D approximation. It cannot apply validly to WTC "Twin Towers" collapse for reasons posted many times.
In that other thread, and many other times, you have made the assertion that “cd/cu is wrong in the case of the WTC towers”.
When I asked you “why you thought that it was wrong”, you didn’t tell me the basis for your assertion, but asserted that my question was a derail.
Although your assertion was, somehow, not.

So, I OP’d this thread.

Seems pretty straightforward to me.

Originally Posted by ozeco41 View Post
The OP issued this "challenge":
You’ll have to enlighten me on your distinction between “asking a question” & “issuing a challenge”.
I thought I asked you, politely, a simple question.

Originally Posted by ozeco41 View Post
… and AFAIK no other member has made that assertion.
Let the other members speak for themselves, please.

Originally Posted by ozeco41 View Post
It conflates the two parts of my statement - simply stated as "CD/CU is OK BUT it doesn't apply to WTC collapses". I have never said CD/CU is false - merely that it doesn't apply to WTC collapses. So a straw-man by implication misrepresenting my position.
Not a straw man. I’ve only ever discussed CD/CU (or ACD) in the context of the WTC collapse.

As before, you state, “"CD/CU" is a valid model where it applies, but it doesn’t apply to the WTC”.

As before, I’ll ask you to please clarify for me what factor differentiates the conditions under which you think it applies, from those conditions in which it does not apply.

In that context, hopefully you make clear WHY you think that it does not apply to the WTC.

Originally Posted by ozeco41 View Post
Your assertion Oystein is that Bazant may have been pretending or similar for purposes of encouraging debate. No problem for me tho' I doubt it if we read the full setting.
Bazant is a very, very serious man. I am quite sure that he doesn’t “pretend” anything.

Originally Posted by ozeco41 View Post
IF Bazant is "pretending" it means that he knows that the 1D approximation does not fit WTC event and is trying to raise discussion so that others recognise it. He already has one convert - me. Except that I worked it out for myself.
You are asserting that the collapse can not be mathematically modeled by a 1D set of equations.
Of course, this is wrong.
Bazant already did so. As have several other people.

How much the ACCURACY of the model suffers from a 1D assumption is a different matter.
I’ve seen lots of assertions, from you & others, that the collapse can NOT be modeled with a 1D assumption. Equivalent to asserting that “the accuracy drops to a uselessly low value”.

I’ve yet to see any proof or analysis as to why you believe this to be the case.

Originally Posted by ozeco41 View Post
And it should be easy to prove to anyone prepared to stop playing games and enter serious discussion. Starting - step one - define what they are talking about. The REAL 9/11 WTC collapse event.
Yes, I have been talking about the REAL WTC collapse event.
And about Bazant’s analysis that asserts that the crushing down action is very asymmetric.
And whether Bazant’s conclusions accurately reflect what happened in the real WTC collapses.

Perhaps as an example of serious discussion, you might be inclined to address the points that I brought up in the OP…
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Old 7th May 2016, 04:03 PM   #79
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Originally Posted by tfk View Post
...
I’ve seen lots of assertions, from you & others, that the collapse can NOT be modeled with a 1D assumption. Equivalent to asserting that “the accuracy drops to a uselessly low value”.

I’ve yet to see any proof or analysis as to why you believe this to be the case.
I would assert that a more accurate description of what was happening up to and including the visible downward motion of the 4 facades and roof.... would be that the insides... outside the core slabs and inside the core slabs and beams and columns were slowly over time becoming disengaged from the structural matrix and dropping down through the plane strike zone onto the upper floors of the lower section and accumulating a threshold mass which would be the crush front of the runaway progressive floor collapse.

I would further assert that there were very few buckled columns... and the downward movement was a result of mis aligned core columns pushed out of alignment by heat expanded beams/girders as the column to column connections were unrestrained and just a few splice plates.

Ultimately there was a few columns supporting what was left of the core structural matrix and they did buckled and are responsible for the tilting and lateral translation of the upper facade, hat truss and a few floors within the hat truss and roof of course. Most of the rest of the inside from the crash zone to the hat truss has already separated from the matrix and dropped done onto the lower section in the last moments before "release".

So it was not the top block crushing /crashing into the bottom one. It was a few remaining columns, sections of attached floors and the facade columns hitting the floors outside the core which were still attached to the facade.

This was an accelerating progressive process over the 1 1/2 hr post impact for 1 wtc... and less for 2 wtc.
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Old 10th May 2016, 06:01 PM   #80
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Originally Posted by tfk View Post
...As before, you state, "“CD/CU" is a valid model where it applies, but it doesn’t apply to the WTC”.

As before, I’ll ask you to please clarify for me what factor differentiates the conditions under which you think it applies, from those conditions in which it does not apply.

In that context, hopefully you make clear WHY you think that it does not apply to the WTC.
The hilited section is the core of a claim I have made on numerous occasions and supported with as much reasoned argument as was appropriate at the time. Since you correctly identify my claim in a post which also raises multiple process, personal and other extraneous comments I will present my argument supporting my claim in this post. I may - in a separate post - respond to such examples of the other issues which may help us resolve any differences. So see this post as:

Part #1 The Technical Issue. This is the claim I will support:

The "Crush Down/Crush Up" ["CD/CU"] mechanism as presented in the paper "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions" by Bazant and Verdure in 2007 is not valid as an explanation for the actual - "real event" - WTC Twin Towers collapses.


Please note that my claim goes to the technical validity of the B&V 2007 assertions about CD/CU. Not Bazant's motivations, skills, reputation or whether or not he intended in B&V that CD/CU apply literally to WTC Twins 9/11 collapses. I intend to address the straight forward technical issue - "Is it valid or not for WTC Twins?" I may be interested in pursuing the other issues at a later second or third stage.


Summary of Context for My Claim and Supporting Argument.

The scenario is the collapse of the WTC "Twin Towers" on 9/11. Explained as a matter of engineering forensics where the extant hypotheses dismiss claims for malicious human intervention in the form of CD.

Both "Twin Towers" collapses involved two (or three) stages - viz "initiation" which allowed the "top section" to fall and "progression" which completed the global collapse. For purposes of this explanation we can also recognise a "transition" stage. The boundaries between the two or three IMO are not critical. If that setting presents any problems please say what problems, why they are problems and what you would need to remove any barriers to reasoned discussion.

I will identify three issues of evidential fact which are fatal to claims that CD/CU applies to the "Twin Towers". One for each stage - "initiation", "transition" and "progression".

There are two significant issues which you have raised. One is a "way forward" which I have discussed at some length with other members and elsewhere. The other is a fundamental misunderstanding that you rely on.

However I need to address the the central issue of confusion which is the same one which has caused problems in discussions for many years. So briefly here it is.

Columns, Limit Cases and the "Real Event Mechanisms".


Bazant in B&Z 2002 IMO correctly identified two issues which I take as premises for this explanation. They were:
1) He applied the concept of a "limit case" and the concept of "limit case" is valid as he with Zhou used it in 2002;
2) In the same paper he clearly distinguished the "limit case" from the real event which was too complicated to analyse in the time and other limits at that time.

The essential issue for purposes of this explanation is that the limit case case presented maximum resistance to collapse by including all columns taking axial loading. He recognised that the "real mechanism" involved less than "all columns" offering axial loading resistance. I think we are agreed on those two and the distinction.

I would also assert that later research has established that - for the real mechanism of the progression stage - the number of columns offering full strength resistance in axial loading was essentially zero. If you do not accept that premise it matters not - this explanation does not rely on "essentially zero" - the original Bazant premise of "less than all" will suffice.

So we have two distinctly different situations - the "limit case" model which never happened but includes all columns providing maximum resistance via axial loading and the "real event" which had fewer columns contributing such resistance. And I would assert "fewer" in the real event was "essentially zero" but the exact proportion is not critical here.

Which brings me to those "...three issues of evidential fact which are fatal to claims that CD/CU applies to the "Twin towers".

All three relate to the wrong reliance on the "all columns in line" or "limits case" model which did not happen in the "real event".


#1 - Why CD/CU in not valid in progression stage.
(a) B&V is explicit in that the CU/CD model is the "all columns in line" or "limit case" model THEREFORE not the mechanism of the "real event"
(b) B&V is explicit that it is a 1D model which - by definition - is "homogenising" - it puts the columns "in-line";
(c) The maths provided in support of B&V is also based on "columns in line".

The real event was definitely not "all columns in line" HENCE the B&V CD/CU applied to WTC is falsified.

There are some issues to note for later follow up. They include:
(p) Your explanation and application of 1D "homogeneity" is not correct. In brief you recognise "homogeneity" of the falling mass of debris - but your explanation is actually 2 or 3D not 1D and you do not recognise "homogeneity" for the lower tower which is where the 1D resistance occurs. Fuller explanation if needed - it is not relevant to discusion of my claim.
(q) You go outside the scope of my claim abut B&V. I do not "assert that the collapse can not be mathematically modelled by a 1D set of equations". In fact I have on previous occasions suggested a direction for improvement for B&V. What I do assert is that B&V 2007 does not model the actual WTC collapses. Your opinions on areas for possible improvements align closely with my own. This bit of your post:
Quote:
You are asserting that the collapse can not be <<"is not at present" mathematically modelled by a 1D set of equations.
Of course, this is wrong.
Bazant already did so. As have several other people.


How much the ACCURACY of the model suffers from a 1D assumption is a different matter. << Which I've discussed previously but is not within the scope of this current explanation.
I’ve seen lots of assertions, from you & others, that the collapse can NOT be modeled with a 1D assumption. << I've said "it is plausible" BUT "I doubt it is practical/pragmatic" Equivalent to asserting that “the accuracy drops to a uselessly low value”. << Not really - the challenge would be to get it UP to a practically useful accuracy.

I’ve yet to see any proof or analysis as to why you believe this to be the case.

#2 - Why CD/CU in not valid in transition stage.
Best shown by a graphic. CD/CU needs the columns in line resisting falling by taking axial load. This graphic shows dramatically the extreme example - why the columns would never be in line:

That same graphic also shows why CD and CU started essentially at the same time - at the start of progression.

The arrows show how the perimeter columns put concentrated loads on the open office space floors of the outer "tube". "Downwards from above on the left and upwards from below on the right.

And those are the two extreme examples but the same situation applies to all six other sides - the falling "Top Block" fell with column ends already misaligned.

So Crush Up could never wait till the bottom to occur after Crush Down.

#3 - Why CD/CU in not valid in initiation stage.
This goes to the heart of the Szamboti misunderstanding and misapplying Bazant.

The "B&Z Limit Case" concept was valid - as a limiting explanation of the progression stage. BUT it used an artifice to do the initiation. B&Z "dropped" the top block. Szamboti took that literally and quite a few others have fallen for the trap.

How can the Top Block ever be "dropped" to land with uniform concurrent impact across the full array of columns?....

I've postulated - tongue in cheek - use of a 1500ft high mobile crane to take the weight of the Top Block - and a quick release hook. Take weight >> cut all columns >>>drop.

The scenario is IMO impossible. (Whilst the actual (real) mechanism by "scrunch down" not drop automatically ensured column ends missing.)

BUT the more serious previous paragraphs have already falsified B&V's claim that CD/CU as per their 2007 paper is valid for WTC collapses.

Conclusion and directions for further comment from me.
(X) This post gives a sufficient introduction to my support of the claim that:

The "Crush Down/Crush Up" ["CD/CU"] mechanism as presented in the paper "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions" by Bazant and Verdure in 2007 is not valid as an explanation for the actual - "real event" - WTC Twin Towers collapses.

(Y) I'm preparing a response to your counter claim tfk - watch this space; AND

(Z) I may respond to the plethora of extraneous matters you have raised - especially those that raise valid points for ongoing discussion.

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