I found the missing Jolt.

[FalseFlag]

The contention always was that ALL vertical support must be removed in order for free fall and that this meant all columns needed to be exploively removed.. Debunkers pointed out that various mechanisms meant that such full removal of columns was not required. Tony agrees.
It is not necessary for all vertical support to be removed over 8 storeys in order to have the collapsing structure achieve free fall.

Please provide a link to support your claim. Thanks.

I am looking for the part where Tony agrees completely with the statement.

 

[tfk]

What is interesting here is you provide no basis for your claims. Lateral strength of columns goes down with unsupported length. The more slender the column the less force is required to pull it inward. If the entire east side interior fell per the NIST story how much lateral force would it have taken to pull those now laterally unsupported 40 story columns inward? Let's not forget that they say the collapse started at the 13th floor and first went down to remove support of column 79 and then up after it buckled.

You need to show that an inward pull on the east side columns by the falling beams would be less than the lateral strength of an unsupported column at all times. People here should know that the connections of the beams to the columns were welded seats inside the flanges and top clips welded to the web of the column. There were two 7/8" diameter bolts at the seat and two at the top clip. These bolts were ASTM A325 with a proof strength of 105 ksi and thus a shear strength of 57.7% of that or about 60.6 ksi. A 7/8" diameter bolt has a shear area of .601 in^2 so each would require about 36,000 lbs. to shear. This means the bolts would apply 144,000 lbs. at the connection before breaking. tfk needs to show that the columns could take this without deforming in a permanent way at each beam connection to the east wall after columns 79, 80, and 81 buckled. The drawings show there were 17 interior beam connections to the east wall at each floor. After those three columns allegedly buckled per NIST the entire east side interior would have been pulling on that wall with 144,000 lbs. x 17 at each floor. That is about 2.5 million lbs. per floor and if 30 stories were pulling on it there would have been about 75 million lbs. pulling it inward. In spite of that, NIST and tfk just want to tell you the connections broke before the wall deformed because it was stronger and because it was strong it could wait for the rest of the interior to come down before it decided to give it up and come down itself.

You know, Tony, it is embarrassing that you were able to - somehow - get yourself a Mechanical Engineering degree. You’re like the guy who gets falling-down drunk at an office party & then starts hitting on someone else’s wife. The first time this happens, you’re likely to let it go to poor judgment. The 50th time it happens, the moron just pisses everybody off.

You’re on your 1500th time.

Stop seeing just lines on a piece of paper, and start TRYING to think about real hunks of metal, relative strengths, & directions of forces.

First of all, get the connections correct. There were NO top clips used on any of the external connection on the east wall.

Here’s the framing drawing. Look at the callouts for the external wall connections. They are all “STP” connections.

NCSTAR1-9, vol 2, pg 27
Fig 2-21

Here’s a picture of an STC (Seat & Top Clip) connection.

While, there is no image of an STP connection, you simply replace the Top Clip with a Top Plate. Since it’s purpose is merely to prevent rotation of the beam (not carry gravity loads), that plate will likely be significantly thinner than the seat plate. Just as the top clip shown above is much smaller sections than the seat plate & stiffener plate.

So, there are the parts.

Why don’t you sit down, imagine that the right end of this long, long, (big hint: LONG) girder/beam is descending with a collapse of the core. What does your fevered imagination tell you is going to be the local MOTION of the girder/beam at the connection shown?

What is going to happen at the point labeled, "What Happens Here??".

Is that beam/girder going to SLIDE horizontally, to the right?
Answer: No.

With the correct motion of the girder/beam, is the failure mode going to be a SHEAR failure of 4 bolts?
Answer: No.

Are the top clip bolts going to fail at all?
Answer: No.

What is going to be the failure mode of the Top Plate Assy?
The plate-to-column weld is going to tear.

How are the seat bolts going to fail?
Answer: Pure tension. The threads are going to strip or the head/shoulder of the bolt is going to pop.

How much inward force is going to be applied to the external column during this failure?
Answer: A tiny amount. It’s going to put a relative small, local bending moment on the column, and there will be a small inward deflection of the external column to allow the geometry changes to occur.

Even if it somehow magically didn't deform while the interior was allegedly coming down, the east side exterior should have buckled under its own weight once the interior beams supporting it fell per the NIST story, but in that fantasy it waits for the alleged progressive interior collapse to take the west side interior down and only then do exterior columns buckle …

What gives tall,thin walls their stiffness, Tony? Lateral support.
Tall, thin walls, alone, are very unstable.

But if they are braced in a direction normal to the walls, then they become stable.

I attempt to stand a flat piece of cardboard on its end, it falls over.
If I take the cardboard, and glue it into a giant trapezoid, then suddenly it becomes very stable.

When the inner core collapsed, was the eastern wall isolated from the north & south walls?
Or were they all still attached to each other?

What else gives strength & stability to tall thin walls, Tony?
Linear density of the columns (i.e., columns/foot).

How did the linear density of the exterior wall columns compare to the linear density of the core columns, Tony?
Look at Fig 2-21 above, Tony.

… only then do exterior columns buckle under their own weight with the entire exterior coming down as a unit. What an absolute crock the NIST story you are trying to defend is.

Yup, there is a crock running around here, all right.
But it ain’t NIST’s crock, Tony.

“… buckle under their own weight …”
Oh, really, Tony?

And in the collapse of the core of a building, can you think of anything, anything at all, that might be putting a LATERAL LOAD onto the inner walls of the building, down near the bottom of the collapse.

I’m just curious … do you think that all the 47 stories of debris are going to stack themselves, neatly, into a nice, neat pile, the same width & breadth as the footprint of the building?

When little Tony Szamboti was playing with his Lincoln Logs, and built a tall “building” which then collapsed, did the logs end up stacked in a nice neat pile, all within the “footprint” of the building?
Or did they tend to spread out a bit?

Do you think that the debris might have put a teensy bit of outward, lateral force on the external walls, down low, as it collected into a pile?

Did the walls “collapse under their own weight”, Tony?

The daylight visible after the east penthouse comes down is only in the top story windows. That does not provide any proof that the entire east side interior came down, after initiating at the 13th floor, to cause the east penthouse to fall. It only proves the east penthouse fell below the roofline.

So, we have heavy fire in the lower stories of the building.
We have NO fires, of any size, in the top stories of the building.

And having witnessed this, it is your (moronic) contention that the failure of the EPH had NOTHING TO DO with the multi-story fires on the 5th - 13th floors.

It was just a friiggin’ coincidence that suddenly, without any damage in the 45th - 47th floors, without any fires in the 45th - 47th floors, without any change whatsoever in the physical structure of the 45th - 47th floors, those structural components are simply going to pick this moment to suddenly fail.

Is that what you are suggesting, Tony?
That it was a coincidence?
That the failure of the 45th - 47th story vertical framing had NOTHING TO DO with the fires in the lower floors?

This is as brain-dead as the morons who allege that the collapse of the towers had nothing to do with the planes flying into the side. That it was “just a coincidence”.

You’re an embarrassment to the profession, Tony.

I won't even get into your denial that WTC 7 was in free fall during its descent. False Flag already asked you to show your work there.

It is fully expected that False Flag be utterly clueless about the details of the “ill posed math problem” associated with taking two derivatives of coarsely sampled data. And with the implications of forcing a “linear interpolation” onto any arbitrary velocity data.

Because he is a complete amateur and a willful, clueless idiot.

It is willful mendacity for an engineer, who has been beaten about the head & shoulders for years over these same, explicit arguments, to disclaim knowledge of these issues.

Why must you constantly lie, Tony?
You really, really, really should be ashamed of yourself.

 

[tfk]

Would that be "embarrassing", as in someone who insisted that "the foundations of the WTC were accelerating at G for 31 years"??

Are you claiming that they were not?

I am not "claiming" that they were not.

Any more that I would "claim" that 1+1=2.

I am telling you that they were not.

Are you sure about this?

Quite certain.

Why don't you tell us what you "claim" they were doing.
With respect to the ground's frame of reference.

We'll leave celestial mechanics out of this discussion.

What is at least one of the action-reaction pairs if the foundation is the first part?

Why don't you try to do a competent force diagram, and see what you get.

You should know that you're embarrassing Tony.
This is one stupid claim that he made years ago, that he'd just as soon NOT be brought up.

I think it's hilarious, because it shows how easily confuzzled Tony (Da Twoof's "engineering star") gets with simple concepts.

 

[tfk]

It actually isn't even a question. It is a false dilemma created by those who somehow still want to believe WTC 7 was not taken down by controlled demolition.

LMAO. Says the clown who refuses to take his stupid assertions to any competent, independent panel of structural engineers.

Who REFUSES to discuss this topic with competent people.
Who, instead, posts incompetent crap on the internet.

C’mon, Tony.
False Flag, MicahJava are basing their stupidity on YOUR assurances to them that you are correct in your stupidity. You have a responsibility to them, an obligation to them, to show that you’re not a coward about these issues.

So tell them. Tell False Flag, MicahJava & the others why you, & Gage & Cole bring your crap to architects. Guys that do NOT know about failure modes, stress analyses, progressive failures, or collapse dynamics. Tell them why you clowns have NEVER brought your nonsense to the ASCE or SEAoNY. Tell them why you will NEVER do so.

Explain it to them, Tony.

False Flag, Micah. I told you that you should be demanding of those that you choose to believe.
Here’s your chance.

Are you going to learn anything?

WTC 7 came down even with the horizon …

Stupid, irrelevant argument. That is false.

It came down approximately even with the southern horizon.
It didn’t come down even with the eastern horizon in the slightest.

There goes your stupid argument, Tony.

The question of “why did it come down approximately even with the southern horizon is an interesting mechanical question.

With a very, very simple answer, which has nothing whatsoever to do with explosives or CD.

and at free fall acceleration for over 100 feet within half a second after it started to fall.

Approximately free fall acceleration.
After 0.5 seconds of zero acceleration.

Hey Tony, when buildings are “blown”, using explosives, how often do they hang in the air for 0.5 seconds after the charges go off?

Did you study you physics at the Acme Road-Runner School of Engineering?
Was Wylie Coyote your physics prof?

The only possible reason for that is that all of its core columns were removed over at least eight stories starting at the center and moving outward over a fraction of a second.

Close, but no cigar.

The answer is that the external walls were much stronger, due to their close column spacing and short lateral bracing, than the connectors that connected them to the internal beams & girders. And that there was a failure mode in these connections that did NOT require huge pull in forces when the connections failed.

So this left the external walls standing, when the eastern portion of the core collapsed.
And it left the outer walls of the North, West & South walls standing for a few seconds while the core columns DID collapse, over about 8 stories (5th to 13th).

But you’ve got the failure at the center, backwards.

It failed at the center of the building last. Not first.
And this has a fair amount to do with why it did fall nearly straight down.

Down low, on the 5th thru 13th stories, the center rows of columns, Groups 3 (C73 - C75), Group 4 (C70-C72) & Group 5 (C67 - C69) hung in the longest, and failed last. (See NCSTAR1-9, Fig 12-58) Group 5 failed last.

So, just before global collapse, the building was supported at its center of mass (since the eastern core had long since collapsed) and all around the periphery by the external columns.

This is a nice, symmetrical support geometry, even if it is only temporary.
THIS is why the building failed approximately symmetrically. Because the last remaining supports were distributed symmetrically around the periphery, and at the center.

But the falling debris caused the external walls of the western end of the south & north walls to buckle, down low. As seen in NIST’s simulation.

Do you see the outward 3-hinge buckle, that I’ve emphasized in red?

The rubble pile is conical with the exterior laying on top.

And did the lateral extents of the rubble pile stop at the inside edges of the columns, or did they extend just a bit further out.

Fire and progressive collapse could not possibly do that so quickly,

What a stupid thing to assert.

At the start of the ultimate collapse, the stress overloads move thru the steel at about 5000 m/sec. About 16,000 ft/sec. The component failures will happen much more slowly than this, of course, as parts bend & flex before failing. But there is no problem whatsoever, with the stress waves & last, global collapse moving thru the external wall & remaining core columns in less than 1 second.

even if a fire induced failure started at the center and worked outward, as some here have tried to speculate.

Nope.
Started at the East end of the building. Floors 13 down to 5. Then upwards, from 13 to roof.
The external walls stood, because the connections from the columns to the beams were very, very weak when the inner end of the beam (attached to the core) moved downward, thereby rotating the end of the beam about a pivot point just inside the seat bolts.

Then an 8 story failure (floors 5 thru 13) moved west thru the core.
Again, the external walls stood.

A 2nd 8 story failure (floors 5 thru 13) started at the west end, and moved east.

The two met in the middle.

At this point, just before global collapse, the building was a 34 story building, with a collapsed eastern core, and a sturdy outer trapezoidal frame, standing on 8 story stilts (the outer columns, from the 5th to 13th floors). The last core columns failed, and the outer walls buckled, pushed outward by the falling internal debris.

Whenever a tall (in this case, 8 story), bolted together wall buckles, its load carrying capacity goes rapidly to just about 0. Because the failure mode is usually stopped bolts or welds.

Under these conditions, a NEAR zero resistance (compared to the weight of the remaining building) is surprising to no competent mechanical or structural engineer. It’s not “at zero”, it’s “NEAR zero”.

A NEAR zero resistance produces an acceleration that is NEAR TO “G”. It’s not “at G”, it is “NEAR G”.

The total explanation for everything that happened is that the external walls of the building were more robust than the connectors that joined the columns to the beams.

It’s really quite simple.

Even if you can’t understand it.

 

[tfk]

That photo is showing the roll to the south at the end of the collapse, which has nothing to do with and is not indicative of what I am talking about.

"The end of the collapse", Tony, is when the roof meets the top of the debris pile.

So, your "it's parallel with respect to the south horizon" is gravely significant.

But the fact that it is "tilted with respect to the eastern horizon" is of no significance whatsoever.

LoL.

That's an amusing world in which you dwell, Tony.

There is no deformation of the exterior at the beginning of the exterior collapse when the NIST report claims the entire east side interior had come down several seconds before to cause the east penthouse collapse. How can that be?

The connections along the inside exterior wall had snapped ~12 seconds before the start of global collapse, Tony.

The pull in forces on the exterior wall during those connection failures was very small. Little deformation would be expected.

The eastern edge of the north wall was unloaded.
No deformation would be expected.

"How can that be?"
Easy.
And peasy.

 

[fuelair]

Proof?

180!!!!!

 

[jaydeehess]

Please provide a link to support your claim. Thanks.

I am looking for the part where Tony agrees completely with the statement.

It took all of five seconds to find another poster saying exactly this
http://www.internationalskeptics.com/forums/showpost.php?p=9314026&postcount=28

Let me see what else I find.

 

[LSSBB]

Tom, great explanation. I feel like I'm watching a great economist trying to convince Hugo Chavez to admit to his chavisimist followers that socialism doesn't work, though.

 

[jaydeehess]

http://www1.ae911truth.org/news-section/41-articles/872-freefall-and-building-7-on-911-by-david-chandler.html
Hilite and bolds mine.

he fact remains that freefall is not consistent with any natural scenario involving weakening, buckling, or crushing because in any such a scenario there would be large forces of interaction with the underlying structure that would have slowed the fall. Given that even known controlled demolitions do not remove sufficient structure to allow for actual freefall, how could a natural fire-induced process be more destructive? Add to that the synchronicity of the removal of support across the whole width of the building, evidenced by the levelness of the roofline as it came down, and the suddenness of onset of collapse, and the immediate transition from full support to total freefall. Natural collapse resulting in freefall is simply not plausible. It did not happen. It could not happen. Yet freefall did in fact happen. This means it was not a natural collapse. Forces other than the falling upper section of the building suddenly destroyed and removed the supporting columns for at least eight stories across the entire length and width of the building.

Apparently, as of 2014, AE911T was content with Chandler expressing the view that ALL COLUMNS for 8 floors height, were removed "suddenly".

So, I assume that FF and TSz disagree with Chandler?

 

[jaydeehess]

Indeed the contention that a period of free fall is indicative of demolition has never been more than unsupported bald assertion.
The contention always was that ALL vertical support must be removed in order for free fall and that this meant all columns needed to be exploively removed.. Debunkers pointed out that various mechanisms meant that such full removal of columns was not required. Tony agrees.
It is not necessary for all vertical support to be removed over 8 storeys in order to have the collapsing structure achieve free fall.

No, now we are told that only interior columns need be removed with explosives, and that the NW and NE corners beginning their downward movement in sync is what is indicative of interior explosive use. Little mention of free fall.
Odd though, debunkers point out that the commonly accepted scenario includes destruction of interior columns too.
How is it that destruction of only interior columns both can and cannot cause the east and west faces to fail at the same time?

Please provide a link to support your claim. Thanks.

I am looking for the part where Tony agrees completely with the statement.

Tony says that only the core columns need be taken out. The NIST scenario has the core columns being destroyed.
Chandler stated clearly that ALL support over 8 storeys had to be removed. Debunkers said no, Tony says no.

But Tony says that the observed collapse cannot be brought about by the NIST scenario of core destruction.

So, again I ask, how is it that destruction of core columns both can, and cannot, result in the observed collapse?

So does Tony fully agree? Well he notes a period of free fall, and he states that the exterior columns need not have bee blown out with explosives to result in that period of free fall. So yes, Tony fully agrees.

 

[jaydeehess]

"The end of the collapse", Tony, is when the roof meets the top of the debris pile.

So, your "it's parallel with respect to the south horizon" is gravely significant.

But the fact that it is "tilted with respect to the eastern horizon" is of no significance whatsoever.

LoL.

That's an amusing world in which you dwell, Tony.

.

Its typical parsing of reality that truthers engage in constantly.
-Free fall in WTC7 is 2.25 seconds long. --- OK but note that the building had been descending for 1.75 seconds before that period and that the entire collapse sequence takes nearer 20 seconds. Truther reply is to completely ignore this.
-Three WTC structures completely destroyed. ---- Ok but in fact all 7 WTC structures were destroyed/unrepairable, along with several other buildings. Truther reply is to completely ignore this.
-As you point out "even with the horizon" only applies from one angle and only through part of the collapse. "Symmetry" also only applies, approximately, to the fall of the NE and NW corners, for part of the global collapse. The building split in two, one portion being twice the size of the other(ie. not symmetric), one portion twisted and fell to the NE whereas the larger portion tilted south (ie. not symmetric)
- There was great hue and cry that the Verizon and Post Office buildings were not impacted by WTC7's collapse. In reality the long axis of WTC 7 is East to West and tilting to either the East or West therefore is rather difficult to accomplish. A fact ignored by truthers.
"It was done to limit collateral damage" is the call. Tell that to the thousands of dead and the owners of the destroyed structures including the church. Tell that to the Fitterman Building owners, tell it to the people who lost value in their pensions in the economic aftermath of 9/11/01.

 

[Oystein]

https://www.youtube.com/watch?v=JnLcUxV1dPo

At 5:30
7:35 and quite well at 8:00

Thanks.
All three views that you direct me to are with a camera on ground level looking up from relatively near.
If you compare with shots from cameras that are far away in upper stories of other highrises, you cannot really spot that kink. E.g. 4:20.
This proves that the kink went mainly in the horizontal (north-south) dimension, while the north face roofline remained almost straight. As Tony contends.

This implies that, while a part of the eastern wall of the north face was pulled in by the failing eastern core, the columns on the north face buckled within a very short time interval of each other.

However, even if this tilt is characterized as due to east section pull in, it happens before the failure of the east exterior columns.

Right.

If, as is contended, all exterior columns fail at once then the roofline would fall and remain horizontal, as would all other floors.

Right.

Similarly for the western section. In order for the north exterior to demonstrate all these floors tilting towards the kink, ...

I don't get what you mean by this

...the north face exterior columns must be buckling. They must be further along in buckling nearer the kink than towards the east and west, AND, of course, the east and west face exterior columns then fail after the north face exterior columns.

Perhaps, but that apparently is (almost) imperceptable.

No wonder the east and west fail, they've been pulled out of vertical.

I thin, more importantly, the failure of the entire core means the wall has lost lateral support.
Or put differently, to marry both views: The buckling core turns lateral support into lateral load that actively works to buckle the wall by pulling it out of plumb.

Due to the shorter distance between kink and east than between kink and west, the east exterior tilts more. BUT recall that the west has no SW corner columns, which will serve to have the west exterior fail at a lesser tilt than the east which has bot NE and SE corners intact.

East ... wall, or east side of north wall?

 

[GlennB]

One minor detail that I can't remember being analysed much (it might well have been though) is the behaviour of the western rooftop structure. Call it the W Penthouse or WP for the sake of a name.

It begins to fall at the same time as the N roofline, but the WP falls noticeably faster in the early stages. Also, the eastmost part of the WP falls fastest.

I lack the video skills to analyse this properly, so these are just eyeballed observations and estimates. It's probably clearest on the Rather video:



Thoughts? This probably totally proves CD, but I find it interesting

 

[jaydeehess]

Thanks.
All three views that you direct me to are with a camera on ground level looking up from relatively near.
If you compare with shots from cameras that are far away in upper stories of other highrises, you cannot really spot that kink. E.g. 4:20.
This proves that the kink went mainly in the horizontal (north-south) dimension, while the north face roofline remained almost straight. As Tony contends.
.....Perhaps, but that apparently is (almost) imperceptible.......

"Almost imperceptible", yet to my eye it is there. Perhaps dominant in the N-S inward, ( I fail to see that as "horizontal" though") but also in the N-S and downwards.
Basically both /\ looking down on the north face, and \/ looking at the roofline from the south.

This implies that, while a part of the eastern wall of the north face was pulled in by the failing eastern core, the columns on the north face buckled within a very short time interval of each other

No argument there. It did happen quickly. However the very fact that the line of the kink is lower than the east and west walls demonstrates that exterior failures start on the north face, about 1/3rd of the way from the east face.

I don't get what you mean by this

My poor quick diagram:

I think, more importantly, the failure of the entire core means the wall has lost lateral support.
Or put differently, to marry both views: The buckling core turns lateral support into lateral load that actively works to buckle the wall by pulling it out of plumb.

Sure, and some characteristics of each portion, east and west of kink, would speed that portion's collapse, while others would slow it. For instance, while the eastern section is smaller than the western, each has very different core construction. The east has very large trusses but no cantilever girders like the west does. The east has two intact corners, NE and SE. The western portion lacks a SW corner and has other south face damage.

East ... wall, or east side of north wall?

East wall versus west wall. There is more pull in exerted on the east wall. The distance between east face and kink is shorter than to the west face. So a deflection of x meters at the kink means a lesser angle along the members connecting kink to west than connecting kink to east.

 

[jaydeehess]

One minor detail that I can't remember being analysed much (it might well have been though) is the behaviour of the western rooftop structure. Call it the W Penthouse or WP for the sake of a name.

It begins to fall at the same time as the N roofline, but the WP falls noticeably faster in the early stages. Also, the eastmost part of the WP falls fastest.

I lack the video skills to analyse this properly, so these are just eyeballed observations and estimates. It's probably clearest on the Rather video:



Thoughts? This probably totally proves CD, but I find it interesting

What is implies is a progression of core failure from the vicinity of col 79, to the west. Note that if this is core failure low down in the structure, say below the 8th floor, the effect at the roof is delayed. Thus the core destruction has continued further west than the hole that swallows the western roof structures. By the time the western roof structures are falling in the core is almost completely destroyed lower down, so global collapse occurs while the western structures are falling in. Note also that eastern progression is much slower. Probably due to the heavier construction and the fact that the east doesn't have cantilever girders supporting 40 storeys over the original Con-Ed substation.

 

[Oystein]

Gotcha, jdh (your poor diagram).
The kink still goes mainly inward, not down.

 

[Oystein]

One minor detail that I can't remember being analysed much (it might well have been though) is the behaviour of the western rooftop structure. Call it the W Penthouse or WP for the sake of a name.

It begins to fall at the same time as the N roofline, but the WP falls noticeably faster in the early stages. Also, the eastmost part of the WP falls fastest.

I lack the video skills to analyse this properly, so these are just eyeballed observations and estimates. It's probably clearest on the Rather video:



Thoughts? This probably totally proves CD, but I find it interesting

The west penthouse starts descending from the east, with center and west portion following behind.
The eastern corner of the WPH clearly starts descending before the north wall does.
The center of the north wall descends before the NW corner does.

Because the NW corner falls last, it actually accelerates the most.


Sequence:

Columns 79-81 buckle - EPH kinks and falls
Girders from c79 tug eastern part of north wall inwards - north face kink begins to form
East core falls to the ground, loads next row of core columns laterally
Easternmost row of 3 main core columns (c76-78) buckles - east edge of WPH starts to descend
In rapid successions, all other core columns buckle - all of WPH descends
Falling core tugs walls inside
Walls buckle (on north wall: From about center outward) and decend
After a second or so, each column has failed, and partial freefall ensues (the west core did so even before the north wall did, because it started a slight bit earlier)

Reference ought to be made at this point to the work of achimspok and femr2. Some of this has gone down the abyss of broken links and imageshack forgetting images; Major_Tom has saved some of it to his "book".

 

[jaydeehess]

Gotcha, jdh (your poor diagram).
The kink still goes mainly inward, not down.

The graphic generator on this tablet ain't great.

Ok, I see that, but,,,,,, there is also some "down" at the kink which pretty much requires that the north exterior column has failed at that point. I don't find it unusual either, since that is in line with the apparent initial column failure, col79.

 

[JSanderO]

The Con Ed was mostly in the NW quadrant. The moment frame remained coupled to the foundation there and broke loose last... the movement resulting was rotation about the NW quadrant above Con Ed. The torque / twist caused the kink as the columns connecting col 73 to the north facade held the west part from probably last floor sections to drop... those west of col 73 to the nw corner. The twist can be explained by the NE quadrant leading the collapse. Perhaps... The 2+ seconds of approximate FF acceleration tells us that the collapsing moment frame broke free at the 8th floor... just above the 2 story section of load transfer structures.

 

[jaydeehess]

What gives tall,thin walls their stiffness, Tony? Lateral support.
Tall, thin walls, alone, are very unstable.

But if they are braced in a direction normal to the walls, then they become stable.

When the inner core collapsed, was the eastern wall isolated from the north & south walls?
Or were they all still attached to each other?

I keep mentioning that the eastern portion of the structure had two intact corners. In addition, it's south face was in better shape than that of the western portion. So of course it can resist the relatively minor inward pull when the core collapses.
Glad a real engineer has stated much better than I, what I was getting at.

Western portion is a different tale.
When the longer western core fails, I envision those cantilever trusses tilting down at their core end and being pushed to the north by the force of the building above. The north face columns of the western portion of the structure buckled outward (north) below the 8th floor.

So, as Oystein points out, the eastern portion of the north face was pulled inward (south) from the top to bottom at the line of the kink. The western portion has no SW cover column support plus some south face damage, and the lower, below 8th floor, North face columns under the cantilever trusses, have buckled outward (north).

It's now not very unusual to have seen the eastern portion rotate and fall to the general northeast direction, and for the western portion to have rotated about its center of gravity during the 8 floor fall, to end up mostly in the space between WTC7 & 5.