WTC7: Is AE911's (and NIST's) Focus on A2001 Justified if it Was Not "Key" in NIST's Global Model?

[Mick West]

However, we agree that A2001 was not pushed off of its seat.

We do? We that's my point. If, in NIST's LS-DYNA model, A2001 is not pushed off its seat, then the focus of AE911T's study on A2001 is misplaced. As was discussed two years ago.

You are claiming to know better than NIST what triggered the cascade of floor collapses by looking at a video simulation. But they have the failure data and you don’t so your assumption is not valid.

The LS-DYNA model shows that A2001 was not walked off its seat. The preliminary report's diagrams shows A2001 did not walk off its seat (Figure 11-36). The final report's says that A2001 DID walk off its seat, but they did not do new simulations showing what the effect would be. NIST never really explained this change. So maybe someone should ask them about that.

 

[Christopher 7]

While it is true that other failures occurred before A2001 on floor 13

In the context of the Hulsey draft report, which is the context, the topic currently, this is all the facts we need.

No, that is not all we need.

Hulsey focused on the A2001 girder collapse because NIST said that is what triggered the collapse.

11:40 “Next point. Why focus on girder A2001 collapse when NIST did not use that in their global collapse analysis.”

That is simply not true. It may not be clear in the simulation video but NIST was very clear about the failure of A2001 being the trigger that led to the total collapse of the building. They have the data so there is no justification to say otherwise.

 

[Mick West]

Hulsey focused on the A2001 girder collapse because NIST said that is what triggered the collapse.

Even taking that at face value, Hulsey is ignoring all the other damage (which seems a lot more significant in the LS-DYNA).

Before A2001 starts to move there's already SIX similar sided girders and associated floor sections falling, the top ones having a free fall of at least three floors ahead of them


Then by the time A2001 (from floor 13) hits floor 12, there's already significant damage been done


And if you continue the simulation, A2001 stops (and flops around unrealistically, because of limitations in the model), the beams and the slab to the East (right) stop, much of the slab to the West (left) stops, massive destruction continues unrelated to A2001

As far as can be seen here, A2001 does not initially fall off its seat, fails by buckling, not walk-off, and contributes hardly at all to the collapse.

Hulsey models none of this.

 

[Oystein]

No, that is not all we need.

Hulsey focused on the A2001 girder collapse because NIST said that is what triggered the collapse.

You should perhaps keep in mind the three key objectives of the Hulsey report - page 1 of hos draft report:

The objective of this study, therefore, was threefold: (1) Examine the structural response of WTC 7 to fire loads that may have occurred on September 11, 2001; (2) Rule out scenarios that could not have caused the observed collapse; and (3) Identify types of failures and their locations that may have caused the total collapse to occur as observed.

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You will immediately notice that these key objectives do not contain the strings "NIST" nor "A2001", and thus Hulsey would have been misguided to focus solely on NIST and A2001.

Objectives (1) and (3) are entirely unrelated to anything NIST may or could ever have done. His work on those two objectives should not be affected in any way, shape or form by whether NIST has done any work, forwarded any explanations, or what those may have been. Any and all work towards those objectives, if done right, could have been identical if NIST did not even exist.

The only place where NIST enters in is objective (2), where Hulsey intends to review previous studies and explanation, specifically those advanced by NIST, Arup and Weidlinger.

As has been pointed out above, Hulsey must necessarily fail to tackle the Arup hypothesis by his decision not to look at structural response to cooling cycles, and must necessarily fail to tackle the Weidlinger hypothesis by ignoring on purpose any and all structural responses to any and all fires at and near floors 9 and 10.

So he's left with the NIST report.

Now YOU, Chris, admitted that "it is true that other failures occurred before A2001 on floor 13" - in the NIST simulations as well as in reality (I presume you were thinking of the former). Those other failures are then the necessary context for assessing what happens when A2001, too, fails.
Hulsey chose to ignore that context.
By this choice, he failed his objective by default.

And these are all the reasons we need to recommend that the study and draft report be binned entirely, and be reset to zero - start anew.

 

[Christopher 7]

Hulsey focused on the A2001 girder collapse because NIST said that is what triggered the collapse.

Even taking that at face value, Hulsey is ignoring all the other damage (which seems a lot more significant in the LS-DYNA).

Before A2001 starts to move there's already SIX similar sided girders and associated floor sections falling, the top ones having a free fall of at least three floors ahead of them

True. (except for the free fall part - but that is not relevant to the crux of this disagreement)

Then by the time A2001 (from floor 13) hits floor 12, there's already significant damage been done

And if you continue the simulation, A2001 stops (and flops around unrealistically, because of limitations in the model), the beams and the slab to the East (right) stop, much of the slab to the West (left) stops, massive destruction continues unrelated to A2001

All true except for the floor area to the north-west of column 79. I found a quote that confirms what I have been saying. Although floor 14 collapsed before A2001 on floor 13 and did more damage, it was the collapse of the A2001 girder on floor 13 that triggered the initiating event, the buckling of column 79.

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below—some of which were already weakened by fires—triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. NCSTAR 1-9 Vol. 2 p. 611 [PDF p. 273/677]

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Note that it says "led to loss of lateral support to Column 79 in the east-west direction." That is consistent with what I have been saying. The collapse of floor 14 took out the girders and floor areas to the south of column 79. But the coup de grâce was the failure of floor 13 that started a cascade of floor failures which took out the girders supporting column 79 on the west side, leaving column 79 unsupported in three directions over nine floors.

This is relevant to the Hulsey report in that I am rebutting Mick's comment about that report:

11:40 “Next point. Why focus on girder A2001 collapse when NIST did not use that in their global collapse analysis.”

Hulsey's report focused on A2001 in floor 13 because NIST said that was the triggering event.

The quote from the NIST final report on WTC 7 above confirms that NIST did use the collapse of A2001 in the global collapse analysis (but the video doesn't show it precisely).

Without the triggering and the ensuing initiating events, there would have been no progressive collapse.

 

[econ41]

Agreed Oystein.
I would also identify another level of problem.

The project has from the earliest statements made by Hulsey been fatally flawed by invalid global claims. The most serious probably the claim - stated in various ways - that the project can would prove or has proved "Fire could not cause the collapse of WTC7". That is a global negative claim which cannot be proved in the context of the Hulsey study.

And the same problem of "global claims" is apparent in the quoted objectives which are:

The objective of this study, therefore, was threefold: (1) Examine the structural response of WTC 7 to fire loads that may have occurred on September 11, 2001; (2) Rule out scenarios that could not have caused the observed collapse; and (3) Identify types of failures and their locations that may have caused the total collapse to occur as observed.

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All three omit the essential qualifier "some".

If atated: "(1) Examine the structural response of WTC 7 to SOME fire loads that may have occurred on September 11, 2001; (2) Rule SOME out scenarios that could not have caused the observed collapse; and (3) Identify SOME types of failures and their locations that may have caused the total collapse to occur as observed." ... then the objectives are valid. But even if Hulsey can satisfy those valid objectives it still does not "prove" the main global claim of "Fire could not cause...."

 

[Oystein]

...
Hulsey's report focused on A2001 in floor 13 because NIST said that was the triggering event.
...

No, it (the report) does not focus on A2001 - only a minor part of it may.
But even if it did, it has been pointed out to you already several times that focussing on a single girder is not valid, cannot possibly be valid, if it ignores, on purpose and by design, any and all other connection and other damages incurred by hours of fire development on much more than just two floors. Which is what Hulsey did: Ignore high temperatures on most floors, ignore fire development (regionally differentially, heating and cooling), ignore practically all other connection damages.

NIST may have focused their discussion in SOME subsections of their hundreds of pages of detailed analysis on girder A2001, but they did so always in the CONTEXT of all other damages - and all the other sections of the NIST reports document all the other failures.

And of course the final, global collapse analysis with LS-DYNA, as Mick has shown to you with great clarity, progresses because there are so many other things going on that you and Hulsey deliberately ignore.

You need to stop ignoring all the other fire damage.

 

[Christopher 7]

Hulsey focused on the A2001 girder collapse because NIST said that is what triggered the collapse.

No, it (the report) does not focus on A2001 - only a minor part of it may.

I was responding to a statement Mick made in his video “Some Problems with the UAF/Hulsey/AE911Truth WTC7 Draft Report”.

11:40 “Next point. Why focus on girder A2001 collapse when NIST did not use that in their global collapse analysis.”

I have shown that Mick's statement is incorrect. NIST did use the collapse of the A2001 girder in their global collapse analysis.

But even if it did, it has been pointed out to you already several times that focussing on a single girder is not valid, cannot possibly be valid, if it ignores, on purpose and by design, any and all other connection and other damages incurred by hours of fire development on much more than just two floors. Which is what Hulsey did: Ignore high temperatures on most floors, ignore fire development (regionally differentially, heating and cooling), ignore practically all other connection damages.

Although other damage caused column 79 to be unsupported in the south direction, all the other damage did not leave column 79 unsupported in three directions over nine floors and did not cause the building to collapse. Without the push-off of A2001 at column 79 on floor 13, there would have been NO initiating event and NO global collapse. That is why that single girder is so important.

The floor framing structure was thermally weakened at Floors 8 to 14, with the most substantial fire-induced damage occurring in the east region of Floors 12, 13 and 14. Even though each floor had been weakened over hours of exposure to separate and independent fires, it was not until there was substantial damage to the long span floors in the northeast region of Floor 13 that the initial failure event, i.e., the buckling of Column 79 was triggered. NCSTAR 1-9, Vol. 2, p. 572 [PDF p. 234/638]

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[Jeffrey Orling]

Tell me again... How can anyone know exactly where the structural failures WAS (singular) not were... plural which was the trigger of the global collapse? The clues I see were the drop of the EPH... some distortion of reflections on the facade glass.... smoke and flames seen from the exterior (mostly viewed from the north)?

Another oddity (to me) which I never see discussed... is what started the "massive fires" and where was that? For example why the region around col 79 in the low teens which is the region NIST discusses?

It appears to me that all of these collapse musings and forensics are largely based more on (not unreasonable) assumptions and theoretical models and less on data. There are several axial lines of support (76. 77. 78. 79, 80 & 81) under the EPH and any of them failing would lead to the structure (EPH) above collapsing down leading to what was observed. However, col 79 looks like it carries the largest single axial load of the columns below the EPH. ref pages 12-17 appendix to the NIST report.

 

[Joe Hill]

Without the push-off of A2001 at column 79 on floor 13, there would have been NO initiating event and NO global collapse.

Why "push-off", as if that's the only option? Could A2001 not have been "pulled" off it's Column 79 connection?

 

[Christopher 7]

Rebuttal to comments in “Some Problems with the UAF/Hulsey/AE911Truth WTC7 Draft Report”

11:40 “Next point. Why focus on girder A2001 collapse when NIST did not use that in their global collapse analysis.”

Here are more quotes that confirm NIST did use the collapse of girder A2001 on floor 13 as the trigger of the global collapse. (see post 188 for my first NIST quote confirming that NIST did use the collapse of girder A2001 on floor 13 as the trigger of the global collapse.)

girders between Columns 44 and 79 and Column 26 and 81 failed due to girder walk off of the bearing seat NCSTAR 1-9, Vol. 2, p. 537 [PDF p. 199/603]

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The collapse of Floor 13 onto the floors below, some of which were already weakened by fires, triggered a cascade of floor failures in the northeast region of the building.

The floor failures progressed down to Floor 5, where debris accumulated, and spread across the east floor area, due to the effects of impact loads from falling debris on thermally weakened floor areas.

Critical Column 79 became laterally unsupported between Floors 5 and 14 in the east-west and south directions as a result of the progression of floor system failures. NCSTAR 1-9, Vol. 2 p. 604 [PDF p. 266/670]

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Initial Local Failure for Collapse Initiation. Fire-induced thermal expansion of the floor system surrounding Column 79 led to collapse of Floor 13 that triggered a cascade of floor failures. This, in turn, led to loss of lateral support to Column 79 over nine stories, resulting in the buckling failure of Column 79. NCSTAR 1-9, Vol. 2 p. 609 [PDF p. 271/675]

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We agree that the video model appears to show that the A2001 girder on the 13th floor fails due to sagging but the text of the final report says that it was due to A2001 on the 13th floor being pushed off of its seat.

 

[Mick West]

Here are more quotes that confirm NIST did use the collapse of girder A2001 on floor 13 as the trigger of the global collapse.

Critical Column 79 became laterally unsupported between Floors 5 and 14 in the east-west and south directions as a result of the progression of floor system failures. NCSTAR 1-9, Vol. 2 p. 604 [PDF p. 266/670]

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A2001 is to the NORTH of Column 79. So how would a collapse to the north trigger floor failures to the east-west and south, but not in the north.

 

[Christopher 7]

A2001 is to the NORTH of Column 79. So how would a collapse to the north trigger floor failures to the east-west and south, but not in the north.

I already explained this.

Since the collapse of floor 14 caused the collapse of the floors to the south of column 79, and the floors to the east of column 79 did not collapse on floors 12-8 until column 79 buckled, then all that’s left is the floors and girders to the West of A2001 of floor 13 that could have collapsed due to the failure of A2001 on floor 13. This, according to NIST, is the last straw that left column 79 unsupported in three directions over nine floors – and it buckled.

And I followed up with this:

I found a quote that confirms what I have been saying. Although floor 14 collapsed before A2001 on floor 13 and did more damage, it was the collapse of the A2001 girder on floor 13 that triggered the initiating event, the buckling of column 79.

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below—some of which were already weakened by fires—triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. NCSTAR 1-9 Vol. 2 p. 611 [PDF p. 273/677]

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Note that it says "led to loss of lateral support to Column 79 in the east-west direction." That is consistent with what I have been saying. The collapse of floor 14 took out the girders and floor areas to the south of column 79. But the coup de grâce was the failure of floor 13 that started a cascade of floor failures which took out the girders supporting column 79 on the west side, leaving column 79 unsupported in three directions over nine floors.

I read Chapter 12 again and found this:

The global simulation was first initialized under gravity loading over 4.5 s of simulation time. Then damage and temperature initialization states were applied over 4 additional seconds. Collapse propagation in the global model required approximately 16 additional seconds after initialization, for a total of about 25 s of simulated time NCSTAR 1-9, Vol. 2, p. 544 [PDF p. 206/610]

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12.3.2 Model Initialization and Loading Sequence
Last, the fire-induced damage obtained from the 16 story ANSYS analysis, including damage to floor beams, girders, and connections, was applied instantaneously. The heated, damaged structure was then free to react. NCSTAR 1-9, Vol. 2, p. 563 [PDF p. 225/629]

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We have been thinking that the LS-DYNA analysis and the global simulation were the same but they are not. The LS-DYNA model had the damage applied instantaneously but the simulation had the damage applied over a period of 4 seconds.

I admitted that I was wrong about Hulsey getting the ANSYS and LS-DYNA models mixed up. Now I would like you to admit that you were wrong about NIST not using A2001 being pushed off of its seat on floor 13 in their global collapse analysis.

 

[Jeffrey Orling]

Here are more quotes that confirm NIST did use the collapse of girder A2001 on floor 13 as the trigger of the global collapse. (see post 188 for my first NIST quote confirming that NIST did use the collapse of girder A2001 on floor 13 as the trigger of the global collapse.)

girders between Columns 44 and 79 and Column 26 and 81 failed due to girder walk off of the bearing seat NCSTAR 1-9, Vol. 2, p. 537 [PDF p. 199/603]

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The collapse of Floor 13 onto the floors below, some of which were already weakened by fires, triggered a cascade of floor failures in the northeast region of the building.

The floor failures progressed down to Floor 5, where debris accumulated, and spread across the east floor area, due to the effects of impact loads from falling debris on thermally weakened floor areas.

Critical Column 79 became laterally unsupported between Floors 5 and 14 in the east-west and south directions as a result of the progression of floor system failures. NCSTAR 1-9, Vol. 2 p. 604 [PDF p. 266/670]

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Initial Local Failure for Collapse Initiation. Fire-induced thermal expansion of the floor system surrounding Column 79 led to collapse of Floor 13 that triggered a cascade of floor failures. This, in turn, led to loss of lateral support to Column 79 over nine stories, resulting in the buckling failure of Column 79. NCSTAR 1-9, Vol. 2 p. 609 [PDF p. 271/675]

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We agree that the video model appears to show that the A2001 girder on the 13th floor fails due to sagging but the text of the final report says that it was due to A2001 on the 13th floor being pushed off of its seat.

Sagging per se is not a failure. Every loaded beam sags - deflects. Too much deflection is not acceptable but may not be a mechanical failure. The matter needs to be framed as what would be the mechanical implication of excessive sagging. How does excessive deflection impact the end/bearing of the beam. Does it lead to the beam to column connection failure? Or does it lose so much capacity that it buckles?

 

[Mick West]

I read Chapter 12 again and found this:

The global simulation was first initialized under gravity loading over 4.5 s of simulation time. Then damage and temperature initialization states were applied over 4 additional seconds. Collapse propagation in the global model required approximately 16 additional seconds after initialization, for a total of about 25 s of simulated time NCSTAR 1-9, Vol. 2, p. 544 [PDF p. 206/610]

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​

12.3.2 Model Initialization and Loading Sequence
Last, the fire-induced damage obtained from the 16 story ANSYS analysis, including damage to floor beams, girders, and connections, was applied instantaneously. The heated, damaged structure was then free to react. NCSTAR 1-9, Vol. 2, p. 563 [PDF p. 225/629]

​

We have been thinking that the LS-DYNA analysis and the global simulation were the same but they are not. The LS-DYNA model had the damage applied instantaneously but the simulation had the damage applied over a period of 4 seconds.

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This is entirely incorrect. The global simulation IS the LS-DYNA model being referred to here. You are taking a small part of 12.3.2 out of context. The full section is:

12.3.2 Model Initialization and Loading Sequence
The global model was initialized as follows to minimize any dynamic effects associated with loading
sequence.

• First, gravity was applied slowly to the 47 floor structure over 4.5 s of elapsed simulation
time to damp residual vibrations and eliminate dynamic response. The loads were applied
smoothly with a sinusoidal load curve.

• Then, the debris impact damage from the collapse of WTC 1 was applied to the structure
instantaneously by removing damaged elements from the model that were no longer capable
of bearing their loads. The structure was then allowed to damp residual vibrations for 2 s.

• Next, the structural temperatures were applied smoothly with a sinusoidal curve and allowed
to damp residual vibrations for 2 s.

• Last, the fire-induced damage obtained from the 16 story ANSYS analysis, including damage
to floor beams, girders, and connections, was applied instantaneously. The heated, damaged
structure was then free to react.

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This is the exact same 4.5 + 4 initialization and damage application as from your earlier quote (which is from section 12.2.2). The 4 seconds comes from the 2 seconds of settling after debris damage application plus the 2 seconds of temperature application and continued settling. This differs from the 4.5 seconds, which is a gradual application of gravity.

No settling period is needed after the sudden application of the ANSYS damage, because "settling" is just running the simulation, which in this case is the building collapsing. This all is illustrated in the figure 12-32



After section 12.3.4 there's a more detailed description, of how this all works. Section 12.4.4 then describes in detail how this led to the buckling of C79, without mentioning the walk-off (which, as was discussed years ago, is in a different part of the report, and possibly refers to model runs that were not shown)

Global model = Global Simulation = LS-DYNA simulation - in which A2001 appears to buckle, and not fail at the C79 connection

 

[Christopher 7]

A2001 is to the NORTH of Column 79. So how would a collapse to the north trigger floor failures to the east-west and south, but not in the north.

You did not dispute this part:

Since the collapse of floor 14 caused the collapse of the floors to the south of column 79, and the floors to the east of column 79 did not collapse on floors 12-8 until column 79 buckled, then all that’s left is the floors and girders to the West of A2001 on floor 13 that could have collapsed due to the failure of A2001 on floor 13. This, according to NIST, is the last straw that left column 79 unsupported in three directions over nine floors – and it buckled

I found a quote that confirms what I have been saying. Although floor 14 collapsed before A2001 on floor 13 and did more damage, it was the collapse of the A2001 girder on floor 13 that triggered the initiating event, the buckling of column 79.

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below—some of which were already weakened by fires—triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. NCSTAR 1-9 Vol. 2 p. 611 [PDF p. 273/677]

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Note that it says "led to loss of lateral support to Column 79 in the east-west direction." That is consistent with what I have been saying. The collapse of floor 14 took out the girders and floor areas to the south of column 79. But the coup de grâce was the failure of floor 13 that started a cascade of floor failures which took out the girders supporting column 79 on the west side, leaving column 79 unsupported in three directions over nine floors.

In other words, NIST did use the failure of A2001 on the 13th floor in their final analysis and it was the trigger that led to the initiating event - the buckling of column 79.

 

[Christopher 7]

In the video simulation, the A2001 girder on floor 13 is doing something it could not do in reality. It's sagging several feet, but that is impossible. A spreadsheet for the floor beams in the NE corner of the 13th floor shows elongation vs sag. Since loads are proportional, the sag of the girder would be roughly the same as the floor beams for any given temperature. The sag (noted on the right as deflection) at 600°C is 5-1/2 inches.



Figure 10-39 shows that the A2001 girder on floor 13 never got above about 450°C.

 

[Oystein]

In the video simulation, the A2001 girder on floor 13 is doing something it could not do in reality.

By "in reality" you actually mean "in some other model", right?

It's sagging several feet, but that is impossible. A spreadsheet for the floor beams in the NE corner of the 13th floor shows elongation vs sag. Since loads are proportional, the sag of the girder would be roughly the same as the floor beams for any given temperature. The sag (noted on the right as deflection) at 600°C is 5-1/2 inches.


...

Where is that spreadsheet from?

 

[Christopher 7]

The global simulation was first initialized under gravity loading over 4.5 s of simulation time. Then damage and temperature initialization states were applied over 4 additional seconds. Collapse propagation in the global model required approximately 16 additional seconds after initialization, for a total of about 25 s of simulated time NCSTAR 1-9, Vol. 2, p. 544 [PDF p. 206/610]

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This is the exact same 4.5 + 4 initialization and damage application as from your earlier quote (which is from section 12.2.2). The 4 seconds comes from the 2 seconds of settling after debris damage application plus the 2 seconds of temperature application and continued settling. This differs from the 4.5 seconds, which is a gradual application of gravity.

It could be interpreted as the same 4 seconds except for the sequential collapses in the simulation. Had the damage from the ANSYS model been applied instantaneously, everything would have collapsed at the same time. But that is not what happens in the simulation. The collapses happen over a period of several seconds as would be the case if the damage from the ANSYS model were applied over a period of 4 seconds.

There is a subtle difference in the two initialization quotes. The LS-DYNA model initialization specifies damage from WTC 1 but the global simulation does not. This leaves open the possibility that the damage applied in those 4 seconds included the damage from the ANSYS model, which appears to be the case.

12.3.2 Model Initialization and Loading Sequence
...
Then, the debris impact damage from the collapse of WTC 1 was applied to the structure
instantaneously

The global simulation was first initialized under gravity loading over 4.5 s of simulation time. Then damage and temperature initialization states were applied over 4 additional seconds.

You did not dispute my comment in post #96. Are you willing to admit that NIST did use the collapse of A2001 on the 13th floor in their final analysis?

 

[Christopher 7]

By "in reality" you actually mean "in some other model", right?

No. I mean "in the NIST report" as noted in Figure 10-39.
There is no other model in the NIST report.
In NIST's ANSYS analysis, the beams and girders failed at temperatures at or below 400 °C.

“The initiating local failure that began the probable WTC 7 collapse sequence was the buckling of Column 79. This buckling arose from a process that occurred at temperatures at or below approximately 400 °C (750 °F)” NCSTAR 1A, p. 21 [PDF p. 63]

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The spreadsheet was made by Tony Szamboti and David Chandler.

 

[Mick West]

Are you willing to admit that NIST did use the collapse of A2001 on the 13th floor in their final analysis?

Well, that depends on what you mean by "final analysis" - my point in this thread is that they did not use the A2001 walk-off in the global LS-DYNA model runs that they show in their report. You can clearly see the connection does not fail via walk-off, it fails via some failure the girder itself.

The reality of the girder failures via buckling is a different issue. The question at hand is if "Is AE911's (and NIST's) Focus on A2001 Justified if it Was Not "Key" in NIST's Global Model?"

 

[Christopher 7]

Well, that depends on what you mean by "final analysis" - my point in this thread is that they did not use the A2001 walk-off in the global LS-DYNA model runs that they show in their report. You can clearly see the connection does not fail via walk-off, it fails via some failure the girder itself.

The reality of the girder failures via buckling is a different issue. The question at hand is if "Is AE911's (and NIST's) Focus on A2001 Justified if it Was Not "Key" in NIST's Global Model?"

As I have already shown, the NIST scenario hinges on the walk-off of A2001

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below—some of which were already weakened by fires—triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. NCSTAR 1-9 Vol. 2 p. 611 [PDF p. 273/677]

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But NIST couldn’t use the walk-off in the video because, as the Hulsey report shows, that is impossible for several reasons.
1. Thermal expansion could not push the girder far enough to push it off of its seat.
2. Even if it could, the girder would be trapped by the side plate on column 79.
3. Even if the girder could get beyond the side plate, the web stiffener, which NIST omitted, would have prevented the lower flange from buckling.

The video simulation is not consistent with the NIST scenario because the NIST scenario is impossible.

Their own video proves that their scenario didn’t happen.

The extreme sagging of A2001 is also impossible. The video shows something that could not happen. i.e. the video is not valid either.

 

[deirdre]

Their own video proves that their scenario didn’t happen.

so, your answer to the thread title question is "no"?

 

[Christopher 7]

so, your answer to the thread title question is "no"?

No, my answer is not no. NIST is very clear that, in their scenario, the walk-off of A2001 on floor 13 was the triggering event that led to the total collapse of WTC 7. Without that walk-off, there would be no collapse. It was the key element in NIST's scenario. So focusing on that girder is appropriate.

AE911Truth and the Hulsey report confirmed the impossibility of that happening and NIST's own video simulation shows that it did not happen. The video simulation was released at the same time as the final report so NIST did not change their scenario. The video simulation is supposed to show A2001 being pushed off of its seat, but it doesn't. (because that is impossible) The collapse did not happen the way NIST said it did and therefore, the NIST final report on the collapse of WTC 7 is a fraud.

 

[deirdre]

Without that walk-off, there would be no collapse

You don't know that. There was no walk off in the simulation video, but the building still collapsed.

 

[benthamitemetric]

No, my answer is not no. NIST is very clear that, in their scenario, the walk-off of A2001 on floor 13 was the triggering event that led to the total collapse of WTC 7. Without that walk-off, there would be no collapse. It was the key element in NIST's scenario. So focusing on that girder is appropriate.

You are focusing only on NIST's simplified summary narrative that highlights a small number of the millions of events that were observed in NIST's local model, which, as you have been shown several times by Mick, clearly doesn't tell the entire story of what actually happened in NIST's global model. That said, I do agree with you that NIST did focus on the walk-off of A2001 as a key element of the scenario they observed in the local model that lead them to believe column 79 reached a state in such local model where it would buckle (leading them to then switch to the global model for further analysis). But, that said, you are absolutely incorrect about what AE911Truth proved with respect to whether such a walk-off was possible, as I will further note below.

AE911Truth and the Hulsey report confirmed the impossibility of that happening and NIST's own video simulation shows that it did not happen.

False. AE911Truth did not test the NIST scenario. Importantly, AE911Truth failed to model a fire progression (did you know that the walk-off of A2001 in NIST's model occurred while column 79 itself was being pushed to the west due to the eastwards fire progression that AE911Truth did not simulate?), used temperatures pulled from the cooling phase of the NIST fire progression scenario, and modeled fire damage within WTC7 in a much more limited area than did NIST, even though the video and photographic evidence from the day clearly shows significant fires in other areas as well, which were factored into the NIST model. It is axiomatic that one cannot disprove something that it did not even test, and AE911Truth did not test whether A2001 would walk off in the NIST scenario (or in any reasonably similar scenario) because it did not test the NIST scenario (or any reasonably similar scenario).

The video simulation was released at the same time as the final report so NIST did not change their scenario. The video simulation is supposed to show A2001 being pushed off of its seat, but it doesn't (because that is impossible).

Nope. You are confusing NIST's global and local models. The video shows the global model, not the local model.

The collapse did not happen the way NIST said it did and therefore, the NIST final report on the collapse of WTC 7 is a fraud.

Both unproven, as noted above, and illogical because the failure of a very complicated, and appropriately caveated simulation to perfectly recreate a real life scenario with absolutely certainty does not make that simulation a fraud. NIST describes the collapse scenario in its report as the most likely scenario it found to lead to the observed collapse, not the only scenario that could have led to, or the actual scenario that certainly did lead to, the collapse in reality. NIST carefully describes the limitations to its approach and the input data it used therein. AE911Truth, in contrast, makes a bold, absolute and unscientific claim that it proved a negative it didn't even come close to proving (which claim, it is worthwhile to note, AE911Truth and Hulsey have been making since before Hulsey even completed his local model).

 

[deirdre]

The extreme sagging of A2001 is also impossible. The video shows something that could not happen. i.e. the video is not valid either

this is kinda off topic but since you keep bringing up the slight sag of A2001 in the LSD-NYA model, Hulsey's report had absolutely impossible rubber beams, columns etc. So why you think he proved anything with those models is a bit hypocritical.

 

[Christopher 7]

You don't know that. There was no walk off in the simulation video, but the building still collapsed.

According to NIST, the walk-off of A2001 on floor 13 was the trigger that left column 79 without lateral support in the east-west direction. In the NIST scenario, there would have been no collapse without the failure of A2001 on floor 13. The fact that the video does not show what NIST said happened is proof that they lied.

 

[Christopher 7]

You are focusing only on NIST's simplified summary narrative that highlights a small number of the millions of events that were observed in NIST's local model, which, as you have been shown several times by Mick, clearly doesn't tell the entire story of what actually happened in NIST's global model.

I have focused on what NIST said was the event that triggered the total collapse. If it didn't happen that way, then the NIST report is a fraud.

That said, I do agree with you that NIST did focus on the walk-off of A2001 as a key element of the scenario they observed in the local model that lead them to believe column 79 reached a state in such local model where it would buckle (leading them to then switch to the global model for further analysis).

Correct. The input to the LS-DYNA program for further analysis included the A2001 on floor 13 walk-off of its seat.

The fire-induced floor damage was input to the LS-DYNA model to determine if the predicted floor failures would lead to an initiating collapse event, followed by a failure progression to global collapse.
When the ANSYS analysis had reached a point where buckling instability of columns appeared imminent, the accumulated damage due to thermally-induced failures of floor framing was summarized as input for the LS-DYNA model. The transferred data also included the temperature of structural components at that time and buckled beams and girders. NCSTAR 1-9, Vol. 2, p. 535 [PDF p. 197/601]

Content from external source

The ANSYS walk-off of A2001 was part of the LS-DYNA input data.

The following findings are based on the ANSYS finite-element analysis of the structural response of WTC 7 to the fires observed between Floors 7 to 14:
• The failures in the floor systems were caused by the following structural responses to
elevated temperatures:
o At temperatures less than approximately 400 °C, restrained thermal expansion of beams
and girders caused axial compressive forces to develop in the beams and girders, which
led to the following connection failures:
− bolt shear failure in fin, knife, and seated connections,
− girder walk off of seated connections after all the bolts had sheared at Columns 79
and 81 NCSTAR 1-9, Vol. 2, p. 536 [PDF p. 198/602]

Content from external source

you are absolutely incorrect about what AE911Truth proved with respect to whether such a walk-off was possible

On the contrary. See https://www.ae911truth.org/evidence...ts-fraud-exposed-in-nist-wtc-7-reports-part-2

AE911Truth failed to model a fire progression

It is not necessary to model the fires. The photographs of the fire progression show that the fire on floor 12 had burned out in the area of the collapse initiation over an hour before the collapse. See: https://www.ae911truth.org/evidence...04-fraud-exposed-in-nist-wtc-7-reports-part-1

(did you know that the walk-off of A2001 in NIST's model occurred while column 79 itself was being pushed to the west due to the eastwards fire progression that AE911Truth did not simulate?)

As Hulsey demonstrated (and common sense dictates), it was not possible for thermal expansion to push column 79 to the west because it was surrounded by concrete floors. The center of the building was the point where thermal expansion would not move anything. Expansion spread out from there in all directions. Any expansion in the east part of the building would be to the east.

AE911Truth did not test whether A2001 would walk off in the NIST scenario

That's why AE911Truth commissioned Hulsey.

Nope. You are confusing NIST's global and local models. The video shows the global model, not the local model.

No confusion. As noted above, the global model includes the A2001 walk-off, or at least NIST says that it did. Either it is there or NIST is lying.

AE911Truth, in contrast, makes a bold, absolute and unscientific claim that it proved a negative it didn't even come close to proving

AE911Truth and the Hulsey report, separately and together proved that the NIST scenario is impossible. (for reasons I listed above) That's not proving a negative, it's proving the NIST scenario is untenable.

 

[Christopher 7]

this is kinda off topic but since you keep bringing up the slight sag of A2001 in the LSD-NYA model, Hulsey's report had absolutely impossible rubber beams, columns etc. So why you think he proved anything with those models is a bit hypocritical.

It was not a slight sag. It was about 3 feet which is impossible as I noted. (Fraud)
As I have previously stated, I share Mick's criticism of Hulsey's models. They are not realistic looking and not convincing at all.

 

[deirdre]

AE911Truth and the Hulsey report, separately and together proved that the NIST scenario is impossible. (for reasons I listed above) That's not proving a negative, it's proving the NIST scenario is untenable.

Proving the NIST scenario impossible*, is not proving fires could not have caused the collapse.
If that is the case then why bother spending all that money on the Hulsey study? AE911 could just point to the other studies which came up with different fire collapse causes, and say "see.. if NIST is wrong then fire must not be able to collapse a building".

*I'm not saying hulsey proved this.

It was not a slight sag. It was about 3 feet which is impossible as I noted. (Fraud)

it is wicked slight compared to all Hulsey's stuff.
if people (Nist/Hulsey) make a mistake, that doesn't make them "liars".
if people (Nist, Hulsey) are stuck with limited-ability computer programs, that doesn't mean they committed "fraud".

 

[benthamitemetric]

On the contrary....

If you want to discuss AE911Truth's arguments, you have to incorporate them into your post per forum rules, not just link to them. Otherwise, I may as well just link to the NIST report as a counterargument. Not productive.

As Hulsey demonstrated (and common sense dictates), it was not possible for thermal expansion to push column 79 to the west because it was surrounded by concrete floors. The center of the building was the point where thermal expansion would not move anything. Expansion spread out from there in all directions. Any expansion in the east part of the building would be to the east.

How did Hulsey demonstrate that which he did not test? Hulsey did not test any fire progression and therefore can say nothing definitive about the effects of a fire progression on the structure. And why would the location of the center of the building necessarily have any bearing on or relevance to the damage that several localized roaming fires inflicted upon the portions of the building they burned through? (You are getting close to stumbling on a major, obvious flaw in Hulsey's report and presentation, but I'll give you a chance to find it yourself before we discuss it further. Mick has noted it several times already in these forums.)

That's why AE911Truth commissioned Hulsey.

And yet Hulsey failed to test any realistic scenario in which the fires in the building were roaming (as we know happened in reality and in the scenario NIST tested) and he failed to test how the fires in areas outside of the two small areas he artificially and unrealistically cordoned off in his test would affect such areas. In essence, in his local model, he treated the entire building as fixed and pristine except for two floors, and then he applied an unrealistic heating simulation to a portion of those floors. That's not what happened in reality or in the NIST scenario, so I am struggling to see how you think it definitively ruled out what could have happened in reality or the NIST scenario.

No confusion. As noted above, the global model includes the A2001 walk-off, or at least NIST says that it did. Either it is there or NIST is lying.

NIST is very clear about how it fed the ANSYS data into the LS-DYNA model and you are mischaracterizing that process, either unwittingly or intentionally. The failure state of the structural elements in the ANSYS model was transferred to LS-DYNA, not their exact failure mode. It's not surprising then that the LS-DYNA simulation starts without the walk-off. It's hard to see how this would materially alter the failure analysis, however, given that the ANSYS model had demonstrated a series of failures sufficient to allow column 79 to buckle, and the LS-DYNA model is essentially starting off at the same point.

Contrast this to Hulsey's ridiculous models where he does not document even a single element of the building failing as a result of his unrealistic, spacially-limited, and completely artificial heating scenario. The Hulsey report does not say anything about the failure criteria they had for any connection other than the A2001 connection to column 79 (and even then, its not clear if he modeled failure criteria for A2001 in his two floor model or just in an even more localized model of just that connection). Were failure criteria properly modeled in the Hulsey local model? His report doesn't say, but the various "rubber building" animations we have from his global model seem to indicate he did not model connection failures at all there at least.

AE911Truth and the Hulsey report, separately and together proved that the NIST scenario is impossible. (for reasons I listed above) That's not proving a negative, it's proving the NIST scenario is untenable.

Amazing that you think they were able to do that without ever testing the NIST scenario or anything even reasonably similar to it.

 

[Christopher 7]

*I'm not saying hulsey proved this.

The 3 points I listed prove beyond all doubt that the walk-off of A2001 was impossible.

1. Thermal expansion could not push the girder far enough to push it off of its seat.
2. Even if it could, the girder would be trapped by the side plate on column 79.
3. Even if the girder could get beyond the side plate, the web stiffener, which NIST omitted, would have prevented the lower flange from buckling.

 

[Joe Hill]

The 3 points I listed prove beyond all doubt that the walk-off of A2001 was impossible.

Assuming you are correct, "the walk-off of A2001 was impossible", therefore______________(what?). What point are you trying to make?

 

[Christopher 7]

If you want to discuss AE911Truth's arguments, you have to incorporate them into your post per forum rules, not just link to them. Otherwise, I may as well just link to the NIST report as a counterargument.

From "Part 2: Magical Thermal Expansion" https://www.ae911truth.org/evidence...ts-fraud-exposed-in-nist-wtc-7-reports-part-2

To get the shear studs on the floor beams to fail, NIST had to assume high steel temperatures. It applied the heat in 1½ seconds over the entire northeast part of Floor 13. This faulty method of calculating temperatures, though, does not allow for the reality of heat dispersal or for the inevitable beam sagging.
Interestingly, NIST's model heated the floor beams but not the concrete slab. Since concrete expands at 85% the rate of steel, leaving this expansion out of the calculations of the shear studs failure is fraudulent.

Content from external source

"The girder and beam temperatures were assumed to be 500° C and 600° C, respectively, and the slab was assumed to remain unheated.” — NCSTAR 1-9, Vol. 1, page 349 [PDF page 393]

Content from external source

“Ramping of the temperatures for the beams and the girder then commenced at 1.1 s, leveling off at temperatures of 600° C for the beams and 500° C for the girder at 2.6 s. These temperature histories were prescribed uniformly for all nodes of the beams and the girder, respectively.” — NCSTAR 1-9, Vol. 1, page 352 [PDF page 396]

Content from external source

An errata published by NIST in 2012 corrected the “mistake” (about the width of the column seat) that had been made in the final report.

Content from external source

"The bearing seat at Column 79 was 11 12 in. wide. Thus, when the girder end at Column 79 had been pushed laterally at least 5.5 6.25 in., it was no longer supported by the bearing seat.” See June 2012 Text Changes to the NIST Reports. http://www.nist.gov/customcf/get_pdf.cfm?pub_id=901225

Content from external source

NIST assumed that all the expansion would occur on one end of the floor beams, which is quite impossible. Furthermore, NIST failed to account for beam sag that would have prevented the floor beams from expanding lengthwise more than 5.392 inches at 600° C even if all the expansion were on one end.

Content from external source

Note that the maximum expansion is 5.728 inches at 654° C, because loss due to sagging exceeds elongation due to thermal expansion after that.

Content from external source

But the impossibilities don't stop there. Another thing that makes walk-off impossible is that even if the floor beams could have expanded 6.25 inches on one end and even if no sagging had occurred, the side plate on column 79 would have prevented the girder from falling off its seat. The girder would have expanded in length until it was pressing up against the column between the side plates.

Content from external source

NIST omitted these web/flange stiffeners that would have prevented the bottom flange from folding as required for their collapse to begin. The girder would have to be pushed almost all the way off the seat, not just half way, before the bottom flange would buckle.

Content from external source

In late October 2013, NIST finally admitted that they did not include the stiffeners in their finite element analysis. Their rather puzzling excuse was that since the web did not buckle it was not necessary to include the web stiffeners in the graphic or finite element analysis (even though they would have prevented the bottom flange from folding and thus preventing the girder from failing).

Content from external source

NIST’s drawing of column 79 omits the web/flange stiffeners that would have prevented the girder's failure.

Content from external source

Frankel’s original column drawings (above and below) show the 3/4” web/flange stiffeners in place.

Content from external source

How did Hulsey demonstrate that which he did not test?

We have gotten off of the topic which is Mick's incorrect assertion the the walk-off of A2001 on the 13th floor was not "key" in NIST's global model.
As I noted in post #102, the walk-off of A2001 was the KEY element in the NIST scenario.

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below—some of which were already weakened by fires—triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. NCSTAR 1-9 Vol. 2 p. 611 [PDF p. 273/677]

And in post #109 I posted the NIST quotes that confirm that failure was part of the input to the LS-DYNA model.

The fire-induced floor damage was input to the LS-DYNA model to determine if the predicted floor failures would lead to an initiating collapse event, followed by a failure progression to global collapse.
When the ANSYS analysis had reached a point where buckling instability of columns appeared imminent, the accumulated damage due to thermally-induced failures of floor framing was summarized as input for the LS-DYNA model. The transferred data also included the temperature of structural components at that time and buckled beams and girders. NCSTAR 1-9, Vol. 2, p. 535 [PDF p. 197/601]

The following findings are based on the ANSYS finite-element analysis of the structural response of WTC 7 to the fires observed between Floors 7 to 14:
• The failures in the floor systems were caused by the following structural responses to
elevated temperatures:
o At temperatures less than approximately 400 °C, restrained thermal expansion of beams
and girders caused axial compressive forces to develop in the beams and girders, which
led to the following connection failures:
− bolt shear failure in fin, knife, and seated connections,
− girder walk off of seated connections after all the bolts had sheared at Columns 79
and 81 NCSTAR 1-9, Vol. 2, p. 536 [PDF p. 198/602]

The video simulation does not show the walk-off. To be kind, it could be assumed that this is due to the limitations of the computer video simulation.

As far as can be seen here, A2001 does not initially fall off its seat, fails by buckling, not walk-off,

And if you continue the simulation, A2001 stops (and flops around unrealistically, because of limitations in the model)

However, there is no mention of the extreme and impossible sagging (about 3 feet) of the A2001 girder in the ANSYS analysis which was the only input to the LS-DYNA model.

But NIST said that the critical damage occurred at temperatures below 400° C.

Content from external source

“The initiating local failure that began the probable WTC 7 collapse sequence was the buckling of Column 79. This buckling arose from a process that occurred at temperatures at or below approximately 400° C (750° F).” — NCSTAR 1A, page 21 [PDF page 63]

Content from external source

Since the loads are proportional, the A2001 girder would have sagged about the same as the K3004 floor beam. And as the expansion/sagging spreadsheet above shows; at 400 °C, K3004 would have sagged less than an inch.
So the sagging of A2001 in the video simulation is fraudulent.

 

[Christopher 7]

Assuming you are correct, "the walk-off of A2001 was impossible", therefore______________(what?). What point are you trying to make?

That Mick is wrong about the A2001 girder not being a 'key' factor on the collapse which is the title of this thread.
"Is AE911's (and NIST's) Focus on A2001 Justified if it Was Not "Key" in NIST's Global Model?"

 

[Joe Hill]

That Mick is wrong about the A2001 girder not being a 'key' factor on the collapse which is the title of this thread.
"Is AE911's (and NIST's) Focus on A2001 Justified if it Was Not "Key" in NIST's Global Model?"

So, you are saying it didn't "walk off", but it is a key factor? How so?

 

[Christopher 7]

So, you are saying it didn't "walk off", but it is a key factor? How so?

It was a key factor in the NIST collapse scenario - but it did not happen. Without the walk-off of A2001, the collapse does not happen. Therefore, the NIST report does not explain the destruction of WTC 7.

The video simulation has the collapse happening but it uses an impossible extreme sagging of A2001 to trigger the collapse.

 

[Mick West]

Without the walk-off of A2001, the collapse does not happen.

What are you basing that on? NIST does not say that, and their simulation does not say that.

NIST basic hypothesis is that fire-damaged caused the collapse of floors around C79, causing it to fail, triggering a progressive internal collapse leading to sudden global collapse. They attempted to narrow down a single starting point for the collapse in a narrative, but in their simulation used simplified (and unrealistic) aggregated damage from the fire model as a starting point. It is possible that neither of these have a close match to the precise sequence of events - but those events are going to forever remain hidden to us.

Fire and WTC1 collapse damage are the most obvious root causes here. The investigation focused on trying to find out how the fire could cause a collapse. Even if the A2001 walk-off, or any of the applied fire-damage in the simulation, was proven to be utterly impossible (and it has not, except in abstraction) then that still does not prove that collapse from fire is impossible.

The ultimate point of these interminable discussions is (on the part of truthers) to argue the case for a new investigation. Most truthers find the case of WTC7 to be hugely compelling evidence. But it's not. There's never going to be new investigation by the government. The best you can hope for is that academia continues to be interested and that someone eventually exploits modern computing capabilities (and perhaps AI) to establish a more precise baseline fidelity, run a more comprehensive series of simulation.

NIST's study could have been better, obviously. But it was good enough. People in power have what they think of as real issue to deal with, and there's no reason at all to dredge this up again.

 

[Jeffrey Orling]

All of these computer simulations run with the fire/heat inputs and mechanical damage from WTC1 falling debris. Both of these are educated guess because there were no transducers recording the heat from fires during the entire day and there was no forensic survey of the structural damage.

It is settle science that steel and heat don't get on well and so structural steel in most buildings.... depending on occupancy... have to use various forms of fire protection including sprinklers which prevent steel from getting hot, distorting and losing capacity. Sprinklers were lost when WTC1 came down. There was no attempt to fight the fires. Fires were observed from the outside on the east side and on the lower floors. But these are imprecise observations.

The collapse was "runaway" in that one structural failure triggered another and another and so on in rapid runaway fashion. The structural design did not include "strategies" for arresting run away failures. The design relied on factor of safety and fire protection... and they lost the sprinklers. This alone looks like a formula for a run away rapidly progressing collapse.

The design was also vulnerable to catastrophic collapse because it required numerous mass load transfer structures because the office space was built over an existing Con Ed sub station. For sure this was both unusual and meant that there were fewer and offset axial load paths bedrock.

The collapse of the EPH is a tell that several column lines (axial load paths) beneath it were destroy. The collapse mass of the floor sections from the EPH down appears to be what triggered the East to West progression of structural failures and the entire loss of axial load paths in the building's interior at the lower levels of the building (above the Con Ed???).

NIST's play by play may have been incorrect the details...and there may be many way to play to get to the same outcome. It's interesting to speculate and try to model. But if they all lead to the same outcome.... does it really matter?