How Transfer Structure Failure Led to "Free Fall" acceleration for part of WTC7's Collapse.

[Abdullah]

The thread

How Buckling Led to "Free Fall" acceleration for part of WTC7's Collapse.​

kept going offtopic into transfer structure failure instead. So this thread is created to move discussion of that failure mode.

This mechanism was the one initially proposed by FENA, and it is still supported by some senior Metabunk users. Though the later, more detailed NIST analyses suggest that buckling was the mechanism, we shall assume for the purpose of this thread that NIST may be wrong.

 

[Mendel]

The collapse of World Trade Center 7: revisited
November 2020
DOI:10.14264/9f81895
Conference: 11th International Conference on Structures in Fire (SiF2020)

Article:

A fire in the mechanical room would heat columns 77 and 80 as well as the diagonals of truss 2 which connects them. As these columns lose their capacity, their load is transferred to columns 76, 79, and 81. Likewise, the exposed and partially heated truss 1 is also losing capacity due to heating thus transferring its own capacity to the core and to column 79. Given that column 79 is likely to have been heated due to a diesel fire in its location, and that it also is the most heavily loaded column, it is likely that it would have failed. From this, it was clear that failure of any one of truss 1, truss 2, or column 79 would overload the other two and lead to their failure. It was, therefore, that combined heating of truss 1 and truss 2, and potential heating of column 79 was the primary factor for global collapse of WTC 7. The initiating failure could have been either failure of column 79 or of truss 2, because a collapse event beginning at either of these two points had the potential to manifest the kink observed in the penthouse and cause its sinking as was seen in the videos.

Source: https://www.researchgate.net/publication/347108749_The_collapse_of_World_Trade_Center_7_revisited

The upshot of this paper is that column 79 was not the Achilles heel by itself.

That's step one of the collapse phase, and it's basically a toss-up what broke first, truss or column (both broke). However, that is all about the interior of the building.

The "free fall" discussion is about the collapse of the outer shell of the building, which occured almost simultaneously, but slightly later and separately, and involved the structural elements supporting that shell failing, e.g. by buckling. Why they buckled (or not?) must be discussed with awareness of what happened inside the building (see above).

 

[Jeffrey Orling]

The perimeter is what was measured at FFA.
This means nothing more than whatever was supporting the facade observed in FFA lost axial support. FACT
The moment frame and curtain wall was above the Con Ed sub station.
The north facade included a moment frame and attached curtain wall. It also included a several 3 story belt trusses
To span the Con Ed sub station the design required girders anchored at the core where there was a transfer girder running east west over the north columns of the core.


Girder in magenta color.

Failure of the axial structures any of 73, 74, 75, 77, 78, 79, 80, 81 E3, E4 would lead to the collapse of TT1, TT2 and the the magenta girder which support the 8 - MG27s which in turn supported the north facade/moment frame.

Further... collapse of all the floors to the north and east of the core would undermine these columns at the base including the 27 axial locations that supported the moment frame/facade. The axial structures at the base were not designed to contain the lateral loads of 47 floors of debris.

 

[Abdullah]

@Jeffrey Orling but my question is how could the girder fail across the entire north side of the core? Wouldn't the failure stop at column 70?

 

[Jeffrey Orling]

@Jeffrey Orling but my question is how could the girder fail across the entire north side of the core? Wouldn't the failure stop at column 70?

Perhaps the MG27s lost core side support when the magenta girder was pushed westward and the MG27s slid off their beam seats?

 

[Jeffrey Orling]

The failure of transfer trusses 1 & 2 were a consequence of other failures.

 

[Jeffrey Orling]

@Jeffrey Orling but my question is how could the girder fail across the entire north side of the core? Wouldn't the failure stop at column 70?

Why stop? the entire magenta girder moved westward and it likely cause the south end displacement and loss of support of the MG27s and buckling of columns 61, 64, 67, 70 & 73.... and also the collapse of TT3

 

[Abdullah]

@Jeffrey Orling that girder is not a single girder, but a line of girders

 

[Jeffrey Orling]

@Jeffrey Orling that girder is not a single girder, but a line of girders

Doesn't matter.. the are co-linear end to end bolted to the side of the columns.

 

[Abdullah]

@Jeffrey Orling but then you need to drag the column through the slab

 

[Jeffrey Orling]

@Jeffrey Orling but then you need to drag the column through the slab

Why?
Slabs "end" at the girder because the core is elevator shafts not slab.
Girders were likely on north side of the columns



have a ball!

 

[econ41]

Has anyone interested in this thread worked out why "transfer truss failure" cannot be the sole cause of the observed FFA of the perimeter shell??

Remember that the NIST scenario - whatever its possible shortcomings - has the failure of the whole structure resulting from buckling in the levels above the bottom 7-8 storeys. So if you want to disagree with NIST - be my guest. But the arguments for failures below the load transfer arrangements over the Con Ed substation must look at all the column failure options. Not simply the indirect failures possibly attributable to transfer truss failure.

 

[Jeffrey Orling]

Has anyone interested in this thread worked out why "transfer truss failure" cannot be the sole cause of the observed FFA of the perimeter shell??

Remember that the NIST scenario - whatever its possible shortcomings - has the failure of the whole structure resulting from buckling in the levels above the bottom 7-8 storeys. So if you want to disagree with NIST - be my guest. But the arguments for failures below the load transfer arrangements over the Con Ed substation must look at all the column failure options. Not simply the indirect failures possibly attributable to transfer truss failure.

Econ41 will likely recall that I suggested the TTF theory for "global collapse" years ago. My mistake was to assume that the transfer truss failures were the INITIAL failure not a a result of "something else" which was, I now believe the collapse of the entire east side floor slabs and beams / steel supporting the floors and framed into the core. Structure was too massive for heated beams to "disturb" the TT's, But once all the slabs and steel framing the East side collapsed onto TT1 & TT2.... a runaway chain of events ensued taking out the girders (magenta), north of the core... TT3 and the leading to the collapse of the core, and slabs all around the core and the MG27s which removed a large portion of the support of the moment frame... and to the undermining of the columns at the base.

"Global collapse" obviously has to involve runaway failures of the axial structures...

++++

I believe all the WTC collapses involve " pancaking" or runaway unstoppable floor collapses. All were "initiated" most likely by heated lateral bracing expanding leading to their failure and that left columns missing bracing which were weakened and buckled. Lateral steel failure led to floor collapses, and column buckling.
Open office space column free plans are "vulnerable" to runaway collapse including entire floor areas.

 

[econ41]

Econ41 will likely recall that I suggested the TTF theory for "global collapse" years ago.

I've agreed with you for about 10 years that TTF was probably significant - specifically in the FFA of the perimeter shell. I have always held reservations about TTF as a sole cause... I've always seen it as a probable contribution.

 

[Jeffrey Orling]

I've agreed with you for about 10 years that TTF was probably significant - specifically in the FFA of the perimeter shell. I have always held reservations about TTF as a sole cause... I've always seen it as a probable contribution.

I believe the building's engineer Cantor mentioned this... and FEMA did as well. I don't recall that either attributed initiation of the event to TTF.
I guess we will never know if the floor collapse would have been isolated to the floor area around failed lateral steel on the East side... leaving the remaining building intact. The transfers were efficient means of imparting lateral displacement in the tower.

 

[econ41]

I don't recall that either attributed initiation of the event to TTF.

I've never analysed the structural details. My main focus has been on the reality of the bridging over the Con Ed Sub and the need for cantilever beams. Failure of a cantilever is the blatantly obvious first place to look when it creates a 7-8 storey "gap" AND the FFA was 7-8 storeys. Since nobody was paying much attention I've been mostly content to keep suggesting "Have you considered....." because, if they haven't, their argument has a big hole in it.

That approach is consistent with my SOP - I first take the manager's big picture overview. IF there are fatal errors in the "big picture" the details are probably moot. (Hence my focus through 4-5 years of the Hulsey farce. I kept repeating the fatal error of big picture logic. It is NOT POSSIBLE to prove a global negative claim "fire couldn't cause collapse" in the context of WTC7.)

 

[Jeffrey Orling]

I've never analysed the structural details. My main focus has been on the reality of the bridging over the Con Ed Sub and the need for cantilever beams. Failure of a cantilever is the blatantly obvious first place to look when it creates a 7-8 storey "gap" AND the FFA was 7-8 storeys. Since nobody was paying much attention I've been mostly content to keep suggesting "Have you considered....." because, if they haven't, their argument has a big hole in it.

That approach is consistent with my SOP - I first take the manager's big picture overview. IF there are fatal errors in the "big picture" the details are probably moot. (Hence my focus through 4-5 years of the Hulsey farce. I kept repeating the fatal error of big picture logic. It is NOT POSSIBLE to prove a global negative claim "fire couldn't cause collapse" in the context of WTC7.)

So... the proper starting point in explaining or understanding is to accurately "record" the observations. In the physical/mechanical world an observation reflects its cause...
In the WTC collapse we have pre collapse "movement"... smoke, flames and so on. Each observation is a tell... but it may not be of a unique cause.
++++
Hulsey's got "it wrong" because his premise.... fires can't destroy steel buildings (or something similar) was flawed. He tried to prove this negative. That's strange because the reaction of steel to heat is well known and "settled science". If heat can't "ruin" a steel frame... what else can? An explosion of course! Voila!
But...
Heated steel weakens and expands... and these changes can change the frame fatally.... as we saw in all three towers.

 

[Thomas B]

If heat can't "ruin" a steel frame...

There's a bit of talking past each other on this between truthers and debunkers, I think. Everyone agrees that heat can ruin a steel frame. What the truthers claim is that there is not enough fuel in a typical skyscraper to produce the kind of heat you'd need ruin a frame. An office / apartment fire can deform a steel structure locally, but it cannot, truthers argue, occasion a global failure.

The key to this is their understanding of the frame as basically a steel cage that can easily redistribute loads from any given "hole" in the structure (i.e., local failure). That's something I've had to rethink myself in order to get my mind around these collapses. And I'm not all the way around yet!

 

[Jeffrey Orling]

There's a bit of talking past each other on this between truthers and debunkers, I think. Everyone agrees that heat can ruin a steel frame. What the truthers claim is that there is not enough fuel in a typical skyscraper to produce the kind of heat you'd need ruin a frame. An office / apartment fire can deform a steel structure locally, but it cannot, truthers argue, occasion a global failure.

The key to this is their understanding of the frame as basically a steel cage that can easily redistribute loads from any given "hole" in the structure (i.e., local failure). That's something I've had to rethink myself in order to get my mind around these collapses. And I'm not all the way around yet!

So this goes to the question... for example... would "removing" a single column ALWAYS lead to global collapse?

There is no one answer. But as lateral steel does distribute (floor) loads (and redistribute loads) in the case of a "failed columns" to intact columns of the structure... the concern would be how much additional capacity does each column have? When a steel member is "designed/selected" to carry a certain load... the section chosen ALREADY has more capacity. Factor of Safety refers to the assembly rather than the individual members... But a each member probably can support 2x the design load.

"Buildings commonly use a factor of safety of 2.0 for each structural member. The value for buildings is relatively low because the loads are well understood and most structures are redundant."

So let's say the floor loads are uniform throughout the building... removing a column means the adjacent columns receive the failed column's load. In a grid it would mean that the load of one failed columns would move to the 8 surrounding columns... adding an 12.5% additional load which is well within the safety factor.

x x x
x o x
x x x

 

[Thomas B]

There is no one answer.

Well, there are many buildings. But for each load path diagram there is a single discrete answer to what it would take to occasion global failure.

 

[Jeffrey Orling]

Well, there are many buildings. But for each load path diagram there is a single discrete answer to what it would take to occasion global failure.

No there is not... It depends on the loading of the columns

 

[Thomas B]

It depends on the loading of the columns

The loads are in the diagram.

 

[Jeffrey Orling]

The loads are in the diagram.

Perhaps I don't understand.... each column in a plan is a "load path"... The value of the load is the sum of the axial load - load applied from the column above (includes all floor loads. Floor loads are dead loads - weight of the floor itself... and super imposed loads - live (people and "furniture") and dead (partitions and "systems" - plumbing, electrical, mechanical). Live and dead loads vary so it's hard to know with any precision what the applied load to a column is.
Same thinking applies to the lateral structures - beams, girders and floor trusses.

 

[Henkka]

So this goes to the question... for example... would "removing" a single column ALWAYS lead to global collapse?

That would be pretty concerning if so, since it would mean terrorists could collapse various skyscrapers just by planting one bomb big enough to destroy a column. My understanding is that this is generally not thought to be possible, and what happened with WTC 7 was a unique case.

 

[Jeffrey Orling]

That would be pretty concerning if so, since it would mean terrorists could collapse various skyscrapers just by planting one bomb big enough to destroy a column. My understanding is that this is generally not thought to be possible, and what happened with WTC 7 was a unique case.

Structures include "design redundancy" and don't put all the eggs in one basket. 7WTC's design appears to include the makings of a runaway progressive collapse. It was not simply col 79... but the transfer structures needed to span over the sub station.
There is another building with a vulnerable structure... the CitiCorp building.


http://www.slate.com/blogs/the_eye/...that_could_have_wiped_out_the_skyscraper.html

We saw the vulnerability of the twin tower design - column free open office floors... to runaway unstoppable floor collapse. This design was driven by economics.
The more expensive grided/lattice (more expensive) steel frame is not subject to runaway failures.
Transfer trusses/structures are a sort of Achilles Heel leading to global collapse
Grid designs will have a local - not global collapse.... from a local failure.
I would argue that the developers should have built on the vacant lots north of the World Financial Center and left the Con Ed site as is. I am curious as to how the project went forward with a much better option across the street.
We'll never know.

 

[Jeffrey Orling]

read this:
https://www.uh.edu/ethicsinscience/Media/59Story.pdf

 

[Henkka]

We saw the vulnerability of the twin tower design - column free open office floors... to runaway unstoppable floor collapse. This design was driven by economics.
The more expensive grided/lattice (more expensive) steel frame is not subject to runaway failures.

By this, you mean the "tube" structure explained in this Wiki article, right?

https://en.wikipedia.org/wiki/Tube_(structure)

Given its vulnerability, do you think it should be permitted to construct more skyscrapers like this?

 

[Thomas B]

Perhaps I don't understand.

I described it in a bit more detail in the other thread. Maybe you could draw it up?

Thomas B said:

I may not have made myself entirely clear. The diagram I'm imagining is going to be "theoretical".
It's going to resemble the real WTC7 about as much as [@econ41's] A-G diagram. Like [his] diagram, it will be 2D. It's just going to have 10-story columns, and floor trusses between the columns rather than a rigid beam across the top.

With 7 columns, there'll be 60 floor trusses, each connected to two columns.

If we call the load on each floor truss L, the load on each floor connection will be .5L and the load on the top column sections .5L for the perimeter columns and 1L for each of the internal columns, 6L altogether spread over 7 columns (I don't know, maybe the load would be spread more evenly on all the columns?).

The next floor down in its 12L, then 18L, then 24L, etc. (again distributed in some manner over 7 columns).

We then introduce some damage. Like, we remove a floor truss on each side of column C, which doubles its length and therefore reduces its capacity while removing only 2L from its lower portion.

I think this complication can be simplified out of the model:

Live and dead loads vary so it's hard to know with any precision what the applied load to a column is.

Just make every one of those 60 floor trusses carry a standardized load of 1L. I got the idea from Grady's video on the Hyatt Regency collapse:

 

[Jeffrey Orling]

I described it in a bit more detail in the other thread. Maybe you could draw it up?

I think this complication can be simplified out of the model:

Just make every one of those 60 floor trusses carry a standardized load of 1L. I got the idea from Grady's video on the Hyatt Regency collapse:

Am am not sure what you want.
Here is the framing plane for floor 10 ... You can see the floor BEAMS which support the slabs (not trusses)... and the GIRDERS and spandrel beams they are framed into. GIRDERS and spandrel beams are framed into the columns. Design floor live load was probably 100#/SF. get a scale and you can calculated the live load on each beam.... Add the weight of floor slab
Have a ball!

 

[Jeffrey Orling]

By this, you mean the "tube" structure explained in this Wiki article, right?

https://en.wikipedia.org/wiki/Tube_(structure)

Given its vulnerability, do you think it should be permitted to construct more skyscrapers like this?

I think the column free floors with light weight trusses is not a great idea... They meet design specs... but they ARE vulnerable to runaway pancaking collapse.

 

[econ41]

@Henkka, @Jeffrey Orling take care you are repeating the same global claims that I have identified many times in discussions over recent months. Put simply you are alleging "vulnerability" and implying that it is something that designs should prevent. Unconditionally, That is "pie in the sky" dreaming.

Given its vulnerability, do you think it should be permitted to construct more skyscrapers like this?

Vulnerability to what?? All three WTC Towers were subjected to trauma outside their design envelope. It is actually a simple reality that buildings need to be designed to design criteria. And those criteria cannot be infinite. It is not possible to design a functioning building that will withstand anything that is thrown at it.

I think the column free floors with light weight trusses is not a great idea...

Can you prove it with a soundly reasoned argument?

They meet design specs... but they ARE vulnerable to runaway pancaking collapse.

But only under gross trauma well outside the design envelope.

Despite the excess of "pie in the sky" wishful thinking buildings will always need to be designed to criteria. And it will always be feasible to exceed the design criteria if someone has sufficient mal-intent.

The challenge is not "Prevent any collapse no matter what the inflicted trauma".

The real challenge is in two parts: First "Decide what standards should be required - how much gross trauma should be designed for?" and, second, the more complex issue "Improving design practices so we can meet the new standards" << that is the paradigm shift the Dr Torero identifies in his presentation which, so far it seems, has not been appreciated.'

 

[Jeffrey Orling]

@Henkka, @Jeffrey Orling take care you are repeating the same global claims that I have identified many times in discussions over recent months. Put simply you are alleging "vulnerability" and implying that it is something that designs should prevent. Unconditionally, That is "pie in the sky" dreaming.


Vulnerability to what?? All three WTC Towers were subjected to trauma outside their design envelope. It is actually a simple reality that buildings need to be designed to design criteria. And those criteria cannot be infinite. It is not possible to design a functioning building that will withstand anything that is thrown at it.

Can you prove it with a soundly reasoned argument?

But only under gross trauma well outside the design envelope.

Despite the excess of "pie in the sky" wishful thinking buildings will always need to be designed to criteria. And it will always be feasible to exceed the design criteria if someone has sufficient mal-intent.

The challenge is not "Prevent any collapse no matter what the inflicted trauma".

The real challenge is in two parts: First "Decide what standards should be required - how much gross trauma should be designed for?" and, second, the more complex issue "Improving design practices so we can meet the new standards" << that is the paradigm shift the Dr Torero identifies in his presentation which, so far it seems, has not been appreciated.'

A fire leading to failure of the sprinkler system is not exactly gross trauma such as a plane strike. 7WTC "failed" from unfought fires and there was no fuel in the building above floors 5-7. It's not clear that absent jet fuel but no fire fighting if the twins could "fail".

 

[econ41]

A fire leading to failure of the sprinkler system is not exactly gross trauma such as a plane strike.

Actually, a fire "leading to failure" i.e. causing failure of a sprinkler system should already be within the design envelope - the system should be designed to manage fire effects.

7WTC "failed" from unfought fires

Yes. And "unfought" is outside the design envelope. And it is the big problem with those old design practices - "fire should burn out without collapse" was the implicit and partially accepted "old rule". A major flaw central to the need for a "new paradigm" as identified in the Torero address.

and there was no fuel in the building above floors 5-7.

err?? No additional fuel above what the building was designed for??

It's not clear that absent jet fuel but no fire fighting if the twins could "fail".

...but that is not a legitimate scenario. The concentration of office contents and fit-out material fuel plus the availability of jet fuel was an unavoidable consequence of the aircraft impacts. And we have already discussed the reality that we don't know if the Twins would have survived a normal office fire. either with or without active fire fighting.

 

[Henkka]

Yes. And "unfought" is outside the design envelope.

Unfought for how long, though? Would you say that by collapsing after seven hours of unfought fires, did WTC 7 exceed or underperform what could be expected of its design?

 

[Gamolon]

Unfought for how long, though? Would you say that by collapsing after seven hours of unfought fires, did WTC 7 exceed or underperform what could be expected of its design?

What are your thoughts? Do you think WTC7 exceeded or underperformed is design?

What is YOUR definition of unfought fires? There are two types of fire protection. Active and passive (see quotes below). Which of the systems below in the quoted material underperformed or failed to define what an unfought fire is in your opinion? Does a structural engineer analyze or test their structure during the design phase for possible unfought fires as defined using the quoted systems below?

https://www.firerite.co.uk/fire-pro... between,preventing it from spreading further.

Active Fire Protection

Active fire protection requires action to be taken to detect and alert, stop or contain a fire. This may involve a person taking a manual action, such as using a portable fire extinguisher. On the other hand, this may be a smoke detector that triggers an alarm or automatic sprinkler. Automated or digital systems are also considered active forms of fire protection.

Products that come under active fire protection include:

Fire alarm systems – well-maintained alarm systems are designed to detect fires early and allow occupants time to evacuate.

Emergency escape lighting – for use in the event of power failure, this should be trigged automatically.

Fire suppression and sprinkler systems – devices containing either CO2, inert gases, foam or water mist.

Smoke ventilation, including automatic vents – allows smoke to escape from a building whilst keeping corridors and stairwells smoke-free.

Disabled refuge areas – essential for assisting disabled people or people with impaired mobility to evacuate in the event of an emergency.

Fire hydrant testing and maintenance – used by Local Fire and Rescue Services to access water from the underground mains supply.

Emergency voice communication systems (EVCS) – a bidirectional, secure duplex voice communication system to assist the fire service in high-rise or large buildings.

Dry and wet risers – valves and pipework to enable the fire service to pump water on to specific floors of multi-story buildings.

Public address voice alarms – often known as a ‘Tannoy’ or PA system, used to provide pre-recorded messages during an evacuation or in the event of an emergency.

Fire hose reels – used by trained individuals or the fire service to contain fires, they require a specific flow rate and water pressure.

Portable fire extinguishers – there are various types of fire extinguishers for use on different types of fires. Training is required in order to learn how to use fire extinguishers properly.

Passive Fire protection

The objective of passive fire protection is to prevent the spread of a fire throughout a building. Passive fire protection doesn’t necessarily require intervention in the event of a fire, but it does need to be correctly installed and used properly.

Passive fire protection is a vital element of the building’s fire safety strategy. Its role is paramount in safeguarding people, as well as limiting damage to buildings and their contents from fire and smoke.

Despite its name – passive fire protection does not mean that you can set it up and forget about it! Regular testing and ongoing maintenance are still equally important.

There are several products that are considered passive fire protection that can be incorporated into your fire strategy. Here are some examples:

Fire Doors – an internal fire door can slow fire or smoke from spreading throughout a building, allowing more time for evacuation.

Compartmentation and fire stopping – ensures that walls, floors and ceilings are have continuous fire resistance to assist with restricting the size and spread of a fire.

Fire Curtains - secure, unobtrusive and cost-effective alternative to fire doors that can help prevent a fire from spreading.

Fire and smoke dampers – installed where ducts from the heating, ventilation or air conditioning system passes through walls or floors and can help prevent the spread of a fire, although these may be activated by an active system e.g. a fire and smoke damper linked to the main fire alarm system.

 

[Gamolon]

And "unfought" is outside the design envelope.

My opinions is that when discussing unfought fires and design envelope with others is that both need to be defined.

My posts above is to get a common definition of what is considered an "unfought fire" and then using those parameters, discuss what a structural engineer (or other engineer) does to take into account an "unfought fire", which is over and above a "normal fire" and how it is handled in the design.

 

[Mendel]

You're off topic and back in a rut, no longer discussing transfer truss failures and instead discussing fire. I doubt anything written past this point is worth reading because people will keep the topic drifting instead of arriving at a point.

 

[Mendel]

My opinions is that when discussing unfought fires and design envelope with others is that both need to be defined.

My posts above is to get a common definition of what is considered an "unfought fire" and then using those parameters, discuss what a structural engineer (or other engineer) does to take into account an "unfought fire", which is over and above a "normal fire" and how it is handled in the design.

Within the context of WTC7, there is no need to define the finer points of "unfought": "several big fires started simultaneously with no mains water available near the building, and the NYPD in disarray from heavy losses" has got to be far removed from any borderline case of "unfought fire" you happen to choose—and that's not even considering that you don't have any criteria to recognize a good answer to your question.

And it doesn't pertain to the effects of transfer truss failure at all.

 

[Gamolon]

Within the context of WTC7, there is no need to define the finer points of "unfought".
And it doesn't pertain to the effects of transfer truss failure at all.

So fire had no play in the failure of the transfer truss whether directly or indirectly? Is that the thought at this point?

If that's the case, then I apologize for being off topic and will stop discussing fire.

 

[Mendel]

So fire had no play in the failure of the transfer truss whether directly or indirectly? Is that the thought at this point?

the topic is "How Transfer Structure Failure Led to "Free Fall" acceleration for part of WTC7's Collapse."

The transfer structure failure is assumed here, so how the transfer structure came to fail is off topic (unless it pertains to what happened afterwards).
(and your focus on "unfought fire" is doubly off topic, see my previous post).

You don't have to stop discussing fire, but it'd be good if you started a new topic, and did a forum search ("unfought fire" has come up several times since 2013).