Discussion of the definition of unfought fires and are they considered in designing a stucture

[Gamolon]

Discussion of the definition of unfought fires and if those unfought fire scenarios are considered/designed for during the design phase.

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? 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.

 

[NorCal Dave]

Which of the systems below in the quoted material underperformed or failed to define what an unfought fire is?

They don't "define" an unfought fire at all, therefore I don't think one can say the systems "failed". If the systems were designed to completely prevent fire, and/or completely extinguish any fire that does occur with out any outside efforts, then maybe one can say there was a failure.

Note also, this material is not from any type of building code or requirements, it's just a list compiled by a company trying to sell fire protection equipment to property owners.

But I don't think that's what these systems are about. They're risk mitigation tools. Things like fire doors and draft stops slow the spread of fire. Sprinkler systems may extinguish small fires or keep larger fires in check until active firefighting occurs.

In some cases a failure can be attributed. The Grenfell Tower fire started in a refrigerator, but spread rapidly through combustible insulation and an air channel left open between the building and it's new cladding. A failure of a passive system as there were no draft stops to restrict the chimney effect.

The fire was started by an electrical fault in a refrigerator on the fourth floor.[note 1] It spread rapidly up the building's exterior, bringing fire and smoke to all the residential floors. This was due to the building's new cladding and the external insulation, since the air gap between them enabled the stack effect. The fire burned for about 60 hours before finally being extinguished. More than 250 London Fire Brigade firefighters and 70 fire engines from stations across London were involved in efforts to control the fire and rescue residents.

But even here, the building was designed to contain a fire until the fire services arrived (bold by me):

Like many other tower blocks in the UK, Grenfell Tower was designed to be operated under a "stay put policy" in the event of fire. The idea was that if a fire broke out in one flat, thick walls and fire doors would contain the fire long enough for the fire service to bring it under control.[12] Only those in the affected dwelling would be expected to evacuate.[13] The building was designed under the assumption that a full evacuation would never be necessary.

en.wikipedia.org/wiki/Grenfell_Tower_fire

It still managed to burn for 60 hours as firefighters worked on it.

 

[Gamolon]

They don't "define" an unfought fire at all, therefore I don't think one can say the systems "failed".

For a starting point.

Below is what Henkka stated in another thread:

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?

I am trying to determine what Henkka (or someone else) thinks defines an "unfought fire" is. Then we need to determine if WTC7 was designed for these "unfought fires". Then we can determine if WTC7's design exceeded or outperformed the said design parameters.

Like I said there, are two types of fire protection, active and passive. I linked to a site that explains what they believe fall under those categories as examples. There are probably other sites that have more examples.

 

[Henkka]

I am trying to determine what Henkka (or someone else) thinks defines an "unfought fire" is. Then we need to determine if WTC7 was designed for these "unfought fires". Then we can determine if WTC7's design exceeded or outperformed the said design parameters.

I think everyone understands it to mean that the fire was not being actively fought, by firefighters.

You asked me in the other thread what my opinion was on whether WTC 7 exceeded or underperformed, and I guess I can't say anything for sure, I'm no engineer. But as a total layperson, I don't quite understand the idea that WTC 7 was not designed to withstand 7 hours of unfought fires, when other American skyscrapers like One Meridian Plaza have survived extremely severe fires without even partially collapsing.

 

[Thomas B]

I don't quite understand the idea that WTC 7 was not designed to withstand 7 hours of unfought fires, when other American skyscrapers like One Meridian Plaza have survived extremely severe fires without even partially collapsing.

Yes, in this context the fact that the fires in WTC7 were "unfought" may be a bit of a red herring. One Meridian did have firefighting but burned for 19 hours. It doesn't seem likely (and I haven't heard it argued) that if there had been no firefighting during the first 7 hours the building would have collapsed.

 

[Henkka]

Yes, in this context the fact that the fires in WTC7 were "unfought" may be a bit of a red herring. One Meridian did have firefighting but burned for 19 hours. It doesn't seem likely (and I haven't heard it argued) that if there had been no firefighting during the first 7 hours the building would have collapsed.

Yeah this was somewhat discussed in another thread. The fires in One Meridian were fought... sort of. After there was an order to evacuate the building, the only firefighting was done by spraying from adjacent buildings. They had a hard time reaching though, so in effect the fire burned out of control until it was stopped by sprinklers on the 30th floor. Then it just burned until ran out of fuel. It seems extremely unlikely to me that the little bit of water they were able to spray on the side is what made the difference in the building standing or collapsing.

 

[Gamolon]

But as a total layperson, I don't quite understand the idea that WTC 7 was not designed to withstand 7 hours of unfought fires, when other American skyscrapers like One Meridian Plaza have survived extremely severe fires without even partially collapsing.

That's a question you need to ask an engineering firm. Do they design skyscrapers/buildings to withstand scenarios where fires are unfought by firefighters.

 

[Gamolon]

Yes, in this context the fact that the fires in WTC7 were "unfought" may be a bit of a red herring. One Meridian did have firefighting but burned for 19 hours. It doesn't seem likely (and I haven't heard it argued) that if there had been no firefighting during the first 7 hours the building would have collapsed.

Why are you comparing buildings of different designs to behave the same regarding fires?

 

[Gamolon]

You asked me in the other thread what my opinion was on whether WTC 7 exceeded or underperformed, and I guess I can't say anything for sure, I'm no engineer. But as a total layperson, I don't quite understand the idea that WTC 7 was not designed to withstand 7 hours of unfought fires,

So you believe that engineers test their steel structures with unfought fire scenarios and then change their designs if they find that they fail in some capacity during those tests?

 

[Henkka]

So you believe that engineers test their steel structures with unfought fire scenarios and then change their designs if they find that they fail in some capacity during those tests?

I'm only aware of the Cardington fire tests.


Source: https://www.youtube.com/watch?v=Y-buceElLVY


I don't know anything about these tests beyond this documentary clip, though. I haven't like dug through the documents to find out how long they burned this building, for example.

 

[Thomas B]

Do they design skyscrapers/buildings to withstand scenarios where fires are unfought by firefighters.

Why are you comparing buildings of different designs to behave the same regarding fires?

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents. That is, they're designed not to collapse due to fire. 9/11 revealed engineers still had something to learn on this score. One Meridian was designed differently, but I think that the design goal would have been the same: not to collapse due to fire. The worst case is a completely unfought fire. That's the one the structure would be designed to survive.

PS: Some sources I mentioned on another thread about this:

The Society of Fire Protection Engineers puts it this way:

The fire resistance ratings in contemporary design codes were created with the intention that a structure would maintain its load-bearing capacity for as long as a fire could burn, until all the fuel in the compartment was consumed—this is "design for burnout."[6,7]
[6] P.H. Thomas, "The Fire Resistance Required to Survive Burnout–Fire Research Note No. 901, Borehamwood, 1970.
[7] M. Law, "A review of formulae for T-equivalent," Proc. 5th Int. Symp. Fire Saf. Sci., 1997.
Content from External Source

https://www.sfpe.org/publications/sfpeeuropedigital/sfpeeurope5/issue5feature1

As we've discussed before, this was taken up by the WTC7 investigation's advisory board:

Q: If fires start in a building and there is no firefighting effort, is the building expected to come down? Or would it be expected that the building would remain standing after the fires have burned out?

A: Buildings are currently designed based upon E119 test results for building components and subassemblies. [...] This would provide sufficient time for people to evacuate and for automatic sprinklers or manual firefighting efforts to control the fire. [...] The assumption is that the system as a whole will survive that exposure. The implicit assumption is that when there is a situation where the sprinklers do not function, there would be burnout of the building contents without collapse. [... But] The science has not evolved to the point of designing to meet the performance objective of burnout without collapse
Content from External Source

https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf

 

[Henkka]

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents. That is, they're designed not to collapse due to fire. 9/11 revealed engineers still had something to learn on this score. One Meridian was designed differently, but I think that the design goal would have been the same: not to collapse due to fire. The worst case is a completely unfought fire. That's the one the structure would be designed to survive.

PS: Some sources I mentioned on another thread about this:

The Society of Fire Protection Engineers puts it this way:

https://www.sfpe.org/publications/sfpeeuropedigital/sfpeeurope5/issue5feature1

As we've discussed before, this was taken up by the WTC7 investigation's advisory board:

https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf

Right, and it makes total sense too, since anything less throws things into total uncertainty. All buildings have slightly different designs, so how long they would stand in a fire before collapse would vary. If you're not sure when or if the building is collapsing, you can't know for sure when is it safe for firefighters to be near the building. This is what cost the lives of 20 firefighters with the Plasco collapse. If they had known to anticipate that collapse, they would have also just evacuated the area and let it come down.

 

[econ41]

I do not believe that any member cannot understand the concept of an "unfought fire". The basic principles have been spelled out multiple times and are still being ignored.

The key issues are - once again:
(a) Buildings, and specifically steel framed high rise towers such as the WTC Twin Towers and WTC7, are designed to meet a fire rating. Three hours for this discussion of WTC Towers.

(b) The "Fire Rating" serves two main purposes viz:
(i) It allows time for occupants to escape the building; and
(ii) it allows time for active fire fighting to be commenced.

(c) To achieve that rating and as part of an overall scheme of fire protection the building has inbuilt protections - passive forms such as selection of fire resistant materials and provision of insulation, fire resistant doors and other means to limit movement of fires - and semi active systems such as fire sprinklers.

So the design always presumes the combination of passive measures to gain time followed by active fire fighting. And at risk of restating the obvious - if "active fire fighting" is not commenced the fire will be "unfought".

EXACTLY as explained by @NorCal Dave even tho in a slightly different context.

But even here, the building was designed to contain a fire until the fire services arrived (bold by me):

Now there are two overlaying complex issues:

First: The assumption or presumption that buildings are designed for or should survive total burn out of fuel without collapsing. The status of that concept in US fire management is confused. It seems to be an assumed goal but is not specifically defined in regulation.

Second: It is clear that methods of designing for fire protection are not keeping up with the evolution of building design.

Reference has been made in other threads to an explanatory presentation by Dr Torero who, in effect, identifies that design methods are outdated, that there is a need for a "new paradigm" (my term for what Torero says). The need is for performance based design for fires. Whilst the design of the wTC Towers treated fire resistance as a regulatory "add on" of blanket rules. << Another topic for serious discussion. And attempts at such serious discussion have failed in a couple of previous threads.

 

[Thomas B]

Buildings, and specifically steel framed high rise towers such as the WTC Twin Towers and WTC7, are designed to meet a fire rating. Three hours for this discussion of WTC Towers.

As I understand it, the fire rating doesn't apply to the building but to the various local components. A three-hour rating is effectively designing for burnout because no fire will burn in the same place (i.e., heat the same components) for longer than that. Generally, it is assumed that an office fire can burn locally for about two hours.

The length of time that the building is exposed to fire is irrelevant. The question is how long the steel in any given assembly undergoes heating.

PS: Overall, I find the idea that the fire rating is in any way related to the length of time a fire may be left "unfought" before a building skyscraper should be considered at risk of total collapse implausible.

 

[Henkka]

Generally, it is assumed that an office fire can burn locally for about two hours.

Hmm, so do you think the area around column 79 was on fire for the last two hours prior to collapse? So from around 3PM and 5PM. And if that's the case, could the building have collapsed even earlier?

 

[Oystein]

Two issues not covered by local and subassembly fire ratings:

* design methods did not exist to extrapolate from a single localized (e.g. compartment) fire, resisting local burnout from leading to local collapse, to a situation where a large volume of adjacent compartments is srtructurally affected by non-localized fires: you can't guarantee you sub-assembly performs as expected when floors below and above are on fire affecting structural elements adversely (such as sressing colums) that, in the local design perspective, would be considered unaffectes.

* at least one of engineering firms that released studies of WTC7 identified the issue of "pre-heating, where hot gas in one area of a floor would flow towards other aread not yet burning, raising structural temperatures significantly before a local fire breaks out. This problem is more pronounced for buildings with large and open floor spaces like the WTC was famous for

Hence what Thomas quoted:
"The science has not evolved to the point of designing to meet the performance objective of burnout without collapse".

 

[Gamolon]

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents. That is, they're designed not to collapse due to fire. 9/11 revealed engineers still had something to learn on this score. One Meridian was designed differently, but I think that the design goal would have been the same: not to collapse due to fire. The worst case is a completely unfought fire. That's the one the structure would be designed to survive

Based on your statement above that you think buildings are designed to withstand collapse (partial OR total) due to unfought fires, what do you think the reason is for the complete collapse of WTC7?

Did an engineer miss or ignore certain design codes that were in place to make steel structures impervious to collapse due to unfought fires?

 

[Thomas B]

Based on your statement above that you think buildings are designed to withstand collapse (partial OR total) due to unfought fires, what do you think the reason is for the complete collapse of WTC7?

Did an engineer miss or ignore certain design codes that were in place to make steel structures impervious to collapse due to unfought fires?

According to NIST, the kind of expansion that caused the girder "walk-off" was a hitherto unknown mechanism. It was a lack of knowledge.

 

[Thomas B]

Hmm, so do you think the area around column 79 was on fire for the last two hours prior to collapse? So from around 3PM and 5PM. And if that's the case, could the building have collapsed even earlier?

That is one likely possibility (in my inexpert opinion). The fire wandered around the building, heating various parts, moving on (and letting them cool), until it found the weak spot. In that sense it was just bad luck. It could have taken twenty hours of "unfought" fire before it reached a spot that was vulnerable to this kind of expansion and failure.

 

[Gamolon]

According to NIST, the kind of expansion that caused the girder "walk-off" was a hitherto unknown mechanism. It was a lack of knowledge.

That mechanism was outside the "design envelope" at that time then?

 

[Henkka]

That is one likely possibility (in my inexpert opinion). The fire wandered around the building, heating various parts, moving on (and letting them cool), until it found the weak spot. In that sense it was just bad luck. It could have taken twenty hours of "unfought" fire before it reached a spot that was vulnerable to this kind of expansion and failure.

That's kind of worrisome. It raises the question, what lesson should the firefighting industry take from the collapses of WTC 7 and the Plasco tower? It seems like overwhelmingly, steel buildings can be relied to stand in fires. But in these two cases, you got a rather sudden, total collapse of the structure. So is the next burning steel building going to collapse or not? How long will it take? Should you risk the lives of firefighters, or just evacuate the area and let it burn?

 

[Gamolon]

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents.

Doesn't the excerpt below state otherwise? It was ASSUMED there would be burnout without collapse, but there was no specific design criteria/parameters to design a building for that objective as stated by the bolded section below.

Q: If fires start in a building and there is no firefighting effort, is the building expected to come down? Or would it be expected that the building would remain standing after the fires have burned out?

A: Buildings are currently designed based upon E119 test results for building components and subassemblies. [...] This would provide sufficient time for people to evacuate and for automatic sprinklers or manual firefighting efforts to control the fire. [...] The assumption is that the system as a whole will survive that exposure. The implicit assumption is that when there is a situation where the sprinklers do not function, there would be burnout of the building contents without collapse. [... But] The science has not evolved to the point of designing to meet the performance objective of burnout without collapse.

According to that same report., there was a proposed code change for the 2006/2007 code cycle for just this purpose, but it was not approved.

There was also a code change proposal to require providing for burnout without collapse that was submitted to the International Code Council (ICC) 2006/2007 code cycle but was not approved. Two proposals on burnout without collapse have been submitted for the 2007/2008 code cycle. If either of these proposals is approved, design for burnout without collapse would be built-in to all buildings, not on a case-by-case approach.

 

[Thomas B]

That mechanism was outside the "design envelope" at that time then?

No, because the fire that caused it was (if I'm right about this) well within it. It was simple ignorance of the physical forces at work. The best comparison is probably the Tacoma Narrows collapse. The winds that day were not outside the design envelope but aeroelastic flutter was insufficiently understood.

 

[Gamolon]

No, because the fire that caused it was (if I'm right about this) well within it. It was simple ignorance of the physical forces at work. The best comparison is probably the Tacoma Narrows collapse. The winds that day were not outside the design envelope but aeroelastic flutter was insufficiently understood.

So "areostatic flutter" was something that was not addressed by a design code somewhere so it could be avoided. Is that correct?

 

[Gamolon]

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents.

Tell me something Thomas B.

If what you say above is true, that all skyscrapers were/are DESIGNED to survive complete burnout and not collapse, then why did they propose a code change to provide for burnout without collapse as stated below?

There was also a code change proposal to require providing for burnout without collapse that was submitted to the International Code Council (ICC) 2006/2007 code cycle but was not approved. Two proposals on burnout without collapse have been submitted for the 2007/2008 code cycle.

 

[Gamolon]

No, because the fire that caused it was (if I'm right about this) well within it. It was simple ignorance of the physical forces at work. The best comparison is probably the Tacoma Narrows collapse. The winds that day were not outside the design envelope but aeroelastic flutter was insufficiently understood.

I didn't ask about the fire being out of the design envelope. I asked about the mechanism (the kind of expansion that caused the girder "walk-off") CAUSED by the fire.

 

[Thomas B]

I didn't ask about the fire being out of the design envelope. I asked about the mechanism (the kind of expansion that caused the girder "walk-off") CAUSED by the fire.

But that was a structural response not a loading event.

 

[Gamolon]

But that was a structural response not a loading event.

So what? You're saying that you believe all skyscrapers are DESIGNED to withstand collapse due to unfought fires. So if WTC7 was DESIGNED, within the DESIGN ENVELOPE used by engineers, why did it collapse?

 

[Gamolon]

No, because the fire that caused it was (if I'm right about this) well within it. It was simple ignorance of the physical forces at work. The best comparison is probably the Tacoma Narrows collapse. The winds that day were not outside the design envelope but aeroelastic flutter was insufficiently understood.

What, in your opinion, is contained within the "design envelope" for unfought fires that engineers use when designing their skyscrapers? Does it contain design codes/parameters/guidelines that need to be applied to structural components/assemblies to prevent collapse from unfought fires?

 

[FatPhil]

So "areostatic flutter" was something that was not addressed by a design code somewhere so it could be avoided. Is that correct?

I'm wondering how they thought clarinet reeds work.

The interaction of air flow and insufficiently-damped bodies seems perennially misunderstood. I hear that several F1 designers from the 1970s have made comments ranging from the snarky to the sympathetic to the ones suffering from porpoising right now.

 

[Thomas B]

So if WTC7 was DESIGNED, within the DESIGN ENVELOPE used by engineers, why did it collapse?

Because the designers lacked knowledge that was necessary to meet the design objectives.

 

[Jeffrey Orling]

Because the designers lacked knowledge that was necessary to meet the design objectives.

false
The design was fine
Fires were unfought for 7 hrs (active fire fighting)
sprinklers failed

It might be interesting to learn of engineers run any "what ifs?" to see a local "failure" would progress and go runaway or be arrested.

Twin towers column free floors look like a recipe for going runaway
"failure" of the TT1 and TT2 look like a recipe for going runaway

But what scenario would cause those failures?

My sense is that engineers do NOT run "what ifs?"... that they don't design mechanisms to arrest progressive failures... (they don't expect them)

I suspect engineers are more aware of how pancaking/runaway floor collapse can do in a building after the WTC collapses.

++++

WTC7 was built over a con ed sub station. That was (in my opinion} a very bad decision... especially when the lot across the street was available. A system of transfers were needed to accommodate the sub station. And it was that system which enabled the runaway total collapse. That WAS predictable on some level.

 

[Gamolon]

Because the designers lacked knowledge that was necessary to meet the design objectives.

So now that designers and engineers have this new information regarding the previously unknown "walk off" mechanism, what needs to happen for new skyscraper designs in order to address this so it doesn't happen again?

 

[Thomas B]

So now that designers and engineers have this new information regarding the previously unknown "walk off" mechanism, what needs to happen for new skyscraper designs in order to address this so it doesn't happen again?

According to NIST, the connections between the trusses and the columns should be strengthened.

On page 64 of the NIST report:

Had contemporaneous standards and practices been available to expressly
design WTC 7 for prevention of fire-induced progressive collapse, it would have been sufficiently
robust to withstand local failure due to the fires without suffering total collapse.

And page 65:

Possible options for developing cost-effective fixes include:
• More robust connections and framing systems to better resist the effects of thermal expansion
on the structural system.
• Structural systems expressly designed to prevent progressive collapse.

https://nvlpubs.nist.gov/nistpubs/Legacy/NCSTAR/ncstar1a.pdf

 

[Jeffrey Orling]

Note.... when Cantor, the building's engineer, was asked why the whole building collapsed... he sayed it was the transfer structures.

++++

Walk off was enabled by an inadequately restrained girder... resting on a beam seat.

Have a look:

 

[Thomas B]

I'm not sure if this helpful, but imagine Leslie Robertson, John Skilling, and James Quintiere having lunch at the Windows of the World at the top of the North Tower in early March, 1991, a couple of weeks after the One Meridian fire. Suppose they started talking "What if...?"

What if something similar to One Meridian happened 15 floors below them? They imagine sprinklers failing and fire doors being left open -- everything going wrong. Maybe even multiple fires starting at once. Obviously it would take some time for the fire fighters to get on site and set up. They imagine elevators not working. Etc. Etc. A real worst-case "unfought" fire for a few hours that then gets out of control so that the top twenty floors are engulfed in flame and crews below evacuate for fear of (local) floor collapses. (Pretty much like in One Meridian.)

This is early March, so let's say they know what Wikipedia tells us about the condition of the building after the fire.

By February 26, city officials had determined One Meridian Plaza was not in danger of collapse.[12] There was structural damage to horizontal steel beams and floor sections on most of the fire damaged floors. Under extreme fire exposure the beams and girders sagged and twisted and cracks appeared in the concrete floors. However, the overall structure was stable and able to support the weight of the building. Thermal expansion of the steel frame caused some of the granite panels to be dislodged from the building's facade.[4] The streets and buildings around One Meridian Plaza were closed and cordoned off.[12]

https://en.wikipedia.org/wiki/One_Meridian_Plaza#After_the_fire

Having two of the building's designers at the table, they have direct professional knowledge of the WTC design. Having a fire engineer there they'd have that side covered too. Would the possibility of a total progressive collapse of the building occur to them? Or would they imagine the worst case as a burn out? I think the latter. It's what I mean when I say the WTC was "designed for burnout". I don't mean that any specific feature ensured burn out, or that a code required it, only that an overall assessment of the design by knowledgeable professionals would have led them to conclusion that they would not collapse because of a terrible "unfought" fire on the scale of One Meridian.

 

[Jeffrey Orling]

According to NIST, the connections between the trusses and the columns should be strengthened.

On page 64 of the NIST report:

And page 65:

https://nvlpubs.nist.gov/nistpubs/Legacy/NCSTAR/ncstar1a.pdf

The trusses TT1,2 & 3 were on top of columns, and had other columns on top of them. They were not connected to once another

I'm not sure if this helpful, but imagine Leslie Robertson, John Skilling, and James Quintiere having lunch at the Windows of the World at the top of the North Tower in early March, 1991, a couple of weeks after the One Meridian fire. Suppose they started talking "What if...?"

What if something similar to One Meridian happened 15 floors below them? They imagine sprinklers failing and fire doors being left open -- everything going wrong. Maybe even multiple fires starting at once. Obviously it would take some time for the fire fighters to get on site and set up. They imagine elevators not working. Etc. Etc. A real worst-case "unfought" fire for a few hours that then gets out of control so that the top twenty floors are engulfed in flame and crews below evacuate for fear of (local) floor collapses. (Pretty much like in One Meridian.)

This is early March, so let's say they know what Wikipedia tells us about the condition of the building after the fire.

By February 26, city officials had determined One Meridian Plaza was not in danger of collapse.[12] There was structural damage to horizontal steel beams and floor sections on most of the fire damaged floors. Under extreme fire exposure the beams and girders sagged and twisted and cracks appeared in the concrete floors. However, the overall structure was stable and able to support the weight of the building. Thermal expansion of the steel frame caused some of the granite panels to be dislodged from the building's facade.[4] The streets and buildings around One Meridian Plaza were closed and cordoned off.[12]

https://en.wikipedia.org/wiki/One_Meridian_Plaza#After_the_fire

Having two of the building's designers at the table, they have direct professional knowledge of the WTC design. Having a fire engineer there they'd have that side covered too. Would the possibility of a total progressive collapse of the building occur to them? Or would they imagine the worst case as a burn out? I think the latter. It's what I mean when I say the WTC was "designed for burnout". I don't mean that any specific feature ensured burn out, or that a code required it, only that an overall assessment of the design by knowledgeable professionals would have led them to conclusion that they would not collapse because of a terrible "unfought" fire on the scale of One Meridian.

I am sure the issue of evacuation would be raised. This is a tough one.
I suppose they expected the sprinklers to work and for fire fighters to get up to the fire and fight it.
I am sure Robertson and Skilling understood that runaway pancake collapse of the flooring system was a possibility because there was no mechanism to arrest it.
I suppose a tell would be to see what sort of tall high rise steel designed towers they have done since 2001.

 

[econ41]

I must be a "glutton for punishment" but I'm going to have yet one more attempt to establish some focus on this topic to see if we can get the discussion moving forwards.

The OP asks a couple of straightforward questions which have already been responded to and explained in previous threads.

Discussion of the definition of unfought fires and if those unfought fire scenarios are considered/designed for during the design phase.

There are two types of fire protection. Active and passive (see quotes below).

This should be agreed known fact for anyone attempting to discuss the mechanisms of the WTC 9/11 collapses. The reality of that split into "inbuilt passive" measures including sprinklers AND "active fire fighting" should be accepted as a starting premise for reasoned discussion. And it should also be accepted fact that on 9/11, for the WTC7 fires, a deliberate decision was taken to not pursue active fire fighting. The numerous evasions of those two facts are not helping to progress the discussion.

Which of the systems below in the quoted material underperformed or failed to define what an unfought fire is?

Which question raises two points:
1) There is nothing in the several fragmented discussions to date that relies on disputing the definition of "active fire fighting" nor on denying that the wTC7 fires were not "actively fought" by deliberate choice. Given those two facts, the claims that "unfought" is not defined are ludicrous in the context of these discussions.

Does a structural engineer analyze or test their structure during the design phase for possible unfought firesA as defined using the quoted systems below?B

A That question has already been answered by me:

Now there are two overlaying complex issues:

First: The assumption or presumption that buildings are designed for or should survive total burn out of fuel without collapsing. The status of that concept in US fire management is confused. It seems to be an assumed goal but is not specifically defined in regulation.

B The whole topic is confused in the context of WTC collapses on 9/11. So reference to specific details documented in British practice is of no benefit. It refers to the reality that US practice from 1960s-70s does not meet contemporary expectations. The topic that has been raised for discussion in other threads... part of the genesis of this and several other threads OPed because the topic was either too complicated or did not meet other pre-determined expectations of some members.

@Gamolon goes on to quote British standards:

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

Active Fire Protection

Passive Fire protection

... but that detail is not needed - it is a distraction. The factors relevant to these discussions are:
(a) The distinction between "passive" fire protection and "active" fire fighting; and
(b) Understanding that in the scope of these discussions of WTC collapses an "unfought fire" is simply what it says, A fire that was not fought by application of "active fire fighting" processes. However, those are defined in the relevant jurisdiction and fire agency SOPs.

 

[econ41]

@Thomas B This post shows evidence of progress:

The more I study this issue, the more I think that all skyscrapers are designed to survive the complete burnout of their contents.

They should be. They weren't and probably still aren't. The reality still is that the old rules were not good enough by today's expectations.

That is, they're designed not to collapse due to fire. 9/11 revealed engineers still had something to learn on this score.

Despite the obvious self-contradiction. They should be designed not to collapse. They weren't. Probably still arent in USA. And, as I have said several times, there was a lot of confused "wishful thinking".

One Meridian was designed differently, but I think that the design goal would have been the same: not to collapse due to fire.

"Should" have been. It wasn't. Part of the same confused wishful thinking of that old outdated era.

The worst case is a completely unfought fire.

Not quite. The "worst case" it should be designed for is the worst fire scenario the designer decides on. You are still glossing over the possibility of "trauma greater than designed for" and it is a serious complex issue. Don't brush it off.

e.g. Should all high-rise towers be designed to withstand deliberate impact by a fully fueled high-speed airliner? THINK before you say: "Yes!" because my next step will be to up the ante. It is not that simple.

That's the one the structure would be designed to survive.

CORRECT. CORRECT! So - what is the largest fire it should be "designed to survive"??

.....
PS: Some sources I mentioned on another thread about this:
.........
As we've discussed before, this was taken up by the WTC7 investigation's advisory board:

https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf

Please read the excerpts you post:

...The implicit assumption is that when there is a situation where the sprinklers do not function, there would be burnout of the building contents without collapse. [... But] The science has not evolved to the point of designing to meet the performance objective of burnout without collapse

<< Exactly the point I've been making in all these fragments of threads. And the same point central to the presentation by Dr Torero which impressed you.

 

[econ41]

false
The design was fine
Fires were unfought for 7 hrs (active fire fighting)
sprinklers failed

It might be interesting to learn of engineers run any "what ifs?" to see a local "failure" would progress and go runaway or be arrested.

They try to. BUT "Murphys Law" of what-iffing is clear and inexorable:
"No matter how many "what if" scenarios you anticipate - the one that happens will be one you didn't think of."

Twin towers column free floors look like a recipe for going runaway
"failure" of the TT1 and TT2 look like a recipe for going runaway

Ain't 20/20 hindsight wonderful?

But what scenario would cause those failures?

The big "elephant in the room" throughout this series of fragmented discussions. The cause of the progression was well outside any reasonable design envelope. The Towers were not adequately designed for the scale of fire that they were subjected to. And the reason is in two parts. (i) first the scale of the fire was far greater than it would have been reasonable to assume. and (ii) second is the aspect that Dr Torero identifies, @Thomas B agrees with and I have also emphasised. Put simply the structural design and the fire protection design were not integrated. And we cannot know if the Twin Towers would have survived the lesser scale fire scenario they were intended to withstand. They were never tested under such a scenario.

My sense is that engineers do NOT run "what ifs?"... that they don't design mechanisms to arrest progressive failures... (they don't expect them)

Did not. You can take a safe bet that "what iffing" gets a lot of serious attention post 9/11. But don't be too optimistic - I'm onside with the more pessimistic assessment offered by Dr Torero.

I suspect engineers are more aware of how pancaking/runaway floor collapse can do in a building after the WTC collapses.

Probably more aware but, remember, most of the profession still accepts Bazant et simile false explanations of the WTC collapses.