Can Skyscrapers Fall Over on Their Side?

MOST designs are probably not vulnerable. BUT that does not make it a global truism. At least to prima facie standard WTC7 was vulnerable. So the burden of proof is on anyone who claims it was not.
As you know I believe that the failure at column 79 progressed westward through the building because it dislodged one or two of the transfers used because the 40 story tower was erected over an existing Con Ed sub station.
 
I stand by my original 1 dimensional method. It shows the behaviour of the pivot. But let's try again.

Angular acceleration = torque / moment of inertia

Moment of inertia = mass × moment arm²

Torque = mass × acceleration × sine of angle with moment arm

Angular acceleration = acceleration × sine of angle with moment arm / moment arm²

Both the acceleration and angular acceleration variables above are for the center of mass of the building, moving in relation to the pivot. A larger building has a larger moment arm, and therefore rotates less for a given acceleration and arm angle. Also, this is where my original 1D model weighs in, and makes rotation even harder by reducing relative acceleration.
 
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Both the acceleration and angular acceleration variables above are for the center of mass of the building, moving in relation to the pivot.
Could you make a sketch drawing of this, and identify the relevant variables on it, too? Then you'd actually be doing physics, and not merely reproducing formulas.
 
MOST designs are probably not vulnerable. BUT that does not make it a global truism. At least to prima facie standard WTC7 was vulnerable. So the burden of proof is on anyone who claims it was not.
What do you mean by "prima facie standard" here? Do you mean that since it did fail it was "on the face of it" vulnerable. Or do you mean that a look at the design (before it collapsed) would have immediately suggested its vulnerability?

It seems to me that if most designs are not vulnerable then the burden of proof is precisely to show that WTC7 was nonetheless vulnerable, using something other than the collapse itself as evidence.

Surely, anything else begs the question with a truther who is suggesting that the vulnerability was not in the design but caused by deliberate weakening of the structure?
 
What do you mean by "prima facie standard" here? Do you mean that since it did fail it was "on the face of it" vulnerable. Or do you mean that a look at the design (before it collapsed) would have immediately suggested its vulnerability?

It seems to me that if most designs are not vulnerable then the burden of proof is precisely to show that WTC7 was nonetheless vulnerable, using something other than the collapse itself as evidence.

Surely, anything else begs the question with a truther who is suggesting that the vulnerability was not in the design but caused by deliberate weakening of the structure?
In my opinion the vulnerability to a "global" or total collapse of the tower was because the system of load transfers which were supporting columns 79, 80 and 81. When there was a local collapse of floor slabs supported by these columns... the 8 or more slabs and contents crashed down and dislodged the load transfer structures on floors 5-7 on the East side of the tower and the movement of the East side transfer structures involved the girder on the north side of the core... and the cantilever girders they supported the north side of the moment frame... and the transfer structure on the west side of the core. Almost the entire structural system was "undermined" or displaced leading to a global collapse. There has to be lateral progression of failures and the mechanism and structures to do that. 7WTC had these features.
 
What do you mean by "prima facie standard" here?
Just the normal meaning - there is a "case to answer"
Do you mean that since it did fail it was "on the face of it" vulnerable.
Yes, but those of us who have been discussing the WTC7 collapse should already be aware of the several "levels" (or "layers") of vulnerability. So conflating them into one "was it vulnerable?" does not advance discussion.
Or do you mean that a look at the design (before it collapsed) would have immediately suggested its vulnerability?
No. Because we need to define which vulnerability we are discussing. Vulnerable to what?

Let's get the basic stuff a bit clearer:
...show that WTC7 was nonetheless vulnerable, using something other than the collapse itself as evidence.
The fact that WTC7 collapsed proves it was vulnerable to some cause of failure. We need to differentiate at least THREE levels of vulnerability - and in this taxonomic order of importance:
1) The use of steel frames for high rise towers itself introduces a level of vulnerability that does not apply (to the same degree) to other materials e.g. reinforced concrete, concrete-encased steel or hybrid mixes part steel part concrete. THAT fundamental level of "vulnerability" is reflected in the design. Specifically, the "Fire Rating" and the envelope of conditions the fire rating is based on. Provision of fire sprinklers and the expectation of rapid implementation of active fire fighting were conditions that all three WTC Towers were designed for. And for all three WTCTowers, the failure/deliberate non-provision of those two was the primary cause of collapse. And that level of vulnerability comes into play BEFORE we even look at design vulnerabilities;

2) Next consider vulnerability of design - and this has two levels. Level one "Was the design adequate for what it was designed for"? It probably was but we will never know because the 9/11 scenario for all three towers saw trauma well outside - much greater than - the scenario designed for.

3) Was THE DESIGN vulnerable under the far greater imposed trauma. Now, whilst the single column failure - "Blame col 79" - looks attractive there are two key aspects we cannot be sure of. First: Would col 79 have led to a collapse if the actual scenario had been as per the design envelope. i.e. sprinklers had not failed and active fire fighting was undertaken? (And there are two more but let's use those two to support the point) The second is the bigger issue. It is the issue of code provisions for minimising progressive collapse even when the scenario exceeds the design envelope. There is a lot to discuss in that aspect of regulatory philosophy. I won't pursue it now - it doesn't help resolve your issues of c concern.

Back to your questions:
It seems to me that if most designs are not vulnerable then the burden of proof is precisely to show that WTC7 was nonetheless vulnerable, ...
Re-read my comment. I think you are confused by the "double negative" construct. I said, "So the burden of proof is on anyone who claims it was not." << was NOT VULNERABLE. Make sure you are not reversing my meaning - then decide which vulnerability you are referring to because the answers will differ.
Surely, anything else begs the question with a truther who is suggesting that the vulnerability was not in the design but caused by deliberate weakening of the structure?
We cannot answer that question until we are clear as to what we are discussing.
 
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Vulnerable to what?
When you said that the most buildings are not vulnerable, but WTC7 was "prima facie" vulnerable, you were responding to Jeffrey, who had said:
My sense is that designs are not vulnerable (fatal) to a single column failure.
I think that's a good place to start. Truthers don't believe that WTC7 collapsed as a result of the failure of a single column. They believe multiple columns must have been caused to fail simultaneously to bring the building down.

My view is that if we grant that most buildings aren't vulnerable to single column failure, we have the burden of proof to show that WTC7 nonetheless was. And it would beg the question to point to the collapse itself. We have to describe the design in a way that makes the vulnerability clear.

The use of steel frames for high rise towers itself introduces a level of vulnerability that does not apply (to the same degree) to other materials
Does this mean that we are arguing that all steel-framed buildings have this vulnerable? Most buildings aren't steel-framed, so that would explain why most aren't vulnerable. But if we're only saying that some or most steel-framed buildings are vulnerable, we again have the burden of proof to show how WTC7 was different, and, again, without using the collapse itself as the difference.

I think this will always be a sticking point for truthers. I sympathize with them when they find it hard to understand why a building would be designed in a way that would "prima facie" allow it to completely collapse just because a single column fails. The "single column theory" is a bit like the "single bullet theory" that way. To some people, it just seems too implausible. But there are more and less absurd characterizations of the bullet's path, and some people can be convinced that it happened that way. The same may be true of our attempts to show how C79 was a vulnerable point in the design of WTC7.
 
We can probably safely say that catastrophic failures "develop" and progress. A lit match can result in the entire house engulfed in flames. Strategies are used to "isolate" and arrest small failures so they don't progress.
In the case of the WTC all fire prevention and abatement strategies failed and the initial failure... morphed into failures which proved fatal.
In 7wtc the steel framing into cols 79 and probably 80 and 81 suffered from heat... expansion and sagging. This led to local floor collapse over multiple floors and left those columns unbraced and weakened. The local collapse cause the "transfer structures" on floors 5-7 to be displaced and essentially disrupt the performance of much of the steel over the footprint.
One might say 7WTC failed because the horizontal framing into columns failed (first).
Long story short global collapse will almost always be a runaway progression of structural failures.... which destroy the axial structures which "hold up" the building.

Many structures are vulnerable to runaway progressive collapse.

Many systems are vulnerable to runaway progressive failure.
 
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We can probably safely say that catastrophic failures "develop" and progress.
In safe systems, catastrophes are typically the result of several small failures aligning, like the holes in slices of Swiss cheese. Analyses that identify multiple contributary causes are common e.g. in aviation accident investigations.

If an aircraft crashes into a hillside, that's obviously the single event that causes the mayhem that ensues, but there were multiple contributory causes before that without which that single event would not have occurred. Fixating on the impact alone obscures a true understanding of the event.
 
Analyses that identify multiple contributary causes are common e.g. in aviation accident investigations.
The question is whether that's what the WTC7 investigation found. A good comparison might be the de Havilland Comet hull failures, which really did identify some design issues (especially in the design of the windows) and a lack of knowledge about metal fatigue. It's not clear to me that the single-column vulnerability of WTC7 has been identified as a design flaw in the same way. Maybe that's a reasonable way of reading the NIST report's recommendations, but the idea that 9/11 taught important lessons about structural design of skyscrapers isn't, as far as I can tell, part of the public story. In general, the buildings are said to have performed admirably "under the circumstances".
 
The question is whether that's what the WTC7 investigation found. A good comparison might be the de Havilland Comet hull failures, which really did identify some design issues (especially in the design of the windows) and a lack of knowledge about metal fatigue. It's not clear to me that the single-column vulnerability of WTC7 has been identified as a design flaw in the same way. Maybe that's a reasonable way of reading the NIST report's recommendations, but the idea that 9/11 taught important lessons about structural design of skyscrapers isn't, as far as I can tell, part of the public story. In general, the buildings are said to have performed admirably "under the circumstances".
Are you saying that a comprehensive analysis should be able to identify which structural elements failed (and why they failed) to cause complete collapse of these buildings and that the identified failure points should be designed for in any future structure to avoid this happening again?
 
Are you saying that a comprehensive analysis should be able to identify which structural elements failed
I believe NIST has in fact identified which structural elements (probably) failed.
(and why they failed)
This too. The initial failures were caused be expansion due to heat from the fires. Subsequent failures from slender column buckling effects. Etc.
to cause complete collapse of these buildings
As both the models and the reality confirmed.
and that the identified failure points should be designed for in any future structure to avoid this happening again?
This is the tricky part. In the case of the de Havilland Comet a lot of effort (thinking and experimentation) went into figuring out exactly why the hulls failed, and to ensure that "any future" airframe would not fail in the same way. My question is whether the WTC7 collapse has been taken as seriously.
 
The initial failures were caused be expansion due to heat from the fires.
Since this is the initial cause, what more can be done to diminish or eliminate steel expanding due to heat from fires than what is being already done?

The fires were unfought yes? Why was that the case? Also, if the fires were properly fought, do you think WTC7 would have remained standing?
 
what more can be done to diminish or eliminate steel expanding due to heat from fires than what is being already done?
I think the basic intuition is that local failures can be contained structurally. You could have the "initiating event" except it doesn't initiate anything. Column 79 fails as it did, due to fire, but its failure remains a local issue and the bulding remains standing.
if the fires were properly fought, do you think WTC7 would have remained standing?
I think this is obvious. If the fires had been successfully contained WTC7 would not have collapsed. (I think most people assume this true of every remaining skycraper.)

If taken seriously, and no buildings are retrofitted (I don't think any have yet), fires in skyscrapers should henceforth be fought with much greater urgency.
 
I think the basic intuition is that local failures can be contained structurally. You could have the "initiating event" except it doesn't initiate anything. Column 79 fails as it did, due to fire, but its failure remains a local issue and the building remains standing.
So how do you propose that structural engineers test their structures to make sure that no permutation of any local structural failures will cause a collapse?

Let's use column 79 in WTC7 as an example.

Would you start at the first floor and start failing floor beam connections one at a time at each floor? Then move to the second floor? Third floor? Etc.? Then come back and fail floor beams at both floors 1 and 2, going forward and testing all possible failure combinations everywhere?

What about failing floor beams around column 79 and 80 on the first floor to see if that would trigger a collapse?
 
If taken seriously, and no buildings are retrofitted (I don't think any have yet), fires in skyscrapers should henceforth be fought with much greater urgency.
Was this the case with WTC7? That the fires were not fought with enough urgency?
 
I think this is obvious. If the fires had been successfully contained WTC7 would not have collapsed. (I think most people assume this true of every remaining skycraper.)
Ok...

Are we then looking for a structural solution, learned from the WTC7 collapse, that can be applied to all existing and future steel framed skyscrapers to make them 100% impervious to collapse due to UNFOUGHT fires?

We could even take the reason for the failure/s out (fires, bombs, etc.) so the statements reads:

Are we then looking for a structural solution, learned from the WTC7 collapse, that can be applied to all existing and future steel framed skyscrapers to make them 100% impervious to collapse due to ANY combination of structural element and/or connection failures?
 
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Was this the case with WTC7? That the fires were not fought with enough urgency?
My understanding is that fire fighting in WTC7 was completely abandoned at one point. But I'm not sure the expectation (on the part of those who made this decision) was that the building would then totally collapse. (I've heard arguments on both sides of this, and I don't have a clear answer.)
 
So how do you propose that structural engineers test their structures to make sure that no permutation of any local structural failures will cause a collapse?
I think engineers have a lot of well-tested structural theories that allow them to do this. It's the same ones that let them build computer simulations, which, I think, is a major way building designs are "tested" these days.
 
Are we then looking for a structural solution, learned from the WTC7 collapse, that can be applied to all existing and future steel framed skyscrapers to make them 100% impervious to collapse due to ANY combination of structural element and/or connection failures?
I don't understand this question. It sounds like such buildings would also be "impervious" to demolition (which is just a combination of deliberate failures.)
 
I don't understand this question. It sounds like such buildings would also be "impervious" to demolition (which is just a combination of deliberate failures.)
Which is pretty silly correct?

So back to the original:

Are we then looking for a structural solution, learned from the WTC7 collapse, that can be applied to all existing and future steel framed skyscrapers to make them 100% impervious to collapse due to UNFOUGHT fires?
 
Are we then looking for a structural solution, learned from the WTC7 collapse, that can be applied to all existing and future steel framed skyscrapers to make them 100% impervious to collapse due to UNFOUGHT fires?
I think we're looking for designs that don't totally collapse because an unfought fire causes a single column to fail. The solution here is either to make sure than any local part of the structure is redundant, or that there's never enough cumbustible material around any one column to heat it to the point of failure.

In the case of WTC7, we seem to be talking about slightly stronger columns and/or slightly more robust connections that would allow the fires to pass through the area around column 79 without occasioning its failure.
 
I think we're looking for designs that don't totally collapse because an unfought fire causes a single column to fail. The solution here is either to make sure than any local part of the structure is redundant, or that there's never enough cumbustible material around any one column to heat it to the point of failure.

In the case of WTC7, we seem to be talking about slightly stronger columns and/or slightly more robust connections that would allow the fires to pass through the area around column 79 without occasioning its failure.
What about two columns failing? Three? More? Should we be worried about those scenarios also?
 
Was this the case with WTC7? That the fires were not fought with enough urgency?
The water mains failed due to the WTC tower failures, putting the sprinkler system for the lower 20 floors out of commission, and keeping the tanks feeding the upper floor sprinklers from being replenished, as well as making it difficult for fire fighters to access water.

Urgency may not be able to replace a lack of water, especially in the face of other urgent tasks (e.g. searching for WTC tower collapse survivors).
 
What about two columns failing? Three? More? Should we be worried about those scenarios also?
I remember a claim/boast by a Twin Tower engineer that used to circulate among truthers. He had apparently said that all the columns along the base of an entire face (and then some) could be cut and the buildings would still stand in a strong wind. I don't know if it's been debunked, but it does seem reasonable to worry about multiple column failures up to a point.
 
Urgency may not be able to replace a lack of water, especially in the face of other urgent tasks (e.g. searching for WTC tower collapse survivors).
Sure, but there must be a list of buildings that fire departments now must approach as at risk of total collapse if a fire starts in them. It will be important to put those fires out since there's a chance they happen to be near a "critical column". I don't think fire fighters thought they were saving skyscrapers from total collapse before 9/11. That's what I mean by "greater urgency".
 
Sure, but there must be a list of buildings that fire departments now must approach as at risk of total collapse if a fire starts in them (1). It will be important to put those fires out since there's a chance they happen to be near a "critical column" (2) . I don't think fire fighters thought they were saving skyscrapers from total collapse before 9/11 (3) . That's what I mean by "greater urgency" (4) .
I note that you have ignored my explanation of the levels of "vulnerability" involved in the impact of fires on steel-framed buildings. My post #46 refers. So your starting premises for recent posts are either wrong or irrelevant.

FIRST LEVEL - All steel-framed high rises are more vulnerable than those framed with other materials esp concrete. The design of such buildings is premised on that greater vulnerability. the key factor is "fire rating" - a time to allow for (A)occupant escape (which happened in WTC7 and for most below the impact zones for the twin towers and (B) - commencement of active fire fighting. The failure of all three WTC Towers was primarily at this level. All three were subject to fires greater than their design allowed for. All three had a total or partial failure of fire sprinklers. AND there was no effective "active fire fighting" for any of the three. Before you can legitimately start commenting on design features. Before you can get to the WTC7 specific speculation about "critical columns" (2). Get the basic scenario right first.

So discussion of details of the structure is pointless UNTIL properly placed in the context of those three levels of vulnerability which I briefly explained in my earlier post.

So your first comment (1) is a false presumption. ALL fire departments that I know of in AU and I assume the same level of professionalism in US including NYC are well aware of the vulnerabilities inherent in steel-framed high rises. Of course there is a risk of either serious damage or total collapse. It is both building design and event situation specific. Why do you assume that fire departments are incompetent? Based on a - so far in this thread - mostly misdirected "argument"?

Your third comment (3) assumes lack of professionalism in the Fire Dept. They are not ignorant novices.

And (4) is premature until you construct a legitimate supporting argument.
 
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the key factor is "fire rating" - a time to allow for (A) occupant escape ... and (B) - commencement of active fire fighting.
This is an understanding of "fire rating" that I know has been emphasized after 9/11, and which indicates what I'm calling "greater urgency" than what appears to have been the recieved view before 9/11.

As the Society of Fire Protection Engineers puts it:
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

Note the dates of the sources in the footnotes.

That is, the fire ratings of structural elements did not specify the time it should take before the structure collapses, merely allowing for occupants to escape and active firefighting to begin (with some urgency!). The idea was that it would survive the consumption of the available fuel.

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
 
I remember a claim/boast by a Twin Tower engineer that used to circulate among truthers. He had apparently said that all the columns along the base of an entire face (and then some) could be cut and the buildings would still stand in a strong wind.
This sounds like a point on how the WTC design transfers wind loads that was mistakenly generalized to apply to the general stability of the building. Without evidence for this, i.e. what the engineer said and the context he said it in, I'm skeptical that this correctly characterizes what he said.

I believe the hollow tube design of the facade, the load-transferring floors and the central columns do provide enough leverage for the WTC towers to resist wind loads even if one facade was not anchored to the ground, but these columns may still be needed to resist gravitic loads, i.e. carry some of the weight.
 
the central columns do provide enough leverage for the WTC towers to resist wind loads even if one facade was not anchored to the ground, but these columns may still be needed to resist gravitic loads, i.e. carry some of the weight.
The aircraft impacts themselves showed that a significant amount of columns could be removed (through the height of at least one floor) without causing collapse. I'm sure the engineers who built the towers had done the math to figure out how big a hole in the facade could be made (how many perimeter columns could be severed) before the building began to fall down (though not, as we're discussing in this thread, fall over.)
 
The impacts were not "along the base", but around the 80th and 95th floors.
Indeed. It would be interesting to know if the allowable hole gets smaller or bigger or stays the same as we move down the facade of the building. I know the columns get progressively stronger, but I don't know about the moment connections to the spandrel plates.

My point is just that the engineers who designed this structure would be able to answer the question.
 
This is an understanding of "fire rating" that I know has been emphasized after 9/11,
It happens to be correct. Why don't you eitheragre, disagree or ask for more "proof"?
and which indicates what I'm calling "greater urgency" than what appears to have been the recieved view before 9/11.
You did NOTidentify either what youmeant by "greater urgency" or relate it to "fire rating".
As the Society of Fire Protection Engineers puts it:
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
Which is supporting detail and irrelevant to the points I have suggested for discussion. And which you once again ignore. If you do not want to respond to my comments - say so and I will desist from posting.
Note the dates of the sources in the footnotes.
Why? What are you trying to say which is relevant to the points I have explicitly made?
That is, the fire ratings of structural elements did not specify the time it should take before the structure collapses, (1) merely allowing for occupants to escape and active firefighting to begin (2) (with some urgency!)(3).
(1) Again drifting off the point. The relevant point of my comment each time I made it was to identify the primary goals of fire rating. NOT to discuss what fire rating doesn't deal with.
(2) Why the weasel word "merely". Those two are the primary goals of "fire rating". Do you agree or disagree?
(3) I'll count to ten. Can you either stop referring to "some urgency" OR define what you mean and stay with the definition.
The idea was that it would survive the consumption of the available fuel.
Which was the vague, undefined, "wisdom of the day" and wishful thinking even in the designed for scenario. Which did not apply for WTC7 on 9/11 and is irrelevant to the points I have suggested for discussion and you remain reluctant to discuss.
[Repetetive material edited out]
]EX]
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
[/EX]
https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf
Which is precisely the situation I've suggested we discuss BUT related to the three very different levels of "vulnerability" I identified at post #46
 
You did NOTidentify either what youmeant by "greater urgency" or relate it to "fire rating".
I'll try to explain again.

Before 9/11, as I understand it, firefighters believed that they could, if need be, let fires "burn out" without risk of total collapse with all the danger this implies both inside and around the building. There was an "urgency" about saving lives and property within the building that was on fire, but no worry that the whole building might come crashing down if the fires burned beyond the structure's "fire rating". This, as I understand it, is because the fires would move along after exhausting fuel locally, so no part of the structure would be exposed to the relevant heat levels for longer than the ratings allowed.

(I'm getting much of this from the NIST advisory board meeting, by the way.)

After 9/11, given that we now know that some buildings are vulnerable to total fire-induced collapse, I imagine that firefighters approach the task of putting out the fires within the time specified by the structure's fire rating with greater urgency. It's a more immediately pressing matter.

In this thread, we've been discussing whether any part of this urgency comes from the risk that the building might, not just collapse, but fall over into neighbouring buildings. And this does seem to be a risk for at least some of the building types and some portion of the collapses. (The Chinese demolitions and Kostack's simulations have the top ten stories falling well outside the foot print.) This, again, seems to me to increase the urgency of getting fires under control early, and might even justify operations that are somewhat more dangerous to the firefighters than would have been considered reasonable pre-9/11.
 
Before 9/11, as I understand it, firefighters believed that they could, if need be, let fires "burn out" without risk of total collapse with all the danger this implies both inside and around the building.
You have quoted engineers, aka building designers, not fire fighters.

There was an "urgency" about saving lives and property within the building that was on fire, but no worry that the whole building might come crashing down if the fires burned beyond the structure's "fire rating".
Buildings of other types have collapsed from fires; I expect the fire chief did worry about this regarding WTC7, but recognized he could not prevent it without putting his crews in mortal danger.

I imagine that firefighters approach the task of putting out the fires within the time specified by the structure's fire rating with greater urgency.
I resent the assumption that firefighters haven't always striven to control a fire as quickly as possible. What do you suppose are firefighters doing now that they haven't done before? I mean, having crews live at the stations, using sirens to navigate traffic, bringing water to the scene, and constant training reveal a certain sense of urgency in fire fighting already, wouldn't you say?

Was WTC7 not cordoned off? Were neighboring buildings not evacuated?
 
You have quoted engineers, aka building designers, not fire fighters.
I have quoted the Society of Fire Protection Engineers. I assume firefighters are familiar with their work.

I expect the fire chief did worry about this regarding WTC7, but recognized he could not prevent it without putting his crews in mortal danger.
I'd like to see some documentation of these worries. Certainly crews were put in mortal in danger in the towers. And I don't think they went in knowing there was a good chance the buildings would collapse. Their sense of urgency (and their courage) was devoted to getting as many people out alive as a possible before the fires got to them, not before the buildings collapsed, and not in an effort to prevent the collapses by quickly putting out the fires. I don't think total structural collapse was part of the strategy during those first couple of hours.

If you have some reporting to suggest otherwise, I'm all ears.

I'll grant that the thought of collapse might have occurred in the case of WTC7 after both towers failed.

But if the worry really was that the fires couldn't be allowed to burn out without undermining the structure, then I would have expected a lot of attention to be devoted to fighting those fires, preventing the collapse. There was no way to know (I imagine) exactly how much more chaos and destruction a third building collapse would cause. The best strategy would have been to make great efforts (including facing mortal danger) to prevent it.

I resent the assumption that firefighters haven't always striven to control s fire as quickly as possible.
I'm not sure what there is to resent in the idea that firefighting is always done with risk assessements and an evaluation of the likely costs and benefits of particular operations. As quickly "as possible" implies "under reasonable assumptions of risk". It's reasonable to risk your life to save the child in the bedroom, but perhaps not to save the child's favorite doll. Likewise, it's reasonable to risk your life to prevent the catastrophic collapse of a skyscraper in downtown Manhattan. But not to put out a fire that would burn out by itself without causing much more damage than it already had. A total building collapse, after all, is a mortal danger in its own right.

If you're a firefighter and are offended by this, please know that I am full of respect for the work firefighters do, and very aware of the dangers they face. I just assume they have their priorities straight.

And it seems to me that the events of 9/11 taught them something about the possible dangers, and this has reordered some of their priorities. That seems perfectly natural to me.
 
Likewise, it's reasonable to risk your life to prevent the catastrophic collapse of a skyscraper in downtown Manhattan.
No, it's not.
It's reasonable to risk your life to save someone else's, which is why the FDNY heroes went into the WTC towers.
But it's not reasonable to risk your crew's life to save property that can be rebuilt.

I doubt the WTC7 fire was even controllable with the resources at hand; you seem to assume it was. I wouldn't have the evidence and the knowledge to second-guess the fire chief.

You seem to be arguing from the point that the fire chief had the option to defeat the fire, but decided not to. But you have not supported this insulting assumption (which you share with the truthers) with any evidence.

P.S. I've read a fire fighter magazine for over a year, and don't recall any fure protection engineer was ever mentioned. If you want to claim that fire fighters know something, cite fire fighters.
 
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it's not reasonable to risk your crew's life to save property that can be rebuilt.
This can't be right. Surely, firefighters routinely risk their lives putting out fires long after everyone in the building has been evacuated. I don't know the statistics, but there must be some fatalities that prove that even this stage of the work involves mortal danger.

To take one example I happen to be familiar with, in 1949 thirteen members of a crew of smokejumpers died in Mann Gulch after parachuting into a wilderness area where there were no human beings for miles. Wildland firefighting is universally known to be very dangerous, and heroic, work. But the aim is not to save lives.
 
I doubt the WTC7 fire was even controllable with the resources at hand; you seem to assume it was.
I think it's important to keep on topic here. We're discussing whether it would have been reasonable to assume that, if left to burn, WTC7 would, at worst, fall straight down into its own footprint, i.e., not fall over.

You seem to be arguing that a conscious decision was made to let the building collapse, which assumes that it was known that it would collapse. (I'm not sure that's what NIST said. On my reading, there was a mystery to be solved and they found a hitherto unknown kind of progressive collapse in the course of solving it.)

The thing is that if that decision was consciously made then all the risks associated with letting a skyscraper collapse in downtown Manhattan (in the middle of an ongoing search and rescue operation) were also consciously, deliberately accepted. I haven't seen the report in which this decision process is described. If you have, do let me know where I can read about it.
 
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