AE911 New Collapse Hypothesis

[Thomas B]

If a building's basement sustains water damage, does that mean the entire building's/building's design factor of safety was surpassed? Does that mean the entire building's design failed?

Yes, it is a failure of the design to prevent the damage. Now, it may be that the building was never designed to avoid water damage under those particular conditions. So in that sense it's not a "design failure".

It's not something I know a lot about, but, googling it just now, it does seem like there's a lot of knowledge about how to design buildings to avoid flooding. A good engineer would be able to look at a building (or a plan for one) and say whether it's likely to flood under normal and/or extreme rainfall.

 

[Gamolon]

Yes, it is a failure of the design to prevent the damage.

The "building envelope" subsystem failed then correct?

 

[Gamolon]

Yes, it is a failure of the design to prevent the damage.

Did you see this?

https://www.onsitesafety.com/safety-articles/what-is-the-factor-of-safety/

Keep in mind:

Safety factors do not imply that a system is safe and free from accidents. Parts to a whole may all have the same factory of safety, but that does not give the system as a whole the same FoS. Likewise, stress to one part of whole can easily change the stress distribution to the whole itself. Remember, a factor of safety is a good tool to determine how to properly install and use equipment, but many other factors go into determining safety.

 

[Gamolon]

Yes, it is a failure of the design to prevent the damage.

Do you think that a building has factors of safety for individual structural subsystems (floors, interior walls, etc.)?

 

[Gamolon]

Buildings have a known critical load at which they are expected to fail. But it's usually well above (x 2, 3 ... 5 ... depending on the building) anything they're expected to actually have to face.

Here's what I'm driving at.

You seem to believe that there is one, magical, calculated factor of safety that can cover an entire structure.

Let's say that an engineer designs the exterior façade of a building to handle a wind load factor of safety of 3. Then another engineer designs the interior floors to handle a factor of safety of 2.5.

Based on those two factors of safety, what is the single factor of safety for the entire building?

 

[Jeffrey Orling]

Here's what I'm driving at.

You seem to believe that there is one, magical, calculated factor of safety that can cover an entire structure.

Let's say that an engineer designs the exterior façade of a building to handle a wind load factor of safety of 3. Then another engineer designs the interior floors to handle a factor of safety of 2.5.

Based on those two factors of safety, what is the single factor of safety for the entire building?

This is a pointless discussion. The only loads a completed occupied building is designed for are:

live loads - superimposed on the floors​

rain and snow loads - superimposed on the roof​

wind loads - pressure of winds on the windward face of the building​

seismic loads - agitation from unstable support at the foundations​

​

All loads are "led" to the ground/foundations via the columns/axial members​

Damage to the structure will see the loads of the damaged members re distributed to the non damaged ones. As each member is designed for loads BELOW its ultimate yield strength each member as "reserve capacity"... the so called "factor of safety". If there are damaged / removed non functioning columns... their loads are redistributed to remaining intact columns and THOSE columns them have less reserve capacity... their factor of safety has been reduced.

The steel in the towers at the location of the fires was LOSING capacity as heat reduces the yield strength of steel. Heat was driving down the reserve capacity and the "safety factor". At some point the reserve capacity was "consumed" and the columns were performing at the limit of the ultimate yield strength. With more heat the dropping ultimate yield strength was exceeded by working loads. The columns could no longer support those loads and buckled... the supported material - upper floors collapsed.

The mass/weight of the upper floors immediately over loaded the floor slabs they fell on the process repeated rapidly all the way down until all floor slabs were destroyed. The columns were not destroyed in the floor collapse by were unable to remain standing without the bracing the floor slabs and horizontal steel had provided.

EDIT:
load redistributed was illustrated when the planes hit and destroyed multiple columns in the towers. The loads from those destroyed and damaged columns was redistributed to the intact columns. However... those remaining intact columns were then carrying more load - the loads the destroyed columns had been carrying. So whatever the factor of safety was before the plane strike... it was lowered BY the plane strike.

No new loads were applied to the structure with reduced capacity.

Heat from fires led to further loss of capacity and then collapse of the upper blocks.

 

[Gamolon]

This is a pointless discussion.

And that's your opinion which you are entitled to.

My opinion is that it's NOT pointless especially when someone does not understand the terms they are using in the discussion.

Again, Thomas B seems to think there is a single, magical, factor of safety number an entire building that, that when surpassed, will dictate some degree of damage to some area of a structure.

This is simply wrong and I am trying to get him to understand that.

 

[Jeffrey Orling]

And that's your opinion which you are entitled to.

My opinion is that it's NOT pointless especially when someone does not understand the terms they are using in the discussion.

Again, Thomas B seems to think there is a single, magical, factor of safety number an entire building that, that when surpassed, will dictate some degree of damage to some area of a structure.

This is simply wrong and I am trying to get him to understand that.

My point was trying to get Thomas to understand is pointless. I have witnessed explanations to him over and over again and he simply cannot or will not comprehend.
Good luck...

 

[Thomas B]

Here's what I'm driving at.

You seem to believe that there is one, magical, calculated factor of safety that can cover an entire structure.

I was wondering what your point was.

No, that's not what I believe.

The safety factor, as I understand it, is specific to the kind of load. So there'll be one for the live load on each floor and another for the total load on a column (carrying a share of the load of all floors). And there'll be one for the wind load, which, in the case of the WTC involves the entire structural system.

Let's say that an engineer designs the exterior façade of a building to handle a wind load factor of safety of 3. Then another engineer designs the interior floors to handle a factor of safety of 2.5.

Based on those two factors of safety, what is the single factor of safety for the entire building?

I'm not sure how engineers would describe this. But I imagine the "whole building design" approach that I linked to would require the engineers to design all the elements to the same safefy factor for wind.

Or maybe they go easy on superficial features. Or maybe buildings are even designed so that certain elements will fail before others to relieve pressure on critical things like columns, I don't know.

I don't think this bears on the statement I made originally, which only suggested that critical loads can be calculated, and failure, under certain loads, is expected, i.e., predictable.

 

[Jeffrey Orling]

I was wondering what your point was.

No, that's not what I believe.

The safety factor, as I understand it, is specific to the kind of load. So there'll be one for the live load on each floor and another for the total load on a column (carrying a share of the load of all floors). And there'll be one for the wind load, which, in the case of the WTC involves the entire structural system.


I'm not sure how engineers would describe this. But I imagine the "whole building design" approach that I linked to would require the engineers to design all the elements to the same safefy factor for wind.

Or maybe they go easy on superficial features. Or maybe buildings are even designed so that certain elements will fail before others to relieve pressure on critical things like columns, I don't know.

I don't think this bears on the statement I made originally, which only suggested that critical loads can be calculated, and failure, under certain loads, is expected, i.e., predictable.

Buildings do no have a factor of safety. Facades do no have factors of safety.
The factor of safety concept is for each of the individual elements or members of a structural assembly. A "sensible" design is an "economical" one which uses the least material to do the job. So you end up with each member having a similar factor of safety (for the anticipated loads)

When the term "factor of safety" is used for a building it means the individual elements... not the building itself.... because the building is a composite structural system. The building needs to support itself... and the normal expected loads.

 

[Thomas B]

On this whole "factor of safety" issue, I think it might be helpful to go back the post that introduced it. I think it's pretty clear in this context that I don't think FOS is some kind of feature of a building as a whole. We were talking about the height of buildings specifically.

But the point was only that we have pretty good ideas about strong, say, columns have to be to support buildings of a "certain" height. We don't just hope for the best. We do calculations.

Well, my point is that the "certain length" can always be determined by math in advance. That's why buildings are so safe. We know they will stand at a "certain" height, using "certain" materials in a "certain" design, carrying a "certain" load, under "certain" wind conditions. And we build to that height. We're certain. But we even build in a safety margin to be sure.

We don't just build them and see what happens.

 

[Gamolon]

The safety factor, as I understand it, is specific to the kind of load. So there'll be one for the live load on each floor and another for the total load on a column (carrying a share of the load of all floors). And there'll be one for the wind load, which, in the case of the WTC involves the entire structural system.

Your explanation above is completely different than what you have been saying previously. Above you NOW say that there are many individual safeties of factor based on the subsystems themselves.

In quotes you previously made below, you talk of ONE safety of factor applied to an ENTIRE BUILDING.

We know what will happen at a critical load. It will fail. We're pretty sure the building will never experience that load or will experience it only once in a hundred years.

Buildings have a known critical load at which they are expected to fail. But it's usually well above (x 2, 3 ... 5 ... depending on the building) anything they're expected to actually have to face.

 

[Jeffrey Orling]

On this whole "factor of safety" issue, I think it might be helpful to go back the post that introduced it. I think it's pretty clear in this context that I don't think FOS is some kind of feature of a building as a whole. We were talking about the height of buildings specifically.

But the point was only that we have pretty good ideas about strong, say, columns have to be to support buildings of a "certain" height. We don't just hope for the best. We do calculations.

You don't understand structure.
Each story adds more load to the columns... which as has been explained have to be increasingly strong on the bottom because those columns are supporting everything above.

Building height is limited by code and cost and what makes sense.... getting people to the upper floors economically.. vertical conveyance consumes foot print.

A tall building DOES act like a cantilever beam and wind can exert more bending on the structure as it get increasingly tall. It can't flex to much because it will create other problems.. but not structural.

 

[Thomas B]

Your explanation above is completely different than what you have been saying previously.

I think you just overinterpreted my previous statements, which is understandable since I wasn't trying to be very precise. But now that it's cleared up, what were trying to help me understand?

 

[Keith Beachy]

I've said this before, but my view is that controlled demolition is easy to understand (from the point of view of physics) but impossible to believe. If it is true, the engineering profession is completely corrupt, and so is academia in general. A sociologically improbable conspiracy would be required to carry it out and cover it up. So, no, I have never thought that controlled demolition brought down the WTC.

That said, I don't understand how they actually collapsed. I wish there were a good popular book on the subject.

The Towers collapsed because a floor in the WTC fails when loaded past 29,000,000 pounds - and experts know this is why they collapsed after the upper floors failed. NIST knows this, oops, NIST has experts.

Understand, a floor fails when over loaded, and each floor below is overloaded as each floor fails adding to the mass falling. Overloaded because the mass is not only over 29,000,000 pounds, the mass is in a gravity field on earth. Thus the collapse does not stop till the earth is reached. This can be seen in video. Don't forget floors in the WTC don't hold up other floors, they are hanging on the core and shell.

I suppose it's possible that neither of us understands how those towers collapsed. I think that's going to be my assumption going forward. Thanks for your frankness, anyway.

Why did the WTC towers collapse to the ground? Because a WTC floor fails when loaded past 29,000,000 pounds. The top floors failed and their mass and movement caused the first and each floor below to fail instantly as the mass moved down.

A simple momentum transfer of the collapse mass hitting each floor gives the collapse time seen. The top mass falling hits a lower floor and the velocity at impact would be reduced due to the added mass of each floor. I got 12.081 seconds for the collapse time based on momentum transfer of mass in a gravity field.

Did I mention 29,000,000 pounds. NIST knew this, and thus NIST explains why the WTC collapsed. Simple math explains why the WTC collapse. The math is based on adding up the connections of a WTC floor to the core and shell. Add them up and you find when a floor fails. NIST knew this, thus the collapse is explained. This should be common knowledge, there is no need to model it past what a floor can hold because of the design of the WTC.

NIST figured out the collapse, no one read NIST? https://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-towers-investigation#Resultshttps://www.nist.gov/world-trade-center-investigation/study-faqs/wtc-towers-investigation#:~:text=The individual connection capacities ranged from 94,000 pounds to 395,000 pounds, with a total vertical load capacity for the connections on a typical floor of 29,000,000 pounds

18. Was there enough gravitational energy present in the WTC towers to cause the collapse of the intact floors below the impact floors? Why weren't the collapses of WTC 1 and WTC 2 arrested by the intact structure below the floors where columns first began to buckle?
Yes, there was more than enough gravitational load to cause the collapse of the floors below the level of collapse initiation in both WTC towers. The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case). Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC tower (12 floors in WTC 1 and 29 floors in WTC 2), the floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings.

Consider a typical floor immediately below the level of collapse initiation and conservatively assume that the floor is still supported on all columns (i.e., the columns below the intact floor did not buckle or peel off due to the failure of the columns above). Consider further the truss seat connections between the primary floor trusses and the exterior wall columns or core columns. The individual connection capacities ranged from 94,000 pounds to 395,000 pounds, with a total vertical load capacity for the connections on a typical floor of 29,000,000 pounds (see Section 5.2.4 of NIST NCSTAR 1-6C). The total floor area outside the core was approximately 31,000 square feet, and the average load on a floor under service conditions on Sept. 11, 2001, was 80 pounds per square foot. Thus, the total vertical load on a floor outside the core can be estimated by multiplying the floor area (31,000 square feet) by the gravitational load (80 pounds per square foot), which yields 2,500,000 pounds (this is a conservative load estimate since it ignores the weight contribution of the heavier mechanical floors at the top of each WTC tower). By dividing the total vertical connection capacity (29,000,000 pounds) of a floor by the total vertical load applied to the connections (2,500,000 pounds), the number of floors that can be supported by an intact floor is calculated to be a total of 12 floors or 11 additional floors.

This simplified and conservative analysis indicates that the floor connections could have carried only a maximum of about 11 additional floors if the load from these floors were applied statically. Even this number is (conservatively) high, since the load from above the collapsing floor is being applied suddenly. Since the dynamic amplification factor for a suddenly applied load is 2, an intact floor below the level of collapse initiation could not have supported more than six floors. Since the number of floors above the level where the collapse initiated exceeded six for both towers (12 for WTC 1 and 29 for WTC 2), neither tower could have arrested the progression of collapse once collapse initiated. In reality, the highest intact floor was about three (WTC 2) to six (WTC 1) floors below the level of collapse initiation. Thus, more than the 12 to 29 floors reported above actually loaded the intact floor suddenly.

Simple explanation, now you could understand the collapse, if you want.

 

[Thomas B]

NIST knew this, thus the collapse is explained. This should be common knowledge, there is no need to model it past what a floor can hold because of the design of the WTC.

I am of course aware of this part of the explanation. I think it is fascinating. I agree with you that it should be common knowledge; there should be a lot of popular science writing about it.

It amazes me that such large buildings were vulnerable to this kind of failure, and that it was part of the design of the buildings. Not that they were designed to fail like this, but that understanding their failure follows straightforwardly from understanding their design.

It raises a whole bunch of questions for me. But it doesn't sound like you're proposing to get into a discussion of them. I just wanted to say that, yes, I have heard about the 29,000,000 pounds. Thank you.

 

[Gamolon]

I think you just overinterpreted my previous statements, which is understandable since I wasn't trying to be very precise. But now that it's cleared up, what were trying to help me understand?

I'm not to sure about that Thomas B. Below are other quotes where you state a "building", "twice as much weight as it will be loaded with", "safety factor of the building as a whole", etc.

None of your prior descriptions below mention any other subsystem safety factors. Just one for "the building" in its entirety.

https://www.metabunk.org/threads/cl...hallenge-cant-be-met.11675/page-7#post-247023

3. The building will be strong enough to carry twice as much as weight as it will be loaded with when it is destroyed. (I don't know if that's the right safety factor; I'm not sure it has to be exactly right, just that there has to be a significant one. The building should not be right on the cusp of collapse before the collapse is initiated.)

"The building" will be strong enough to carry twice as much as weight as it will be loaded with when it is destroyed. Then you refer to "enough to carry twice as much weight" as a "safety factor".


https://www.metabunk.org/threads/wh...of-the-wtc-collapses.11323/page-4#post-241785

That is, you should be able to "interlace" the load of the tower floor-by-floor so that it has a safety margin of at least (or around) 2 and it should be easily crushable by its own total mass if placed as a single bulk on the top.

"It", in this case, meaning "the tower", has a safety factor of at least 2.

So no, I am NOT "overinterpreting" your previous statements because that's exactly what you stated. That there is some sort of derived safety factor for the building as a whole.

 

[Gamolon]

On this whole "factor of safety" issue, I think it might be helpful to go back the post that introduced it. I think it's pretty clear in this context that I don't think FOS is some kind of feature of a building as a whole.

Great. As long as you understand that. Based on your previous posts, you did not.

 

[Thomas B]

Great. As long as you understand that. Based on your previous posts, you did not.

I'm happy to proceed from there.

 

[Gamolon]

Well, my point is that the "certain length" can always be determined by math in advance. That's why buildings are so safe. We know they will stand at a "certain" height, using "certain" materials in a "certain" design, carrying a "certain" load, under "certain" wind conditions. And we build to that height. We're certain. But we even build in a safety margin to be sure.

We don't just build them and see what happens.

You did it again here!

When you say "we know a building will stand carrying a certain load", you are implying that the "certain load" is a calculated, single number number that when reached, the building will collapse.

It's right there in black and white (and my red bolding) Thomas B.

Again, I did not "overinterpret" anything. You 100% thought this way until recently. Just pointing that out.

 

[econ41]

On this whole "factor of safety" issue, I think it might be helpful to go back the post that introduced it. I think it's pretty clear in this context that I don't think FOS is some kind of feature of a building as a whole. We were talking about the height of buildings specifically.

A good suggestion. Recall also my advice:

And the concept of FoS is best avoided, not invoked, by persons who do not sufficiently understand it.

Much of the recent discussion could have been avoided.

 

[Gamolon]

I'm happy to proceed from there.

Ok then.

 

[Gamolon]

I'm happy to proceed from there.

The upper block was comprised of floors, core columns, perimeter facade, etc.

The lower block was comprised of floors, core columns, perimeter façade, etc.

When the upper block impacted the lower block what individual subsystems do you envision actually impacted? I see the lowest "floor area" of the upper block (concrete, core columns, perimeter façade, etc.) impacting the upper floor area (concrete, core columns, perimeter façade, etc.) and mutually destroying one another because neither of those floor sections (concrete, core columns, perimeter façade, etc.) was designed to take the stress of that type of impact.

In the beginning you have the mass of the upper block descending. Once the upper block impacted the lower block, you still have the mass of the upper block descending, but have added the mass of the debris from destroyed upper floor of the lower block to that descending upper block mass. That will then impact the next floor of the lower block. The descending upper block mass increases with each floor it destroys in the lower block.

At least that's MY simplified understanding.

 

[Thomas B]

At least that's MY simplified understanding.

It's also more or less how I understand the ROOSD model of collapse. And that's certainly something like how it must have happened.

 

[Gamolon]

It's also more or less how I understand the ROOSD model of collapse. And that's certainly something like how it must have happened.

So what more do you need?

 

[Thomas B]

So what more do you need?

There are a few things, but in this thread I was looking for a way of representing it mathematically so that it can be compared directly with Schneider's model.

That, again, was where this whole "safety factor" discussion arose. It was over the question of whether it is possible to represent the resistance of the lower structure to both the progress of the crushing front and the fall of the roofline as functions and plot them on the same grid that Schneider uses.

I provided a rough sketch here:

https://www.metabunk.org/threads/ae911-new-collapse-hypothesis.12146/post-263245

I just used a rough, empirically derived estimate of the resistance so that both curves track a falling object at about 2/3 g (from 400 m and 340 m, respectively.) I'd very much like a way of deriving that rate of fall from the known properties of the towers.

I don't like the absence of a mathematical formulation of the problem and its solution. I want to know how much stronger the buildings would have had to be in order to survive 9/11. How the design would have had to be different. I want this to be calculable.

It's like if you're arguing with Apollo deniers -- you may not understand all the math, but it would be unsettling if there weren't even a rocket equation to refer to. Bazant (and Schneider) provides a mathematical model. ROOSD (and Schneider) says it's wrong. But ROOSD doesn't give us any alternative numbers. It doesn't predict anything quantifiable.

So that's what I need.

 

[Gamolon]

I want to know how much stronger the buildings would have had to be in order to survive 9/11. How the design would have had to be different. I want this to be calculable.

What constitutes your definition of "the buildings" surviving? Two thirds of a tower staying erect? One third of the tower staying erect? The towers staying completely erect and only taking localized damage from the airplane impacts?

 

[Thomas B]

What constitutes your definition of "the buildings" surviving? Two thirds of a tower staying erect? One third of the tower staying erect? The towers staying completely erect and only taking localized damage from the airplane impacts?

I'd love to quantify all those scenarios, yes.

 

[Gamolon]

That, again, was where this whole "safety factor" discussion arose. It was over the question of whether it is possible to represent the resistance of the lower structure to both the progress of the crushing front and the fall of the roofline as functions and plot them on the same grid that Schneider uses.

And there you go again.

You want to represent a "building's" or "structure's" resistance value with one single number. It can't be done. Why? Because there are multiple structural subsystems within one building, each with their own load calculations handling different types of loads.

The point being is that the impact load of the upper block was over ANY of the individual structural subsystems and ended up tearing them apart.

 

[Gamolon]

I'd love to quantify all those scenarios, yes.

Yet again, you didn't answer the question. What scenario would you need to consider the towers as "surviving"? Two thirds of a tower staying erect? One third of the tower staying erect? The towers staying completely erect and only taking localized damage from the airplane impacts?

 

[econ41]

That, again, was where this whole "safety factor" discussion arose. It was over the question of whether it is possible to represent the resistance of the lower structure to both the progress of the crushing front and the fall of the roofline as functions and plot them on the same grid that Schneider uses.

And there you go again.

Yes. Dragging the debate back onto the false, global interpretation of Factor of Safety.

BUT take care that he doesn't drag you, @Gamolon, down his single tunnel rabbit burrow. There is a bigger, more fundamental issue here. He is trying to "force-fit" observations of what really happened onto the false model proposed by Schneider. (Which BTW is the same B&Z "Limit Case" model that generations of both debunkers and truthers misunderstood.) You CANNOT apply real event measurements or observations to a FALSE model and produce valid affirmative outcomes. And all of those framing issues have been explained several times in this and other @Thomas B threads. Thomas B is pushing a false process of comparison onto a false model. THAT is AFAICS the #1 error. Ignorance of how to apply FoS is only one of the supporting factors.

You want to represent a "building's" or "structure's" resistance value with one single number. It can't be done. Why? Because there are multiple structural subsystems within one building, each with their own load calculations handling different types of loads.

Nice try but.... I doubt that a generalised explanation will succeed with Thomas. Tedious it may be but my approach would be to rebut and correct every specific example as they arise... with specific rebuttals. Yes - it takes a lot of patient writing.

The point being is that the impact load of the upper block was over ANY of the individual structural subsystems and ended up tearing them apart.

A bit of a "nit-pick". It did not overwhelm ALL of the sub-systems. Only the ones that mattered for the actual mechanism of collapse. So the global claim "ANY" is a bit risky. One example - progression stage. The floor to column connections were overwhelmed. (i.e. "ROOSD") the column axial strength was not. Or, reversing the usual truther false claim, the collapse mechanism actually took the path of least resistance. The collapse (any collapse??) will at any stage automatically take the path of least resistance which is available or "accessible" at that stage.

 

[econ41]

Yet again, you didn't answer the question. What scenario would you need to consider the towers as "surviving"? Two thirds of a tower staying erect? One third of the tower staying erect? The towers staying completely erect and only taking localized damage from the airplane impacts?

That would probably have been the outcome if there had been sufficient sprinklers and other fire fighting systems able to control the fires.

The "two thirds/one third staying erect" options were not plausible for the Twin Towers. Once progression started it was unstoppable.

 

[NoParty]

If one tests the premise:
"Occasionally a poster just takes pleasure in wasting other people's time,
and will literally never accept any explanation that isn't what he was trying for"
it will sometimes explain a series of posts magnificently!

 

[Jeffrey Orling]

There are a few things, but in this thread I was looking for a way of representing it mathematically so that it can be compared directly with Schneider's model.

That, again, was where this whole "safety factor" discussion arose. It was over the question of whether it is possible to represent the resistance of the lower structure to both the progress of the crushing front and the fall of the roofline as functions and plot them on the same grid that Schneider uses.

I provided a rough sketch here:

View attachment 48670
https://www.metabunk.org/threads/ae911-new-collapse-hypothesis.12146/post-263245

I just used a rough, empirically derived estimate of the resistance so that both curves track a falling object at about 2/3 g (from 400 m and 340 m, respectively.) I'd very much like a way of deriving that rate of fall from the known properties of the towers.

I don't like the absence of a mathematical formulation of the problem and its solution. I want to know how much stronger the buildings would have had to be in order to survive 9/11. How the design would have had to be different. I want this to be calculable.

It's like if you're arguing with Apollo deniers -- you may not understand all the math, but it would be unsettling if there weren't even a rocket equation to refer to. Bazant (and Schneider) provides a mathematical model. ROOSD (and Schneider) says it's wrong. But ROOSD doesn't give us any alternative numbers. It doesn't predict anything quantifiable.

So that's what I need.

Any high rise building could go "RFC" (runaway floor collapse) if there was a mass released that was 2 or 3 times the capacity of a single floor. The Trade center buildings had column free plans out side the core (tube in tube) so the outside floor collapse could not isolated into a bay. There were no bays.
The collapse speed was measured at 100' / sec which is over 60mph. It did not accelerate once it got moving. (measured from the ejections of material through the facade ahead of the collapse front. Obviously anything that is at rest and reaches a constant speed has a period of acceleration. There is no evidence that the mass accelerated. There is evidence that it was a +/-100' / second.

 

[econ41]

If one tests the premise:
"Occasionally a poster just takes pleasure in wasting other people's time,
and will literally never accept any explanation that isn't what he was trying for"
it will sometimes explain a series of posts magnificently!

Yes. A frustratingly valid observation. It has been made several times over the 4 or 5 @Thomas B dominated threads. The most obvious goal >> ensure debate goes round in circles and does not progress.

It is de-facto trolling - the objective of seeking attention and getting "bites". And the trolling goal is assisted by those persons who persist in patiently explaining each and every rabbit burrow derail as if it is intended as a serious seeking for understanding.

AND - in such a scenario - adopting a meta-process position is rarely successful. Few members comprehend the meta-process. Whether by taking the apparent technical topic debate back to legitimate starting premises and re-presenting a valid argument. OR - even less likely to succeed - by explicitly exposing the meta-process trolling purpose.

And the ironic inevitability. In that scenario the better the debunker response, the more explanatory it is the LESS attention it will be given. Down that negative track - if your response is ignored - attracts no comment - it probably means you are doing too good a job of explaining.

 

[Thomas B]

Yet again, you didn't answer the question. What scenario would you need to consider the towers as "surviving"? Two thirds of a tower staying erect? One third of the tower staying erect? The towers staying completely erect and only taking localized damage from the airplane impacts?

Schneider's model has the collapse stopping (without additional energy) at about 300 meters. I would be interested in seeing a description of a structure that would behave that way (i.e., the structure Schneider wrongly imagines the WTC towers were).

Staying completely erect would go more to the initiatiing mechanism (columns less vulnerable to weakening by heat) but it would still be interesting to hear how thick the columns would have needed to be. If there is a structure that would collapse 2/3 of the way down and then stop (probably because too much mass was getting ejected to keep the momemtum going) then I'd love to see that too.

* * *​

You want to represent a "building's" or "structure's" resistance value with one single number.

Not quite. It just has to be a continuous function. It could involve the values of several "numbers".

there are multiple structural subsystems within one building, each with their own load calculations handling different types of loads.

The complexity of this is like calculating load paths, ignoring some as irrelevant/insignificant. @Keith Beachy, above, for example, ignores the columns vertical strength entirely and proposes a "simple momemtum transfer" function and gets a result much like my graph. That's a good start. But I still don't think vertical column strength can be discounted so completely.

It can't be done.

I think you're wrong about that. But I think I understand your reasons and I don't think I have better ones at this time. I think we can leave it there. Thanks for your time.

 

[Redwood]

I suppose it's possible that neither of us understands how those towers collapsed. I think that's going to be my assumption going forward. Thanks for your frankness, anyway.

Except for Truthers, almost everyone understands how the Towers and WTC 7 collapsed. The only disagreements are in the details.

 

[Jeffrey Orling]

Schneider's model has the collapse stopping (without additional energy) at about 300 meters. I would be interested in seeing a description of a structure that would behave that way (i.e., the structure Schneider wrongly imagines the WTC towers were).

Staying completely erect would go more to the initiatiing mechanism (columns less vulnerable to weakening by heat) but it would still be interesting to hear how thick the columns would have needed to be. If there is a structure that would collapse 2/3 of the way down and then stop (probably because too much mass was getting ejected to keep the momemtum going) then I'd love to see that too.

* * *​

Not quite. It just has to be a continuous function. It could involve the values of several "numbers".

The complexity of this is like calculating load paths, ignoring some as irrelevant/insignificant. @Keith Beachy, above, for example, ignores the columns vertical strength entirely and proposes a "simple momemtum transfer" function and gets a result much like my graph. That's a good start. But I still don't think vertical column strength can be discounted so completely.

I think you're wrong about that. But I think I understand your reasons and I don't think I have better ones at this time. I think we can leave it there. Thanks for your time.

Not top down high rise building could arrest if more than 3 or 4 maybe 5 or 6 stories are involved. It's not the column strength because column loads don't change in a collapse of the floors. A typical floor is designed per use by CODE. No office building floor is designed to support more than 3, 4 or may up to 6 times the design load. If a floor is designed for 100#/SF it likely will fail/fracture including supports when loaded with 300-600#/SF. It's is simply too expensive to build that strong, because strong means more material and that means more cost.
The WTC buildings were notable very light and "efficient" designs... but floors were designed to support 80#/PSF.

 

[Mendel]

Now, it may be that the building was never designed to avoid water damage under those particular conditions.

1) What is the safety factor for a type of damage that wasn't anticipated? Can we use a "building safety factor"? Or do we not have safety at all?

2) How about neighboring construction introducing cracks in an outer wall, leading to water seepage, leading to concrete spalling, leading to an inspection report, that does not lead to the necessary remedies being enacted quickly? How safe would a building be against that, and what would a factor of 2.0 mean in this scenario?

Bonus question: What was the designed safety factor of the WTC against a basement bomb?

It is my understanding that, following 9/11, building codes were changed away from that binary safe/unsafe thinking: before, you'd habe your safety factors, and in a "weakest link" manner, you'd not expect the building to necessarily survive if a subsystem was overloaded. It's obviously desirable for a building to only partially collapse in case of a failure, especially if it is occupied at the time, and engineering practice has changed to reflect that.

Your explanation above is completely different than what you have been saying previously.

Yes. And as long as Thomas doesn't acknowledge that, he can always go back to his old position later.

I provided a rough sketch here:

Get the data for the actual collapse (where was the roof line, where was the crushing front, from videos, down to fractions of a second) and graph it, then you'll be talking about the WTC in a meaningful way. It'll cost you less time and effort than you've spent on this thread since you posted the sketch, and is likely to lead to new knowledge.

. I would be interested in seeing a description of a structure that would behave that way (i.e., the structure Schneider wrongly imagines the WTC towers were).

Since you abandoned the cardboard box stack experiment, I no longer believe that's a genuine interest. It'd be easy to model this with cardboard.

 

[Gamolon]

I want to know how much stronger the buildings would have had to be in order to survive 9/11.

I would still like to know what your definition of the towers surviving 9/11 is. What state would the towers have to have been in for you to say they survived?