OOS Collapse Propagation Model

[JSanderO]

But the buildings did not completely collapse because there was a mechanism of "isolation". QED

 

[DGM]

But the buildings did not completely collapse because there was a mechanism of "isolation". QED

Would you consider the fire protections as being a method of isolation?

 

[JSanderO]

Would you consider the fire protections as being a method of isolation?

Not really... I am referring to isolating a mechanical failure...

My opinions mean nothing...I am not the arbiter of fact.

 

[DGM]

Not really... I am referring to isolating a mechanical failure...

My opinions mean nothing...I am not the arbiter of fact.

But they are. They prevent the failure you want to stop once it's started. OOS is not at fault in the collapse, it was the failure to take into consideration circumstances that were well outside the design criteria.

 

[JSanderO]

But they are. They prevent the failure you want to stop once it's started. OOS is not at fault in the collapse, it was the failure to take into consideration circumstances that were well outside the design criteria.

What were the design criteria... 62psf live load?

 

[DGM]

What were the design criteria... 62psf live load?

That the building was not predicted to be hit by a 767 at 500 mph. This disabled the fire protection that initiated the collapse.

 

[JSanderO]

The building survived the plane strike. It didn't survive the fire because of the fire suppression, people could not get out because of the cheesey exit stair design... &WTC came down because they FDNY could not fight the fire and the sprinkler system failed.

FDNY is supposed to fight fires... not sprinkler systems. Yes or no?

 

[DGM]

FDNY is supposed to fight fires... not sprinkler systems. Yes or no?

I don't understand what you're saying. They both fight fires.

 

[Seymour Butz]

No they wouldn't... that's incorrect.

Like the man said, if you only understood BZ.....

 

[JSanderO]

Like the man said, if you only understood BZ.....

You know why this is absurd.

If a floor falls onto the one below and the connections at the seat hold and the slab does not shatter... the column sees the same load only instead of it coming axially from above ( the dropped floor)... it comes from the belt girder beam stub welded and bolted to the web or flange. If you are talking about some sort of dynamic load "increase" from the single floor collapse and the connections hold... this perhaps might exceed the columns capacity...

But this is absurd because if it exceeds the columns capacity it would surely shatter the floor or if that managed to hold probably fail the seat or connection to the column.

This is just nonsense.

 

[Seymour Butz]

If you are talking about some sort of dynamic load "increase" from the single floor collapse and the connections hold... this perhaps might exceed the columns capacity...

"Some sort of....."

Proof that you don't understand BZ.

But this is absurd because if it exceeds the columns capacity it would surely shatter the floor or if that managed to hold probably fail the seat or connection to the column.

This is just nonsense.

What's nonsense is that you're unable to think in the abstract and realize that when a starting assumption says that the floors and connections, etc won't break..... well, then it's part of the argument that they won't break.

Your argument is against a starting assumption. A limiting case.

 

[Major_Tom]

I am not arguing anything other than the column free design is like the long span bridge and a failure will likely take the entire building out. If the building was like the Empire State Building with a grid of columns... it would likely survive and even possibly be repairable.

I would argue that as clever as the engineering was... it also contained vulnerabilities to runaway total collapse.

That is a really good point. In an honest, open investigation you would think that this would have been openly discussed and years later there would have been a written record of such a discussion.


Take the Windsor Tower in Madrid, for example.

There was no sprinkler system and the fire was quite intense and lasted a long time.

This was the result after the fire:

A website linked here examines a few case studies in high-rise fires and in this case it is describing the Windsor Tower. The website also mentions the 'open floor' design of the Windsor Tower.


According to the website there were some local floor failures during this intense and long lasting fire, and also a progressive floor collapse. But the progressive floor collapse was arrested at the level of the mechanical floors.

So there are many possible scenarios which can happen during a floor collapse depending on the specific architecture of a building.

I am almost positive the OOS column free design was driven by cost and the "need" to be innovative and allow those building to be built quickly.

Yes, to cut construction costs and to maximize the space that could be rented out.

DO you think the ESB would have survived such an strike?

In an intelligent investigation within a sane, rational environment, these questions would most probably have been asked and we would have access to some of the conclusions drawn from the resulting discussions. In the case of the WTC towers, there is nothing within the written technical history to suggest this happened.


>>>>>>>>>>>>


Interestingly, the same website which examined the case of the Windsor Tower also examined the WTC collapses. But within the WTC descriptions they simply replicated the popular memes which came from the NIST. This is not surprising since that is pretty much all that exists within the written technical history of the WTC collapses.

 

[JSanderO]

"Some sort of....."

Proof that you don't understand BZ.




What's nonsense is that you're unable to think in the abstract and realize that when a starting assumption says that the floors and connections, etc won't break..... well, then it's part of the argument that they won't break.

Your argument is against a starting assumption. A limiting case.

Mr. Butz... that is a load of crap and has nothing to do with the collapse of the twin towers. My argument is against stupidity... and wasting time with nonsense. That was a load of crap and nothing to do with my failure to accept assumptions or limit cases.

 

[DGM]

Take the Windsor Tower in Madrid, for example.

Perhaps a recommendation for a concrete core and better protection for egress and fire protection could come from a new investigation.

What recommendations are suggested using your model?

 

[ozeco41]

If ROOSD is simply a description of a WTC collapse, then I think the term "WTC collapse" is well worth the few extra keystrokes...

Agreed of course. BUT that didn't happen. Remember the context - 2006-7-8-9 we were dealing with truthers arguing "squibs" and NOBODY put a name on the mechanism which was characteristic of the Twin Towers progression. M_T gave it a "brand name" and the focus went on to - still is on - denigration of M_T.

My opinion simply put:
1) The collapse had distinctive characteristics of mechanism;
2) It needs a label to distinguish it from "progressions" in general and other specific progressions.
3) If someone had suggested "The WTC Twins Progression Mechanism" [WTCTPM] or any other descriptive phrase with optional acronym I would have supported it.

Anyone wanting technical details of the collapse propagation is well advised to at least begin with BZ, which has a brief but quite clear description of "what really happened" before getting into the logic of why it happened.

Mostly agreed.
Disagree "anyone" - "anyone who needs help" is correct - I had explained the outline mechanism in more detail than B&Z before I even heard of Bazant.

Disagree the "technical details" unless you specify what depth of details. Bazant identified a complicated mechanism but did not go very deep in details. Both M_T and I - and probably many others - went a lot further - in my case independent of Bazant.

With that foundation, anyone wanting to augment their understanding and/or mental visualization with details would probably find M_T's "mappings" to be very interesting...

Yes

My question about ROOSD, however, has always been, "So what are you getting at?"

He was descriptively labelling a process which needed a label and did not have one. AND on a forum where many interested persons accepted the need for labels and were happy to use acronyms.

That's for making a succinct point covering the vague feeling I couldn't put words to.

The "contention" is a creature of history Bravin.

A) The process is distinctively different from most observed progression collapses;
B) That distinctive mechanism did not have a label and some of us think it needs one;
C) femr2 coined ROOSD which M_T adopted;
D) If someone with influence had coined another label - even "WTC Twins Progression Collapse" and it had come into common use the arguments over ROOSD would not have risen;

 

[JSanderO]

Fires burned on 4 floors starting on flr 12 in the 62 story tower First Interstate Bank in LA which did not collapse... even sections of it. What was different about that building and the twin towers? Why did FIB survive standing and the twins collapse?

Let's hear it guys... use your imaginations! Think in the abstract!

 

[JSanderO]

Perhaps a recommendation for a concrete core and better protection for egress and fire protection could come from a new investigation.

What recommendations are suggested using your model?

Perhaps a statement that the design played a role in the complete collapse of the twin towers?

Maybe?

 

[ozeco41]

I happen to think that the OOS design is very different from the column grid which I believe has more built in redundancy and ability to isolate locale failures and mitigate them from going "global".

From a conceptual point of view... the designers made the claim that what they did is take the typical grid columns which carry floor loads and move them to a structural skin... which would be part of the wind load strategy by acting as a membrane and offering the stiffness of a 4 sided box. Clever...

But in so doing...not that they removed column cross sectional area.. but the removed all the connections and bracing in a grid... and put all the connections to the axial system probably measurably less reserve capacity and demonstrably less ability to isolate disaster. Think of this analogy:

Say you have a river to cross and you need to build a bridge. You can do one large clear span or have several shorter spans... one after the other. In the first if the span drops the entire bridge is kaput. In the second case if one span fails the rest of the bridge remains and the repair is certainly not as expensive. In both cases the river crossing function has been lost.

I am not arguing anything other than the column free design is like the long span bridge and a failure will likely take the entire building out. If the building was like the Empire State Building with a grid of columns... it would likely survive and even possibly be repairable.

Sander - If you stop at that point you have made a reasonably clear and correct point. Structures with multiple interconnected sub-units tend to have more inbuilt redundancy than structures built with single point failure. And I'll leave that assertion of a base level engineering principle as pedantically generic as I can as a measure of defence against nit-picking. If I write it as "multiple redundancies tend to mean less prone to catastrophic single point failures" it almost goes circular. It should be bleeding obvious - more redundancy - greater separation of sub-entities SHOULD mean less prone to catastrophic global failure.

BUT this next bit is where you start to go into contentious aspects:

I would argue that as clever as the engineering was... it also contained vulnerabilities to runaway total collapse.

True - but watch those innuendoes hanging off your loose definition. Especially the innuendo that there was something wrong with the design.

Simple fact is that any overstressed structure will fail when pushed beyond the limit. AND it will fail at the weakest point.

All WTC Towers were pushed well beyond design parameters on 9/11 and the only legitimate question I can identify is "Should there be mandated regulation to ensue that ultimate failure when pushed beyond the design limits should be by a "soft fail" mechanism.?" I have brought that assertion to your attention several times and - yes - it is a far more sophisticated question than we normally see discussed on forums. So I"ll leave it there.


But now you venture into implied untruths because you do not define your context:

I think the load transfer system in 7wtc contained the same vulnerability to total collapse.

Why is it a vulnerability to fail when pushed way beyond design parameters? Any building pushed that far will fail and the mechanism will seek out the weakest point. Can you eliminate "weakest point" from any design? (<< everyone should think about that one )

Neither design had engineered into them the ability to PREVENT runaway total collapses.

Begging the question of the truth of that assertion - Why should they?

Is this something engineers should consider?

Not just engineers - it is a "Whole of Community" policy matter - engineers are only one link in the chain. Engineers can say "This is how you do it" AND "This is how much it will cost."

Who knows?

Lot's of us can contribute to the debate BUT this one is US specific and it is a matter for policy decisions under "Rule of Law" in a country which has a written constitution as a foundation for "How the US people govern themselves." And it is that fundamental. Building regulations are part of "Rule of Law" and they are achieved by a political balance of many stakeholder inputs.

But it's never a good idea to put all your eggs in one basket.

Near enough a truism. The challenge is to demonstrate it's relevance to this situation.

I am almost positive the OOS column free design was driven by cost and the "need" to be innovative and allow those building to be built quickly.

Of course - those are perfectly valid factors. Can you not stop the innuendo that cost economy and ease of construction are mortal sins? The engineers task is to design something that "does the job" AND can be built efficiently and economically. They are central and legitimate aspects.

 

[DGM]

Perhaps a statement that the design played a role in the complete collapse of the twin towers?

Maybe?

The design had to play a role. It doesn't mean it was a flaw (for WTC7 either). This is obvious and frankly, irrelevant (unless considering design considerations to the extreme).

 

[ozeco41]

The design had to play a role. It doesn't mean it was a flaw (for WTC7 either). This is obvious and frankly, irrelevant (unless considering design considerations to the extreme).

Which are the same three points I have made for Sander on previous occasions.

And "considering design considerations to the extreme" is more a matter of policy than engineering.