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OOS Collapse Propagation Model

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JSanderO said:
Your sarcasm aside... it is my hunch that ROOSD vulnerable designs share a number of structural design features/attributes. Among them are:

1. Hull and core designs which means open long span floor systems
2. wind shear designs which do not include some manner of multi floor bracing which extends from the exterior to and into the core.
3. designs which use the floor plates to transmit wind shear loads to the core
4. cores which are not diagonally braced
5. very light weight floor systems

etc. etc. and so forth
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I would think you would be more interested in the Bazant models then..........They're more useful in helping understand these issues. :D
 
As a structural engineer I have to say that ROOSD is a stupid acronym and will never catch on. The floor collapse did not run very far from the external wall collapse. The wall supported the floor and the floor supports the wall. And sure the trusses must have failed first because you need more than one truss level to fail before the wall starts to go.

Yes engineers have learnt from the collapse and I am sure we will never see bar-joist trusses in a supertall tower. They have some very obvious vulnerabilities.

I think the big omissions by NIST and our Uncle Tom is the lack of attention paid to wind. In 15 seconds or so the area of wind within the tower was pushed out the tower and then came back in to replace the void.
 
Richard the G said:
I think the big omissions by NIST and our Uncle Tom is the lack of attention paid to wind. In 15 seconds or so the area of wind within the tower was pushed out the tower and then came back in to replace the void.
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rubbish... the falling mass inside the facade caused a high pressure region below it and it blasted the floor contents out the glazed areas of the facade... This falling mass *pulled* a negative pressure behind/above it and this caused aire to rush inward on top of it like water pulled down a drain.

The process was like a chaotic gathering mass like a *piston* driving through a square cylinder which was losing its lateral support in the process and toppled over.

The down draft at the end picked up the heat from the debris and spread it and dust laterally in all directions with great force.
 
JSanderO said:
rubbish...
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You both said exactly the same thing. The collapse formed a descending toroidal vortex. That combined with the fire proofing dust gave the appearance of an explosion. This has never been explained to the general public (why it looks like an explosion).
 
JSanderO said:
No evidence of this.
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Not just blacksmiths but also my own experience with making assorted brackets in the workshop disagree with you.

(Or do you mean stuck as in ("look no further" )
 
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JSanderO said:
Core columns not the facade... the braces in the core were heated by fires and expanded... pushing against the columns. Those columns which had lost a brace or two could be pushed. Rinse and repeat.
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Excluding the bracing used for the crane towers, which may have been removed as the towers went up, there was no bracing in the cores on the plane impact levels.

Maybe you should read the NIST report...
 
Are there lessons to be learned from ROOSD? Is any tall building subject to a ROOSD? If not which ones aren't and why aren't they? THAT is the interesting discussion. That is... was there something about the design of the twin towers that made them a good candidate for a ROOSD. Sure they stood for decades... what's up?
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I'm sure there are, many of them. For one thing, with the gift of hindsight terrorists don't need airplanes to create the same drama in the middle of New York City. They could simply initiate localized ROOSD processes by other means in any iconic building susceptible to ROOSD progression to create the same level of horror and shock.

How? By renting out only one portion of a single floor in such a building, the higher the better, and initiating a ROOSD avalanche by using as little as two partial floor slabs.
 
Myriad said:
If you know of a way to address such questions and yield reliable answers without mathematical models and equations, please enlighten the world. Interpretive dance, maybe?
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BV eq 12:

bv_eq12.png



You have been openly misrepresenting this equation for years. This is a 2nd order differential equation with only one variable.

Do you know what the variable z(t) represents or tracks?


Bazant states in BV:

"Eqs. (12) and (17) show that Fc(z) can be evaluated from
precise monitoring of motion history z(t) and y(t), provided
that m(z) and lamda(z) are known. A millisecond accuracy for
z(t) or y(t) would be required. Such information can, in theory,
be extracted from a high-speed camera record of the collapse.
Approximate information could be extracted from a
regular video of collapse, but only for the first few seconds
of collapse because later all of the moving part of the WTC
towers became shrouded in a cloud of dust and smoke (the visible
lower edge of the cloud of dust and debris expelled from
the tower was surely not the collapse front but was moving
ahead of it, by some unknown distance)."


In the first sentence he tells you how to obtain z(t) and find Fc(z). In the last sentence he is telling us he does not know how to identify the collapse fronts in the visual record.



This is what you wrote about the application of this equation and apparently still believe: Dave Rogers and Myriad


There is little in your comments that is the product of critical thought. These comments have much more the quality of a meme than of critical thought.

.
 
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Newtons Bit said:
Excluding the bracing used for the crane towers, which may have been removed as the towers went up, there was no bracing in the cores on the plane impact levels.

Maybe you should read the NIST report...
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not diagonal bracing... lateral bracing... Maybe you should read what I wrote... where is the word *diagonal*?
 
GlennB said:
In this context 'bracing' is taken to mean including diagonal support. Google images of braced frame
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Glenn... I am fully aware of the structure of the twin towers... and my reference was to the lateral bracing which reduces the *un braced* length of a column... The core had bracing... which also supported the floors of course... This is the bracing I was referring to... not braced frames...

thank you!
 
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