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OOS Collapse Propagation Model

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Crazy Chainsaw said:
Exactly why the energetics matter, the few certainties are which ever, mechanism, it has to match the energetics, and collapse times.
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What do you mean by "the energetics"? Clearly, as we learned in statics class if you exceed the capacity (ultimate yield stength) the material experiences "mechanical failure". In the case of a composite floor system or a beam the yield strengths are known. A floor slab designed to support 100psf will fail with 1000 psf superimposed on it. And this is basically what befell the slabs.

The forces to fail connections and slabs was freed from the structural matrix and destroyed the building. Too slender columns cannot stand on their own.

So what else is new?
 
JSanderO said:
What do you mean by "the energetics"
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I think what he means is that, since the aggregate energetics are easy to compute, the law of conservation of energy guarantees if some other (perhaps more detailed) collapse model does not predict the same energy and time values, it must be wrong.
 
JSanderO said:
What do you mean by "the energetics"? Clearly, as we learned in statics class...
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We are beyond "statics" when talking about progressive collapse

JSanderO said:
if you exceed the capacity (ultimate yield stength) the material experiences "mechanical failure". In the case of a composite floor system or a beam the yield strengths are known. A floor slab designed to support 100psf will fail with 1000 psf superimposed on it. And this is basically what befell the slabs.
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True, but as, in the dynamic case, forces and capacities must be treated as a function of time and/or spatial dimensions, requiring you to do integrals at some point, computing energies instead can be the smarter, easier way to go.

JSanderO said:
The forces to fail connections and slabs was freed from the structural matrix and destroyed the building. ...
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These forces were previously locked inside or by the structure?
This is comic book physics.
 
Bravin Neff said:
I think what he means is that, since the aggregate energetics are easy to compute, the law of conservation of energy guarantees if some other (perhaps more detailed) collapse model does not predict the same energy and time values, it must be wrong.
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Correct, the energy values must match, or other dynamics energy sources must be included.

Banzant matches the energy values and collapse times, ROOSD does not.
 
Oystein;10908625 These forces were previously locked inside or by the structure? This is comic book physics.[/QUOTE said:
Absolutely... it's called gravitational potential energy. When it's removed from the structural "matrix" it's potential energy becomes kinetic energy.
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JSanderO said:
Absolutely... it's called gravitational potential energy. When it's removed from the structural "matrix" it's potential energy becomes kinetic energy.
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? What's your proof that the hat truss connections can support the weight of the falling core section? The connections appear to be too weak.
 
Crazy Chainsaw said:
? What's your proof that the hat truss connections can support the weight of the falling core section? The connections appear to be too weak.
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I have no proofs of anything...

In fact I have written many times that if a column or columns are severed at around the 9x floor level (1WTC) the columns above the severed column HANG from the hat truss and the column to column connections probably will give way and those columns will drop dragging sections of floor connected to them down.

Instead of those columns supporting the hat truss they pull DOWN on it or break free of it or a both!
 
JSanderO said:
I have no proofs of anything...

In fact I have written many times that if a column or columns are severed at around the 9x floor level (1WTC) the columns above the severed column HANG from the hat truss and the column to column connections probably will give way and those columns will drop dragging sections of floor connected to them down.

Instead of those columns supporting the hat truss they pull DOWN on it or break free of it or a both!
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I have looked at that, and that may or may not be correct it depends on if the core columns alone can provide enough resistance to hold the hat truss while the core breaks free.
The inward bowing might actually be the moment before the Core breaks from the hat Truss.
Ironicly this would slow the collapse, not speed the collapses, so it might have preempted floor failure.
 
Crazy Chainsaw said:
I have looked at that, and that may or may not be correct it depends on if the core columns alone can provide enough resistance to hold the hat truss while the core breaks free.
The inward bowing might actually be the moment before the Core breaks from the hat Truss.
Ironicly this would slow the collapse, not speed the collapses, so it might have preempted floor failure.
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Your comment is a bit confusing.

The plane severed several core columns... let's say at floor 95. the column above lost it's bearing and cannot "convey" the loads down through a missing column to the foundation. But the loads on those 15 columns is still there and they can either drop or hang from the hat truss structure. Each column to column connection/splice... 4 of them (in this example) will turn to hangers... the full load from above each connection will be seen by the splace plates in tension and bolts will see shear forces. I suspect that those connections will fail... at least the top one which sees the most load... so the 4 columns (12 stories) will likely break free of the hat truss and drop/sag and maybe the floors attached break away and drop?????

The hat truss has lost one location of bearing.

I suspect that what was happening is that there was a process whereby the core columns with the collapse zone were pushed toward the original location of the plane severed column... and in so doing became mis aligned with the columns above... and THOSE columns then became hangers and so on and so on... This was a sort of slow "hollowing out of the core above the strike zone... as columns became misaligned (due to being pushed by expanding beams from heat)...became hangers, broke free and essentially turning the support for the hat truss from one where the core supported it to the facade columns supporting it. There were probably several locations where the loads increased on the facade depending on where the core columns were "lost". At some point the loads exceeded the capacity of the remaining columns which buckled and caused the top section to move laterally and drop almost like a rigid 5 sided box held "square" by the hat truss "end plate"....

Just a guess.
 
JSanderO said:
Bazant probably didn't know the "collapse time"... It's hardly a precisely known value... is it?
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It has to correspond with the energy in the seismic data, of sound transmitted in the collapses for each building and with observations.
 
Major_Tom said:
Myriad said:
There's also some confusion about the import of the descriptor "rigid." There's "Superman could pick it up by one corner and fly away with it" rigid (which real buildings or large portions thereof never are), and there's "able to redirect loads to the remaining available load paths without major deformation" rigid (which the upper blocks were, until they weren't).

Once collapse began, the import of the "rigidity" of the remaining "upper block" was that all of the momentum of the upper block was potentially available to bear (even if only momentarily) upon whatever obstacles below offered resistance.
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All you would have to do is refer to the papers you have been defending to read, or even quote, what Bazant writes on this a to find out what he meant.
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By what stretch of unreason do you conclude that my post about the practical meaning of "rigid," responding to posts by Oystein and Dave Rogers, has anything to do with (let along being a "defense" of) Bazant? Did Bazant register the word "block" as his personal trademark or something?

Careful! You've had some success with your "debunkers unjustifiably defending Bazant" narrative. Showing people that this is the kind of nonsense it's based on could give away the game.
 
Crazy Chainsaw said:
It has to correspond with the energy in the seismic data, of sound transmitted in the collapses for each building and with observations.
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The seismic "data" is fuzzy..... the first possible "seismic" sign would be when the first HEAVY steel from the "upper section" hit the ground. This was at least... assuming that there heavy steel immediately tossed over... about 9 seconds AFTER the top was visibly moving downward.

When was the "last" seismic signature?
 
JSanderO said:
Absolutely... it's called gravitational potential energy. When it's removed from the structural "matrix" it's potential energy becomes kinetic energy.
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Now you are talking. Energy. Yep. Don't mistake energy for forces :)
 
JSanderO said:
Could you explain this statement...
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ROOSD is a narrative, it has no physical-mathematical version where energy is mentioned or accounted for. Correct? So that's the trivial explanation for the "ROOSD does not (matches energy values)" part.

I think Bazant does match energy values. But I could be mistaken.
 
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