Total Building Collapse from a Single Column Failure

[Robrob]

Oh, so there is more data about what happened inside WTC7?

Ohhh....dooo tell!

LOL!

Your point?

 

[Grizzly Bear]

Sure once column 79 buckled (not explained) 40 stories drop like a lead sinker... and then the TTF scenario kicks in. Check Got it.

Thanks for the ref. I see it all clear as day!

I find that you're asking for a level of detail that's simply not feasible. The progression beyond the "single column failure" deals more with the long spans and load redistribution that have to follow when the structure gave out and the design vulnerabilities that were part of the building.

"Column 79" failed and it initiated a progressive collapse. We know based on analyzing the modeling that's where it started. A "best estimate" of the mechanisms that caused that particular column at that particular area was narrowed down based on the visual and model documentation, so beyond what started the collapse initiation we already have a good view on how the rest of the building came down.

But it's near impossible to nitpick the level of detail you're demanding to know precisely with 100% certainty for reasons that OZ already covered earlier.

You have your skepticism, it doesn't bother me, but I'm rather skeptical that the question you're trying to raise is answerable. You're literally asking to have answered a level of detail that requires full, first hand visuals of the initiating failure to even begin dealing with as far as I can tell.

 

[ozeco41]

Oh, so there is more data about what happened inside WTC7?

Ohhh....dooo tell!

LOL!

Less for WTC7 than for the "Twins". Direct evidence of internal collapse - two penthouses fell bodily into the core area.

Plus some monitoring of façade flexures.

But the details less than for the twins where, for example:
a) Visual evidence of at least three contributory mechanisms to the "cascade failure" of the initiation stage;
b) Global visual evidence of the success of the cascade;
c) For the "progression stage" there is:
(i) Visual evidence for "ROOSD"
(ii) Extensive visual evidence and research into both PCPO and where the "sheets" went;
(iii) Enough evidence to confirm "Core strip down" as the principal mechanism for core collapse.

Plus all the pre-existing evidence such as known structural details.

 

[JSanderO]

I find that you're asking for a level of detail that's simply not feasible. The progression beyond the "single column failure" deals more with the long spans and load redistribution that have to follow when the structure gave out and the design vulnerabilities that were part of the building.

"Column 79" failed and it initiated a progressive collapse. We know based on analyzing the modeling that's where it started. A "best estimate" of the mechanisms that caused that particular column at that particular area was narrowed down based on the visual and model documentation, so beyond what started the collapse initiation we already have a good view on how the rest of the building came down.

But it's near impossible to nitpick the level of detail you're demanding to know precisely with 100% certainty for reasons that OZ already covered earlier.

You have your skepticism, it doesn't bother me, but I'm rather skeptical that the question you're trying to raise is answerable. You're literally asking to have answered a level of detail that requires full, first hand visuals of the initiating failure to even begin dealing with as far as I can tell.

Never asked for precise details... just a reasonable, understandable sequence. Not how detailed NIST was about the girder walk off. Then they stopped.

My beef is that it's a leap with way too many huge assumptions to get from girders walking and elongated steed to total collapse or even failure of 8 story heights of column 79. It may well be possible but it has been articulated. Of course it will be a "model" because there is no data... but let's see more specificity... no?

 

[Grizzly Bear]

My beef is that it's a leap with way too many huge assumptions to get from girders walking and elongated steed to total collapse or even failure of 8 story heights of column 79. It may well be possible but it has been articulated. Of course it will be a "model" because there is no data... but let's see more specificity... no?

I think modelling it is an exercise of diminishing returns. This was apparent in their model animations of the collapse since the failure paths constantly increase as you proceed beyond the initial failure. So personally... no...

The leap from "thermal expansion/contraction" --> "girder walk off" --> unbraced column length --> collapse --> is understandable to me anyway. But I already think of the model as a limited-application exercise from the get go. I gotta get to work this morning so this is all I have time to try and clarify... I'll add to this later.

 

[beachnut]

...
My beef is that it's a leap with way too many huge assumptions to get from girders walking and elongated steed to total collapse or even failure of 8 story heights of column 79. It may well be possible but it has been articulated. Of course it will be a "model" because there is no data... but let's see more specificity... no?

It your opinion.

What is the "no data"? People model stuff all the time, and there is data. A silly statement, made up statement. "no data"

What data?

 

[Gamolon]

I wonder... how universal this actually is?

Would column 79 failing at floor 29 have caused the global collapse?

Would any other single column failing on any floor lead to global collapse?

Could any single column failing on any other floor NOT lead to global collapse? (I don't suspect the failure of a column at the roof level would.) If so why or why not?

Is this single column failure applicable to any multi story high rise? Would it have to be steel framed? Would it have to be a minimum building height? Would there have to be a minimum number of floors above the failed column?

If the single column failure global collapse outcome is not more or less universally applicable what was it about 7 WTC's design and column failure at floor 13 that allowed for a single column failure to lead to global collapse?

Aren't these questions an exercise in futility? During the design/analysis phases of building project, how can an engineer be expected to figure out all permutations of possible failure scenarios in order to see if said structure will completely (or partially collapse) collapse?

So the engineer is supposed to run analysis on the following during the design/calculation phases:

1st floor, column 1, complete failure... Does structure remain standing?
1st floor, column 2, complete failure... Does structure remain standing?

...etc. for all columns, all floors...

1st floor, columns 1 and 2 failure... Does structure remain standing?

...etc.

1st floor, column 1 (80% weakening), column 4 (total failure)... Does structure remain standing?

Again, how many permutations of combined component weakening and failure are possible in a structure? This would take forever.

Now in the case of WTC7, we have SOME visual evidence of what happened, but can never know exactly what happened because you would need to run through every single permutation and find one that matches the exact collapse seen in the videos. You'd also need to make sure the resultant debris pile ended up with components landing in the same positions/locations.

 

[Gamolon]

Never asked for precise details... just a reasonable, understandable sequence. Not how detailed NIST was about the girder walk off. Then they stopped.

My beef is that it's a leap with way too many huge assumptions to get from girders walking and elongated steed to total collapse or even failure of 8 story heights of column 79. It may well be possible but it has been articulated. Of course it will be a "model" because there is no data... but let's see more specificity... no?

Didn't NIST produce model collapse videos?

http://www.youtube.com/watch?v=TNEKtvB80us

 

[LSSBB]

Aren't these questions an exercise in futility? During the design/analysis phases of building project, how can an engineer be expected to figure out all permutations of possible failure scenarios in order to see if said structure will completely (or partially collapse) collapse?

So the engineer is supposed to run analysis on the following during the design/calculation phases:

1st floor, column 1, complete failure... Does structure remain standing?
1st floor, column 2, complete failure... Does structure remain standing?

...etc. for all columns, all floors...

1st floor, columns 1 and 2 failure... Does structure remain standing?

...etc.

1st floor, column 1 (80% weakening), column 4 (total failure)... Does structure remain standing?

Again, how many permutations of combined component weakening and failure are possible in a structure? This would take forever.

Now in the case of WTC7, we have SOME visual evidence of what happened, but can never know exactly what happened because you would need to run through every single permutation and find one that matches the exact collapse seen in the videos. You'd also need to make sure the resultant debris pile ended up with components landing in the same positions/locations.

Thanks, Gamalon. The sentence I highlighted is one of the key points NIST critics fail to understand.

 

[JSanderO]

Thanks, Gamalon. The sentence I highlighted is one of the key points NIST critics fail to understand.

Some critics aren't interested in knowing EXACTLY what happened but understanding the sequence which began with fire and ended with total building collapse with a girder walk off along the way. I am one of them.

 

[ozeco41]

Aren't these questions an exercise in futility?...

Not entirely. Whilst Sander's OP questions were poorly structured I have answered them several times through this thread. I have answered those that can be answered and showed what is wrong with those which cannot be answered in their present form.

One issue which is problematic for Sanders questions is that he presumes that failure of a single structural element can lead to global collapse. You assume the same scenario in your post.

So get your thinking around one issue. It is this:

How can a single structural element fail in a real situation WITHOUT it being part of a more extensive failure scenario involving many members?

Human intervention or Motor Vehicle Accident causing impact the only two likely ones IMO and neither of them is relevant for WTC 7 on 9/11. Single columns simply do not fail in isolation within a fire setting.

It is well nigh impossible for a single element to fail without a surrounding context of trauma to other members - all contributing to collapse. Set aside for now all the "yes buts" please - we can deal with them later if we need to.

Now Sanders OP questions are nearly all based on the presumption that a single element can fail without surrounding context of trauma. Gamolon's range of scenarios facing a design engineer depends on the same problematic assumption. Broadly speaking the design engineer does not need to deal with the hundreds of "single element failures" Gamolon postulates for the simple reason that they won't happen. (Allow me the "broadly speaking" for now please. I can deal with "yes buts" once the main point is clear and agreed.)

In the real situation of WTC7 Col 79 did not fail on its lonesome THEN cause other bits to progress to global collapse. Col 79 was one major component which must have failed.....because it was under EPH and EPH fell.

However Col 79 could not have failed unless many/most of its supports and braces had failed BEFORE Col 79. (The only other option I have referred to jokingly in several previous posts is not possible - EPH tripled its weight by magic)

So, if we dig though the fog of this discussion, the only legitimate item of contention in this thread is that Sander does not know which of the members which supported or braced Col79 failed and in what sequence.

Several of us have suggested he never will but lets not go there at this time.



Now let me introduce a "red herring" for those who have done the homework and read what NIST actually said:

The fourth simulation that NIST did using LS-DYNA was precisely the one central to Sanders questions. Viz - "Would WTC7 collapse if Col 79 failed?"

Yes - remove Col 79 and, according to NIST, WTC7 would collapse.

So it's interesting that no-one has commented on that bit of NIST...
...but NIST don't attempt to explain how Col79 could fail without the surrounding context of fires and other failures.

So I'll leave that little bit of a red herring there.

 

[jaydeehess]

Now let me introduce a "red herring" for those who have done the homework and read what NIST actually said:

The fourth simulation that NIST did using LS-DYNA was precisely the one central to Sanders questions. Viz - "Would WTC7 collapse if Col 79 failed?"

Yes - remove Col 79 and, according to NIST, WTC7 would collapse.

So it's interesting that no-one has commented on that bit of NIST...
...but NIST don't attempt to explain how Col79 could fail without the surrounding context of fires and other failures.

So I'll leave that little bit of a red herring there.

Red herring indeed.
NIST wanted to understand the importance of a single point of failure and ran the sim with a pristine WTC 7 and col 79 failed. This indicates that it was quite possible that in a previously damaged WTC 7 that failure of this column would lead to global collapse.

The simple removal of col 79 sim in an otherwise undamaged building needed no context or proximate cause as it was not a forensic investigation of such a condition. It was a best case (for the building's condition), a limiting case.

As an aside it demonstrates one value of computer modeling versus physical modelling. Try running multiple tests like this in a physical model,,,, got a budget?

 

[JSanderO]

What the NIST does say is that the TOTAL failure of the building was ALSO related to the column lines of 79, 80 and 81 and the floors framed into them all dropping (40 stories) and destroying the transfer trusses... and the E-W girder running north of the core and the trusses INSIDE the core and TT3 and on.

So in 7wtc the total collapse was apparently ONLY possible because the collapse of several columns (according the the NIST sequence) destroyed the transfer structures.

This is key and what makes 7wtc unique and probably why... I would guess, a single column failure or two would not take down an entire building.

Of course... as I have suggested it makes perfect sense if the transfer structures failed BEFORE the columns above... but I don't have any data to support this... much the way NIST had no real data to support their scenario... It appears to me that they made up the heat inputs to drive the bracing destruction, perhaps additional floor collapses leaving the column unbraced and it buckled. I can stipulate to that scenario, but there's been little to no meat on the bones so to speak.

 

[ozeco41]

Red herring indeed.
NIST wanted to understand the importance of a single point of failure and ran the sim with a pristine WTC 7 and col 79 failed. This indicates that it was quite possible that in a previously damaged WTC 7 that failure of this column would lead to global collapse.

Ok - would you accept "pink sardine"?

Otherwise spot on.

(I should know better than try to derail you. )

The simple removal of col 79 sim in an otherwise undamaged building needed no context or proximate cause as it was not a forensic investigation of such a condition. It was a best case (for the building's condition), a limiting case.

...I hope you are not suggesting that no-one around here would have problems processing limit cases?

As an aside it demonstrates one value of computer modeling versus physical modelling. Try running multiple tests like this in a physical model,,,, got a budget?

True. And in the case of Twin Towers we already have two far better examples than any physical model - unless you have psikological barriers to accepting reality.

 

[ozeco41]

What the NIST does say is that the TOTAL failure of the building was ALSO related to the column lines of 79, 80 and 81 and the floors framed into them all dropping (40 stories)...

Yes - that much has never been in doubt AFAICS

... and destroying the transfer trusses... and the E-W girder running north of the core and the trusses INSIDE the core and TT3 and on.

Which in the NIST scenario is consequential to Col 79 and in your scenario AFAICS it is causal. And neither - whether causal or consequential - changes the fact that EPH fell. Both are plausible and both complement the known facts of (EPH fell THEREFORE Coll 79 and related structures supporting EPH must have failed). (Forgive the algebraic notation.)

So in 7wtc the total collapse was apparently ONLY possible because the collapse of several columns (according the the NIST sequence) destroyed the transfer structures.

you are reading more into that than NIST claims. The supportable part of the explanation is that "total collapse destroyed the transfer structures" The "ONLY possible" causal relationship is not provable on the available evidence nor IMO implied by NIST.

This is key and what makes 7wtc unique and probably why... I would guess, a single column failure or two would not take down an entire building.

Can't say - the switch from "WTC7" to "an entire building" not sufficiently defined.

Of course... as I have suggested it makes perfect sense if the transfer structures failed BEFORE the columns above... but I don't have any data to support this...

...which I have agreed from the first time you said it is a plausible explanation as a contributory factor.

much the way NIST had no real data to support their scenario...

...my position unchanged - both yours and NIST's explanations are plausible with TT failure and/or Girder walkoff as part of the mechanism. And neither "provable" IMO. The aspect which is "provable" is that sufficient of the bracing and/or supports for Col79 MUST have failed. That much proven by my claims in this and several previous posts. But we don't know which ones failed or what sequence other than MUST have been "before Col 79 failure".

It appears to me that they made up the heat inputs to drive the bracing destruction, perhaps additional floor collapses leaving the column unbraced and it buckled. I can stipulate to that scenario, but there's been little to no meat on the bones so to speak.

Whether NIST "cheated" or not is irrelevant - the braces and/or supports MUST have failed. If NIST said that braces/supports did not fail NIST would obviously be wrong - unless the weight of EPH tripled/quadrupled by magic to grossly overload 79. AFAIK no one is claiming magic increase in EPH weight so it must have failed from some form of buckling/bending/misalignment/corkscrewing. (I am disregarding termite gobbling, WoodsDustification and Mini-Nukes). (and CD )

So don't go chasing what is not and cannot be known - work with the facts that are known or can be determined.

Those facts tell us why it collapsed.

The only missing bit is the exact sequence of brace/support component failures.

 

[DGM]

It appears to me that they made up the heat inputs to drive the bracing destruction, perhaps additional floor collapses leaving the column unbraced and it buckled. I can stipulate to that scenario, but there's been little to no meat on the bones so to speak.

Why would they do this? Why would they need to sway their conclusions to this particular scenario?

 

[Mark F]

- unless you have psikological barriers to accepting reality.

Oh snap!

 

[ozeco41]

Oh snap!

I don't suppose you would believe "spelling error"


...or "unintended"...

 

[tsig]

I don't suppose you would believe "spelling error"


...or "unintended"...

A Freudian slap?

 

[Gamolon]

Not entirely. Whilst Sander's OP questions were poorly structured I have answered them several times through this thread. I have answered those that can be answered and showed what is wrong with those which cannot be answered in their present form.

One issue which is problematic for Sanders questions is that he presumes that failure of a single structural element can lead to global collapse. You assume the same scenario in your post.

How can you know what I based my post on oz? You're making assumptions now. Which is why you're incorrect.

My post has everything to do with a single question which sums up almost everything in this thread.

How can someone determine what will/what did cause global collapse of a structure.

The single column failure scenario is AFTER the fact and even when using visual evidence, we STILL cannot determine exactly what happened. The ONLY way to get a reliable sequence of failure events is to develop computer models and compare each one to the visual data and see which on comes close to what we saw. That would take forever.

Trying to figure out if a structure will globally collapse during the design phase is impossible because of the number of component failure combinations/permutations. It would take forever for an engineer to test ALL possible failure scenarios to make sure none of them could cause a global collapse.