How high could the plane have hit, and still caused a total collapse?

Mendel

Senior Member.
Well, yeah, but it doesn't seem intuitively obvious why a steel building would be more susceptible to a top down, verinage-style collapse than a concrete building.
I'm saying the opposite. You need the verinage to crush the load-bearing elements in that concrete structure, but for the WTC towers, that wasn't necessary and provably did not happen (I linked to pictures of the spire and the fallen facade). To collapse a steel frame, all you need to achieve is to destroy the connections.
 

Jeffrey Orling

Senior Member
The top blocks included several Mechanical floors which were heavier (slabs) and the super imposed loads obviously were much heavier... including water tanks.
There are calculations of the magnitude of a dynamic load required to shatter the typical open office slab.

It's possible/likely that the top blocks came apart as a result of the buckled core columns, releasing loads (floors and superimposed dead loads) which far exceeded the loads to shatter any floor in the lower block. My guess is that the mech floors plus one of two more would have done the job.
 

Henkka

Member
The top blocks included several Mechanical floors which were heavier (slabs) and the super imposed loads obviously were much heavier... including water tanks.
There are calculations of the magnitude of a dynamic load required to shatter the typical open office slab.

It's possible/likely that the top blocks came apart as a result of the buckled core columns, releasing loads (floors and superimposed dead loads) which far exceeded the loads to shatter any floor in the lower block. My guess is that the mech floors plus one of two more would have done the job.
Did you see any of the earlier discussion of how this relates to a type of demolition called verinage? In those, the top 50% of the building is used to crush the lower 50%. But you seem to be saying that in the case of the WTC towers, something like the top 5% might even be sufficient. What makes the difference in your opinion?
 

Mendel

Senior Member.
Did you see any of the earlier discussion of how this relates to a type of demolition called verinage? In those, the top 50% of the building is used to crush the lower 50%. But you seem to be saying that in the case of the WTC towers, something like the top 5% might even be sufficient. What makes the difference in your opinion?
why are you ignoring the fact that these are different building types, and that load-bearing columns in the WTC towers were not crushed? You've seen the pictures.

We can argue about whether the floor slabs dropped down like a stack of pancakes or like a growing pile of rubble (especially since there's not much data supporting either hypothesis), but it's clear that for the "lower half of the building", its vertical load-bearing structures were not subject to verinage.
 
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Henkka

Member
why are you ignoring the fact that these are different building types, and that load-bearing columns in the WTC towers were not crushed? You've seen the pictures.
So what mechanism are you saying "destroyed the connections", specifically in the core of the towers? It was the weight of the upper floors bearing down on them, right? Would you use a different word other than "crushing" to describe that?
 

Mendel

Senior Member.
Would you use a different word other than "crushing" to describe that?
"shearing", probably.

The "weight of the upper floors" is not "bearing down on" the joints, it's bearing down on the floor slab, and its joists transfer it to the load-bearing columns, and the joints linking the joists to the columns fail (shear off) when they're overloaded.

Failure in verinage occurs because the load-bearing elements are obliterated (crushed) in the collapse—in the steel-framed WTC, it's mainly the connections failing that causes the collapse.
 
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Jeffrey Orling

Senior Member
The drop of the tops came after a period of intense fire on the plane strike floors. The likely impact of the heat, was not unlike what happened in 7WTC...lateral steel - beams and girders.... expanded, sagged and led to local floor collapse and more germane in the twin towers... to buckling and "failure" of core columns and loss of axial support for the hat truss which may have held the top blocks together... at least the facade. We don't know whether the interior of the upper blocks broke up before of as part of its collapse/descent into the top of the lower block. The collapse phase did not involve columns, but the crushing of each floor top to bottom by the floors mass of the top block as it increased with each floor it "destroyed" in the gravity driven avalanche tagged ROOSD.
 

Mendel

Senior Member.
It were the connections between the core and the outer facade which were failing. The cores were mostly destroyed by gravity I would say as Mendel has shown in other posts he linked. ( https://www.metabunk.org/threads/ho...he-twin-towers-to-truthers.12072/#post-259237 )
The WTC towers have the core columns, the "hollow box" facade columns, and the floors between them bracing them. The floors connect the core to the "outer facade", and once the floors fail as the building progressively collapses, all these columns are no longer braced properly and topple easily.

Obviously all of this destruction is driven by gravity, so it doesn't explain much to say that.
 

Henkka

Member
The drop of the tops came after a period of intense fire on the plane strike floors. The likely impact of the heat, was not unlike what happened in 7WTC...lateral steel - beams and girders.... expanded, sagged and led to local floor collapse and more germane in the twin towers... to buckling and "failure" of core columns and loss of axial support for the hat truss which may have held the top blocks together... at least the facade. We don't know whether the interior of the upper blocks broke up before of as part of its collapse/descent into the top of the lower block. The collapse phase did not involve columns, but the crushing of each floor top to bottom by the floors mass of the top block as it increased with each floor it "destroyed" in the gravity driven avalanche tagged ROOSD.

I've seen the term "ROOSD" mentioned a couple times on this forum, but not elsewhere. Can anyone give a brief synopsis of the idea? What does the acronym stand for, and also who came up with it?
 

Jeffrey Orling

Senior Member
The WTC towers have the core columns, the "hollow box" facade columns, and the floors between them bracing them. The floors connect the core to the "outer facade", and once the floors fail as the building progressively collapses, all these columns are no longer braced properly and topple easily.

Obviously all of this destruction is driven by gravity, so it doesn't explain much to say that.
It's the "structure" of "anything" that resists gravity... and "gives shape" to things. The structure of the buildings like most other high rises is a frame of steel and steel reinforced slabs. ROOSD was notable because the axial structures were bypassed and the collapsing floor mass gutted the buildings. But the ROOSD began as a result of failed axial members which "freed" the upper block mass to drop and crush the lower block. The typical floors were not designed to support more than perhaps 3 or 4 floor masses.... so once started the building self destructed floor by floor. 7WTC's demise came after the axial structures low in the building were destroyed as a result of a progression of toppling of transfer structures leading to column failures leaving the top (floors, facade/moment frame) with no support. It crushed floor by floor from the bottom during the collapse. Facade and moment frame were likewise destroyed as the collapse down with no support.
 

Jeffrey Orling

Senior Member
I've seen the term "ROOSD" mentioned a couple times on this forum, but not elsewhere. Can anyone give a brief synopsis of the idea? What does the acronym stand for, and also who came up with it?
ROOSD is an acronym for Runaway Open Office Space Destruction.
The twin towers had column free floor space outside the cores.
This was accomplished using lightweight long span steel trusses spaced at 80" OC
The typical steel (or concrete) frame is divided into bays typically about 25'x25'. The bay design can prevent failures from progressing laterally.
Twin towers, were light, "assemblies" built off site, went up fast and were inexpensive to build.
Once a mass / force presented on a floor which exceeded it capacity... the floor would "collapse" and the process would repeat (runaway) all the way to the bottom
 

Mendel

Senior Member.
Once a mass / force presented on a floor which exceeded it capacity... the floor would "collapse" and the process would repeat (runaway) all the way to the bottom
Before someone says this is shoddy design, remember you could fill up a storey completely with water and not exceed the total strength of the floor connections. It took a catastrophic event to trigger this runaway collapse.
 

Jeffrey Orling

Senior Member
Before someone says this is shoddy design, remember you could fill up a storey completely with water and not exceed the total strength of the floor connections. It took a catastrophic event to trigger this runaway collapse.
The loading was dynamic not static.
 

Jeffrey Orling

Senior Member
Before someone says this is shoddy design, remember you could fill up a storey completely with water and not exceed the total strength of the floor connections. It took a catastrophic event to trigger this runaway collapse.
It wasn't shoddy, but it was not as robust as the Empire State building.
 

Landru

Moderator
Staff member
Shouldn't this thread be in Rambles, Open Discussion or ChitChat? Is there a claim that is being debunked?

@Landru
It is drifting off topic. The issue is how high up the tower can a plane crash and still cause collapse. Stick to that.
 

econ41

Senior Member
Shouldn't this thread be in Rambles, Open Discussion or ChitChat? Is there a claim that is being debunked?

@Landru
The OP question is: "How high could the plane have hit, and still caused a total collapse?" and I don't think the discussion is as far off the topic as it may seem.

I think my assessment is as good as we could get. Summarised:
1) Yes a bit higher crash could cause collapse but we are (or "I'm") not sure how much higher - with the suggested target of 6 floors but that has problems we have not yet discussed. So I'll take a safer bet on 8 as my opening bid. ;)

2) Because it would need to be the same type of collapse as actually occurred viz crash plus fires causing other "Top Block" to fall >> triggering "ROOSD" progression. AND

3) "We" are (or more likely "I am" ;) ) sure that progression would lead to global collapse IF we could trigger "initiation".

And all the discussions seem to be about relevant bits of mechanism even tho some members are not rigorously tieing their comments back to the OP question. << HINT HINT ;)
 
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Mendel

Senior Member.
2) Because it would need to be the same type of collapse as actually occurred viz crash plus fires causing other "Top Block" to fall >> triggering "ROOSD" progression. AND
with unknown differences in the aircraft impact damage, as the facade and core columns are less sturdy higher up.

the hat truss would carry less weight but might have a harder time redistributing it?

if we have impact within the top 6 floors, the hat truss would be damaged, and collapse initiation might look different altogether. (what if the aircraft hit closer to the corner?) there's simply a lot we don't know, and won't know without modeling impact damage, fire effects, and the resultant stresses.
 

econ41

Senior Member
with unknown differences in the aircraft impact damage, as the facade and core columns are less sturdy higher up.
Yes. But the net result is it either will or will not trigger progression. And anything other than the "ROOSD" process we saw on 9/11 will arrest.
the hat truss would carry less weight but might have a harder time redistributing it?
Possibly true. But my point is that the net result dominates the OP question. Anything OTHER than a "ROOSD" style progression will halt. AKA "not cause a total collapse".
if we have impact within the top 6 floors, the hat truss would be damaged, and collapse initiation might look different altogether. (what if the aircraft hit closer to the corner?) there's simply a lot we don't know, and won't know without modeling impact damage, fire effects, and the resultant stresses.
Yes. But the key question remains:
Will it initiate a "ROOSD" style global collapse?
 

Mendel

Senior Member.
And anything other than the "ROOSD" process we saw on 9/11 will arrest.
I've been wondering if it would be possible for just half a floor to come down, like if the "hat" breaks in the middle and one half comes down? Intuitively, I'd still expect that to progress, and possibly "eat" inward and over to the other side as it avalanches down, but is that realistic?
 

Jeffrey Orling

Senior Member
I've been wondering if it would be possible for just half a floor to come down, like if the "hat" breaks in the middle and one half comes down? Intuitively, I'd still expect that to progress, and possibly "eat" inward and over to the other side as it avalanches down, but is that realistic?
Seems to me that a partial floor collapse would radiate/spread throughout the floor plan because there was no structural isolation of bays. If the break was very clean perhaps it would not spread... but the floors were composite with rebar and long metal pans.
 

econ41

Senior Member
I've been wondering if it would be possible for just half a floor to come down, like if the "hat" breaks in the middle and one half comes down? Intuitively, I'd still expect that to progress, and possibly "eat" inward and over to the other side as it avalanches down, but is that realistic?
I've given it some preliminary thought - it may not be possible to come to a definitive conclusion.

And I'm sure that it is not a question about "ROOSD" as a process separated from how it was started in the actual 9/11 collapses. In those actual 9/11 scenarios, the triggering of ROOSD resulted from the dropping of a larger "Top Block" than we are considering in this discussion. And the Start of ROOSD saw the concentrated load from those larger top blocks applied as a linear concentrated load as the perimeter columns impacted on the first floor contacted and had the momentum to hit several more floors. The Top Block and upper tower breaking up concurrently. As per this diagram - note the path of the yellow arrows:

ArrowedROOSD.jpg

It is feasible that a lesser Top Block could result in only half or such portion of the first impacted floor falling. I suspect that such a relatively low impact event would not progress to more floors. I'm not sure at this stage. I'm also giving some thought as to whether, if a "half floor" collapse was triggered, it could continue further down the building as a "Half Floor ROOSD" >> and that raises the next question: "Would a tower subjected to half-floor ROOSD over multiple storeys still strand???

I'll give it more thought.
 

Jeffrey Orling

Senior Member
I've given it some preliminary thought - it may not be possible to come to a definitive conclusion.

And I'm sure that it is not a question about "ROOSD" as a process separated from how it was started in the actual 9/11 collapses. In those actual 9/11 scenarios, the triggering of ROOSD resulted from the dropping of a larger "Top Block" than we are considering in this discussion. And the Start of ROOSD saw the concentrated load from those larger top blocks applied as a linear concentrated load as the perimeter columns impacted on the first floor contacted and had the momentum to hit several more floors. The Top Block and upper tower breaking up concurrently. As per this diagram - note the path of the yellow arrows:

ArrowedROOSD.jpg

It is feasible that a lesser Top Block could result in only half or such portion of the first impacted floor falling. I suspect that such a relatively low impact event would not progress to more floors. I'm not sure at this stage. I'm also giving some thought as to whether, if a "half floor" collapse was triggered, it could continue further down the building as a "Half Floor ROOSD" >> and that raises the next question: "Would a tower subjected to half-floor ROOSD over multiple storeys still strand???

I'll give it more thought.
So let's imagine that somehow a small area/concentrated 10,000# load dropped on a WTC floor. I imagine it would punch through the floor, destroying at least a portion of the floor around the impact... and the load would continue as unstoppable until it hit the ground. The question really asks if a large area load which exceeded the floor spec would radiate throughout the floor or simply cause a runaway local collapse.

I think it IS possible if the local collapse is over a larger enough are considering the composite nature of the floor designs. Destroying a section of a floor truss likely would see the area supported by the entire length of the truss effected and likely sag or break and fall. The composite nature spread load support but it could also spread destruction. It's a hard call. Could the tower stand with only 3 of the 4 facades intact? Two if them?
 

Jeffrey Orling

Senior Member
I've given it some preliminary thought - it may not be possible to come to a definitive conclusion.

And I'm sure that it is not a question about "ROOSD" as a process separated from how it was started in the actual 9/11 collapses. In those actual 9/11 scenarios, the triggering of ROOSD resulted from the dropping of a larger "Top Block" than we are considering in this discussion. And the Start of ROOSD saw the concentrated load from those larger top blocks applied as a linear concentrated load as the perimeter columns impacted on the first floor contacted and had the momentum to hit several more floors. The Top Block and upper tower breaking up concurrently. As per this diagram - note the path of the yellow arrows:

ArrowedROOSD.jpg

It is feasible that a lesser Top Block could result in only half or such portion of the first impacted floor falling. I suspect that such a relatively low impact event would not progress to more floors. I'm not sure at this stage. I'm also giving some thought as to whether, if a "half floor" collapse was triggered, it could continue further down the building as a "Half Floor ROOSD" >> and that raises the next question: "Would a tower subjected to half-floor ROOSD over multiple storeys still strand???

I'll give it more thought.
Econ41 uses the image from 2WTC. 1WTC did not as much tilt.... It does seem to laterally translate causing misalignment the column ends, However these column ends were staggered over 3 floors as far as the facade is concerned. And the column ends of the core were not at floor level...nor were the facade column joints aligned with the floor slabs.Panel types_page1.jpg
 

Mendel

Senior Member.
It is feasible that a lesser Top Block could result in only half or such portion of the first impacted floor falling. I suspect that such a relatively low impact event would not progress to more floors. I'm not sure at this stage. I'm also giving some thought as to whether, if a "half floor" collapse was triggered, it could continue further down the building as a "Half Floor ROOSD" >> and that raises the next question: "Would a tower subjected to half-floor ROOSD over multiple storeys still stand
That's pretty much what I've been wondering.
 

econ41

Senior Member
Econ41 uses the image from 2WTC. 1WTC did not as much tilt....
True.
And the different amount of "tilt" is irrelevant.
It does seem to laterally translate causing misalignment the column ends,
Yes there is "macro" level AKA overall lateral translation but it is also irrelevant. Or more pedantically stated - it is redundant. Think from the micro. Many columns failed and in doing so they got shorter overall (the Top Block was differentially moving downwards. So for each individual failing column as it got shorter the ends must be missing or bypassing. The gross, macro level, lateral translation comes later as a consequence.
However these column ends were staggered over 3 floors as far as the facade is concerned. And the column ends of the core were not at floor level...nor were the facade column joints aligned with the floor slabs.
I'm not sure of the relevance of this detail.
 

Jeffrey Orling

Senior Member
My sense is that the destruction which began ROOSD involved floor slabs colliding more so than columns severing floor connections to the columns with regard to the slab outside the core.
The perimeter connections as I recall had the floor trusses resting on and bolted to angle beam seats welded to the spandrel beams at ever other perimeter column and diagonal strut bracing to every other perimeter column.The core side was supported on a continuous "belt girder" cantilever off the 24 outer columns of the core. I believe the concrete slab passed over the top of the girder. Destroying the truss connections would either involved failing the cantilevers or shearing the trusses themselves.
For sure a tilted and displaced upper block tube would do massive damage to the floor is hit.. It remains to be seen if this would "mostly" be destroying the connections to the perimeter or the core columns. My conclusion is the main destruction mechanism was floor to floor impacts.. rather than severing or destroying truss connections to the frame.
 

econ41

Senior Member
@Henkka - Recently in another thread I objected to your use of the term "crushing". It may help if I comment further on this post of yours:
So what mechanism are you saying "destroyed the connections", specifically in the core of the towers?
The cores of the Lower Towers of both Twin Towers were dismantled by a process analogous to ROOSD << which, strictly, refers to the open office space i.e. "OOS"

There were broadly two sub-stages of this "progression stage" viz "early progression" and "established progression" (Both those are my terms BTW.)

In both sub-=stages falling material sheared the core area floor beams off the columns. Analogous to the ROOSD process shearing OOS floor joists off the outer core and perimeter columns. The distinction between "early" and "established" sub-stages >> in "early progression" the Top Block and Lower Tower were still involved in mutual destruction. The Top Block still not broken into separate component parts. In "established progression" sub-stage it was essentially dismantled debris.
It was the weight of the upper floors bearing down on them, right?
That is far too ambiguous. What was falling was, in the early stages, the Top Block as it was breaking up in mutual destruction with the top of the Lower Tower. Later, in "established progression", it was the accumulating and increasing weight of debris. Never the "weight of the Upper Floors" pers se or in any overall sense of the upper levels still being intact.
Would you use a different word other than "crushing" to describe that?
"Shearing" is technically correct had appropriate.. The word "crushing" has a bad history of confusion and is simply wrong EXCEPT when applied bodily - at the "macro" level - e.g. your other thread references to "soda can crushing". An applied weight bodily crushes the whole of the soda can. We are not dealing here with an imagined "large boot" crushing the whole structure of the Tower. And there is no buckling involved at this stage. "Shearing" is the dominant process.
 
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