Towards A Replicable Physical Model Illustrating Aspects of the Collapse of The WTC Towers on 9/11

[jaydeehess]

Exactly.

Thanks, of course in your modeling if this mechanism you can make both floors and columns as strong as you like. It would not change the result significantly since the entire structure depends on the floors providing lateral support to the columns.

 

[Oystein]

Thanks, of course in your modeling if this mechanism you can make both floors and columns as strong as you like. It would not change the result significantly since the entire structure depends on the floors providing lateral support to the columns.

I disagree.

The thread about the Nordenson calculation of whether or not a falling girder in WTC7 would punch out the girder below taught me that there are more significant parameters than just connection strength and impacting KE or momentum. Stiffness of the colliding elements was critical.
I think it is also a critical parameter in Mick's model - as I think I pointed out early in the thread.
If you make the floors infinitely stiff, then you optimize for connection failure.
In reality, the floors must have exhibited considerable elasticity, and also plastif deformations away from the connections, both of which reduce the energy available to fail the connecion - and reduce the peak force.

Mick's floors may be too stiff to faithfully model the pancaking mechanism.
I think this ought to be evaluated and considered in some future version of the model.

 

[Mick West]

I disagree.

The thread about the Nordenson calculation of whether or not a falling girder in WTC7 would punch out the girder below taught me that there are more significant parameters than just connection strength and impacting KE or momentum. Stiffness of the colliding elements was critical.
I think it is also a critical parameter in Mick's model - as I think I pointed out early in the thread.
If you make the floors infinitely stiff, then you optimize for connection failure.
In reality, the floors must have exhibited considerable elasticity, and also plastif deformations away from the connections, both of which reduce the energy available to fail the connecion - and reduce the peak force.

Mick's floors may be too stiff to faithfully model the pancaking mechanism.
I think this ought to be evaluated and considered in some future version of the model.

There's a big difference between a single falling girder, and the huge wave of rubble that was falling once collapse had begun. I think the issues related to springiness are more relevant to collapse initiation. Once the collapse wave got some speed and mass it would barely be slowed by the floor slabs.

 

[jaydeehess]

I disagree.

The thread about the Nordenson calculation of whether or not a falling girder in WTC7 would punch out the girder below taught me that there are more significant parameters than just connection strength and impacting KE or momentum. Stiffness of the colliding elements was critical.

Yes but... in WTC7 its a single structural element, the girder. In the towers its the mass of a dozen floors. In the former it has much less transfer of momentum onto a floor than innthe later.
Besides, Mick's model is more specifically to study the tower collapse's main mode of collapse, floor stripping, rather than the more complex progression both vertically and horizontally, in WTC7.

I think it is also a critical parameter in Mick's model - as I think I pointed out early in the thread.
If you make the floors infinitely stiff, then you optimize for connection failure.
In reality, the floors must have exhibited considerable elasticity, and also plastif deformations away from the connections, both of which reduce the energy available to fail the connecion - and reduce the peak force.

Mick's floors may be too stiff to faithfully model the pancaking mechanism.
I think this ought to be evaluated and considered in some future version of the model.

Yes the floors may have bowed until they pulled away from columns. However, the upper sections of the columns are literally spearheading the upper mass too. Then there is the fact that the mass driving this failure of floors/connections is >> greater than a single structural component, like that girder. Its the mass of the upper section.

 

[Oystein]

There's a big difference between a single falling girder, and the huge wave of rubble that was falling once collapse had begun. I think the issues related to springiness are more relevant to collapse initiation. Once the collapse wave got some speed and mass it would barely be slowed by the floor slabs.

My objection concerns collapse progression, just as it did at the WTC7 issue.
The "big" difference is merely quantitative.
If you are so unconcerned with even order of magnitude, I wonder why you bother to make a point about your commections barely holding 6 floors placed upon them - why not 60, or 0.6?

Sure, eventually (sufficiently far into the avalanche) any floor will be overwhelmed. The interesting part is of course the very first floor.

Remember that some building collapses DO arrest. Whether or not collapse progresses or arrests is a matter of proportions. You have to model the most relevant proportions reasonbly to scale.

I advise you that elasticity and plastic deformation are significant and ought not be ignored when discussing scale.
It may be of little interest if you merely wish to illustrate the mechanism. In that case you'd better explain why you consider the load:capacity ratio significant enough to choose magnets rather than screws.

 

[Mick West]

If you are so unconcerned with even order of magnitude,

I'm not sure what you mean here.

 

[Oystein]

Yes but... in WTC7 its a single structural element, the girder. In the towers its the mass of a dozen floors.

I think this is an invalid shortcut to "evaluation and consideration". That single girder supported an unusually large floor area, and it impacted (essentially) only one connection below, while the twins' floors had many connections attacked at once.

In the former it has much less transfer of momentum onto a floor than innthe later.

How do you know? Have already done the evaluation (read: number-crunching) I advised??

Besides, Mick's model is more specifically to study the tower collapse's main mode of collapse, floor stripping, rather than the more complex progression both vertically and horizontally, in WTC7.

I am talking about floor stripping only, and how the floors deflect elastically and plastically, thus eating KE. Your objection is moot.

Yes the floors may have bowed until they pulled away from columns. However, the upper sections of the columns are literally spearheading the upper mass too.

Mick doesn't intend to model these mechanisms, so your objection is moot.

Then there is the fact that the mass driving this failure of floors/connections is >> greater than a single structural component, like that girder. Its the mass of the upper section.

Neither in reality nor in Mick's model is the full mass of the upper section loading the first few floors.
Your objection is thus moot.

 

[Oystein]

I'm not sure what you mean here.

You have not evaluated how much energy the floors could absorbe elastically and/or plastically, thus you cannot know with confidence whether or not they might significantly slow the collapse.

I fear that the energy dissipation of your model slabs is, to scale, more than an order of magnitude lower than in reality, because they are relatively too strong (stiff).

 

[deirdre]

You have not evaluated how much energy the floors could absorbe elastically and/or plastically, thus you cannot know with confidence whether or not they might significantly slow the collapse.

I fear that the energy dissipation of your model slabs is, to scale, more than an order of magnitude lower than in reality, because they are relatively too strong (stiff).

? so if he just duct tapes 12 floors togther and places them on the top of the model, to simulate how each floor could only hold 12 floors wiorth of weight.. are you saying that would be a better model?

 

[Auldy]

Sure, but there's 37,000 members in that group. Some of them might actually get what I'm talking about.

I read 19,798 (as of 17th of August, 2016), has the number of members dropped by 17,000 members in a few days? If so, maybe due to your great discussion vs juvenile responses? Or am I looking at the wrong facebook group? https://www.facebook.com/groups/286311730249/members/

 

[Mick West]

I read 19,798 (as of 17th of August, 2016), has the number of members dropped by 17,000 members in a few days? If so, maybe due to your great discussion vs juvenile responses? Or am I looking at the wrong facebook group? https://www.facebook.com/groups/286311730249/members/

I meant the "9/11 Truth Movement", the discussion started on there, I was ejected from the group (I think) and then Ken reposted the question about screws in the smaller public group.

 

[Mick West]

You have not evaluated how much energy the floors could absorbe elastically and/or plastically, thus you cannot know with confidence whether or not they might significantly slow the collapse.

It's a simple model, and what it s supposed to illustrate is the inevitability of progressive collapse if the connections of a floor can only support 6 times the weight of the floor, when suddenly applied. Really the intent it to explain to people how it is physically possible to collapse, and explain how the other physical models do not "prove" that collapse progression is impossible.

There' obviously a huge number of differences between the model and the towers, both in areas of complexity and scale. This necessitates compromises in the choice of material and connection functionality. One could argue that the lack of flexibility in the floors is offset by the flexibility in the magnetic joints.

The model demonstrates that such a progressive collapse mechanism is possible. It models the key aspect of 6x loading strength for the floors. Perhaps there are other aspects of the towers' construction that would have prevented or slowed a collapse, and hence prove explosives were used. But I don't see any evidence of that.

 

[jaydeehess]

IIRC, the total mass any one floor space could support was on the order of 30,000 tons. I assume that the weak point would be the connections to vertical support(perimeter and core belt truss)
If the total of six floors + the columnar mass of six floors worth of tower is equal to or greater than this mass then the floor would fail even if one quietly and carefully placed such mass on a floor.

In such a case, energy dissipation through bending/elastic deformation does not enter into the equation.

If the force delivered dynamically is equal to or greater than that represented by 30Ktons in Earth's gravity, again elastic deformation just doesn't enter into this.

Now granted the impact of the upper section was much more complex.
For eg.
-Both towers saw their upper sections tilted at collapse, which means that the first few floors to be affected were progressively destroyed from one side to the other.
-The column ends would be the first points of contact with lower structure and it's likely they simply punched through the concrete. While that might reduce the energy of impact a small amount it also compromises the integrity of the impacted floor space. In addition those column ends are proximate to connections to vertical support and some at least would then crush concrete and strip the support.
-The floor supports of the upper section's floor trusses are designed to take a force that is directed down(of course). Impact with lower structure would impart a force directed up wrt to those connections. Its likely that these connections(upper section floor to perimeter and core belt truss) failed quicker than the floor connections of the lower section.
-After a few levels are destroyed, the collapse driving mass is mostly rubblized but unless mass shedding is greater than mass gain from more floors being destroyed and falling, then collapse continues by overwhelming the floor connections.

A limit case would be to load a floor space suddenly, evenly, and magically with slightly greater mass than a floor space is capable of supporting. Quite obviously and by definition, the floor 'fails'. Now assume that the falling mass simply floats down to the next level and that the mass shed is less than the mas gained by the destruction of one floor.(IOW it's all static loads) That next floor must also fail.

 

[Jeffrey Orling]

IIRC, the total mass any one floor space could support was on the order of 30,000 tons. I assume that the weak point would be the connections to vertical support(perimeter and core belt truss)
If the total of six floors + the columnar mass of six floors worth of tower is equal to or greater than this mass then the floor would fail even if one quietly and carefully placed such mass on a floor.
.

Design load was 58# /SF....

58# x 208' x 208' / 2000# = 1,254tons . Core floor area supported higher loads... so add

42# x 137' x 59' / 2000# = 169 tons

Call the capacity per typical floor 1,400 tons STATIC LOAD

You really need to do the very simple math

of course there were there were shafts which supported no load and the corners.

If one stupidly assume that each column connection shared the load equally...

you had (IIRC) 236 perimeter columns, 47 core columns.. However the 24 perimeter core columns had at MOST 28 connections to the OOS floor and maybe only 24. The 23 in the center of the core and the perimeter columns side supporting the floors and beams into the core would be 24.... the 23 in the center would have 23 x 4 connections...

23+ 24 + 28 + 236 = 311 floor system to column connections

1400 / 311 = 4.6 tons of static load per connection.... THIS IS NOT ACCURATE... because each connection did NOT support the same floor area.

the concrete floor w/o the steel weighed 93# / CU FT

dead load of floor (weight of slab w/o steel trusses or beams) = 94# x 4.5" / 12" x 208' x 108' / 2000#= 762 tons...

Assuming the floor was live loaded to its 58# / SF capacity and the floor w/ steel weighed 800 tons.... the total superimposed LL and dead load per typical twin tower office floor was:

1,400 tons static live load + 800 tons of static dead load.... = 2,200 total LL + DL

NOT 30,000 tons

NB this does not include the weight of the columns... which were not floor loads... and did not "bear on" or stress the floor to column connections. Collapsing columns could add increasing dynamic load as the structure collapsed...but MOST columns did not collapse onto and destroy floor slabs...

Superimposed LL on mech floor as well as static deal load was greater than the typical OOS floors.

 

[jaydeehess]

Was going on something i recal eachy saying.

 

[Jeffrey Orling]

Was going on something i recal eachy saying.

Does what I did make sense to you?

 

[jaydeehess]

Does what I did make sense to you?

If your numbers are correct, very much so

 

[Jeffrey Orling]

30,000 tons = 30,000x2000 = 60,000,000 #

60,000,000 # / 202 x 208 = 1,386 # per SF... light weight conc is about 94#/ft...

You can see static load of 1,386#/ft is rubbish

 

[Oystein]

? so if he just duct tapes 12 floors togther and places them on the top of the model, to simulate how each floor could only hold 12 floors wiorth of weight.. are you saying that would be a better model?

Rule of So applies.
No, I am not saying this at all. I have no idea how you can construe my words that way.

 

[Oystein]

It's a simple model, and what it s supposed to illustrate is the inevitability of progressive collapse if the connections of a floor can only support 6 times the weight of the floor, when suddenly applied. Really the intent it to explain to people how it is physically possible to collapse, and explain how the other physical models do not "prove" that collapse progression is impossible.

There' obviously a huge number of differences between the model and the towers, both in areas of complexity and scale. This necessitates compromises in the choice of material and connection functionality. One could argue that the lack of flexibility in the floors is offset by the flexibility in the magnetic joints.

The model demonstrates that such a progressive collapse mechanism is possible. It models the key aspect of 6x loading strength for the floors. Perhaps there are other aspects of the towers' construction that would have prevented or slowed a collapse, and hence prove explosives were used. But I don't see any evidence of that.

"Possible" - yes.
"Illustrate" - great!
"Inevitable" - no, unless you DO consider and evaluate all other factors (and thus determine which you are justified to leave out)

It's a bit trivial when you actually apply 6 times the weight. But that's not actually what your model does: You apply only 1x the weight when you drop the first free floor - and illustrate how one falling floor results in 12+ times the load (force). However, the load (force) on the connection depends critically, highly significantly on the extensive and intensive material properties, such as elasticity. Think of the guy who recently jumped in freefall from a plane (no parachute) and landed unharmed in a large net. The property of the net to bulge down made all the difference.

I advide you to not underestimate the significance of this.

Your model greatly illustrates the possibility of pancaking collapse.
Be careful not to believe it shows the inevitability.

 

[jaydeehess]

30,000 tons = 30,000x2000 = 60,000,000 #

60,000,000 # / 202 x 208 = 1,386 # per SF... light weight conc is about 94#/ft...

You can see static load of 1,386#/ft is rubbish

I wasn't questioning your numbers.

 

[Davidb]

Collapse was only slightly slower than free-fall

View attachment 18499

See attached .mov file. I'll upload a longer clip to YouTube later with stability tests. Might be tomorrow.

Can you make the demonstration as such that it will throw heavy objects away from the building on its way down? thanks

 

[mm1145]

Can you make the demonstration as such that it will throw heavy objects away from the building on its way down? thanks

not to premept mick but you are going to have to define what heavy means when we are working with a scale model?

 

[Jeffrey Orling]

Can you make the demonstration as such that it will throw heavy objects away from the building on its way down? thanks

Heavy objects were not thrown anywhere as a result of the collapse. Things fell down or toppled over. And a model would have the scale issue again when you refer to heavy.... compared to what standard?

 

[Davidb]

oh I don't know, maybe scale it to something like this would be fine
http://www.911myths.com/html/explosive_force.html
apologies, I had to put in link, scroll half way down to the building with a beam sticking outwhen you get to site. I could not figure out how to cut and paste a photo here
thanks so much

 

[Jeffrey Orling]

oh I don't know, maybe scale it to something like this would be fine
http://www.911myths.com/html/explosive_force.html
apologies, I had to put in link, scroll half way down to the building with a beam sticking outwhen you get to site. I could not figure out how to cut and paste a photo here
thanks so much

That is a facade panel which came from the 84th floor I believe or there abouts which was 1100 feet in the air. It is shown impaled into the the WFC on the 22nd floor IIRC... which would be about 250 feet high... a difference of 850 feet. That corner of the WTC building was about 428 feet from the west face of 1wtc. The piece was part of a much taller and wider assembly of panels which fell off/ toppled over from the west face. The rest of the panels can be seen neatly arrayed East of the WFC's Winter Garden.

 

[Davidb]

That is a facade panel which came from the 84th floor I believe or there abouts which was 1100 feet in the air. It is shown impaled into the the WFC on the 22nd floor IIRC... which would be about 250 feet high... a difference of 850 feet. That corner of the WTC building was about 428 feet from the west face of 1wtc. The piece was part of a much taller and wider assembly of panels which fell off/ toppled over from the west face. The rest of the panels can be seen neatly arrayed East of the WFC's Winter Garden.

Understood, its just the experiment I saw does not resemble what I saw in the video,
anyways thanks
to administrator, please ban me from your forum
cheers to all

 

[Svartbjørn]

to administrator, please ban me from your forum
cheers to all

That's an odd request. Why would you want to be banned, or why do you think you should be banned?

 

[mm1145]

Understood, its just the experiment I saw does not resemble what I saw in the video,
anyways thanks
to administrator, please ban me from your forum
cheers to all

to what respect dose it not resemble what you saw? you are going to need to provide details on what is missing

 

[jaydeehess]

Can you make the demonstration as such that it will throw heavy objects away from the building on its way down? thanks

Mick's model is essentially 2d rather than 3d, model concerns the aspect of internal destruction leading core and perimeter destruction, and you will note that the blocks often do not fall directly in line with their original positions, ie.they fell away from the model.

 

[Oystein]

...what I saw in the video...

What did yu see in which video?
A wall panel flying on a ballistic curve from within the WTC tower footprint to the face of a building several hundreds of feet away, where it got embedded? I sure did not see this anywhere.
However, I have calculated the theoretical minimum amount of explosive material needed to propel a wall panel to the ca. 60 mph lateral velocity that would be required for it to fall to, eg, the WFC on such a ballistic curve. Result: Much more than 100 pounds of high explosives in the most ideal of cases (most energetic known explosives, placed directly on perimeter wall panel, centered on its center of gravity, with a view to optimizing the lateral velocity and NOT to optimizing the desctruction; no significant losses to deformation, heat etc). Since these conditions are unrealistic one and all, a single wall panel would in practice need more like a quarter ton or half a ton of supersonic explosives to achieve that feat.

Very obviously, no such explosion was heard. It would have made a vast impact on lots of stucture and people all around.

Sander is correct: The best explanation for these panels found hundreds of feet away is that large sheets of still connected perimeter wall, several hundreds of feet high, toppled outward like trees. Their top panels would reach the farthest. This is actually seen in some videos, it is consistent with the steel debris layout on the ground, and it is consistent with a model of collapse progress where the floor slabs are punched out by falling weight, leaving the perimeter laterally unsuppoirted over many storeys and thus free to topple outward.

I believe Micks model even shows some of his vertical members falling some distance outward because they topple - although his model is not meant to model this aspect realistically.

 

[Mick West]

However, I have calculated the theoretical minimum amount of explosive material needed to propel a wall panel to the ca. 60 mph lateral velocity that would be required for it to fall to, eg, the WFC on such a ballistic curve. Result: Much more than 100 pounds of high explosives in the most ideal of cases (most energetic known explosives, placed directly on perimeter wall panel, centered on its center of gravity, with a view to optimizing the lateral velocity and NOT to optimizing the desctruction; no significant losses to deformation, heat etc). Since these conditions are unrealistic one and all, a single wall panel would in practice need more like a quarter ton or half a ton of supersonic explosives to achieve that feat.

Are these calculations posted somewhere?

 

[Oystein]

Are these calculations posted somewhere?

Yes, here:
http://www.skepticforum.com/viewtopic.php?f=72&t=25149#p448618

I corrected one mistake here:
http://www.skepticforum.com/viewtopic.php?f=72&t=25149&start=40#p449072
(I had initially calculated a wall panel to weigh something like 30 tons, when high up they were only 6 to 7 tons. That doesn't change the ">10 kg explosives to propel 1000 kg of payload to 60 mph")

 

[Nada Truther]

David and Oy....Whether the calculations are correct or not is irrelevant. The issue with the claim is the inconsistencies with the accusations. "Materials fell much farther out than they could naturally fall, so it must have been explosives." That is basically the claim from the CD community. Although no explosions were heard, this seems legit to them. They will then say that the absence of audible explosions was due to the use of super-secret thermite that is quiet and effective enough to melt the steel and bring the building down. What is the point of using explosives if the thermite will do the job?! Why bother using thermite if you are going to use explosives anyway?! What type of demolition charges blow giant Volkswagon bus sized pieces of steel hundreds of feet away with enough force to embed into another building? I have never seen any CD where giant pieces are flying all over the place. They are usually quite contained with only small debris flying out of the structure.

This may be a topic for another thread, but:

Has anyone ever laid out ALL of the truther theories and seen how they contradict each other? I would love to see that.
"They used quiet burning thermite" vs. "we heard bombs" and accusations like that can't live in the same world together.

 

[Oystein]

David and Oy....Whether the calculations are correct or not is irrelevant. The issue with the claim is the inconsistencies with the accusations. "Materials fell much farther out than they could naturally fall, so it must have been explosives." That is basically the claim from the CD community. Although no explosions were heard, this seems legit to them. They will then say that the absence of audible explosions was due to the use of super-secret thermite that is quiet and effective enough to melt the steel and bring the building down. ...

The claim was that there were "heavy objects [thrown] away from the building on its way down", with the implication that this may not have been a result of the forces occurring from a gravitational collapse - usually, propellants such as explosives are insinuated or claimed.
If you are going to refer to thermite as a mere heat producer, that would have nothing to do with "throwing" beams.
If the claim is that thermite can do what explosives do, only quietly (like, they go "pfff" instead of "BANG"), then you are lef with the problem that any such quite propelling action would have to satisfy Conservation of Momentum and of Energy. A subsonic "explosion" makes the solution only more unrealistic.

 

[Svartbjørn]

Has anyone ever laid out ALL of the truther theories and seen how they contradict each other? I would love to see that.

Thats going on the assumption that all the theories are coming from the same camp. They're not. There are SOME groups that say that it was CD, there are OTHER groups that say it was Thermite, there are a few reeeeeaally fringe groups that say it was a holographic projection that timed with massive bombs inside the building to cause the illusion of a plane hitting the towers etc, which then used CD or Thermite to cause the buildings to fall.. and then there's everything in between.

Thats the beauty of what Mick was trying to do with this model, he was trying to show that the buildings CAN fall the way they fell because of gravity.. the big issue is that gravity cant be scaled. The pieces dont move EXACTLY like the 'stuff' moved because the pieces arent the same size or mass..so people try to pick holes in the model not understanding what a model is or what its for. They expect and want an exact duplicate, when the only way to do that is to exactly duplicate every single variable (known or unknown) to make an absolute perfect reflection of what happened on 9/11.

 

[Nada Truther]

They expect and want an exact duplicate, when the only way to do that is to exactly duplicate every single variable (known or unknown) to make an absolute perfect reflection of what happened on 9/11.

And there's no guarantee that the EXACT same scenario is going to yield the EXACT same result either. I think most people understand Mick's model. Just the ones that WON'T believe it think that it is not helpful.

 

[Svartbjørn]

And there's no guarantee that the EXACT same scenario is going to yield the EXACT same result either. I think most people understand Mick's model. Just the ones that WON'T believe it think that it is not helpful.

Thats exactly the point. No matter what happens, no matter how great the model is.. someone.. somewhere will find a reason to say that its not good enough. Mick's model, for the general lay person (like me who doesnt know jack and/or shit about architectural engineering or the physics behind it) is great... but for the people who are really deep into 9/11 the only thing that will ever suffice is a perfect replica.

 

[jaydeehess]

David and Oy....Whether the calculations are correct or not is irrelevant. The issue with the claim is the inconsistencies with the accusations. "Materials fell much farther out than they could naturally fall, so it must have been explosives." That is basically the claim from the CD community. .

Yes, and it is a claim purely based on personal incredulity. Not only is it calculable how far horizontally an object can travel, one can perform a scale demonstration.
On a ten foot high platform, say a rented scaffold, erect a 6 foot tall 2X4 with a dish nailed to the top of it. In the dish place a few fishing sinkers. Now allow the 2X4 to topple outwards. Now measure how far from the base of the scaffold those weights end up, having begun falling from 16 feet up.

 

[Kenn]

UPDATE: Here's the model I eventually arrived at:

Source: https://www.youtube.com/watch?v=flo62pdaIMI


The following thread shows how I got there.


-----------------------------------------------------------------------------------------------

There has been much discussion as to the precise sequence of events during the collapse of the World Trade Center twin towers. The collapse discussion is generally divided into initiation (why it started to collapse) and progression (why it continued to collapse all the way down). Some people suggest it is impossible for the upper part of a structure to "crush" the bottom part of the structure, they build models to try to demonstrate this.

Those models are wrong, because they rely on the supporting columns being crushed as the collapse mechanism. The "official story" is that the floors gave way at their points of attachments to the columns. i.e. the failure begins with floors being stripped away from the columns.

http://www.nist.gov/el/disasterstudies/wtc/faqs_wtctowers.cfm

12. Was there enough gravitational energy present in the WTC towers to cause the collapse of the intact floors below the impact floors? Why weren't the collapses of WTC 1 and WTC 2 arrested by the intact structure below the floors where columns first began to buckle?

Yes, there was more than enough gravitational load to cause the collapse of the floors below the level of collapse initiation in both WTC towers. The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case). Since the number of floors above the approximate floor of collapse initiation exceeded six in each WTC tower (12 floors in WTC 1 and 29 floors in WTC 2), the floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings.
...
This simplified and conservative analysis indicates that the floor connections could have carried only a maximum of about 11 additional floors if the load from these floors were applied statically. Even this number is (conservatively) high, since the load from above the collapsing floor is being applied suddenly. Since the dynamic amplification factor for a suddenly applied load is 2, an intact floor below the level of collapse initiation could not have supported more than six floors. Since the number of floors above the level where the collapse initiated exceeded six for both towers (12 for WTC 1 and 29 for WTC 2), neither tower could have arrested the progression of collapse once collapse initiated. In reality, the highest intact floor was about three (WTC 2) to six (WTC 1) floors below the level of collapse initiation. Thus, more than the 12 to 29 floors reported above actually loaded the intact floor suddenly.

To illustrate that it's the floors that are failing first, and not the walls, I (and others) have built simple models that show floors being stripped away from walls. Now it's important to remember that these models are illustrative. Because of the square-cube law of scaling it is very difficult to get something truly representative. The intent is firstly to illustrate that an upper portion of a structure can cause the destruction of a much larger lower portion, and secondly to illustrate roughly how this happened in the WTC towers.

My very first attempt some time ago was done with Jenga blocks (regular sized cuboids of wood) and thin strips for the floors. It was moderately successful in illustrating the principle.

But it suffered from numerous problems: very springy floors, overly segmented columns, and a long and fiddly reset time. More significantly it did not simulate the breaking of the seated connections (i.e. where the floors meet the wall) - instead the floors were more jostled out of place. It is also quite small.

So I decided to devote some occasional time to a better model, about which this thread will be a continuing work-in-progress discussion.

I decided to make a free-standing model, with wider "floors" to make it more three dimensional. Each floor section consists of 12" sections of 1x4 dimensioned lumber (0.75" x 3.5" cross section). To simulate the seated connections I stapled a 1" wide strip of laminated paper to the end of the "floor".

[Update: The laminated paper and screws method has been replaced by a vastly better magnets and plates method. The following is left to show how the model evolved]

View attachment 18062

For the columns, I use a 24" (2 foot) tall piece of similar lumber with drywall screws in it at 4,12 and 20" This spacing allows a floor every 8", three floors per column segment, with the column splices being mid-floor.

View attachment 18063

The flexible plastic then sits atop the screw "seats".
View attachment 18064

View attachment 18065

Here's the actual seated connections in the WTC:

The friction with the screw threads provides some stability, and the bending of the plastic past the screws simulates the failure of the seated connection. The huge advantage of this method of simulating seats is that nothing is broken, and so the model can be easily re-assembled. My first assembly attempt looking like this:

View attachment 18066

And my first drop result being this:



There are many obvious problems with this, but I hope to extend it to two floors, and possibly double width with some kind of "core". I will likely have to switch to 2x4s for the columns for stability.

I welcome discussion in this thread regarding the model, what it does or does not illustrate, and suggestions for improvement. But please try to keep any discussion around the model, and not drift off into other 9/11 related topics.

For a detailed overview of the structure of the towers, and the difficulty in modeling them even on a computer, I would recommend reading NIST NCSTAR 1-2 Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers. The linked version here is "unlocked" so you can copy and paste from it:

https://www.metabunk.org/files/NIST NCStar 1-2 101012_unlocked.pdf[/QUO

Good job with your model, Mick. NIST spent $20 million on their study and, as evidenced by the footnote (below) from their final report on WTC Towers 1 and 2, didn't care to venture into the behaviour of the building after "collapse became inevitable." I think you should apply for a job with them. Oh, BTW, I'm flattered that someone went to the trouble of assigning me a profile pic. It says a lot.

"The focus of the Investigation was on the sequence of events from the instant of aircraft impact to the initiation of collapse for each tower. For brevity in this report, this sequence is referred to as the "probable collapse sequence," although it includes little analysis of the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable."

This is the single most important and telling bit of text from this NIST report. Wow.