Creating A Physical Model of the Initiation of the collapse of the World Trade Center Twin Towers

econ41

Senior Member
good summary
how extensive the model is depends on how much imagination/intelligence the doubter has. So simpler models can model heat weakened columns will collapse. But is that really questioned?
Thank you. Yes it must meet the needs of the doubter. And that means any doubter across the range - we should attempt to meet the needs of all. And some will question heat weakening which is the #1 key feature of the collapse initiation stage. So - YES - we must at least incorporate heat weakening. How far to go is a separate question. The whole event is complex and I suggest that means take the explanation in steps. Dont assume all the details can be in one model.

The remainder of your post contains a lot of details which fall into three broad categories:
1) Details of method which we can address in further discussion of preliminary trials of methods and materials. Shown in green for further discussion;
2) Issues which push and extend the scope of the model beyond what is needed. Shown in orange - do we need to broaden the objective or scope??.; AND
3) Some issues which are outside the scope of a model of "initiation" >> they refer to "progression". Shown in RED - NOT "initiation stage". I'll colour code some examples:
[[........EDITED]]

I don't think a column 2D column grid is a problem... the floors can be drilled and the candle columns place in the shallow holes on both sides of the floors.

So you will want to place some super imposed live and dead load on each floor (same).
The columns should buckle from say 4 or 5 of these floor loads

I also believe that the floors need to be something that will fracture and not remain as solid plate under excessive load.
Why? we want to model both heat failed columns and floors that shatter as the crash down to the floor below.
[[.....EDITED - examples only shown]]

Perhaps use 4 thin acetate sheets on each floor so that the perimeter can contain the heat????

So - put simply - we need to agree the objective AND watch out for - take care to avoid - the endemic problems of "Objective Drift" or "Project Creep". But a lot of good ideas for consideration.
 
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Jeffrey Orling

Senior Member
Thank you. Yes it must meet the needs of the doubter. And that means any doubter across the range - we should attempt to meet the needs of all. And some will question heat weakening which is the #1 key feature of the collapse initiation stage. So - YES - we must at least incorporate heat weakening. How far to go is a separate question. The whole event is complex and I suggest that means take the explanation in steps. Dont assume all the details can be in one model.

The remainder of your post contains a lot of details which fall into three broad categories:
1) Details of method which we can address in further discussion of preliminary trials of methods and materials. Shown in green for further discussion;
2) Issues which push and extend the scope of the model beyond what is needed. Shown in orange - do we need to broaden the objective or scope??.; AND
3) Some issues which are outside the scope of a model of "initiation" >> they refer to "progression". Shown in RED - NOT "initiation stage". I'll colour code some examples:


So - put simply - we need to agree the objective AND watch out for - take care to avoid - the endemic problems of "Objective Drift" or "Project Creep". But a lot of good ideas for consideration.
I did a little research into matzos,toothpicks and candles and made the following drawing.

MATZOS CANDLE MODEL_page1.jpg
This is one floor level... I did not show the acetate strips or the "plane hole".

Matzos have perforations at about 1/4 oc to allow them to be easily broken!

One would have to run some preliminary experiments to see how much (uniform) super imposed live and dead load a sheet of matzos will support before breaking. Easy experiment - rest the matzos spanning between 2 pieces of wood... slowly pour on sand... until the matzos cracks .

In the model probably use about 1/4 of the failure weight as the super imposed load for each floor. It does not have to be sand... just scattered object which add up to 1/4 of the failure weight.

start with a 24x24 sheet of plywood and draw the CL / grid for all the columns. Melt some wax... Use 1/4" Ø candles x +/-5" tall ... cut square at the wick end.

Thru dill each candle at 2" from its end for the toothpick

Cut and insert toothpicks into each candle

Dip the candles into melted wax and the stick it in place on the grid with the tooth pick in the orientation as shown in the drawing.

Break the matzos to the sizes in the drawing and place on the toothpicks

Cut acetate into 4 7/8" strips to rest on the tooth picks.

Add the superimposed live load on top of the matzos

Repeat for floor 2... dip the candles and stick them on the candle ends - the end will be 3" above the matzos... let the wax harden and place the next floor of matzos and add the live load...

repeat for floor 3, 4, 5 and so on... until you have "enough floors"

Leave a section of the acetate in the center of a long span side open (plane hole) on the second level. You can also remove 2 facade candles perhaps as well.

Set up video camera

Use heat gun to blow hot air into the plane hole. There should be enough openings for the heat air to circulate and escape / leak out.

Candles should at some point get weak and

either the tooth picks will fall out
they loose strength and buckle
matzos may also loose strength and crack
Matzos will fall and matzos floor will now be supported 2 superimposed live loads and another layer of cracked matzos

As more heat fills the model... the next level up with collapse and then the level above that and finally the lower matzos floor will be over loaded and it too will collapse.

NOTE... to demonstrate the runaway collapse will require that the facade plane hole be at 4 or 5 levels up and the model be at least 9 or 10 levels high.

OAL the model would be 18" x 18" x 50" tall - ten level
 

econ41

Senior Member
.......Repeat for floor 2... dip the candles and stick them on the candle ends - the end will be 3" above the matzos... let the wax harden and place the next floor of matzos and add the live load...

repeat for floor 3, 4, 5 and so on... until you have "enough floors"

Leave a section of the acetate in the center of a long span side open (plane hole) on the second level. You can also remove 2 facade candles perhaps as well.
.......

NOTE... to demonstrate the runaway collapse will require that the facade plane hole be at 4 or 5 levels up and the model be at least 9 or 10 levels high.

OAL the model would be 18" x 18" x 50" tall - ten level
An impressive lot of details Jeffrey...

BUT the objective is to model the "initiation stage". Not the progression stage. So not "...to demonstrate the runaway collapse...".
 

Jeffrey Orling

Senior Member
An impressive lot of details Jeffrey...

BUT the objective is to model the "initiation stage". Not the progression stage. So not "...to demonstrate the runaway collapse...".
understood...
But... in the twins there are 3 story columns... so when the columns fails if it does so because of inadequate capacity... this can only happen by:
a - adding NEW loads to the column via super imposed loads​
b - lower the column's axial capacity because it is heated​
c - remove bracing increasing slenderness ratio and induce Euler buckling​
d- remove some of the cross sectional area​
e - reduce the bearing area (column to column connection misalignment)​
or a combination of the above.

(a) occurs means "new material" must be added as super imposed live load. Essentially this means that loads from the floor above lands on the uppermost of the 3 floors the columns supports. This sounds like a failed floor crashes down in part or in whole. That needs to be explained/modeled.

(b) comes from the raging fires.

(c) sounds like failure of the connection or destruction of the trusses or beams framed into the column. Connection failure could be a heat caused failure... or an over load caused failure... or a bolt shear / withdrawal failure

(d) would require mechanical lower impact to web and or flange

The only cause which does NOT involve a "mechanical cause) are (b) - heat
and cause (e) heated beams expanding and displacing the connection. Perhaps (c) could be a heat cause of the beam fails from heat cause bucking

So heat could cause 3 (b, c & e) of the 5 failure modes. (a) and (d) require a mechanical cause

The model I suggested would fail from heat causing loss of capacity and buckling. It might also cause the beam seats to fail perhaps.

A heat cause Euler bucking would need beams, floors and or connections to fail from heat.

Mechanism (a) involves mass from upper floors over loading a lower one... which is how the ROOSD works. But this becomes a which came first? the chicken or the egg conundrum. So "adding" load from above is not an initiation mode.... It is a progression mode.

But this DOES get to the discussion of how did heat cause the tops to "drop". I suggest that the heat's main action was on beams which "destroyed" the integrity of the structure and its capacity to keep the load paths as they were designed to be. And "column failure" was the "result". Load redistribution likely cause column failures leading to more load redistribution and more column failures until capacity was driven below demand.

It should be noted that 2wtc did not have the concentrated load of an antenna. It's failure seems to be growing loss of capacity on the SE quadrant of the core leading to the mostly intact top block collapsing and tilting to the SE.

So 2wtc's collapse may give a clue to the dropping of the top block of 1wtc... Was it loss of axial capacity from a growing almost symmetrical load redistribution? If so... this sounds like lateral structures played a key roll as they are the mechanism for load redistribution. Drop was from loss of capacity,
 

Jeffrey Orling

Senior Member
Back to the matzos model.

It may make sense to change the model's dimensions so that the core's floor are 2 full width size matzos. I have revised the drawing to make fabrication easier: B, C, & D floor matzos are easily cut / broken along manufacturer's perforations. A is full size.

uses:
matzos - full sheets (7"x 7") and partial sheets broken at perforations
1/4" and 3/8" candles
full length and cut toothpicks
5" wide strips acetate

candle lengths to be 5"

requires solid plywood base... rule out column grid.
drill candles at 2" from bottom

Perform load test with single sheet of matzos... determine breaking load. Load model floors uniformly with 1/3 breaking load
loads can be both combustible and non combustible materials

Model should be minimum 6 levels high
Removed columns, cut acetate on lower floor only
apply heat through hole

NOTE possibly remove 2 center core candles opposite "hole"

MATZOS MODEL r2_page1.jpg
 

econ41

Senior Member
understood...
You say that you understand the goal but... Sorry Jeffrey, but in your lengthy explanation you are circling with unnecessary speculations. Here's why:
RESTATING THE GOAL
1) The objective is to model the initiation stage for Twin Towers collapse(s);
2) As a means of explaining that stage to lay persons or truthers who need visual models to help their comprehension; AND
3) In Mick West's words which I fully support "....the purpose of a physical model is illustrative, not investigative.."

DEFINING THE SCOPE
The initiation stage involved initial damage from aircraft impact which created a starting point for accumulation of fire caused damage which allowed the "Top Block" to start moving downwards. So the challenge is to model what caused the Top Block to move downwards. And we have that mechanism already defined by two fully compatible hypotheses viz the NIST explanation and the one which I propose which is less specific on one factor which does not affect the argumentation we need.

OUTLINE OF THE MECHANISM
The "initiation stage" caused the Top Block to start moving downwards because columns lost their capacity to carry their designed loads in axial compression. And the failures of columns took the form of a cascading sequence failure triggered by heat weakening and driven by load redistribution. That is my description and it is totaly compatible with the NIST hypothesis. (and many others.)

NOTE the vertical vectors are what matters. Loss of vertical load carrying capacity. The NIST explanation asserts that a horizontal vector - joist sagging causing inward bowing - was the triggering cause. BUT that detail does not affect what we need to do for a simple demonstration model. (Unless we decide to model the NIST explanation which I do not advise - AT THIS STAGE) The net result of the inwards bowing was >> loss of load capacity in axial compression. So the joist sag > inward bowing DETAIL does NOT change the net cause of Top Block falling viz loss of carrying capacity in axial compression. Similarly your speculations about beams and horizontal vectors - whether you are right ot not - do NOT change the key factor >> loss of load capacity in axial compression. Please read that carefully because I can explain it more fully if you or anyone else is not clear. For the level of modelling we are discussing the vertical loads are the ones that we need to deal with.

So - let's look at your five main factors:
But... in the twins there are 3 story columns... so when the columns fails if it does so because of inadequate capacity... this can only happen by:
a - adding NEW loads to the column via super imposed loads << NOT relevant to our scenario
b - lower the column's axial capacity because it is heated <<The main feature of the PRIMARY mechanism we are trying to model
c - remove bracing increasing slenderness ratio and induce Euler buckling << No need to detail because it has NET result of lowering vertical load carrying capacity
d- remove some of the cross sectional area << NOT relevant to our scenario
e - reduce the bearing area (column to column connection misalignment) << NOT relevant to our scenario
or a combination of the above. << "Yes - but we only need to consider "b" because it subsumes "c" and the others are not relevant.
And again with respect I suggest your speculations are either NOT advancing discusion OR - with some irony - jumping too far ahead or too deep into complexities.

I'll omit detailed comments on some of your remaining points
But this DOES get to the discussion of how did heat cause the tops to "drop". << Yes I suggest that the heat's main action was on beams which "destroyed" the integrity of the structure and its capacity to keep the load paths as they were designed to be. << Possibly contributory but we need to model the vertical vectors And "column failure" was the "result". << That is the key point Load redistribution likely cause column failures leading to more load redistribution and more column failures until capacity was driven below demand. << Agreed tho it probably restates what should be the starting point of discusson. It has been said a number of times.

It should be noted that 2wtc did not have the concentrated load of an antenna. It's failure seems to be growing loss of capacity on the SE quadrant of the core leading to the mostly intact top block collapsing and tilting to the SE. << Probable irrelevant to our modelling challenge - at least at the first stage.

So 2wtc's collapse may give a clue to the dropping of the top block of 1wtc...<<Maybe Was it loss of axial capacity from a growing almost symmetrical load redistribution? << Doubtful If so... this sounds like lateral structures played a key roll as they are the mechanism for load redistribution. << They are NOT the key contributor to load re-distribution. Secondary contributor at best and not relevant to our simple model. Drop was from loss of capacity, << Yes - that was the starting point of discussion.
 

Jeffrey Orling

Senior Member
You say that you understand the goal but... Sorry Jeffrey, but in your lengthy explanation you are circling with unnecessary speculations. Here's why:
RESTATING THE GOAL
1) The objective is to model the initiation stage for Twin Towers collapse(s);
2) As a means of explaining that stage to lay persons or truthers who need visual models to help their comprehension; AND
3) In Mick West's words which I fully support "....the purpose of a physical model is illustrative, not investigative.."

DEFINING THE SCOPE
The initiation stage involved initial damage from aircraft impact which created a starting point for accumulation of fire caused damage which allowed the "Top Block" to start moving downwards. So the challenge is to model what caused the Top Block to move downwards. And we have that mechanism already defined by two fully compatible hypotheses viz the NIST explanation and the one which I propose which is less specific on one factor which does not affect the argumentation we need.

OUTLINE OF THE MECHANISM
The "initiation stage" caused the Top Block to start moving downwards because columns lost their capacity to carry their designed loads in axial compression. And the failures of columns took the form of a cascading sequence failure triggered by heat weakening and driven by load redistribution. That is my description and it is totaly compatible with the NIST hypothesis. (and many others.)

NOTE the vertical vectors are what matters. Loss of vertical load carrying capacity. The NIST explanation asserts that a horizontal vector - joist sagging causing inward bowing - was the triggering cause. BUT that detail does not affect what we need to do for a simple demonstration model. (Unless we decide to model the NIST explanation which I do not advise - AT THIS STAGE) The net result of the inwards bowing was >> loss of load capacity in axial compression. So the joist sag > inward bowing DETAIL does NOT change the net cause of Top Block falling viz loss of carrying capacity in axial compression. Similarly your speculations about beams and horizontal vectors - whether you are right ot not - do NOT change the key factor >> loss of load capacity in axial compression. Please read that carefully because I can explain it more fully if you or anyone else is not clear. For the level of modelling we are discussing the vertical loads are the ones that we need to deal with.

So - let's look at your five main factors:

And again with respect I suggest your speculations are either NOT advancing discusion OR - with some irony - jumping too far ahead or too deep into complexities.

I'll omit detailed comments on some of your remaining points
I don't disagree with your post. The model which I "re-designed" demonstrates loss of capacity from heat softening / weakening the candle columns.

But I am stuck on the fact that heat was not the sole cause of loss of axial capacity of the columns.

YES heat likely was the primary cause of for lack of a better word... distortion of the frame.

YES the initial plane damage DID begin a load re-distribution process

I wonder if removing some of the inside the core matzos would more accurately represent the fact that the core contained many elevator and mechanical large shafts... not floor which facilitated heat to move to other floors. The model has columns of a single, not 3 story heights which is different from real world.

Do you think a single floor collapse from heat is all that is needed to demonstrate initiation?

Multiple floors with the heat (and the hole) closer to the middle height of the model should / could demonstrate how the tower did not resist the initial floor collapse... which really was all the floors above the initial failure floor.... dropping as a block. Above the middle (hole location) would be the "top block", Below it would be the stone cold intact tower below.

Side view of the model - 7 stories...
MATZOS MODEL SIDE VIEW r2_page1.jpg
Plane damaged floor - break edge of A to create A'

MATZOS MODEL PLANE HOLE FLR r2_page1.jpg
 
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econ41

Senior Member
I don't disagree with your post.

But I am stuck on the fact that heat was not the sole cause of loss of axial capacity of the columns.
That sure looks like disagreement to me. I've identified two sub-stages of "initiation" (1) viz initial aircraft impact damage FOLLOWED by (2) the stage we are discussing where heat caused accumulating damage resulting in "Top Block" moving downwards AKA "falling". So if heat was NOT the sole cause of loss of axial capacity AFTER the aircraft impact what was? Explosive CD?? Thermite??
YES heat likely was the primary cause of for lack of a better word... distortion of the frame.
It was the primary cause. Why the hesitation in moving forward? And what do you suggest was a secondary cause of failure? And why "distortion of the frame" rather than FAILURE?
YES the initial plane damage DID begin a load re-distribution process
AND heat continued it. And those heat effects accumulated to cause "Top Block" moving downwards AKA the completion of the "initiation stage".

OK we are circling the same points without even progressing agreement as to what we are seeking to demonstrate. Mick West and I have identified simple models including both linear and essentially 2D versions. You propose a much more complex model which goes beyond the "initiation stage" It looks good but we haven't even started to debate whether or not it would be practical. Or whether a model which goes further than initiation could be a suitable form of model to demonstrate the initiation stage.

So I will take a back seat on further discussion. I may consider building a working model of my simplified "line of columns" model using candles which seem to be the best material for mimicking the key aspect of heat triggered sequenced cascade failure of columns driven by load re-distribution. Buy some candles. Dig out my workshop heating tool which looks suspiciously like a hair drier. (I have another one for shrinking heat shrink tubing - it is higher temperature but it is not as big as the hair drier.)
 
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Jeffrey Orling

Senior Member
My last comment on heat in the initiation.

Econ41 seems to be assigning one effect of the heat... weakening the columns to below service loads which caused them to buckle.

I suggested other impacts of heat on the structure:

expanding beams which led to displacement, joint shearing, weakening bracing below its ability to support the floor loads
destroying bearing angles
dropping floors effectively makes the columns less stable because of increase in slenderness ratio.

Heat did MORE than weaken columns.

+++++

The stages of the collapse "transitioned" from one to the next.
 

econ41

Senior Member
My last comment on heat in the initiation.

Econ41 seems to be assigning one effect of the heat... weakening the columns to below service loads which caused them to buckle.
CORRECT except it is not "seems to be assigning". I've several times made my argument explicilty clear.

I'll give it ONE more try.
We are discussing - explaining - the initiation stage of Twin Towers collapses;
... with a view to modeling as much as we need to model of THAT stage
....to assist explaining to truthers and laypersons who need physical models to assist their comprehension.

The net result of the "initiation stage" was that the "Top Block" "fell downwards"
.... because the columns lost the capacity to resist vertical downwards applied loads;

READ CAREFULLY - because that is true independent of whatever caused the columns to lose vertical axial compressive strength. << now read it again.
So whatever horizontal or other vectors contributed to the loss of column compressive strength the NET result was that they lost compressive strength. Whatever helped that loss. THEREFORE there is no need for any of us to confuse the debate by speculating about the details of other forces which either contributed to the NET result - loss of axial compressive strength OR to other aspects which are irrelevant to the current discussion. And SPECIFICALLY it is a waste of effort identifying details which are irrelevant and which we cannot quantify THEN using them as the excuse to claim we cannot complete analysis when we can.
I suggested other impacts of heat on the structure:
Yes - several times. Just as I have several times attempted to put the focus of reasoned argument back on the key relevant factor which is loss of column vertical compressive strength. By all means feel free to prove me wrong with my argument that failure of columns to carry vertical loads is the key factor in explaining the "drop" of Top Block which completed the initiation stage.
Go for it. PROVE me WRONG!
Heat did MORE than weaken columns.
Maybe. BUT name ONE heat effect that is relevant to the argument I make - ONE heat effect that changes the key factor.

In fact - to avoid further obfuscation ... AND prove that it is relevant.

The stages of the collapse "transitioned" from one to the next.
Please stop. YES we know that it was the main starting premise. The stages are "initiation". "transition" and "progression". And they overlap rather than "transition" from one to the next by clean breaks. But details aside the fact of stages was the starting premise.
 
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Jeffrey Orling

Senior Member
I would say that it's something which does not need demonstration.... when something loses the support which keeps is "standing" it will collapse. Even truthers accept this.

What they seem hung up on (guessing here) is that:
a) the towers were too strong to have support drop below service loads with only bombs destroying columns... as is done in commercial CD (no loads were added)​
b) the weaker / lighter top cannot destroy the stronger/heavier bottom​

ROOSD is a solid explanation for a top down collapse based on the simple principal that a component fails from being over loaded. It was a cold process.

The "initiation" was about how column capacity was made incapable of supporting the service loads which had not changed.

Key principals are:
1- When somehow fewer and fewer columns are doing the supporting of the service loads they can become overloaded and collapse

2 - When a column fails its loads are transferred laterally to other columns and this may lead to the transferred to columns being overloaded and they fail

Heat was the main energy input during the post plane strike phase.
The plane damage likely cause load redistribution

There has been discussion about a does a single column failure in a high rise lead to total building collapse. It should not if the collapse is local and does not migrate or translate laterally through the structure. So in 7wtc we believe that the failure of column 79 kicked off a rapid series of failures in other columns which led to too few columns left to support the service loads. The rapid failure were the result of lateral transfer of loads quickly leaving too little capacity. The argument was that the failure of col 79 was a heat cause. The collapse of 7wtc was a runaway load redistribution leading to buckling of columns throughout the footprint. That buckling was NOT directly heat caused.

So as no one doubts that a too weak column will fail... the challenge may be to show what made so many columns fail causing the all floors above to collapse. THAT would be several mechanisms... not simple heat. In fact in the 7wtc example the heat was localized in the NE sector of the building... yet all column ultimately failed.

So... initiation was a heat driven/started process to a locally compromised structure which led to loss of capacity by load transfer to most of the structure which then collapsed in a footprint wide failure from loss of capacity.

So no... heat alone cannot be isolated as the sole cause of all axial structure failures at and above above the plane strike zones of the twin towers.

My sense is what the doubters don't comprehend is the runaway/progressive load transfer failure process involving the entire footprint.

You can have a 1D model where a beam is supported by a row of columns and show that as columns are "removed" or heat weakened to the point of buckling... the beam will collapse. This will not satisfy doubters.
 
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econ41

Senior Member
Sorry @Jeffrey Orling - but there is no point in me continuing to post reasoned on-topic explanations in face of your unwillingness to progress discussion of the OP topic which you originally suggested.

Your latest example. First you correctly summarise the challenge as:
the challenge may be to show what made so many columns fail causing the all floors above to collapse. THAT would be several mechanisms... .......

So... initiation was a heat driven/started process to a locally compromised structure which led to loss of capacity by load transfer to most of the structure which then collapsed in a footprint wide failure from loss of capacity.
So you agree the challenge. Which incidentally I have put to you several times.

Then you deny the primary role of "heat" AND deny the role of "initiation was a heat driven/started process" which you just affirmed in your previous sentence:

... not simple heat. ......

So no... heat alone cannot be isolated as the sole cause of all axial structure failures at and above above the plane strike zones of the twin towers.
Well make your mind up. I have now several times explained why heat is the key process which has the NET result of reducing axial load carrying capacity. If you want to insist that heat wasn't the cause please identify what other driving process was. Are you suggesting use of Explosives? Incendiaries?

And please stop the constant distraction to irrelevancies such as this:
In fact in the 7wtc example the heat was localized in the NE sector of the building... yet all column ultimately failed.
Well we are not discussing WTC7 BUT you go very close to explicitly agreeing my main point for the Twin Towers collapses. viz "localized" origin of heat led to "all column ultimately failed". Yes that is true for WTC7 and it was also true for the Twin Towers but you persist in having a bet both ways. Make your mind up please.

Then once again you restate the challenge:
My sense is what the doubters don't comprehend is the runaway/progressive load transfer failure process involving the entire footprint.
Yes. That is the reason we are supposed to be discussing and progressing discussion of building models as a means of explaining. You are re-stating what was the starting premise for the thread. Which YOU defined!!!

You can have a 1D model where a beam is supported by a row of columns and show that as columns are "removed" or heat weakened to the point of buckling... the beam will collapse. This will not satisfy doubters.
More circling debate. "We" (or more likely "I") have already identified that some doubters will need more than others. AND identified the options for 1D (linear), 2D (fuller floor plan) and 3D versions. Including the problems with 3D models which drift into the "progression" stage when the topic is "initiation".

Bottom line.
Sorry Jeffrey but this is at least the fourth time that I have attempted to break your circling the issues and suggested staying on focus, on topic and moving discsussion forward. I can see no point in continuing. I'm out of here.
 
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Jeffrey Orling

Senior Member
You have reduced the complexity to a simple... heat weakened columns... they failed.

I don't accept that.

++++

How many column's capacity dropped below service load by heating? 50% more?

How many columns saw loads exceeding their capacity from acquiring more loading from "transfer" from other failed columns?

Did any "cold columns" fail from loss of bracing?

Did any columns fail from loss of bearing?

Is it your belief that only heat led to column failure?
 
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econ41

Senior Member
You have reduced the complexity to a simple... heat weakened columns... they failed.

I don't accept that.
OK - we are circling debate pursuing the "heat triggered" explanation.

Remember that way back I identified the two "framing options" where the NIST hypothesis is a subset of the total range of possibilities. We had two possible paths to pursue and we are not getting anywhere trying to progress the "heat driven" path we chose.

So why not try the other path? Frame the argument by accepting NIST's version which has joist sag induced inwards bowing of perimeter columns as the trigger?

Put the candles to one side - in fact forget heat (I'll explain why later###). Do it "cold". Artificially "pull in" a "perimeter column" or row of columns. It depends whether we go for a linear 1D model or a fuller floor plan 2D model. And - yes - it is implicitly 3D because we need 2 or 3 storeys for the Euler buckling increased effective length of perimeter columns.

Flesh out Micks more recent model - spaghetti columns in a fuller array - more columns. We could possibly model the "joist sag pull in" tho I doubt it would be practical to do it by heating without setting the whole model on fire.

Let's "change horses" and go for it. Nothing like a deliberate change of "paradigm" when debate is locked - stuck in a rut.
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### Why "forget heat"? If we go for a "cold initiation" with the NIST explanation of perimeter inward bowing as the trigger. That implies a hard to define balance between heat weakening if any and the loss of axial capacity resulting from column misalignment. The "pDELTA" aspect. My "Engineer's Gut Feeling" says misalignment was primary and heat weakening secondary if of any consequence. BUT we will never get the right balance in a model made in a home workshop. So focus on the inward bowing misalignment. The subtleties if we try to balance the two would only add confusion for a lay person target audience. ( And that is if we could even agree among ourselves. :rolleyes:) Plus I think a pure melting candles heat driven model is more persuasively dramatic BUT it does look "less like" the real thing....

.. back to the drawing board.
 
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Jeffrey Orling

Senior Member
OK - we are circling debate pursuing the "heat triggered" explanation.

Remember that way back I identified the two "framing options" where the NIST hypothesis is a subset of the total range of possibilties. We had two possible paths to pursue and we are not progressing the "heat driven" path we chose.

So why try the other path? Frame the argument by accepting NIST's version which has joist sag induced inwards bowing of perimeter columns as the trigger?

Put the candles to one side - in fact forget heat (I'll explain why later###). Do it "cold". Artificially "pull in" a "perimeter column" or row of columns. It depends whether we go for a linear 1D model or a fuller floor plan 2D model. And - yes - it is implicitly 3D because we need 2 or 3 storeys for the Euler buckling increased effective length of perimeter columns.

Flesh out Micks more recent model - spaghetti columns in a fuller array - more columns. We could possibly model the "joist sag pull in" tho I doubt it would be practical to do it by heating without setting the whole model on fire.

Let's "change horses" and go for it. Nothing like a deliberate change of "paradigm" when debate is locked - stuck in a rut.
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### Why "forget heat"? If we go for a "cold intition" with the NIST explanation of perimeter inward bowing as the trigger implies a hard to define balance between heat weakening if any and the loss of axial capacity resulting from column misalignment. The "pDELTA" aspect. Gut feelng says misalignment was primary and heat weakening secondary if of any consequence. BUT we will never get the right balance in a model made in a home workshop. So focus on the inward bowing misalignment. The subtleties would only add confusion for a lay person target audience. And I think a pure melting candles heat driven model is more persuasively dramatic BUT it does look "less like" the real thing....

.. back to the drawing board.
This is why I wrote about the complexity of causes... or perhaps... it's heat... but heat is doing stuff to different parts of the structure.... which lead to loss of axial capacity. NIST has "hot" floor trusses bucking the facade... Econ has "hot" columns losing capacity and buckling... core and or facade.

I dismissed NIST's idea because it seemed to me that you would need columns on all 4 perimeters to be pulled in a buckle... short and long span... clearly not responding the same to heat... Really the heated trusses pulling in likely occurred but it was a local phenomena and methinks there would have been load redistribution in the facade rather than global buckling and failure.

I know you don't want to discuss revisit all this stuff. Suffice it to say it seemed to me... and to others that the initiation was core led... but even how that involved the entire perimeter was hard to explain.

What we CAN see is that the initiation occurred at the plane strike zone.... we can't see what was happening inside... aside from some flames and lots of smoke.

I see the initiation as a process which manifest over time... driven by heat and mechanical damage the heat was doing. So if a column failed... because it was pushed or pulled out of axial alignment.... the cause may very well be heat.... but the column did not "go soft" from heat... it buckled for other technical reason. It DOES make sense that there was some sort of load re distribution in play leading to fewer and fewer columns carrying all the loads until the remaining columns simply were overwhelmed... no more capacity.
For sure we can agree that load redistribution is a cold, not a hot process.

Enough! I am repeating myself and we are not getting closer to a credible motel of the collapse. Simplifying in my mind doesn't cut it. And I don't know how to model the complexity.

Even my 3D multi story model seems to rely on heat softened collapsing columns... though it does show some of the progression... kinda.

And of course you can't model what you don't understand. And you can't convince someone unless it resembles the real world event.
 

econ41

Senior Member
@Jeffrey Orling - I'm going to hate myself for my patience and persistence BUT
This is why I wrote about the complexity of causes... or perhaps... it's heat... but heat is doing stuff to different parts of the structure.... which lead to loss of axial capacity. NIST has "hot" floor trusses bucking the facade... Econ has "hot" columns losing capacity and buckling... core and or facade.
Once again you agree my main point of argument - "...heat is doing stuff .... which lead to loss of axial capacity"
And BOTH what NIST explains and what I explain are correct. They are NOT alternate total mutually exclusive explanations they are BOTH true parts of the same complex picture
Really the heated trusses pulling in likely occurred but it was a local phenomena and methinks there would have been load redistribution in the facade rather than global buckling and failure. << Not "likely occurred" it is OBSERVED recorded FACT. And again the two points you raise "load redistribution" and "global buckling and failure" are NOT mutually exclusive alternates they are BOTH part of the same complex scenario.

I know you don't want to discuss revisit all this stuff. Suffice it to say it seemed to me... and to others that the initiation was core led... but even how that involved the entire perimeter was hard to explain. << My hints were not very subtle. ;) If you want to introduce "core led" then post your arguments. NOTE however - my explanation is global and does not need to differentiate what "led" at this stage - and remember our aim is a legitimate generic model for lay persons. I know it is moderately hard to explain. But I have been doing it for years.

What we CAN see is that the initiation occurred at the plane strike zone..<< Not in debate.. we can't see what was happening inside..<< Some of us can visualise easier than others. Remember - that is why some people need models - the very reason we are having this discussion. . aside from some flames and lots of smoke.

For sure we can agree that load redistribution is a cold, not a hot process. << Careful - it is neither per se. We can make simplifying assumptions provided we remain aware of both the assumptions and their limitations.

Enough! I am repeating myself and we are not getting closer to a credible motel of the collapse. Simplifying in my mind doesn't cut it. And I don't know how to model the complexity. << You are too pessimistic. We actually have several models. Two physical models by Mick with their own limitations BUT they exist and are persuasive because they exist in physical 3D reality. We have your paper drawings of a 3D evolving model. And we have four of mine even less well defined than any because so far I've only posted ONE simplified 2D diagram. And I am visualising several additional 1D, 2D, 3D and 4D (3D dynamic) models. Because for me visualising 4D is a damn sight easier than either drawing or writing words. Which takes us right back to square one. Some of us are better visualisers than others. Anyone want a side line discussion of NLP???
Then this final bit of motherhood:
And of course you can't model what you don't understand.
Despite our efforts to design models without heeding my cautions about FIRST agreeing what we are trying to model....
...and why. ;) truthers aren't the only ones who try to start debate in the middle or even at the end.

And I will deliberately NOT go anywhere near this "can of worms":
And you can't convince someone unless it resembles the real world event.
... unless your name is Hulsey and your task is to persuade truthers who are already CT obsessed and indoctrinated >> BUT that is a whole different topic. :mad:
 
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econ41

Senior Member
OK @Jeffrey Orling - credit where credit is due - THIS is a good summary that we should both agree with:
I see the initiation as a process which manifest over time... driven by heat and mechanical damage the heat was doing. So if a column failed... because it was pushed or pulled out of axial alignment.... the cause may very well be heat.... but the column did not "go soft" from heat... it buckled for other technical reason. It DOES make sense that there was some sort of load re distribution in play leading to fewer and fewer columns carrying all the loads until the remaining columns simply were overwhelmed... no more capacity.

NOW the question is: "How do we model it?" because reality was a combination of two "triggers" - perimeter inward bowing OR heat weakening - and both were probably involved which ever "led" for the specific tower.

BUT our goal is to build a model that helps laypersons or truthers understand. And I doubt that we can combine both in one model PLUS I think the combination would confuse the target audience. (I THINK - gut feeling from me the trainer. I cannot prove it. :rolleyes: )

So I think (?? more opinion!!) That the best compromise could be two models. Whether or not any of us are motivated to build one or both of them. Mick's 3D spaghetti model #2 is a reasonable basis for demonstrating perimeter inward bowing as a trigger. My candles model whether 1D or 2D version is good for the heat weakening model. And your 3D details accurate plan COULD be usefull depending on how far we go with the detailed realism aspect. But don't get your hopes up. It is well within my workshop skills to build the candles heat weakening model but I'm not motivated to do so.... At this stage.
 
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Jeffrey Orling

Senior Member
The whole "model program" probably needs to reach the 4D stage... which for doubters who made the challenge, is the mostly likely way to convince them that bombs were not necessary would be a 4D model This means the model should not have some of the columns away... or pouring material to add load.

The 4D model needs to simulate a multi-story failure... showing heat at one of the mid level floors leads to the failure of columns on THAT level which leads to the levels above (top block) dropping and their mass then destroys the "cold" levels below.

I realize that this would include a transition from initiation to beginning of ROOSD. I suspect that is necessary because as mentioned previously... the entire collapse process with whatever mechanisms were in play during the collapse and whatever names are given to the time periods... collapse was a process.... It was one from static to dynamic... from standing to collapsed.

I am guessing that the 4D model which will collapse from "applied heat" will experience the mechanical causes... such as load redistribution because heat caused local failure has to honor the laws of physics and engineering. So were you to melt one leg of a 4 legged table and measure the forces at the floor of the remaining 3... it would be the same as the 4 legged table...each leg now carrying 1/3 of the load instead of 1/4 of the load... loads were transferred.

The 4D model can simulate mechanical failures driven by heat and it can fail the entire structure in a credible way. But it would take a bit of experimentation.
 
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econ41

Senior Member
Remember the objective. Build a model which explains Twin Towers "initiation stage" to those truthers or laypersons who need physical models to help their undestanding.

It is NOT "Build as complex a model as we can conceive to prove how clever we are or how good we are at building models."
 

Jeffrey Orling

Senior Member
Remember the objective. Build a model which explains Twin Towers "initiation stage" to those truthers or laypersons who need physical models to help their undestanding.

It is NOT "Build as complex a model as we can conceive to prove how clever we are or how good we are at building models."
I am not advocating complexity.... I am advocating a model which appears to show to doubters that heat can cause the tower to collapse (not burn up).
 
I was thinking that the candles deformability might be a problem. I just does not scale well.

How about spaghetti?

2021-04-03_14-51-53.jpg

I picture a bottom 1" plate of wood with spaghetti-sized holes in a pattern (perhaps with core and walls). The holes go through the plate so broken pieces can be pushed out when inserting new ones. They should per drilled with a drill-press to get them perfectly perpendicular.

The plate is clamped on a flat surface, which acts and the base of the columns. Equal length columns are inserted. A top plate is added, consisting of a piece of wood with some foam tape on the bottom to even out minor variations in length. Weight is carefully added to the top plate until it is at 1.2x its static load capacity.

Then columns are removed. This can be done initially with some kind of analog to the airplane impact. Perhaps shooting the columns with a salt gun. Perhasp firing in some light object with a rubber band. Or you may have to just clip them.

Then gradual removal. There three options here:
  1. Fire. Which might be difficult to isolate. But a small torch could be used to burn away some columns.
  2. Water. This might be a better way of simulating the effects of fire. Water causes sphagetti to lose its stiffness gradually, which should cause gradual load transfer up to sudden failure.
  3. Manual removal - by clipping.
This seems promising, in my head.
Such a model of the weight of the floors that the columns can support using pasta, wooden blocks and weights is shown in this documentary starting at 45:52
Source: https://www.youtube.com/watch?v=DgwlFY-4Txc


Given how heating pasta without water just makes it more burnt, crisp and brittle instead of soft, it's possibly that exposing the pasta to steam from nearby heated water could have the effect of softening it over time, similar to how steel heats up and becomes soft with exposure to the heat from fires.

To simulate the steam only affecting the upper floors, there could possibly be an elevated platform with a pot of boiling water just a meter or so from the level of the upper floors, with a fan blowing the steam into the upper levels.

This would model how not only the impacted floors, but the floors above were heated, and would also be realistic because while the steam would be heated above ambient air temperature, the air closest to the boiling water would be expected to be hottest, similar to how the air closest to fires on the impact floors is hottest, but the smoky upper floors are still much warmer than the surrounding air at that level. It would also have some of the heat diffusing below the impact floor level, similar to how there was still heat and smoke reported a few floors below the impact zone.

Unlike the more simple model shown in the documentary, I would think the model would have to be taller, where there would have to be more wooden blocks representing a significant number of floors above and below where the initial floor collapse occurs (represented by removal of the wooden slabs), and with there being also much more strands of pasta to model the the rigid, tightly spaced steel exterior perimeter and rectangular interior of core columns. To accomodate the space for core columns could potentially mean making rectangular holes in the center of the wooden blocks before they are affixed at each level, or it could just mean that before attaching the next wooden block, the core columns from the lower wooden block would have to be attached at the center of the block first.

The first approach with the core columns would mean they are very long and more prone to bending even before heating, while the second approach would mean the core columns are shorter and more stiff prior to bending from heating.

this:

"Conclusions This paper examined the effects of fires on the behavior of multi-story steel-framed buildings. It can be concluded that, even in the context of the structural fire engineering approach of modern design codes, predictions of behavior based on furnace tests or numerical modeling of isolated members are unreliable. The behavior of the members within a continuous, compartmented structure is very different from the behavior of isolated members. Structural continuity, restraint to thermal expansion provided by the adjacent members, the beam-to-column joints, and the tensile membrane action of the composite slab have demonstrated a significant positive influence on the bevahior of the entire structure in the event of a fire. Data from the Cardington fire tests and the subsequent experimental and analytical studies provide fundamental information that is very important for researchers studying the performance of steel-framed buildings in a fire for many years to come so as to develop new design approaches that take into account the interaction between structural members in a fire. The developments that have already taken place in the past few years have been very significant in understanding the reality of structural behavior in a fire, which will undoubtedly lead to the emergence of new rational fire engineering design methods that may allow us to construct safer, more effective, and more efficient fire-resistant buildings in the future."

Plane destroyed integrity ie beam restraint... which let the heated beams expand and led to "expanding" local collapse.... which led to dynamic loading from collapsing floor sections.... and there you have it.
There has been an update to the Cardington fire tests recently, where the modeled fire is more similar to the type of fire that affected the towers, a traveling fire, instead of a flash over
First paper
Second paper

Traveling fires are arguably less conventional than traditional fires, as the fires are simulataneously ingnited over multiple floors at once and are focused on a specific area of a floor before traveling to other areas, much like the initial fires in the trade centers started in one corner and then burned out and moved to other areas.

It also underscores how the 9/11 attacks were unprecedented in that the traditional way of undermining buildings through isolated explosions from bombs (with the explosions only causing localized damage and failures and fires that could still be put out by sprinklers) was not attempted, instead the planes were used as battering rams, bombs and incendiaries all in one that covered wide areas of floor space and cut off all standpipes to sprinkler systems that could fight the fires.

As the recent documentary "Rise and Fall: The World Trade Center" mentioned, there was only one main standpipe to the sprinkler system in the towers, and those pipes were severed during the initial plane impacts.
 
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