The 9/11 Forum

I agree with Achimspok the the 5,600 CCs would be the natural pivot object in a rotation to the south.

But the north wall would have to become longer for such a pivot point to develop.

ATTENTION:
not to mix up WTC1 and WTC2.

WTC1 clearly rotated around an axis across the north face and I absolutely agree with MT-
WTC2 rotated in a more difficult manner - imo probably hinged in two points at the 500CC row like visualized in a Gif some posts above.

MT, please notice that also the rotoscoping femr did referring to WTC2. Since we all agreed about the tilt (hinge, angle, time) of the top of WTC1 there is nothing new about it. So just go on with your WTC1 calculation and don't be confused about us who meanwhile guessing about WTC2 tilt.

http://www.911myths.com/WTC2TIP.pdf

Sorry Dr. G but the observed data are wrong!


First, one should define what is "tilt" and what is "collapse". Imho, the tilt of the top (both towers) are the collapse but not some "pre-collapse" tilting. Btw, the collapse started prior to the tilting and progressed across the east face (WTC2) to both corners. Once it reached the corners the tilting started. Therefore the tilt is at least stage 2 (if not stage 3 after an invisible core collapse).

If I interpret the term "collapse" as the term for straight downwards acceleration then NIST would be right for the precondition of a hinge across the west face considering a lateral shift towards west. But the precondition of NIST was an axis about diagonal through the core (NE corner - SW corner) and therefore NIST is wrong too.
A "pre-collapse" tilt of 7°(NIST) around an axis through the NE corner of the core would lift up the NW corner of the building.

The the precondition of the linked Greening paper is an axis across the west face and a summation of the rotational and vertical drop of the east roof line.
At 0.5 seconds - no observed tilt angle but 1.9m observed drop of the east roof line???
What angle was used to calculate the (hypothetical) rotational drop to subtract it from the observed drop to calculate the hypothetical "true drop"???

The visible collapse needed about 0.9 seconds to progress across the east face. By subtraction of 0.9 seconds the tilt at 3.2s - 0.9s= 2.5s reached 9.9°.
Dr.G's observation is close to that angle but he calculates a true drop distance of 12.4m (more than 3 floors). May be for the center of mass? May be the east face?

rotational drop of the east face = SIN(10.2*PI()/180)*64 = 11.11m

No idea how to get a rotational drop of 13.1m plus a vertical drop of 12.4m.
It's about the moment when the west face broke after it kinked already about one floor down and to the west.

A little later the paper compares the calculated data with the observation and get a "curve fit" and missing 2° tilt at time zero. Conclusion of the paper: The top began to tilt for 2° before the top dropped as well.
Considering the folded floor and an axis through the NW corner 2° might be approximately right. The later data - as far as the calculation apparently matches the (wrong) observation - appear highly questionable.

Major_Tom wrote:

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An alternative: The "slouch" model.

OWE once mentioned his impression of the WTC1 earliest movements was that of "slouching" to the south. This is a more probable effect of removing the strength of the south wall.

Remember, our model is only 2-D and doesn't include the west or east walls yet. So when you think of that large expanse of deadweight which the OOS south region is, I think "slouching" makes more sense.

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Our 2-D model where torque acts through only 3 groups of CCs and the north and south walls may help us understand why an axis of rotation somewhere near the south wall could be inevitable.


Remember that the size of the torque arm is very important in how much torque a structural member can deliver.

Even though the 5,600 CC and 9,1000 CC rows are basically of the same strength, the 5,600 CCs are much more vulnerable to being overloaded once it is their turn to carry the extreme load. They have a torque arm less than half that of the 9,1000 CCs.


There is reason to believe that the 9,1000 CCs provide the only source of resistance sufficiently strong to push back against such a rotation once the south wall loses strength.


If the 9,1000 CCs yield, I don't see much chance of the 7,800 CCs , weaker and with a shorter torque arm, being able to follow up with much resistance.

This would bring us to the 5,600 CCs and the north wall.............

I agree with Achimspok the the 5,600 CCs would be the natural pivot object in a rotation to the south.

But the north wall would have to become longer for such a pivot point to develop.

We are under the physical constraint that the north wall cannot expand in length. This means the pivot axis must appear to be close to the north wall.

Now what would happen if only the north wall and the 5,600 CCs remained and all othe supports were removed?

My guess is that the fixed length of the north wall would allow the pivoting hat truss to act as a lever with can crush the 5,600 CCs even more effectively. The 5,600 CCs only have about 65 ft of torque arm and you have an upper block lever just above it which expands for 207 ft. It will take much less downward torque to crush these columns than for the 9,1000CC row.


So what torque resistance would I anticipate for WTC1 (with no east wast perimeter walls) if the south wall was removed?

It mostly depends on the 9,1000 row. If you can take out that row I do not see much left to stop the tilting, hence resistance will fall off dramatically.

The 9,1000 columns may act as a "hump". Once the process gets over that hurdle, or "hump", it may encounter less resistance.

An issue which needs to be considered as far as the hat truss being able to transfer load is it's connections to the perimeter and whether or not the outrigger beams would buckle. The failure loads here would limit the amount of load it can transfer to the core.

I edited this reply to include the buckling issue.

T_Szamboti --- I earlier (and probably repeatedly) on an earleir thread posted the outrigger connection strengths from the NIST report. Those connection were plenty strong enough.

David B. Benson wrote:T_Szamboti --- I earlier (and probably repeatedly) on an earleir thread posted the outrigger connection strengths from the NIST report. Those connection were plenty strong enough.

I do not believe the four south side outriggers and their connections to the south wall were strong enough to transfer the full load of twelve stories of the south wall and half of the weight of the flooring outside the core on that side onto the core columns.

My point is that I believe they are the weak link in the chain and thus the limiting factor in how much load would be transferred to the core columns from a south wall failure. Additionally, if these connections or the outriggers themselves fail little of the south wall load would be transferred to the core columns. The NIST also artificially increased the yield strength of the outriggers. Why would they do that?

You need to get specific if you think the hat truss outriggers could transfer the entire load from a south wall failure to the core columns.

Another reason to doubt that the hat truss transferred the south wall's loads and it's floor loads to the core columns and caused a core failure, is that if it were true then any core failure is more likely to happen at it's weakest point below the hat truss. That would have been at the 106th floor, not the 98th floor which had stronger core columns.

I agree, Tony. It just doesn't make sense. All those floor slabs just hanging in mid air supported only by the hat truss system after the south wall gives....

And it can transfer all that weight to the 1000 CCs?

There has to be a limit to the number of dead weight floor slabs the outriggers can hold suspended in mid air if the 1000 CCs temporarily hold.


(Actually, in a 3-D model containing the east and west walls, I think the building just may hold considering how well it held on the WTC1 north face after having more than half it's perimeter columns cut. But it holds as a result of the spandrel plates, not because the outriggers can hold all the weight.)

In our 2-D model they probably cannot hold all the weight. If they cannot transfer all that weight after the south wall looses strength, then there is a limit to the excessive load that can be transferred to the 1000 CCs.

This supports the idea of "slouching" (in our 2-D case). There in no guarantee that loss of the south wall can overload the 1000 CCs if the outriggers have limited capacity to transfer the load.

Instead, the south wall can sag or start to fall on it's own. (In the 2-D model where we have no east or west walls.)

Major_Tom wrote:(Actually, in a 3-D model containing the east and west walls, I think the building just may hold considering how well it held on the WTC1 north face after having more than half it's perimeter columns cut. But it holds as a result of the spandrel plates, not because the outriggers can hold all the weight.)

The load would predominantly transfer to the east and west perimeter walls through the spandrels and the NIST analysis itself shows the additional load on the southern columns of the east and west walls is only 69% on columns which can take 500% of their design load. Additionally, a rigorous analysis would also show that the central core columns wouldn't be affected much by a south wall failure.

This is why I believe the NIST attempt to use the south wall failure as the cause of a global collapse is nonsensical, and why they stop their probable global collapse sequence discussion short after showing the south wall could fail from inward bowing and floor disconnection. It was apparently the best that could be done with the evidence at hand and the mandate I believe the NIST was given to show a natural cause. It could not be what really happened and the tilt cannot occur with their proposed failure mode either.

On a brighter note Happy Holidays to everyone here! I do think this is a good forum that is generally free from ad hominem where most of the posters are legitimate people who attempt to use a scientific approach and I want to thank Greg Urich for starting it up.

ETA that the NIST hypothesis actually has serious problems generating a tilt.

T_Szamboti --- I earlier (and probably repeatedly) on an earleir thread posted the outrigger connection strengths from the NIST report. Those connection were plenty strong enough.

Sure, to know the outrigger connection strengths is crucial for any further analysis. If these connections were plenty strong enough then one cut per 1000CC somewhere between B6 and 106 would be enough to transfer a huge amount of load to the perimeter and subsequently overload the weaken area. If so then the inward bowing might be a direct result of CC failure.
How much load could the outrigger transfer to the perimeter? ...about 50% of the load bearing capacity of the perimeter columns of the south wall at the elevation of the IZ?

T_Szamboti wrote:
On a brighter note Happy Holidays to everyone here! I do think this is a good forum that is generally free from ad hominem where most of the posters are legitimate people who attempt to use a scientific approach and I want to thank Greg Urich for starting it up.

ditto that sentiment. hopefully it will just get better and better, like it did in 2009.

So why didn't NIST model the collapse initiation sequence for WTC1, which is the part we all want to see most?

The only clue I get is from Bazant and Verdure. Here we see the talking points of the official story summerized. Notice the official reason given for not simulating collapse initiation in bold (bolding mine)

From the paper:

"Review of Causes of WTC Collapse


Although the structural damage inflicted by aircraft was severe, it
was only local. Without stripping of a significant portion of the
steel insulation during impact, the subsequent fire would likely
not have led to overall collapse (Bažant and Zhou 2002a; NIST
2005). As generally accepted by the community of specialists in
structural mechanics and structural engineering (though not by a
few outsiders claiming a conspiracy with planted explosives), the
failure scenario was as follows:

1. About 60% of the 60 columns of the impacted face of framed
tube (and about 13% of the total of 287 columns) were severed,
and many more were significantly deflected. This
caused stress redistribution, which significantly increased the
load of some columns, attaining or nearing the load capacity
for some of them.

2. Because a significant amount of steel insulation was stripped,
many structural steel members heated up to 600°C, as confirmed
by annealing studies of steel debris (NIST 2005) (the
structural steel used loses about 20% of its yield strength
already at 300°C, and about 85% at 600°C (NIST 2005);
and exhibits significant viscoplasticity, or creep, above
450°C (e.g., Cottrell 1964, p. 299), especially in the columns
overstressed due to load redistribution; the press reports right
after September 11, 2001 indicating temperature in excess of
800°C, turned out to be groundless, but Bažant and Zhou’s
analysis did not depend on that).

3. Differential thermal expansion, combined with heat-induced
viscoplastic deformation, caused the floor trusses to sag. The
catenary action of the sagging trusses pulled many perimeter
columns inward (by about 1 m, NIST 2005). The bowing of
these columns served as a huge imperfection inducing multistory
out-of-plane buckling of framed tube wall. The lateral
deflections of some columns due to aircraft impact, the differential
thermal expansion, and overstress due to load redistribution
also diminished buckling strength.

4. The combination of seven effects—(1) Overstress of some
columns due to initial load redistribution; (2) overheating
due to loss of steel insulation; (3) drastic lowering of yield
limit and creep threshold by heat; (4) lateral deflections of
many columns due to thermal strains and sagging floor
trusses; (5) weakened lateral support due to reduced in-plane
stiffness of sagging floors; (6) multistory bowing of some
columns (for which the critical load is an order of magnitude
less than it is for one-story buckling); and (7) local plastic
buckling of heated column webs—finally led to buckling of
columns (Fig. 1(b)). As a result, the upper part of the tower
fell, with little resistance, through at least one floor height,
impacting the lower part of the tower. This triggered progressive
collapse because the kinetic energy of the falling upper
part exceeded (by an order of magnitude) the energy that
could be absorbed by limited plastic deformations and fracturing
in the lower part of the tower.

In broad terms, this scenario was proposed by Bažant (2001),
and Bažant and Zhou (2002a,b) on the basis of simplified analysis
relying solely on energy considerations. Up to the moment of
collapse trigger, the foregoing scenario was identified by meticulous,
exhaustive, and very realistic computer simulations of
unprecedented detail, conducted by S. Shyam Sunder’s team at
NIST. The subsequent progressive collapse was not simulated at
NIST because its inevitability, once triggered by impact after column
buckling, had already been proven by Bažant and Zhou’s
(2002a) comparison of kinetic energy to energy absorption capability.
The elastically calculated stresses caused by impact of the
upper part of tower onto the lower part were found to be 31 times
greater than the design stresses (note a misprint in Eq. 2 of Bažant
and Zhou 2002a: A should be the combined cross section area of
all columns, which means that Eq. 1, rather than 2, is decisive)."

Remember Dr Bazant is the Author of this paper. Between them (Bazant and Sunder) they just skipped over any explanation of a WTC1 collapse initiation sequence and both parties seem to agree it is unnecessary. Neither party seems too curious about why the entire WTC1 core failed south to north in less than one second.


In this artistic rendition of the official story they tap-dance around a WTC1 collapse initiation in which all columns fail in less than one second, during which time the upper block rotates less than 2 degrees.

Only outside idiots like us would dare to question such professionalism. Certainly not the more civilized, wiser world of specialists in structural mechanics and structural engineering.

How's the air up there, guys?

Since I've never seen any simulation for WTC1 of the original collapse initiation chain of events and I don't see any FEA coming soon, I propose a humble 2-D stick model approach to our own little analysis of lateral collapse propagation.


In the 2-D model the east and west walls of WTC1 are missing. They don't exist. This allows us to visualize the simpler mechanism of pure south to north core column failure all by itself.

This can later be expanded to a simple 3-D model by adding depth and the east-west perimeter walls.




This may be like an "old school" FEA. The days before computer graphics.

This image shows what a 2 degree tilt around the north wall 98th floor axis looks like. In a perfectly rigid model we see that each column must shorten simultaneously for this to occur. The yellow area shows the overlap at 2 degrees.

If you believe that such simultaneous shortening of all core columns as shown can occur in under one second, then maybe the rigid model is for you.

If you do not believe simulteneous overloading of all CCs (causing the witnessed shortening) is possible, then the perfectly rigid model is not an option.

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The question is this: By what mechanism is the initial damage front propagating northward?

Interestingly, the only failure sequence that is consistant with the rigid model is simultaneous failure of all core columns with the north wall left connected. Only then can it pivot as a rigid body.

In this 2-D stick model, once a portion of the south wall is removed, if the hat truss system can support all the weight of the OOS south slabs and perimeter wall, the load will be transferred to the 1000 CCs and the rest of the core.

If the outriggers cannot handle holding up all those slabs the south wall and OOS slabs will sag quickly and could start to fall.

That is slouching. We will fully transfer the load to the core or we'll get slouching and possibly partial collapse.

........................................................................

In this 2-D stick model the initial lateral collapse can propagate damage south to north in only three ways:

1) Successive overload: A column fails transferring it's weight to nearby columns., which are overloaded and fail, and so on.

2) Push and pull: failing columns tug or push other columns down through lateral braces or flooring

3) Some type of shock propagation through material by which damage can propagate.

Using combinations of these 3 types of movement we will look for a natural way to destroy the whole core in less than one second to match the observed duration of the hinge.

Major_Tom wrote:Remember Dr Bazant is the Author of this paper. Between them (Bazant and Sunder) they just skipped over any explanation of a WTC1 collapse initiation sequence and both parties seem to agree it is unnecessary. Neither party seems too curious about why the entire WTC1 core failed south to north in less than one second.


In this artistic rendition of the official story they tap-dance around a WTC1 collapse initiation in which all columns fail in less than one second, during which time the upper block rotates less than 2 degrees.

Only outside idiots like us would dare to question such professionalism. Certainly not the more civilized, wiser world of specialists in structural mechanics and structural engineering.

How's the air up there, guys?

Yes, there is a huge explanation gap between where the NIST leaves off and Bazant picks up on the collapse of WTC 1.

On top of that neither the NIST or Bazant are correct on their respective ends of the collapse explanation for which the entire middle is missing. In my mind the NIST is just flat out wrong, because they have no way to get to the collapse of the core columns from south to north in a short time interval to allow the one story drop, which Bazant simply assumes and goes on to describe what he believes would happen afterward. Here he is also wrong but could be forgiven as his model for progressive collapse is at least viable if there were a dynamic load, which would have been reasonable to assume, but which later close observation and measurement shows did not occur.

I think the high profile of the NIST and Bazant have allowed them to simply bluster their way to what could be considered a plausible explanation if it is not heavily scrutinized. The interesting question is whether the bluster is intentional or that they are just fooling themselves and do not truly understand that they have not explained these collapses.

On top of that neither the NIST or Bazant are correct on their respective ends of the collapse explanation for which the entire middle is missing.

Sunder claims to take it to the point of collapse initiation, and Bazant after a one story freefall. How can they not know they skipped over the part where the entire core fails in less than one second?

Tap-dancing over the most important part.

Written by Dr Bazant from B&V:

"In broad terms, this scenario was proposed by Bažant (2001),
and Bažant and Zhou (2002a,b) on the basis of simplified analysis
relying solely on energy considerations. Up to the moment of
collapse trigger, the foregoing scenario was identified by meticulous,
exhaustive, and very realistic computer simulations of
unprecedented detail, conducted by S. Shyam Sunder’s team at
NIST. The subsequent progressive collapse was not simulated at
NIST because its inevitability, once triggered by impact after column
buckling, had already been proven by Bažant and Zhou’s
(2002a) comparison of kinetic energy to energy absorption capability."

How the f*ck can they not know they skipped over the initial south to north failure progression for WTC1, the most important and suspicious part of the collapse?

Major_Tom wrote:

On top of that neither the NIST or Bazant are correct on their respective ends of the collapse explanation for which the entire middle is missing.

...
How the f*ck can they not know they skipped over the initial south to north failure progression for WTC1, the most important and suspicious part of the collapse?

They just lied. I can understand that NIST is an official organization and could not tell something like "the towers could not collapse by their own even with aircraft impact and subsequent fire; there should be explosives planted before the impact".

But Bazant is not involved in the strikes, he is not an official people, and he is one of the biggest specialists in material resistance; he can tell the truth; even if not tell the truth, he can remain silent before making an in depth analysis. No, he produced a full report in "two" days in which he lied in a perfect manner and led the world into a wrong direction. That behavior of Bazant is very suspect. But what for he lied?