The 9/11 Forum

Please some advice?

Some ... yes... It appears to be rotating as well as dropping and in so doing the collision of the bottom appears to have absorbed the rotational energy. Someone like Enik should make a 3D wire frame animation GIF of the top sections' movement into the lower section. I think that would clear up the actual movement.

Many people actually expected the top to tip over the side and fall to the ground next to the tower.... but as it didn't they conclude it was exploded before that could happen... as if the explosive destruction was a *better outcome* than the tipping over the side. But it actually appears to mostly have rotated into the bottom.

The way I saw it was that the there was angular momentum acquired by the top section, but it dissipated quickly as said section started to disintergrate thus acting like a fluid if you see what I mean? Stopping the angular monentum, hence why it continued to fall downward as a pose to tip over the side, as it was no longer a rigid object, which begs the question why does richard Gage expect to see the upper section on the ground more or less intact?

Richard Gage is willfully ignorant and refuses to accept physics and the actual observations. He is on a mission to promote explosive controlled demolition and frames his comments and sees the destruction from THAT filter. He is a science and gravity denier... So it seems.

I suspect ego and pride is at work here. How could he, at this stage of the *game* admit he got so many fundamental *things* wrong... things he, his advisers and *experts* should not have botched. The way he deals with this is repeating the same mis-statements and ignoring evidence that shows them to be wrong.

Sort of a sad situation and he has so many people who think he's god's gift to the truth movement and a sort of a blue ribbon reliable professional who simply wouldn't make such blunders.

Can trace two corners and provide rotation/time data...

femr2 wrote:Can trace two corners and provide rotation/time data...

Thanks that's good of you. Although I would need help interpreting such data probably. (Novice).

SanderO wrote:Richard Gage is willfully ignorant and refuses to accept physics and the actual observations. He is on a mission to promote explosive controlled demolition and frames his comments and sees the destruction from THAT filter. He is a science and gravity denier... So it seems.

I suspect ego and pride is at work here. How could he, at this stage of the *game* admit he got so many fundamental *things* wrong... things he, his advisers and *experts* should not have botched. The way he deals with this is repeating the same mis-statements and ignoring evidence that shows them to be wrong.

Sort of a sad situation and he has so many people who think he's god's gift to the truth movement and short of a blue ribbon reliable professional who simply wouldn't make such blunders.

My thoughts entirely!

Illuminist14 wrote:

femr2 wrote:Can trace two corners and provide rotation/time data...

Thanks that's good of you. Although I would need help interpreting such data probably. (Novice).

Greetings again Illuminist. Hi femr2.

I am interested in a tightly focussed part of this issue. Does anyone know if the top section rotation/tilting for WTC2 stopped before gross downwards movement commenced?

My gut feeling is that the rotation would transition directly into gross downwards translation. Reasons being that the rotation is a direct consequence of the cascading failure of the fire and impact zone. Once the cascade went exponential there was no mechanism to limit it - or stated in more PC sceptical language "I cannot think of a mechanism which would stop a process that was inherently an exponential runaway."

The reason for my interest is a comment in a thread which Illuminist started "on another forum"

Illuminist was exploring the possibility that a lower down impact of the aircraft into a Twin Tower could have caused toppling. A response by a poster named "tfk", referring to toppling, included this comment:

I do not believe that this is true. Not certain, I just don't believe it.

Specifically, I don't believe that there is anything that you could do to get a tower, built with a lattice array of columns like the WTC, to topple to the side, even if this was your goal....

...which started me thinking. I decided to "think out in the open" on that other forum - dead ends, warts and all. I'm not shy nor scared of getting initial thoughts wrong...

I have made a bit of progress but a long way from any definitive conclusions. I'm trying to see how far I can get by defining the mechanism by reasoning and gross observables but fine measurements could help on the possible sticking point of "did rotation stop".

The consequence then follows that the dynamic processes of "ROOSD/core strip sown and forget the perimeter it is no longer involved" would simply swamp the overturn or "toppling" dynamics. We know that WTC2 did not topple - if I can work out why then see if it translates to a lower impact. So that's the "plan" for what it is worth.

So does anyone know whether or not the tilting/rotation stopped or kept going for WTC2?

And, for those who are inquisitive and have all their shots up to date, the thread I'm referring to was started by Illuminist as OP and is at http://forums.randi.org/showthread.php?t=239259

My "warts and all thinking out loud" approach seems to have bluffed everyone - not a single response....

Ozzie,

I have no data measurements to support the following. I offer only *informed opinion*.

Tower 2's top section got moving in a similar mechanism to the downward movement of WTC1. But there were some differences. The significant similarity is that both were core led and facade *assisted* failures.

The damage to the axial paths (columns) was quite asymmetrical due to the angle of the plane entry and the fact that it was off the center axis. As in WTC 1 the initial column destruction was not sufficient to over come the reserve capacity (FOS remained more than 1) of the remaining columns. The very strong (carrying 7.5% of the floors loads) corner core column WAS destroyed in WTC 2 and not in tower 1. The nature of the damage was akin to felling a tree with an axe... the load path for the tree is moved to the remaining part of the trunk and this begins to set up a moment as part of the mass is essentially cantilevered... and is what accounts for the rotation.... with the axis (virtual hinge) was about the last few remaining column(s) on the diagonally opposite to the plane destroyed corner.

As in WTC 1 the failure occurred when the FOS dropped below 1 in the remaining columns to the NW. These columns were *overwhelmed* and began to buckle... and the moment caused the floors above to rotate AND drop. The drop is evident from the horseshoe column which shows that its working length was severely reduced when it folded over to the plane damaged side of the structure.

It seems inconceivable that the entire mass of the upper section could ONLY rotate on the remaining column(s) - the virtual hinge... because this would mean that those few columns were able to support the entire mass of the upper block and function as a actual hinge..

The remaining columns obviously offered more resistance as they buckled than the few columns remaining on the plane damaged side... so we have the moment and the rotation develop.

Once the two sections began to crash together... beginning on the plane damage side... the frame apparently began to come apart. We can see a kink at the hat truss section which apparently being stronger was a natural fault line. The colliding floors and columns not only slowed the descent but the rotation... and only the sections which had rotated/translated out side the foot print managed to remain outside and drop to the ground... I don't think they would have rotated back into the facade below.

It appears to me that there was initial rotation and then that more or less ended as the top section crashed into the bottom section.

There is no way that a plane could knock over a tower with the strength of the connections of the a typical steel frame. A plane with more momentum would perhaps slice right through it... and one with less would simply do less damage to the structure and leave some columns etc destroyed.

What happened with the twins is that the plane damage was supplemented over a period of time by heat weakening... and there were so few columns to begin with in the core and the FOS was low enough that the amount of heat was able to sufficiently weaken the remaining columns to drive the aggregate FOS to below one. That buckled the remaining core... and led to the ROOSD process.. which in turn led to the facade peel and the core self buckling from Euler forces.

I suspect the Sears Tower or the Empire State building would have seen a partial collapse above the damaged floors with a local ROOSD perhaps within some column bays below that.

Perhaps.

SanderO wrote:Ozzie,

I have no data measurements to support the following. I offer only *informed opinion*.
.....
Perhaps.

Thanks for the thoughts Sander. I appreciate how you are prepared to put your thinking on view and it has given me a step forward.

I've been doing the 2-4 AM insomniac's shift here so I will give a reasoned response in a few hours time..

OK - I got busy yesterday so I'm 24 hours late. Tough but the real world keeps running. (Seized wheel bearing on the trailer for my car - Grr Plus out in the open and it started to rain - double Grr. )

So let's see if I can do some serious thinking. First another 'thankyou' to SanderO for his thoughts. I think that I understand all that you wrote Sander but I won't comment in detail at this time. The key point which spurred me to further insight is this:

SanderO wrote:It appears to me that there was initial rotation and then that more or less ended as the top section crashed into the bottom section.

...because the manner in which 'the top section crashed into the bottom section' seems to be the issue of most confusion - whether we look at Bazant's various efforts or the concerns expressed by Tony Szamboti and David Chandler. (Flow on point #1 for another post.)

They all seem to get confused over a central single assumption - that being that something moved downwards and crashed into columns. I suggest that is demonstrably and obviously untrue once you 'see' why. The main error in that wrong assumption is that once the top portion was moving downwards the column ends had already passed each other - they were 'too late' in sequence to impact. (Some details to explain there but that is the main flaw of their reasoning.)

So let me set some context:
First my objective is to understand the transition from 'initiation' to 'progression' so that I can answer the specific question 'Would a lower down aircraft impact at WTC2 have resulted in toppling?" ( Foreshadowing my conclusion which will be 'No toppling but I'm only 90% confident at this stage'. )

Second is the main technical premises I plan on using which are:
To reason from the basis of two definable key stages in the collapse of WTC2:
1) The point when the tilting top block approached the limit of tilt at 22^o; AND
2) The time when gross downwards translation of the top section commenced.

We know, or can argue with reason, that two key factors apply at these stages:
A) The columns of the 'moving down' bit had failed - that is the low side and core columns in the tilted top section situation with WTC2 OR all of the columns when gross downwards movement has started for either tower; AND
B) The corresponding ends were not in axial end for end relationship capable of transferring significant load - must be so because the relevant portion of tower was moving downwards.

Excuse the pedantic expression of the second point. Let me clarify. The relationship of the top part of each failed column to its bottom part was one of several possibilities:
a) Column had buckled then broken and ends were already bypassing each other;
b) Column had buckled/bent/folded into a 'U' or even 'pretzel' and the ends of the top and bottom parts already bypassing each other; AND/OR
c) The (relatively) undamaged portions of the top part was still falling though a gap towards its bottom part with several possibilities when they met - the two boundary examples will do:
(i) The buckled/bent ands are so shaped that the two parts will be deflected so that the ends keep bypassing - i.e back to same scenario as "a)" and "b)"' OR
(ii) The ends are sufficiently squared that axial load can be transferred BUT this will lead to instant repeated failure and put us back to the start of this list of options.
...and those two all we need because they define the two outcomes which are - the two ends bypass each other with near zero force OR the two ends come into contact and immediately failure occurs reducing the forces to near zero hence 'insignificant' - and puts us back to the previous outcome.

Lets now examine the situation as the tilting top portion of WTC2 approaches 22^o. 'Approaches' rather than 'has reached' because I don't wish to pre-empt the question of 'Did it stop at 22^o?' - I don't think it did stop as I will now explain but I am avoiding the circular logic of proving my assumption.

As the 'tilting top' approaches 22^o we know;
1) All low side columns have failed and are either bypassing or about to bypass for reasons given in the preceding section. Therefore there is only 'insignificant' resistive force available. No 'significant' force from full strength or near full strength axially loaded columns.
2) All core columns had also failed and providing only 'insignificant' resistance - same reasons as above. (Note also it matters not whether core or perimeter went first - both lead to the same situation.)
3) The 'high side' columns were the only ones capable of providing resistance approaching 'significant' they were already entering a failure by bending/buckling state and precisely what stage they were at is not of importance in the argument I am pursuing; AND
4) The perimeter columns of the 'other two sides' were in various stages from failed at the 'low end' to 'still resisting' at the 'high end' and exactly what the situation was does not affect my argument.

So we have a 'toppling' or 'tilting' moment caused by failure of the impact and fire zone which moved the virtual pivot towards what was to become the 'high side' - the offset from 'virtual pivot' to 'gravity force on centre of mass' providing the moment leverage arm.

And we have 'insignificant' resistive forces on the low side with at most 'could be significant' forces on the high side. And the 'low side' is dropping OR the 'top portion' is rotating which are different aspects of the same bit of geometry. In this situation from where does the resistance at the 'low side' come to halt the tilting or rotation?

If we need a diagram or two I will draw them but....the tilting rotation would not stop.

So what happened?

I have picked a single defined point out of a dynamic continuum. The underlying process is the cascading failure of the impact and fire zone. We were at the stage where the 'high side' columns (and part of the 'other two sides') were the only ones which may till have been providing significant upwards resistive force. (And the may is a valid bounding case - if I'm wrong the following argument is strengthened.)

The resistive force of that minority of those remaining resisting columns could not survive the progress of the cascading failure. The downwards force vector from the weight of the 'top portion' scarcely reduced by the 22^o tilt or by the net angular acceleration of the 'rotation' of the top portion. All that based on gut feeling ball park guesstimates - but remember that we are in a situation where there is a massive order of magnitude difference between the 'significant' and the 'insignificant' processes. And the downward movement of 'top portion ' is dominated by large 'significant' forces whilst the resistance to tilting is only opposed by 'insignificant' forces.

So the tilting would continue except....

The downwards 'progression' or 'global collapse' took off at such speeds that rotation even if it continued may not have won the race. PLUS the transition to ROOSD included mechanisms to destroy the integrity of the top portion AND to constrain most of the falling top portion within the lower tower. Explanations if needed.

So there is my outline of an explanation of a mechanism. Stated briefly I expect that any objections will fall into three categories:
1) Identification of things that I have thought through, assessed as not changing the outcome and omitted from explanation for simplicity;
2) Aspects where my reasoning is at this stage incomplete - including possible areas where we need mathematics to determine which way to go; AND
3) Bloody great holes in my logic which will either be 'pluggable' or 'fatal'.

So take this as 'Stage 1' - my preliminary hypothesis being 'tilting at WTC2 would not stop' - femr2 or some other member may be able to falsify that one and send me back to the drawing board.

Otherwise I can move on to the hypothetical case of a lower down impact.

EDIT - For some reason I had quoted 8^o tilt for WTC2 - blame it on age or brain fart. Now corrected to 22^o - it doesn't change the arguments because we are still in 'ball park guestimation stage'

Ozzie,

Interesting but I do need to see some diagrams....

"preliminary hypothesis being 'tilting at WTC2 would not stop"

What does that actually mean? Are you saying that the rotation would continue until what degree? Could the horizontal roof with the floors attached below rotated to vertical.. that is 90°? Or more?

It appears to me that the top's rotation was halted by its disintegration as the bottom *dug into* the upper floors of the lower section. Aside from providing the ROOSD kick off mass... the collision of the FLOOR plates seems to have caused the frame to break apart. How many plate collisions did this take? Dunno.

I think your discussion of what happens to the columns and their resistance is not even an issue... Much of the columns of the lower section were destroyed and incapable of resisting in an significant manner to the load paths to foundation. At best the upper columns were like the tynes of a fork (47 for the core) punching downward and meeting no resistance whatsoever.. a typical floor plate is effectively no resistance as is air!

I like to think of this as two hair brushes being pressed together at an angle... even twisted a bit... the bristle simply slide past one another.

The tower of course had those pesky little floor plates *stuck* to the columns and those got nicely shattered in crush up, crush down.. and in so doing messed up the bracing for the columns.. the plates WERE the bracing!

So one enough floors mutually destructed they did in a hole bunch of columns as well.... especially in the descending section... it was not only weaker but it lacked the connection to the foundation to provide rigidity. Look at the top in the photos... it does a bit of wobble as it drops and just before it breaks apart.

Also think of whether the top could support itself at 90°... it can't I suspect... the floors would be columns and the columns would be concentrated loads on the edge of the floors. That couldn't happen because the lower section could not begin to support the top at 90°. But even if you could slice the top off... pick it up with a Ozzie SkyHook... rotated to 90°and gently place it on terra firma... it would collapse on its own weight.

The load paths were becoming increasingly disrupted in the upper section that the more it tilted the less rigid the entire frame was. And it wasn't in free fall and stress free... there WAS resistance.. JOLTING the frame and the plate... as they were meeting the lower section.

My thesis is that it HAD to stop... What would happen to someone standing on the roof as the top starts to tilt.... do a little thought experiment...

SanderO wrote:Ozzie,

Interesting but I do need to see some diagrams....

I'm not surprised - I'm in the minority as an NLP 'Visual' who thinks easily in 3d moving pictures. Several war stories from my career in a design office where the bosses were strictly non-visuals.

SanderO wrote:..."preliminary hypothesis being 'tilting at WTC2 would not stop"

What does that actually mean?...

it means that this is my first documented think through the issues - haven't got it all sorted out yet - looking for input from folk who can match or better my level of analysis. Pure 'reasoning' may get me to a final conclusion - I achieved it with my explanations of what I didn't call ROOSD back in 2008. By pure reasoning I mean taking readily accessible observable evidence, adding known facts/principles of engineering/physics and assessing what would happen. For example you can legitimately support 'ROOSD' with only ball park estimates of forces. Reason being that all the progressive collapse forces are 'overwhelming' - so you don't need decimal point maths. If the weight of several storeys is placed statically onto a single floor it will shear - even less if applied dynamically. So ball park is needed.

On this current hypothesis I may need details. e.g. femr could probably and may already have measured to see if tilt/rotation stops. If it did my brain will need to rethink...

SanderO wrote:Are you saying that the rotation would continue until what degree? Could the horizontal roof with the floors attached below rotated to vertical.. that is 90°? Or more?..

actually covered very briefly - the downwards movement was so fast that toppling would get left behind PLUS (you identified this in next paragraph) the top portion both got broken up and its bits mostly channelled inside the lower perimeter tube.

SanderO wrote:...It appears to me that the top's rotation was halted by its disintegration as the bottom *dug into* the upper floors of the lower section. Aside from providing the ROOSD kick off mass... the collision of the FLOOR plates seems to have caused the frame to break apart. How many plate collisions did this take? Dunno....

Yes. I identified disintegration as a factor. Also don't overlook that the outer perimeter columns would initially act as a 'knife edge' - depending on which wall we talk about the upper section perimeter went either inside or outside the lower section perimeter. Where top perimeter fell outside lower perimeter would act 'knife edge upwards' to shear off top portion floors as those floors descended. Conversely with top perimeter falling inside lower perimeter the top section perimeter would shear off the floors in lower section. At least the first floor or two. And in some sort of competition with falling already separated debris - who knows what the balance. But it doesn't change the logic. Floors become disconnected in both top and lower portions and therefore top section starts to disintegrate.

We have a fundamental set of differences in this next paragraph.

SanderO wrote:...I think your discussion of what happens to the columns and their resistance is not even an issue... Much of the columns of the lower section were destroyed and incapable of resisting in an significant manner to the load paths to foundation. At best the upper columns were like the tynes of a fork (47 for the core) punching downward and meeting no resistance whatsoever.. a typical floor plate is effectively no resistance as is air!

I like to think of this as two hair brushes being pressed together at an angle... even twisted a bit... the bristle simply slide past one another....

Yes - I said wire baskets in my previous explanations. BUT I am now trying to detail understand and leaving it as "not an issue" does not help progress. And strongly beg to differ on column strength not even an issue. This is the territory of Bazant's explanations and Tony Szamboti's sort of following Bazant with 'Missing Jolt' and D Chandlers work. And with all of all of them column strength and column involvement is the central factor where I say they went wrong. I am interested in the mechanism which actually happened. Not in the confused thinking of Bazant abstract models or those who follow their own abstractions possibly led astray by Bazantian misunderstandings.

Let me take a rain check on thse next paragraphs:

SanderO wrote:...The tower of course had those pesky little floor plates *stuck* to the columns and those got nicely shattered in crush up, crush down.. and in so doing messed up the bracing for the columns.. the plates WERE the bracing!

So one enough floors mutually destructed they did in a hole bunch of columns as well.... especially in the descending section... it was not only weaker but it lacked the connection to the foundation to provide rigidity. Look at the top in the photos... it does a bit of wobble as it drops and just before it breaks apart.

Also think of whether the top could support itself at 90°... it can't I suspect... the floors would be columns and the columns would be concentrated loads on the edge of the floors. That couldn't happen because the lower section could not begin to support the top at 90°. But even if you could slice the top off... pick it up with a Ozzie SkyHook... rotated to 90°and gently place it on terra firma... it would collapse on its own weight.

The load paths were becoming increasingly disrupted in the upper section that the more it tilted the less rigid the entire frame was. And it wasn't in free fall and stress free... there WAS resistance.. JOLTING the frame and the plate... as they were meeting the lower section.

SanderO wrote:...My thesis is that it HAD to stop...

What would cause it to stop? I have detailed an hypothesis which goes to the structural and dynamic realities. There was nothing to stop it once it started rotating. Except that the bottom fell out before it got past 8^o (Note - should be 22^o).

SanderO wrote:What would happen to someone standing on the roof as the top starts to tilt.... do a little thought experiment...

Out to 8^o tilt they would have no difficulty remaining standing and avoiding sliding down the slope. (Edit - my wrong use of 8^o - should be 22^o and change 'no difficulty' to 'a little bit of difficulty' ) But when gross downwards translation started ('falling' at a large proportion of FFA) the falling would take them down with it. At about 1/3 apparent weight.

EDIT - For some reason I had quoted 8^o tilt for WTC2 - blame it on age or brain fart. Now corrected to 22^o - it doesn't change the arguments other than the comment in the last paragraph because we are still in 'ball park guestimation stage'

Ozzie,

I appreciate this discussion. We have to leave the math to the physicists and engineers. The facade would function as a knife edge. Excellent observation... rather blunt but it would certainly cleave a 4" thick slab/plate and once the slab/plate was separated from its moorings to the facade it would collapse as the core side could not support it as a cantilever.

I suspect this motion could be somehow modeled in a 3d animation and one could literally see what hits what and when... of course depending on the location of the virtual hinge. Maybe this is something that Enik of Achimspok or femr2 could produce. It would go a long way to dispelling the notion that the tilting top was blown up before it fell over the side.

I am not sure of the logic of blowing it up before it fell over (as if it could)... but perhaps the idea is that it was intended to be blown up but something went wrong and it began to tilt and the explosions just went off in any case. I find it increasingly difficult to understand the CD thesis. But that's off topic.

SanderO wrote:Ozzie,

I appreciate this discussion. We have to leave the math to the physicists and engineers...

I also appreciate your willingness to lay your thinking out as part of a discussion. Thanks again.

The place where maths fits is one of two factors that separate us 9/11 thinkers into different 'schools'.

I have mentioned the first factor on previous occasions. It is the distinction between:
1) The school of people who try to work out what really happened - in my language defining the mechanism of collapse. femr2 and Major_Tom are definitely of that school just as I am and you also seem to be of like mind. We have differences of emphasis but all trying to understand what really happened. A good clue in one example being that both M_T and I 'worked out' collapse progression in the shape of what M_T called ROOSD. He went a lot further than I did but the same principles explaining what really happened based on reasoning derived from evidence.
2) The other school, and far larger, is of those people who work from abstractions - most academics starting with Bazant and his colleagues. And a hell of a lot of 'debunkers' who lack the ability to work things out for themselves so they attach their wagon to Bazant or NIST.

There is a third groups who cause a lot of confusion in debates on Internet. Those who get confused between 'what really happened' and 'what Bazant or NIST said as an academic approximation' and lack the clarity of thinking to sort out the overlaps.

SanderO wrote:...The facade would function as a knife edge. Excellent observation... rather blunt but it would certainly cleave a 4" thick slab/plate and once the slab/plate was separated from its moorings to the facade it would collapse as the core side could not support it as a cantilever....

Yes and thank you. It is part of my approach of 'visualising' what could really happen. Similar to your 'wire brush'. Since it can involve guessing things we could not see you ("I") have to be careful to ensure that conclusions are valid whether it is right or wrong - otherwise it is little more than conjecture. But - on this example of 'knife edge' - femr (and M_T IIRC) were able to confirm that some outer perimeter walls fell inside and others fell outside the lower tower perimeter. So that was one factor of confirmation. Therefore "knife edge up' and 'knife edge down' were both plausible factors. I tend to accept femr or M_T's technical findings as the default hypothesis - they are usually very good as you know. BUT knowing that 'knife edge' is plausible is still a fair way from knowing it must be true. So other possibilities have to be exhausted as well.

SanderO wrote:....I suspect this motion could be somehow modeled in a 3d animation and one could literally see what hits what and when... of course depending on the location of the virtual hinge. Maybe this is something that Enik of Achimspok or femr2 could produce. It would go a long way to dispelling the notion that the tilting top was blown up before it fell over the side....

There is a very important proviso with 'modelling'. That is you cannot model until you have a clear concept of what you are modelling. That is where my comments about Bazant and Tony Sz's 'Missing Jolt' fits in. I think (and can show why) Bazant's underlying simplification leads to errors. Simply put he leaves the columns in place providing resistance through the collapse. Initially in B & Z he was clear that it was a 'limiting case' - that was OK but from there he and a lot of others started to forget the 'limiting case limit' and take Bazant's ideas way too far - outside the limits of his assumptions. The Le and Bazant paper criticising Tony's Missing Jolt OR David chandlers work (possibly both - he doesn't name them) is simply wrong. I can easily show why. That doesn't make Tony or D Chandler right by the way - that's a false dichotomy. What is does say is that he hasn't proven them wrong. I happen to think that they are wrong - ironically because they make the same error as Bazant. And Bazant therefore is 'right for the wrong reasons' - a bad situation to get into - it fools too many people.

Bottom line - you cannot build a model of 'something' unless you know what the 'something' is. And many people base models on undefined assumptions producing either garbage results OR (even worse) getting 'right answers for wrong reasons'.

Which brings me back to that 'Second Factor' which I didn't get to at the start. Maths like models (it is modelling) has to apply to a valid mechanism. No point trying the maths until you know what you are applying it to. So back to my preference of working out what happened as first step. So we see:
1) The school of those who try the Maths AFTER they get a clear understanding of what they are applying the maths to; AND
2) The school of those who dive into maths before they get the underlying modelling right. Le and Bazant definitely in this school in the paper where they criticised some unidentified persons posting on the Internet:

Le and Bazant (2011) wrote: "Recently, though, a new objection, pertaining to the smoothness of the observed motion history of the tower top, has been raised and disseminated on the internet.
This objection is based on the intuition that, if the collapse of WTC towers were gravity driven, then the existing amateur video of collapse would have to show a pronounced velocity drop at the moment at which the upper falling part impacted the lower intact story...

SanderO wrote:...I am not sure of the logic of blowing it up before it fell over (as if it could)... but perhaps the idea is that it was intended to be blown up but something went wrong and it began to tilt and the explosions just went off in any case. I find it increasingly difficult to understand the CD thesis. But that's off topic.

I've generally given up allowing for explosive or thermXte possibilities unless I need to be very rigorous in logic. 2007-8-9 I would always leave the option in place "aircraft impact damage, accumulating damage from unfought fires and the possible assistance of some human interventions (CD)..." But it is 2012 and the default hypothesis is "no CD" which has not been effectively challenged in over ten years. So IMO time to leave it behind. PLUS it is my own position but in rigorous argument your own position doesn't come into play till you have built the chain of reasoning. And I can be cold bloodedly objective when I try and can leave my conclusion out of discussion till we get to them.

So, back on the OP question:
"did the tilting wtc1 upper section acquire angular momentum?"
Y'es it did - it must have because one side dropped causing 'tilting' and one side down tilting means rotation and rotation by movement means angular momentum.

So the OP is a trivial question...BUT

...the real issue is 'was it enough to cause toppling if the aircraft impact was lower down?'

I think 'no' but I'm probably at the stage where I understand them mechanism but may need to turn on the maths to prove a couple of factors before the conclusion is assured.

Cheers.