The 9/11 Forum

Ozzie,

In my little thought experiment I used FOS 2.. that meant that half the columns could support the actual load.. so half the columns would carry the load (and assumed strong enough bracing to support the cantilever.

Another thought or two.

1. Suppose the west side (fulcrum) columns remained attached to the tilting top. The horizontal vector of the tilting top exerted a NW force on the fulcrum column and they folded (buckled) not the the SE but the the NW effectively causing the bottom of the tilting and falling top to translate NW digging MORE into the tower than had the buckling been toward the SE.

Help me understand the rotation aspect of the motion. I think of rotation as having a fixed *center*.. hinge or fulcrum... which effectively causes the motion of the object to rotate about it... and so it's direction of movement is constantly changing.. here we go round the merry go round. If it were not *restrained* it would fly off in a straight path... (catapult which then of course is pulled toward earth and has an arcing motion)

Are we talking about a kind of catapult here with the gravity force much stronger than the rotation ( change angle of horizontal) force... the top is not flying off *straight* but the rotation of most of the mass is WITHIN the structure and so the effect is it is destroyed or disintegrated or (turned to a fluid of building parts which in so doing lose their horizontal vector. If the structure is remains tethered to the core columns (witness the severely bent columns - the *horseshoe*) the fulcrum or hinge was DROPPING while it was translating. But we can't be sure if the buckling was TOWARD the SE or AWAY from it, The latter would cause the descending top to move more INTO the bottom

I'll sort the trace soon.

Or, you could watch the video's...upper section of WTC1 clearly continues to rotate as it descends/fragments until obscured by smoke-n-dust.

We have achimspok's graphs of tilt alngle, stretching long after NW corner release.

femr2 wrote:I'll sort the trace soon. (1)

Or, you could watch the video's...upper section of WTC1 clearly continues to rotate as it descends/fragments until obscured by smoke-n-dust.(2)

We have achimspok's graphs of tilt alngle, stretching long after NW corner release.(3)

Thanks femr

In priority:
(2)A good reminder - recall I set out on a thought exercise and was reaching the point where I needed to go back to the source evidence. So I will do the 'careful watch of videos' thing - it seems from your summary here that it matches my thinking. There is some advantage in that overall because it says that two different approaches converge to the same (range of) conclusions. "Range of" because nothing definite at this stage.

(3)I will also search for achimspok's graphs. I tend to overlook achimspok's contributions and enik's because your work and Major_Tom's are usually more in the range of my interests. In fact the evidence I have called on most times by reference on other forums is probably M_T's work in identifying details of perimeter 'peel down'. I think it is the closest we have to definitive 'proof' of how those few big girders got thrown hundreds of feet.

(1)So no need to progress tracing at this stage or at least there is no urgency. The other two pointers have given me good leads. Thanks.


PS Any bets that I get through this 'project' only to find that it has all been done before? Still the benefit is in the mental exercise at least as much as the outcome conclusions.

Hi Sander. Thanks for the thoughts - I'll take them serially paragraph or sub topic at a time
...and let's all remember that I am using my preferred approach to this type of problem challenge which is;
1) Work from macro level evidence;
2) Based on what is observable from the record plus what is known of the structural aspects plus what can be reasoned; WHILST
3) Initially using 'ball park' guesstimates for as long as valid progress conclusions can be reached THEN
4) calling on more detailed evidence - mechanisms, numbers, structural analysis. whatever.

..and I am thereby (hopefully - tell me if I miss something ) avoiding the errors of losing track of context or applying detailed maths over wrong premises.

OK with that reminder lets look at this:

SanderO wrote:Your image loaded on my server here= http://conleys.com.au/webjref/tt%20fulcrum.pdf
Ozzie,..

(I've had to cheat to put your picture there - attachments don't link in quotes.)
A good illustration - I would not hesitate to use it in explanation with two provisos:
1) The most important is that it shows 'integral blocks' and that is definitely what did not happen in at least two important ways:
(i) break up of both top and bottom 'blocks' started in the range of stages covered by the drawings; AND
(ii) the interface between top and bottom was complicated multi structural element interactions not 'integral rectangular block on ditto'.

I know you and I don't have that in mind so it does not detract from our debate.
If I was explaining 'initiation/transition to ROOSD' it would either be to a professional person with little 9/11 WTC knowledge who would understand the realities OR it would be to a less qualified lay person to whom I could explain the actual details as the explanation progressed. So a valuable drawing and useful. (Are there any royalty charges? )

The second proviso is a positive one - the drawing shows the movement of the 'virtual fulcrum' - a point worth emphasising.

SanderO wrote:...In my little thought experiment I used FOS 2.. that meant that half the columns could support the actual load.. so half the columns would carry the load (and assumed strong enough bracing to support the cantilever....

It doesn't work out that simply. Cutting half the columns does not mean that the remaining columns carry double load. It depends on the physical layout of the remaining columns.

As first stage of explaining that take this simplified example:

So we have a simplified WTC'x' Twin Tower. Top 'block', total mass 400 whatevers and standing on three columns A, B and C. Scenario 1A we see the columns loaded A=100, B=200 and C=100. Reasonable for a typical building.

Now cut column 'C' - does the loss of 100 support spread evenly across the other two - No!. Does it spread proportionally across the other two i.e. 33 to A and 67 to B. No again.

What happens is either Case 2A OR Case 2B depending on whether the 'top block' is a rigid block (unlikely) or a flexible structure - the realistic option.

So point Number one - the loss of support at Column 'C' would see the load on 'A' reduce to zero; all the load carried by 'B' and the load on 'B' therefore doubling.

Do that again with Case 1B - uniform distributed loads of 133 to each of three columns. Same result - zero on Column 'A' and 400 on Column 'B' and, if the 'FOS' was 2 that puts Col 'B' into overload and probable failure. So removing one third of columns causes failure with FOS of 2.

Let's now look briefly at Case 2B - flexible top structure.

Initially it looks like the same result - Zero on column 'A', 400 on 'B' and zero on 'C'. BUT the flexible structure will have sagged downwards either side of the central 'B' column. The left side sagging over Col 'A' will try to put load on 'A' but overall cannot because nothing on 'C' to balance. So a bit of dynamic balancing will see left side and right side sagging BUT left side still in contact with Col 'A' net result double sag at 'C' and zero sag at 'A'. And that tilts the top with the consequence that the Centre of Mass moves outside of Col 'B' - the 'top block' would topple if it was flexible - and not held back by Column 'A' where the load goes negative - Col 'A' is in tension..

Both cases obviously simplified to illustrate the point. However it is analogous to the model of 'WTC2 Tilted Top' I have been discussing where:
-- Column 'B' approximates 'core';
--Column 'C' approximates 'low side perimeter'; AND
-- Column 'A' approximates 'high side' perimeter.

I have started an eleven columns model to take this explanation further - so I can support my response to your 10 column example. I said it would fail at 7 remaining if all the columns were in one row and removal from one end takes out three at that end.

Alternatively if you had an 11 long row of columns under a two dimensional building and took out 5 columns (2, 4, 6, 8, 10) leaving uniform doubled spacings the redistribution say 440 total mass distributed 40 per column, remove 5 leaves 440 distributed over 6 uniformly spaced columns or a load of 73.3 on each of the remaining columns which were designed for 40. So, with FOS 2, you survive - like this:


Therefore, as I said way back, " It depends on the physical layout of the remaining columns."

I can complete the '11 columns model' if you wish, And I chose 11 over 10 because removing half of 10 ends up non symmetrical.

I'll post this much and come back with another post addressing your other paragraphs.

PART 2

SanderO wrote:...Another thought or two....

This may take a few posts - I'm not fully clear on where you are coming from PLUS the underlying physics has several main components.

SanderO wrote:...1. Suppose the west side (fulcrum) columns remained attached to the tilting top. The horizontal vector of the tilting top exerted a NW force on the fulcrum column and they folded (buckled) not the the SE but the the NW effectively causing the bottom of the tilting and falling top to translate NW digging MORE into the tower than had the buckling been toward the SE....

Yes---but-----
Within the limit of the 'ball park maths' my gut feeling is that the horizontal translation forces/effect are second or even lower order. Therefore swamped by the bigger issues of transition to gross downwards translation in a race with continuing toppling which in turn has its origin in tilt from low side column and core failure which in turn translates by pure geometry into a rotation. Those three (1) Downwards; (2) Tilt and (3) Rotation being IMNSHGF#in that descending order of magnitude and the lateral forces from the remaining attached columns being far less. Remember that the downwards, tilt and rotation 'vectors' are all dealing with the remains of full column strength plus the remnant strengths of floor joist connector and core beam shear off forces WHILST the horizontal forces you are harnessing for your concept derive from the remaining 'high side' columns and are dependent on bending moment resistance of those columns when loaded about their weaker axis - radially into or out from the building. A quite weak set-up. Any significant force in that direction are likely to break the bolted field joints of the columns which are designed for axial loads - not bending. BUT that is far as even I am bold enough to conjecture before we engage some numbers. (Or we can access supporting visual evidence.)

(And that last few sentences possibly impenetrable. Try reading sentence by sentence. I may need to expand the explanation. )
# "IMNSHGF" where 'GF' == 'gut feeling' - not 'girl friend'

SanderO wrote:...Help me understand the rotation aspect of the motion. I think of rotation as having a fixed *center*.. hinge or fulcrum... which effectively causes the motion of the object to rotate about it... and so it's direction of movement is constantly changing.. here we go round the merry go round....

For the situation we are considering there are two big forces and a resulting drop, tilt and rotate. All three are related but the maths can be applied to each separate 'vector'. Plus some secondary forces which I will leave out of the drawing at this stage but we will need to get to them in due course. This is what we have seen as a free body and 'first order forces' only:

The two 'first order forces' are:
1) The weight mG acting vertically down effectively from the Centre of Mass. AND
2) The vertical upwards resistance R_F 'Resistance of Fulcrum'.

The existence of those causes motions and causes other forces to come into play. I'll see if I can put these onto the drawing using my limited graphics skills.
1) The lack of support under the RHS causes that side to drop == causes 'tilt'
2) (There are remnant resistive forces under that side but small magnitude as already discussed in [previous posts)
3) The geometry of 'tilting' a rectangular block means it rotates.
4) That means 'Induced Rotational Momentum' (IRM on the drawing) And that momentum has the associated rotational acceleration and velocities. All same as Newtons F=mA of linear acceleration. The 'F' becoming 'torque' for the rotational situation. And it comes from the moment of the opposing R_F and mG THEREFORE
5) A horizontal force is required at the fulcrum pivot. (This is sort of the horizontal force you were musing abut in your previous paragraph.) That force is not opposed by a force per se - it causes the horizontal acceleration vector of the tilting top block - and is transitory - it only exists whilst the top block rotation is getting faster.

I will pause there fro two reasons.
1) I'm getting tired and have to return to work (school bus driving is one of my retirement 'time fillers')
2) I need feed back as to what your next bit of puzzlmwnt means.

So rain check at this stage on:

SanderO wrote:... If it were not *restrained* it would fly off in a straight path... (catapult which then of course is pulled toward earth and has an arcing motion)

Are we talking about a kind of catapult here with the gravity force much stronger than the rotation ( change angle of horizontal) force... the top is not flying off *straight* but the rotation of most of the mass is WITHIN the structure and so the effect is it is destroyed or disintegrated or (turned to a fluid of building parts which in so doing lose their horizontal vector. If the structure is remains tethered to the core columns (witness the severely bent columns - the *horseshoe*) the fulcrum or hinge was DROPPING while it was translating. But we can't be sure if the buckling was TOWARD the SE or AWAY from it, The latter would cause the descending top to move more INTO the bottom

Ozzie,

First I made a cartoon and could not possibly manage to illustrate all the processes at play nor was that my intention with that cartoon. The yellow represents destroyed building... with no virtually no loads paths functioning... but it's conceivable that the columns in the yellow zone were like brush bristles still connected to the frame. Perhaps. The yellow obviously represents the ROOSD mass for the parts within the foot print. I left the outlines of the two *block* in the each stage only to show the amount of crushing/destruction of each in the process and of course the bottom of the top was not descending as a rigid structure into the top of the bottom.

I began a thread a while back about the progression of failure of the core columns... Another cartoon thought experiment.. I've attach the pdf I made for that discussion. Clearly the load redistribution is rather complex and def related to multiple factors. The cartoon was simply a mean to illustrate that the virtual hinge/fulcrum might have moved NW not SE... in a sort of reaction to the rotation or horizontal component of the tops motion... MOSTLY down but a small amount NW.



The impact in tower 1 was more symmetrical as would be the progression of destruction because of the column configuration. The hat truss did not bear on all core columns and so it's part in load redistribution would not involve some columns. And finally load redistribution seems to be linked to the strength of the bracing and rigidity of the bracing connections... as these ARE the load paths for redistribution (aside from the hat truss). But the bottom line for understanding the PLAN view of the movement is that there was translation (probably to NW) along with the obvious much greater downward motion. Let's wait and see what sort of 2D plots femr2 comes up with from the e-w and n-s axes for the motion of the top at least... which can be seen (somewhat).

I suspect the hurdle to understanding the movement/destruction is to account for the apparent almost instant change from a descending block (at least the top part of it visible) from an organized tilting block of many stories of the building into what appears to be total destruction. POOF. The truth movement sees this as evidence of massive or multiple simultaneous explosions. That is to say that their logic is that the top section had to continue and fall off/over the side and if it didn't then the destruction seen was the result of explosive devices.

This is very much akin to what they see in the top of WTC 1... they do not see it as descending and being crushed and destroyed from the bottom up (like a typical CD)... They see the top being exploded and sending its parts flying over the side. Does it make sense for a collapsing 16 story structure up there NOT to have parts of it fall/fly off outside the footprint? Why not? It's kinda hard to imagine material NOT being tossed all over the place including outside the footprint when a 16 story structure *collapses*.

This mis-perception might be due to the failure to understand (imagine) the part that moving air caused BY the motion/collapse played. Each floor of the tower contained 18,000 cu yards of air along with the contents. When the collapse/destruction occurred on that floor (or portion of it) as a result of collapse ONTO it... the air within had to be displaced. If the ceiling (floor) above my study were to collapse I image the window glass bursting and the papers and so forth flying out... not to mention everything inside getting beat up by the concrete floor falling on top of it. In the case of the WTC floors we are talking about a huge volume of air moving out of the footprint in a tiny fraction of a second.. perhaps .1 sec. That amount of air moving off of a 1 acre footprint in /1 sec would create quite the destructive wind/overpressure directed outward and destroying most of the floor contents and forcing them through the windows. This sort of over pressure IS LIKE the over pressure of an explosion... perhaps not as much or energetic... but similar in nature... gas in motion.

I suspect that this sort of thing was also in play in the crush/interaction zone of the top and bottom in WTC 2... it was responsible for the dust shroud around the bottom obscuring vision of that zone. So again we can't make this seem as neat interactions which DIDN'T create enormous destruction AND movement or air which carried with it the destroyed floor contents and so forth.

In some vids it looks to me that the top sort of held together and dropped INTO the obscuring dust canopy... whether with or partially outside the footprint as the dust canopy was substantially larger than the building's footprint.

What we have is a observation/understanding or what we are seeing problem which Tom has worked so hard to illustrate. We can't begin to explain the event if we can't accurately describe what we are actually seeing. What is the mapping, identity and motion of the things we see? Some people HAVE imagination AND some understanding of physics to inform their observations. Others see the world through a hollywood special effects filter (mis)informing their *understanding*. And Chandler, for example, is obviously not immune to seeing the event through some filter. And many turn to him as a go to guy to explain what they are seeing.

ozeco41 wrote:As first stage of explaining that take this simplified example:

2B looks familiar...

Plagiarism???

SanderO wrote:Ozzie,

First I made a cartoon and could not possibly manage to illustrate all the processes at play nor was that my intention with that cartoon.

Understood - my point being I would use it and the deliberate simplifications would not hinder it being a useful aid to understanding.

SanderO wrote:...I began a thread a while back about the progression of failure of the core columns... Another cartoon thought experiment.. I've attach the pdf I made for that discussion....

I saw it at the time and another good effort. I have a copy of the pdf in my records. Couldn't comment one way or the other without a lot of serious thought but I commend the mental effort as worthwhile.

SanderO wrote:....I suspect the hurdle to understanding the movement/destruction is to account for the apparent almost instant change from a descending block (at least the top part of it visible) from an organized tilting block of many stories of the building into what appears to be total destruction. POOF...

Yes - it is a significant feature. I'm not familiar with the 'transition' stage research on this forum but IMO the perimeter inside/outside lower tower and consequent 'knife edge' removal of floors would be one factor IMO - as I said somewhere in a recent post. There are two (at least) legit ways of analysing these complex events - detailed visual observations or reasoning from broad evidence and dealing with all the possibilities. Or a blend of the two as I outlined at the start of the recent post.

SanderO wrote:... The truth movement sees this as evidence of massive or multiple simultaneous explosions. That is to say that their logic is that the top section had to continue and fall off/over the side and if it didn't then the destruction seen was the result of explosive devices...

The truth movement seems to be dominated by 'thinking out from the inner details' rather than 'thinking inwards from the known facts/evidence/observation/measurements'
..that to me is the most prevalent thought process issue. Then add all the other preconceptions stuff:
1) Commitment to it must have been inside job Therefore CD therefore lets look for evidence...
2) etc

SanderO wrote:...This is very much akin to what they see in the top of WTC 1... they do not see it as descending and being crushed and destroyed from the bottom up (like a typical CD)... They see the top being exploded and sending its parts flying over the side. Does it make sense for a collapsing 16 story structure up there NOT to have parts of it fall/fly off outside the footprint? Why not? It's kinda hard to imagine material NOT being tossed all over the place including outside the footprint when a 16 story structure *collapses*...

Definitely. At the very least it is not clear cut the way they present it. The underlying problem being their innate 'appeal to incredulity' in the form 'I don't understand therefore...' and the unstated assumption 'There cannot be anything that I cannot understand...'

you and I know differently. There is a lot I don't understand...accounting for one. So don't go there spouting opinions....rather admit limits and ask questions.

Next two paragraphs understood and generally agreed.

SanderO wrote:...What we have is a observation/understanding or what we are seeing problem which Tom has worked so hard to illustrate....

probably at least as much effort as anyone...

SanderO wrote:...We can't begin to explain the event if we can't accurately describe what we are actually seeing. What is the mapping, identity and motion of the things we see? Some people HAVE imagination AND some understanding of physics to inform their observations.

that last bit being me - my strong point as an engineer has been three dimensional visualising - a lot of engineers not strong in that arena - I mentioned the 'NLP' thing a couple of posts back. I may post a couple of War Stories from my younger days when I spotted errors my bosses couldn't/therefore wouldn't see.

SanderO wrote:...And Chandler, for example, is obviously not immune to seeing the event through some filter. And many turn to him as a go to guy to explain what they are seeing.

Yes. Tragic really. He makes the same base errors of wrong assumptions that some others specialise in.

Cheers - have to go bus driving.