WTC7 and the NIST free fall failure

[achimspok]

On the NIST website "Questions and Answers about the NIST WTC 7 Investigation (Updated 09/17/2010)" you find the following:

In a video, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe. How can you ignore basic laws of physics?

In the draft WTC 7 report (released Aug. 21, 2008; available at http://wtc.nist.gov/media/NIST_NCSTAR_1A_for_public_comment.pdf), NIST stated that the north face of the building descended 18 stories (the portion of the collapse visible in the video) in 5.4 seconds, based on video analysis of the building collapse. This time period is 40 percent longer than the 3.9 seconds this process would have taken if the north face of the building had descended solely under free fall conditions. During the public comment period on the draft report, NIST was asked to confirm this time difference and define the reasons for it in greater detail.

To further clarify the descent of the north face, NIST recorded the downward displacement of a point near the center of the roofline from first movement until the north face was no longer visible in the video. Numerical analyses were conducted to calculate the velocity and acceleration of the roofline point from the time-dependent displacement data. The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel (a single element in the video image) at the roofline. This pixel became brighter as the roofline began to descend because the color of the pixel started to change from that of the building façade to the lighter color of the sky.

The approach taken by NIST is summarized in Section 3.6 of the final summary report, NCSTAR 1A (released Nov. 20, 2008; available at http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR 1A.pdf) and detailed in Section 12.5.3 of NIST NCSTAR 1-9 (available at http://wtc.nist.gov/NCSTAR1/PDF/NCSTAR 1-9 Vol 2.pdf).

The analyses of the video (both the estimation of the instant the roofline began to descend and the calculated velocity and acceleration of a point on the roofline) revealed three distinct stages characterizing the 5.4 seconds of collapse:

* Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
* Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)
* Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity


This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below.

http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.cfm

That short free fall was/is discussed a lot.
I tried to "replicated" the NIST measurement.

HOW DID NIST MEASURE THE FREE FALL?

According to NIST_NCSTAR_1-9_vol2 12.5.3. NIST used the "camera 3".

That's the view NIST used for the measurement:

In the Draft Report NIST states: "The elevation of the top of the parapet wall was +925 ft. 4 in. The lowest point on the north face of WTC7 visible on the camera 3 video (section 5.7.1) prior to any downward movement was the top of windows on floor 29, which had an approximate elevation of +683 ft 6 in."

That information got lost in the final NCSTAR 1A Report.

However, just a small part of the "top of windows on floor 29" is visible.
To measure the fall of the building NIST had to measure a vertical path above the visible top of the windows.

Therefore we have to know how NIST defined the "parapet wall".

NIST defined "parapet wall" for the same elevation they defined as "roofline" in the final report.

Hence, we have to measure that path:

The following image shows that NIST was aware of a difficult problem to measure the fall down the described path:

The "screenwall" is visible above the roofline and had an elevation of about two additional floors and the lack of contrast allows no direct tracking of the roofline.

So how was NIST able to measure the fall of the perimeter wall?
They answer the question in the FAQ:

The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel (a single element in the video image) at the roofline. This pixel became brighter as the roofline began to descend because the color of the pixel started to change from that of the building façade to the lighter color of the sky.

In other words, NIST did not measure the parapet wall! They measured the fall of the screenwall about 2 floor heights above the parapet wall. They took the time and subsequently calculated a fall speed for the smaller fall distance.

And there is a second problem with the NIST method.
The perimeter wall didn't bow downwards as visible from a different vantage.

Instead the perimeter wall stayed vertically straight even during the fall for several floors.
The motion of the perimeter wall as visible from "camera 3" is nothing but the bowing of the perimeter towards the core.

In other words, NIST measured the drop of the "screenwall" + the transition of the falling screenwall into the horizontal bowing of the perimeter wall + the transition into the vertical motion of the perimeter wall.

The red curve shows the motion NIST measured:

The fat bright blue curve is a calculated free fall.
The lower curves are the trackings of several floors in the NIST measure path. The slow onset of motion of these lower curves is the result of bowing away from the camera.

Since NIST gave the real elevations along the path it is possible to calculate the velocity for the entire motion.

That's a pretty different result.

In the Final Report as well as in the FAQ NIST described their result this way:

* Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
* Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)
* Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity

The NIST "stage 1" includes about the frames 150 ... 202 of my motion tracking measurement.
That NIST "slower than free fall" stage 1 includes the following real events:
- the screenwall on top of the core started to move (frame 150...155)
- the screenwall reached about free fall (frame 156...170)
- the screenwall disappeared behind the parapet wall (frame 170)
- the perimeter wall bows towards the core (frame 170...180)
- the perimeter wall dropped above gravity (frame 180...200)

That's where stage 2 at "gravitational acceleration (free fall)" begins.
That means there is almost no vertical motion slower than freefall but for the very first 0.17 seconds AND that short amount of "slower than free fall" is probably stretched by the symmetrical averaging of the velocity over 9 frames.

So how is it possible that the perimeter dropped faster than free fall?
Simply imagine some dumbbell like object that rotates vertically and fall at the same time.

Core and perimeter were still connected by the floor system. Once the core dropped at gravitytational acceleration the core-floor-perimeter acted like a spring system. Firstly, the core pulled the perimeter inwards. Secondly, the perimeter failed at a very low elevation and was shot downwards by the "floor-springs". The falling core was slowed down at the same time until the entire system fell as one unit.
Of course the center of mass of the entire system cannot exceed gravitational acceleration but the perimeter can and it tells a lot about the intact inner structure of the upper and visible building part.

I leave it up to you to decide if either NIST did several "beginners mistakes" in a row while being very aware of the higher screenwall or if NIST just tries to hide the facts. The measurement itself is unambiguous.

 

[switchpoint]

based on video evidence, was approximately

Kind of says it all.

 

[Dave Rogers]

Just one point, other than that this is all futile nitpicking:

In other words, NIST did not measure the parapet wall! They measured the fall of the screenwall about 2 floor heights above the parapet wall. They took the time and subsequently calculated a fall speed for the smaller fall distance.

The quote clearly states that NIST used the change in pixel colour to establish a start point for the timing of collapse. At no point does it suggest that they conflated the position of the screenwall with that of the roofline, nor that any of their measurements of position are taken from the screenwall.

Dave

 

[achimspok]

Just one point, other than that this is all futile nitpicking:



The quote clearly states that NIST used the change in pixel colour to establish a start point for the timing of collapse. At no point does it suggest that they conflated the position of the screenwall with that of the roofline, nor that any of their measurements of position are taken from the screenwall.

Dave

Right, they didn't mention a lot. But if they measured a vertical fall down to the windows they mentioned then they had no chance to measure the parapet wall especially triggered by the change of a pixel from "gray" to "sky color".

On the other hand they got the same "stages" I measured but interpreted the measured movement in the wrong way.
If they indeed would have find some way to measure the fall of the parapet wall then they would get different "stages"/"times", wouldn't they? I thought it is quite easy to understand.

Where are the 1.75 seconds (50 frames) of "slower than free fall" of the parapet wall besides the inward bowing?

...futile nitpicking, you say it.

 

[Myriad]

Where are the 1.75 seconds (50 frames) of "slower than free fall" of the parapet wall besides the inward bowing?

What inward bowing? There is bowing but I do not see any horizontal contraction of any part of the face of the building. Note that the building squashes outward horizontally in your animated gif of frames 140-170, the opposite of "inward" bowing. What you call inward bowing is, therefore, falling, at inconstant rates across the width of the facade, and at acceleration less than free fall, reflecting the start of buckling of the facade columns below.

Respectfully,
Myriad

 

[femr2]

What inward bowing? There is bowing but I do not see any horizontal contraction of any part of the face of the building. Note that the building squashes outward horizontally in your animated gif of frames 140-170, the opposite of "inward" bowing. What you call inward bowing is, therefore, falling, at inconstant rates across the width of the facade, and at acceleration less than free fall, reflecting the start of buckling of the facade columns below.

Respectfully,
Myriad

No, it's primarily non-vertical movement. An optical illusion from the Cam#3 viewpoint if you will. A side-effect of the global twisting of the building.

 

[alienentity]

No, it's primarily non-vertical movement. An optical illusion from the Cam#3 viewpoint if you will. A side-effect of the global twisting of the building.

Myriad's correct.

But to address the OP by achimspok....

Given that there is no evidence of controlled demolition in this collapse anyway, this is nothing but obsessive nitpicking. However...

To address one statement of yours which I think is blatantly incorrect,
'Motion of the perimeter wall as visible from "camera 3" is nothing but the bowing of the perimeter towards the core.'
It's very easy to falsify that statement as your own green line clearly shows a vertical drop of the parapet wall about midway thru the building, as well as an extensive horizontal distortion of the building.

As to whether they measured from the screenwall as you allege or the parapet wall: The first video I made examined that same question, that is - did the drop take 5.4s or not?

The answer, contrary to what you and David Chandler allege, is 'yes'.
5.4s is, as the NIST stated, 'approximately' the time it took to fall 18 floors.

Incidentally, you also attempt to muddy the waters by alleging that the video clip they used (camera 3) is somehow less accurate than another 'from a different vantage'. Funny thing that, because as it happens the second vantage is the one I used, since I wasn't aware of the Camera 3 clip at the time.
In my video I documented the vertical and horizontal motion of the building, and carefully (and correctly) identified the parapet wall, distinct and very easy to distinguish from the structures of the Penthouses and screenwall.

You allege:
'And there is a second problem with the NIST method.
The perimeter wall didn't bow downwards as visible from a different vantage.'
Yes, it does. You are incorrect again.



Finally, you wrote an analysis regarding the behavior of the building. While I think your ideas are not without merit, they are far to generalized and simplified to correctly describe the mechanics of the collapse, IMO.
I think the NIST described, in words, much more accurately, the sequence of collapse events. And this is not really surprising, since you can't possibly infer from the videos the complex events that were taking place out of sight. For that information, even to speculate, you need to reconstruct the collapse in much greater detail, as NIST did.

btw, I find your term 'beginners mistake' really childish and frankly disingenuous. To imply that somehow teams of professional engineers are mere 'beginners' is really unconscionably disrespectful and deceitful. Really, it is you and I who are the 'beginners', and who need to learn.
Clearly, achimspok, you are choosing not to learn the facts, but instead you are attempting to obscure them through some rather transparent methods of dissembly.

I apologize for being harsh, but I really don't like dishonest people.

 

[achimspok]

What inward bowing? There is bowing but I do not see any horizontal contraction of any part of the face of the building. Note that the building squashes outward horizontally in your animated gif of frames 140-170, the opposite of "inward" bowing. What you call inward bowing is, therefore, falling, at inconstant rates across the width of the facade, and at acceleration less than free fall, reflecting the start of buckling of the facade columns below.

Respectfully,
Myriad

Cam 3

Top view

Sorry, there is just inward bowing without vertical component prior to FREE FALL. What you call "inconstant rates" is just the transition from fall of the screenwall into bowing of the parapet wall into the falling of the perimeter. No reflecting of buckling whatsoever. The NE corner tilted north while bowing, that's it.

 

[femr2]

Myriad's correct.

The apparent vertical displacement is an optical illusion from the Cam#3 viewpoint. Go cross reference it with other viewpoints.

To address one statement of yours which I think is blatantly incorrect,
'Motion of the perimeter wall as visible from "camera 3" is nothing but the bowing of the perimeter towards the core.'
It's very easy to falsify that statement as your own green line clearly shows a vertical drop of the parapet wall about midway thru the building, as well as an extensive horizontal distortion of the building.

You are yet again misinterpreting the effect of the Cam#3 perspective. It's not primarily vertical motion at all.

As to whether they measured from the screenwall as you allege or the parapet wall: The first video I made examined that same question, that is - did the drop take 5.4s or not?

Not...

<5s.

The answer, contrary to what you and David Chandler allege, is 'yes'.
5.4s is, as the NIST stated, 'approximately' the time it took to fall 18 floors.

A bad NIST value isn't made any better by adding quotes to 'approximately'.

Incidentally, you also attempt to muddy the waters by alleging that the video clip they used (camera 3) is somehow less accurate than another 'from a different vantage'.

Incorrect. The point is showing how the viewpoint perspective affects interpretation of the motion, which you've clearly not 'got'.

Funny thing that, because as it happens the second vantage is the one I used, since I wasn't aware of the Camera 3 clip at the time.

Hilarious

In my video I documented the vertical and horizontal motion of the building, and carefully (and correctly) identified the parapet wall, distinct and very easy to distinguish from the structures of the Penthouses and screenwall.

...and so you did not use a point in the middle of the facade. NIST really shouldn't have either, as they messed up identifying where it actually was

etc...

I apologize for being harsh, but I really don't like dishonest people.

Begin by being *right*.

 

[JimBenArm]

So you're saying that NIST didn't fall at free-fall velocity?
Man, that changes everything.

 

[femr2]

Just one point, other than that this is all futile nitpicking:



The quote clearly states that NIST used the change in pixel colour to establish a start point for the timing of collapse. At no point does it suggest that they conflated the position of the screenwall with that of the roofline, nor that any of their measurements of position are taken from the screenwall.

Dave

So you must, therefore, be suggesting that NIST used a different point to determine the position/time graphs included within the report... ?

Dave, What point did NIST use to generate Fig 12-76 ?

 

[Myriad]

Cam 3
[qimg]http://img69.imageshack.us/img69/6567/c3view.gif[/qimg]

Top view
[qimg]http://img138.imageshack.us/img138/2995/topview.gif[/qimg]

Sorry, there is just inward bowing without vertical component prior to FREE FALL. What you call "inconstant rates" is just the transition from fall of the screenwall into bowing of the parapet wall into the falling of the perimeter. No reflecting of buckling whatsoever. The NE corner tilted north while bowing, that's it.

Interesting claim, but your two animated views are inconsistent. In the cameras-eye view, the left (southwest) corner moves left, apparently to be consistent with the video. In the top down view, that corner moves north and a little east, and so would not move left from the cameras-eye viewpoint or any viewpoint near it. Something's been fudged there.

Also, horizontal spreading of the wall, as depicted in the first animation, caused only by inward bowing as depicted in the second, would require the wall to stretch (without fracturing, or causing all the windows to break). Not plausible.

Respectfully,
Myriad

 

[achimspok]

Myriad's correct.

But to address the OP by achimspok....

Given that there is no evidence of controlled demolition ...

Alienentity, I know your video since you made it. I wrote you several times to correct your "beginner failures". You simply add the times of different FALLING building part divide your sum by the distance and get some slow motion collapse. I even made a little video in response called "Little debunker riddle". You obviously do not or want not understand the nonsense you have blown out into the public. So how can I explain you some problem in 3 dimensional space. After all these years, I have no idea.

btw, I find your term 'beginners mistake' really childish and frankly disingenuous. To imply that somehow teams of professional engineers are mere 'beginners' is really unconscionably disrespectful and deceitful. ...

Well, if it wasn't a "beginners mistake" then it was intentionally. How do you like it?

 

[achimspok]

Interesting claim, but your two animated views are inconsistent.

No, they aren't. It's the same 3D model and the same animation in two different views. I just split the windows because otherwise each window would be very small.
http://img515.imageshack.us/img515/2706/move00021.png

Also, horizontal spreading of the wall, as depicted in the first animation, caused only by inward bowing as depicted in the second, would require the wall to stretch (without fracturing, or causing all the windows to break). Not plausible.

Imho any vertical displacement of the wall should cause a lot of broken windows. The horizontal bowing offers the possibily of deformation between each window.
No need to stretch the wall. What for? The east side was hollowed out and tilted north while the rest of the building contracted.

 

[Dragon37]

Oh joy, yet more blather regarding the free fall. The OP goes through a hell of a lot of "study" just to throw the free fall into question. All that was achieved was to reinforce what I have always said is that in the scope of the overall collapse it means nothing. Whether it was there or not, the free fall that is, doesn't make CD any more plausible.

If the deniers ever bothered to consider the entire event, 9/11 that is, they would realize that their focusing on a few things here and there makes them look foolish. The reason they have no working hypotheses for the entire 9/11 event is because there are massive gaps that require massive generalizations and leaps of faith to explain what went down on 9/11.

 

[Dave Rogers]

So you must, therefore, be suggesting that NIST used a different point to determine the position/time graphs included within the report... ?

http://femr2.ucoz.com/_ph/7/563913536.png

Dave, What point did NIST use to generate Fig 12-76 ?

OK, you may be right. It may have been the same point.

So, we've determined that when achimspok uses a different methodology to measure the rate of fall of a different point on WTC7 using a different definition of T=0, he finds that the collapse took place at a slightly different rate. What does that tell us, other than that NIST didn't waste their time obsessing about the fine details of what happened to WTC7 after collapse initiation, when it was already certain to be completely destroyed?

Dave

 

[alienentity]

...and so you did not use a point in the middle of the facade. NIST really shouldn't have either, as they messed up identifying where it actually was

etc...

Femr2, you're tedious and repetitive. Just to clarify one of your misinterpretations/assumptions, yes, I used a point about midway.

So unroll your eyes, because you're talking wet.

Further, your constant misinterpretations of blatantly obvious details are not even entertaining, they're just plain irrelevant. Both camera angles show vertical displacement.

I measured it, Chandler measured it (but from the right corner, which moves later, as was also documented by NIST) and it's a fact. Stop trying to obfuscate - God only knows what you hope to accomplish....hoping that people will dismiss the entire report, throwing the baby out with the bathwater, so to speak?

Tell you what, I'll throw out your incorrect analysis, and stick with what I've already verified for myself.

Thanks for playing the 'attempt to revise physical reality' game.

 

[beachnut]

Oh good grief! It wasn't the Taliban that attacked the US, it was Al Qaeda!

How are we supposed to take criticisms seriously when basic errors of fact are so blatantly pushed? If I remember correctly (correct me if I'm wrong), I don't think a single person involved in the plot was even Afghani, and yes, I'm talking about the planning stages too.

And after ignoring the internal collapse of WTC7 and studying the facade, we have a final conclusion of fire did it.

19 terrorists did 911, as 911 truth want to be engineers are hung up on NIST, unable to comprehend an internal collapse of WTC7.

Beginner mistake or incompetence?

Core and perimeter were still connected by the floor system.

Sources? Proof? Alas, only opinions from non-engineers with paranoid conspiracy theories.

 

[achimspok]

Oh joy, yet more blather regarding the free fall. The OP goes through a hell of a lot of "study" just to throw the free fall into question. All that was achieved was to reinforce what I have always said is that in the scope of the overall collapse it means nothing. Whether it was there or not, the free fall that is, doesn't make CD any more plausible.

If the deniers ever bothered to consider the entire event, 9/11 that is, they would realize that their focusing on a few things here and there makes them look foolish. The reason they have no working hypotheses for the entire 9/11 event is because there are massive gaps that require massive generalizations and leaps of faith to explain what went down on 9/11.

CD? Free fall means 9.81m/s². You can measure it. I did. Any problem about that? ...besides the constructed prerequisites for a buckled theory?

 

[alienentity]

Well, if it wasn't a "beginners mistake" then it was intentionally. How do you like it?

False choice fallacy.

I dug thru a few of your posts on my channel, here's a sample of the kind of serial denialism of your approach:

'achimspok has replied to your comment on WTC 7 NIST Debunked Pt 1 (Hi Res):
Yes, the kerosene was smelled all over Lower Manhattan. And I would cite the Naudet Bros.: "Later they figured out that jet fuel..." That's the point. Start using your brain. Btw 10.000 gallons is non-sense. On the other hand fluids fall like fluids no matter how many gallons.
You can reply back by visiting the comments page.'

'achimspok has made a comment on WTC 7 NIST Debunked Pt 1 (Hi Res):

OK, your Jet-A traveled at 500mph into the tower took a 90° turn to travel down the shaft... still in a tank? ...because IF the tank would be destroyed during the impact the vapor had a serious problem to travel at that speed.
So take the volume of the shafts, take a 3psi overpressure (NIST) and calculate how far the pressure could push the (burning) vapor ((little help: 77th floor)). What happens next (any other day but on 9/11)?
You can reply to this comment by visiting the comments page.'

'achimspok has made a comment on WTC 7 NIST Debunked Pt 1 (Hi Res):
And to end this near to stupid discussion: The myth of jet fuel fireballs are exactly the LESS LIKELY because you just had 3 express shafts, no falling cabins than #55, a destroyed west side, witnesses and physics. Just bring it together and don't repeat what you've been told.
You can reply to this comment by visiting the comments pag'

Yes, according to self-appointed guru, achimspok, the jet-fuel fireballs are a 'myth'.
All those eyewitnesses who reported the flames, fireballs, white smoke and jet-fuel smell in the subbasement etc... can all be safely ignored.
The victim who had his skin burned off (reported by Rodriguez) was just an illusion - that must've been done by thermite or something magic that we've never seen.

Yeah, good work achimspok. Keep fighting against the truth with all your heart. It'll get you a long way, maybe you can become the next leader of the Republican party, or work for a standup guy like Tony Blair, who would never tell a lie.