The 9/11 Forum

Check the 2nd one for example at

http://www.wideo.fr/search/?q=demolition+abc

Very interesting.

And the link from the other thread

http://www.dailymotion.com/video/x17lks_demolition-tour-abc-balzac-vitry_news

This mode of demo means that commercial companies have been working with the practical mechanics of "crush-up, crush-down".

Since this type of demo is a controlled case of the very type of demo the hypothetic case that BZ and it's offshoots are taking about, it means that all these ideas given by BZ, BGLB and others are testable.



In the videos,

1) Does the upper block retain it's form?

2) Don't both upper and lower block seem to destroy one another?

3) Does the movement of the upper and lower block conform to the equations of motion in BGLB or it's offshoots?

Does the initial speed of decent of the upper block of this demo where we know all supports were intentionally removed at the same time, compare to the initial WTC 1 movement?


Every equation and idea in BGLB is testable by comparing it's predictions to known cases of demos using a "crush-up, crush-down" technique.

How do they measure up to the test?


In this demo, can anyone distinguish a zone of compacted material on which some upper block "rides"?


To crush this building, the technicians who planned this demo felt that 3 floors of initial fall would be sufficient.

BZ predicts that only one floor would be needed to finish off everything below floor 96? of WTC 1.

Major_Tom wrote: 1) Does the upper block retain it's form?

Depends on mass. As Bazant & Le calculate, some initial crush-up indeed occurs. The amount obviously depends upon momentum.

2) Don't both upper and lower block seem to destroy one another?

I can only imagine, since I don't/can't watch videos. Not relevant to the developments in BLGB, since there is no three story free fall in the collapse of WTC 1.

3) Does the movement of the upper and lower block conform to the equations of motion in BGLB or it's offshoots?

Provide me with well done measurements and I'll be happy to calculate the degree of conformity. I anticipate little until after the two blocks collide and thereafter fair agreement to a crush-down equation.

Does the initial speed of decent of the upper block of this demo where we know all supports were intentionally removed at the same time, compare to the initial WTC 1 movement?

Make some measurements from the video. My initial conjecture is that the demo starts near free fall acceleration, much greater than the (nominal) 0.7g for WTC 1.

To crush this building, the technicians who planned this demo felt that 3 floors of initial fall would be sufficient.

Engineering conservatism.

The point is that if you could see the video linked, none of the things predicted actually take place.

They exist in theory only. Mpst everyone reading is able to watch video and they can see with their own eyes that the upper block does not ride the lower block over some "zone B".

These ideas are presented with very little thought that they can be tested by using known demolitions.

When we look at crush-up, crush-down in actual demolitions, the predictions made about the upper block and "zone B" in the papers you site are seen to exist only in the imaginations of their respective writers.

Major_Tom --- One of the simplifications in B&V is homogeneity. May not apply, even approximately, to such a small structure as I imagine this one to be. In any case it would only be applicable after the impact between the upper and lower part.

Still, you can probably estimate the mass of the upper part to determine the KE after falling three stories. Do the same for WTC 1 falling one story. Then compare what I will call the energy intensity, energy per square meter.

These are not all frames but 1/3 of them. You can wonder why they didn't remove 1 story of this completely stripped and pre-weakened building. In the other video there is a better view of the resistance and you see mass moving away from the footprint but I have to figure out how to d/l it

http://i43.tinypic.com/2qtz48i.jpg

Einsteen:

Nice set of images!

Can you provide the time interval between each frame?

My guess is about 0.25 seconds ......

Einsteen --- Thank you for the still images!

I don't see any crush-up of the upper portion, just its descent into the obscuring fines (dust).

But I claim no partidular ability in photo-interpretation, preferring to rely on the judgements by others.

Dr. G, that should then be 3/25=0.12, the framerate was 25 fps and I took every 3rd one.
DBB, it is indeed hard to see what happens, more will follow later

The videos linked show the CD from a few different angles.

When did this demolition take place?

I ask because B & V presented their work at the 2006 ASCE progressive collapse conference (maybe 2005 one). Obviously the demolitionists would have considerable interest in attending that conference series, so might have obtaining the idea of this demolition method by listening the Professor Bazant present the B & V paper.

Einsteen:

Thanks! I would say (very roughly!) that the building was about 56 meters tall since it had about 16 stories (14 + 2 for the entrance lobby) and your average story height is ~ 3.5 meters. Looking at the set of frames you can estimate the time for the right hand corner roofline to drop 2 stories (relative to the long black building in the background) is about 10 frames. So we have a drop of 7 meters in 1.2 seconds in which case the acceleration was (2x7)/(1.2)^2 = 9.7 m/s^2, or pretty close to g! There is, however, the old problem of defining t(0) since the building does not appear to start dropping until about frame three... (?)

So we have a drop of 7 meters in 1.2 seconds in which case the acceleration was (2x7)/(1.2)^2 = 9.7 m/s^2, or pretty close to g!

Makes sense since a 2 floor section of all the columns seems to be intentionally removed. After this 2 or 3 story fall we expect the acceleration to noticably decrease, which it seems to do.


In the OP video link we can see the upper block becomes totally destroyed during this process. We can see it being destroyed. No surprise for me because this is what I would expect to happen. Crush-up seems to happen at about the same rate as crush-down.

Einsteen --- Would you be so kind as to produce some jpg files from the OP video link? I would like to view the claimed "total distruction" of the upper portion for myself.

To compare with what Bazant & Le have written regarding initial crush-up.

I would like to view the claimed "total distruction" of the upper portion for myself.

It is a demo, David. Destruction is the idea.


Interesting that the demo planner chose to collapse 2 floors located about half way up the building.

Could he have known from experience that crush-up happens at about the same rate as crush-down, hence the middle of the building is chosen?

The upper block destruction is visible even in the photos einsteen posted earlier. Notice how for the visible face, the top visible portion seems to "disappear" at about the same rate as the bottom visible portion.

In the OP link you can see the destruction of the top portion and even the destruction of the roof.