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Demolitions using a falling upper block...

Examples and case studies of demolition, and other progressive and cascading failures

Re: Demolitions using a falling upper block...

Postby T_Szamboti » Wed Feb 11, 2009 10:28 am

Dr. G wrote:T. Szamboti:

I find it interesting that you apparently want to compare the collapse of WTC 1 with the collapse of the ABC Tower in France, and consider one to be "natural" and the other, presumably, to be "unnatural". The question is: which is which?

But be that as it may, when you say there was negative acceleration in the ABC Tower collapse, I am not so sure. And I have measured the collapse rate over the first 2.5 seconds and all I can say is that a jolt is possibly present, but only as a reduction in downward acceleration after 7 meters of drop. However, negative acceleration is never present as far as I can tell.

What I find most interesting right now is how the ABC Tower was "pulled" by those clever French engineers, and the possibility that there may have been an acceleration greater than g over the first 7 meters. Now this is reminiscent of WTC 7

But this shows that the ABC demolition was far from being "natural", thus I would not expect WTC 1 to replicate the ABC collapse - on the contrary, I would expect it to be quite different!


Dr. G,

I don't know how you are measuring the fall of the upper block in the abc tower, but we are using the same recognized method which forced the NIST to acknowledge the freefall of the upper block of WTC 7 for 2.25 seconds.

The slope on the velocity curve actually reverses direction in the plot of the data taken of the fall of the upper block from the abc tower demolition. This is a negative acceleration and provides evidence of a mechanism for the load amplification necessary to allow the statically undersize load above to overload the columns below. This is not present in the measurements of the fall of the upper block of WTC 1, and since there is no other natural mechanism to allow the upper block to overload the columns of the lower block, it's destruction had to have been assisted by means other than the weight of the upper block.

We aren't getting greater than g acceleration in our measurements of the fall of the abc tower upper block. If you are, I think it is likely to be measurement error. Even if there was greater than g acceleration, possibly due to some form of whip action, it is insignificant to the issue of whether or not an impulse occurred to provide a natural mechanism for the destruction and collapse of the lower block to occur.
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Re: Demolitions using a falling upper block...

Postby Dr. G » Wed Feb 11, 2009 2:51 pm

T.S:

I am using freeze-frame measurements on about 14 images captured from the excellent "Mort d'un Batiment" video. I acknowledge that this is rather crude, but I would like to see your actual data to see how you arrived at your negative acceleration claim. In my latest effort I do see some sort of hiatus in the collapse progression at a drop of about 7 meters, which would be consistent with a jolt after a 2-storey drop. However, I don't see this on Einsteen's smearogram posted yesterday (does anyone else see it?), although the image our estimable Einsteen put up is very small. That's why I asked him to blow it up! I believe that the smearogram technique is the best we have to resolve these and related questions (i.e. WTC 1, 2 and 7) ....
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Re: Demolitions using a falling upper block...

Postby Major_Tom » Thu Feb 12, 2009 1:36 am

On a couple of einsteen's points,

I think that this collapse is interesting, not because of the simultaneous symmetrical initiation but because of the fact that this one of the few videos that potentially could be used to check the crush-down crush-up theory.



Yes, it is set up like our own little crush-up, crush-down experiment.


I recently did some primitive experiments at home with big plastic lego blocks which I didn’t really close (by stacking them but not pushing them together) and if you drop that on the floor the blocks at the bottom first are pushed together as expected, in this equal mass/force situation. But a crush-down is a totally different experiment, I couldn’t really reproduce it, although scaling is relevant it seems very sensitive to the difference in friction forces, but as expected if you place a stack of them and push the upper block down with your hand they all are pushed together at the same time and I thought that also happened by dropping a heavy object on it.



This lego idea can show us how an impact would affect a "crush-up" column or section as opposed to a "crush-down" column or section....

This is a primitive but very interesting little experiment. The crush-up section absorbs the impact near it's base. The base of the column acts as a "shock absorber". The energy of the impact serves to cause deformation near the base of the impacting section.


A crush down column or section absorbs the energy along it's entire length????? Complicated. But it is an experiment we can all duplicate at home.

anyway,


The video, of course, should be studied in more detail, but my first temporary impression is that
- the tilt of the top section (it started in fact non-tilted) becomes relevant after some collapse time and is due to the relevant resistance of the material
- the top section is absolutely not intact during the “crush down”
- there are no violent ejections like wtc1,2 only some dust.



Dr DDB, the second point above is rather important, no?

The upper block is indeed vulnerable, crushable and we see it being crushed in the videos.

Einsteen's legos may suggest that the upper block is deformed and destroyed from the bottom up since the crush-up section absorbs (and hence is deformed and destroyed) near it's base.


- there are no violent ejections like wtc1,2 only some dust.[/



Great point. Depending on the initial measured accelerations, the ejections of dust in ABC and the towers should have a similar intensity.

After all, it is just displaced air.

There is no reason for the initial air ejections from ABC and WTC 1 and 2 to have noticably different intensities.

But they do!

In fact, we may expect the ABC to have more rapid initial ejections than WTC1 due to it's higher initial acceleration. But it doesn't. The WTC1 initial ejections are much more forceful.
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Re: Demolitions using a falling upper block...

Postby T_Szamboti » Thu Feb 12, 2009 3:47 am

Dr. G wrote:T.S:

I am using freeze-frame measurements on about 14 images captured from the excellent "Mort d'un Batiment" video. I acknowledge that this is rather crude, but I would like to see your actual data to see how you arrived at your negative acceleration claim. In my latest effort I do see some sort of hiatus in the collapse progression at a drop of about 7 meters, which would be consistent with a jolt after a 2-storey drop. However, I don't see this on Einsteen's smearogram posted yesterday (does anyone else see it?), although the image our estimable Einsteen put up is very small. That's why I asked him to blow it up! I believe that the smearogram technique is the best we have to resolve these and related questions (i.e. WTC 1, 2 and 7) ....


Below is the data for measurements of the roof of the abc tower.

Time (sec)______ Distance (ft.)______Velocity (ft./sec)

0.000_____________0.000
0.200_____________0.000_____________3.026
0.400_____________1.210_____________8.069
0.600_____________3.228____________13.120
0.800_____________6.458____________18.163
1.000____________10.493____________23.206
1.200____________15.741____________25.231
1.400____________20.585____________26.232
1.600____________26.233____________28.249
1.800____________31.885____________26.240
2.000____________36.729____________24.223
2.200____________41.574____________24.215
2.400____________46.415____________24.215
2.600____________51.260

The equation used to find velocity was (Dn+1 - Dn-1)/(Tn+1 - Tn-1) so there is no velocity determined for the last distance measurement.
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Re: Demolitions using a falling upper block...

Postby einsteen » Thu Feb 12, 2009 8:25 am

Major Tom,

Assume you have a building with equal floor masses and strength of the stories. In the static situation the force at the columns below story i=1..n is

i*m*g

and the force at the columns below story i+1 is (i+1)*m*g

Assume the strength of the stories are fixed and m is a variable that can be increased, if you increase m then the story at the bottom will fail first because the biggest force is applied to it.
If m=0 for all stories (and you assume that the columns have no mass) then if you put a force on the top it breaks at a random point or at the point that is the weakest part, due to some small variation in its strength (that doesn't work for a theoretical model).
This was the static case, now if it is dropped from some height and the masses are m>0 then the crush-up is IMHO due to the same kind of effect.
It is not because of a crumbling zone at the bottom but because of the mass.

Now if we look at a building (again equal mass/strength) in which a force is slowly applied at the top, assume we have a static situation of a top section in which the mass increases, what would happen ?

If the masses of the building itself are zero then we have the same thing as before. Do you remember the spaghetti experiment, in which a weight is dropped on a piece of spaghetti ?
That does not break only at the top but the forces are redistributed through the whole piece, it breaks for example at 3 parts, this will not happen for real columns, but for real steal columns we will not get a crush-down if a force is applied.
The situation with masses m>0 is a little bit more difficult because of inertia etc. One should setup differential equations which is not easy. As I said the experiment is primitive and I'm not sure, maybe I'm indeed wrong. I thought I saw some blocks
pushed together, but also one between it that wasn't, not strictly from the top. If you slowly apply a force then it is surely a homogenous situation. If you slowly do that and the first story fails first then the one below is stronger. The crush-down
could also be caused by the fact that stories become stronger to the bottom.

the difference between crush-up crush-down in a equal mass/strength system can be seen if you think about the variable mass:
- If you have a building and increase its mass uniformly the stories at the bottom fail first. If
- If you have a building and increase only the mass of a rigid top section (which means a increasing force is applied at the top) then
for sure not the remaining top story will break first, in fact even the one at the bottom will fail first then. but I'm absolutely not sure about the dynamic situation, I think I'm stupid.
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Re: Demolitions using a falling upper block...

Postby Dr. G » Thu Feb 12, 2009 6:11 pm

T. Szamboti:

Thanks for posting your data. My data are actually quite similar, especially over the first 1.2 seconds....

I have converted your numbers to metric and plotted the results as shown below:

Image

However, if I was shown this data without knowing any details and simply told it's from a collapsing building, ..... and I was asked for comments, ..... here's what I'd say:

This building's collapse had an induction period of about 1.2 seconds after which it fell at a more or less constant velocity of about 7.73 m/s or 25.4 ft/s. This implies that the downward force of gravity "pulling" the building down was pretty much balanced by the upwards force of resistance. This behavior is quite common for collapsing buildings. The jolt you claim to see at 1.8 seconds is really hardly noticable and it also makes no sense that this alleged jolt occurs after a drop of 9.14 meters (or 30 feet). I say this because when we look at the video we see the first hard impact occurs at more like 7 meters (or 23 feet) which corresponds to 2-floor heights, as expected.
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Re: Demolitions using a falling upper block...

Postby David B. Benson » Thu Feb 12, 2009 7:40 pm

Dr DDB, the second point above is rather important, no?

Not until I can see it, to think how this agrees/disagrees with Bazant & Le.

The WTC1 initial ejections are much more forceful.
Much bigger building; 12 acre-feet of air was rapidly ejected.
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Re: Demolitions using a falling upper block...

Postby einsteen » Thu Feb 12, 2009 10:02 pm

Honey I blew up the kid

Image
http://i39.tinypic.com/ev8cap.jpg

I have a tool that is able to scale up images with a so-called s-spline xl method, that is used for this one with a factor 4, still no smearo data of course...that has to wait, maybe the perpendicular video is better for that after averaging a couple of points.

As said before the lighther shade of gray is due to the tilting, but that implies of course that if the video was taken from the other side we would see that different acceleration.

Then the h(t) function changes from convex to concave (or vice versa), we also saw that for wtc7 but only later in the collapse because there the resistive force becomes more relevant.

What does that mean convex to concave ? The derivative h'(t) has a maximum at a point t1 or the 2nd derivative h''(t1)=0, if further study implies that there exist a t1 for which h''(t1)=0 then we have zero acceleration at that point or a real negative acceleration at t>t1, which means it then really decelerates.
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Re: Demolitions using a falling upper block...

Postby Dr. G » Fri Feb 13, 2009 12:18 am

Thanks Einsteen,

That's great!

As to concave vs. convex, the answer my friend is complex ....

Or to give the answer a new complexion,

As to concavity vs. convexity, the answer is complexity!
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Re: Demolitions using a falling upper block...

Postby T_Szamboti » Fri Feb 13, 2009 1:49 am

Dr. G wrote:T. Szamboti:

Thanks for posting your data. My data are actually quite similar, especially over the first 1.2 seconds....

I have converted your numbers to metric and plotted the results as shown below:

Image

However, if I was shown this data without knowing any details and simply told it's from a collapsing building, ..... and I was asked for comments, ..... here's what I'd say:

This building's collapse had an induction period of about 1.2 seconds after which it fell at a more or less constant velocity of about 7.73 m/s or 25.4 ft/s. This implies that the downward force of gravity "pulling" the building down was pretty much balanced by the upwards force of resistance. This behavior is quite common for collapsing buildings. The jolt you claim to see at 1.8 seconds is really hardly noticable and it also makes no sense that this alleged jolt occurs after a drop of 9.14 meters (or 30 feet). I say this because when we look at the video we see the first hard impact occurs at more like 7 meters (or 23 feet) which corresponds to 2-floor heights, as expected.


I don't know how you could determine what you are saying from the graph you posted here, as it is not velocity vs. time, it is just distance vs. time, and therefore can't be used to discern a jolt or anything about acceleration or deceleration. You need to plot velocity vs. time to see acceleration or deceleration as it is the slope of the velocity curve that represents acceleration or deceleration.
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Re: Demolitions using a falling upper block...

Postby Major_Tom » Fri Feb 13, 2009 1:51 am

Quite a smearogram.



The 2 floor fall point seems to be a transition between a high acceleration phase and a practically constant velocity phase. This transition is smooth.

We know a major collision occurs here, yet the top of the building is seen to move smoothly through this point. Hmmmm.




Is this transition after 2 floors of falling really smooth like the smearogram suggests?

We know that if this collision happened between 2 rigid point-masses the collision point would be very noticable. There would be no smoothness.


So why is it smooth? (I think the structures, upper and lower, are absorbing the shock. What do you think?)

Dr G says

I believe that the smearogram technique is the best we have to resolve these and related questions (i.e. WTC 1, 2 and 7) ....



It appears that a person can put a horizontal time axis and vertical displacement axis directly over the smearogram and plot h(t) that way.

I am a bit confused over the smoothness of the smearogram near the 2 floor fall point. Only a mistake or a massive absorbtion of the shock can explain this.

These 2 points,

1) destruction of the upper block with crush-up happening at about the same rate as crush-down

2) the capacity of the crushing front to absorb large shocks

in themselves blow away the assumptions of BZ and their offshoots.


It means the expression for upper block mass and how this mass delivers it's energy to the lower block in BZ and it's offshoots has no basis in reality.
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Re: Demolitions using a falling upper block...

Postby Dr. G » Sat Feb 14, 2009 1:55 am

T.S. and Major Tom:

Well, I've had something of an epiphany, ....... on Friday the 13th no less!

I have finally looked at the velocity change by a point-to-point data analysis using Einsteen's excellent smearogram of the ABC "verinage" demolition. Here's what I found:

Image

The jolt is there!

But it starts at ~ 1.2 seconds and a drop of ~ 6 meters, as I suggested before ...

I am stunned that this information lies buried in an apparently s-m-o-o-t-h drop vs. time curve.

So T.S. thanks for the advice .......

Interesting indeed, but not necessarily relevant to the collapse of WTC 1, 2 & 7.
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Re: Demolitions using a falling upper block...

Postby T_Szamboti » Sat Feb 14, 2009 3:36 am

Dr. G wrote:T.S. and Major Tom:

Well, I've had something of an epiphany, ....... on Friday the 13th no less!

I have finally looked at the velocity change by a point-to-point data analysis using Einsteen's excellent smearogram of the ABC "verinage" demolition. Here's what I found:

Image

The jolt is there!

But it starts at ~ 1.2 seconds and a drop of ~ 6 meters, as I suggested before ...

I am stunned that this information lies buried in an apparently s-m-o-o-t-h drop vs. time curve.

So T.S. thanks for the advice .......

Interesting indeed, but not necessarily relevant to the collapse of WTC 1, 2 & 7.


Yes, the distance graph can hide acceleration and deceleration. Short of a full reversal in direction it will appear smooth. This is why you need to calculate velocity between each measurement point and graph it, if you want to determine acceleration or deceleration.

The first small deceleration your graph shows could be measurement error with a small deviation as it appears it only has one point taking it down. It is hard to say what is going on with the second one but my data there showed a lesser acceleration but no deceleration. However, the last drop is certainly a real deceleration since there are several points involved, and it occurs at 1.6 seconds into the fall. This is what my data showed also and it would have occurred about halfway into the third story. I think they took out three stories and the large impulse occurred at about 30 feet into the drop, due to the three stories of rubble taking up about six feet of vertical space. That would be about an 84% reduction in volume just by the three floors falling themselves before it got pounded by the intact upper block.

I am wondering how can you say this isn't necessarily relevant to the upper block of WTC 1?
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Re: Demolitions using a falling upper block...

Postby Major_Tom » Sat Feb 14, 2009 5:32 am

Yes, the distance graph can hide acceleration and deceleration. Short of a full reversal in direction it will appear smooth. This is why you need to calculate velocity between each measurement point and graph it, if you want to determine acceleration or deceleration.


That is apparent. Interesting that the smearogram is pretty darn smooth. Good lesson.

I can see it a bit in the original graph but it is subtle.
Image

It doesn't become noticable until you plot v(t)


I think they took out three stories and the large impulse occurred at about 30 feet into the drop, due to the three stories of rubble taking up about six feet of vertical space.


A couple of us are seeing the initial give over 2 stories, not 3. A simultaneous "hinging" of individual columns, each part of the hinge being one story tall, hence 2 stories total.

I'll go back and review more carefully.

Link to the video Dr G posted earlier

http://www.strimoo.com/video/12509995/Mort-d-un-batiment-MySpaceVideos.html

There was manipulation of the building exterior over 3 or 4 stories. Main fall seems to be over 2 stories but the building could have been prepped mainly over 3 stories.

I see one collision after 2 stories, another after 3 (or 30 ft?)
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Re: Demolitions using a falling upper block...

Postby T_Szamboti » Sat Feb 14, 2009 2:07 pm

Major_Tom wrote:
A couple of us are seeing the initial give over 2 stories, not 3. A simultaneous "hinging" of individual columns, each part of the hinge being one story tall, hence 2 stories total.

I'll go back and review more carefully.

There was manipulation of the building exterior over 3 or 4 stories. Main fall seems to be over 2 stories but the building could have been prepped mainly over 3 stories.

I see one collision after 2 stories, another after 3 (or 30 ft?)


That is a good video of the demolition. It also shows more prep work seems to have been done to the first two stories than the third.

I agree that it appears that two floors were completely dropped.

However, a standard story in an office building is approximately 12 to 13 feet tall. The full impulse, that the data shows, happens at about 1.6 seconds. The data was taken every 200 milliseconds and the velocity drops between roof fall distances of 26.2 and 31.9 feet, so the collision takes place within that range. So even though 30 feet is not an exact figure, it is probably safe to say that the collision seems not to be taking place at the bottom of the second floor but within the third floor.

I think the collision does take place at the bottom of the second floor now and an explanation for it is that we are measuring the roof's fall to determine the velocity data. It is likely that there was a short latency period, due to local failures occurring at the bottom of and even throughout the six story or 72 to 78 foot tall upper block, before all of the mass of the upper block was involved in the collision and the roof slowed. Only a perfectly rigid and infinitely strong upper block structure would transmit the impulse to the roof without some latency.
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