Physics Of 9/11 Events - Part 3, continued from: 9/11 Events- New thread

Since the curves are essentially identical, there is no rational basis for guessing which is which.

Einsteen gave a decent summary of why this is so:

http://forum.physorg.com/index.php?showtop...ndpost&p=276920

Arthur

So, if I pick one of the other CD's to extract, you'd expect that the curves would match these... based on that reasoning. Correct? If not, why?

I wouldn't expect much difference.

But, if a difference was found, I suspect a closer analysis of the CD would likely show the reason.

Arthur

I did posit a guess, I just didn't care to posit it, for a bunch of reasons. heh.

Actually, I was more interested in the pre-collapse part of the graphs. For WTC 1 there is some slow decay of about 20 cm preceding the main drop. For a CD there will be none.

Exactly.

Any more takers before I post the pre-collapse curves?

DBB:

The only research paper I have been able to find that actually measures the rate of collapse of a building during a CD was published by E. Yarimer and C. Brown in the Conference Proceedings known as "Structures Under Shock and Impact IV" published in 1996.

The most interesting part of Yarimer and Brown's paper is their Figure 5 which shows a measured drop vs. time plot for the November 1995 CD of a 20 storey building, the Standwell East Tower, in Rowley Regis near Birmingham in the UK.

Y & B's Figure 5 shows a CD with a very flat curve for the first 1.8 seconds of the collapse. I would estimate that the total drop of the roof of the building was no more than 2 meters in the first 2 seconds of the collapse, increasing to 20 meters in the following 2 seconds. The authors speculate that the extended collapse initiation observed for this building was caused by "the progressive spreading of fractures from the charge locations to the rest of the floor before a general downward motion could begin."

Thank you. That is an extremely pertinent and useful observation.

OK. Here both curves show the first 0.2 floors of deflection. The datasets were obtained by different methods but they have similar extraction accuracy, one method is just noisier than the other.




http://i24.tinypic.com/wu08bb.png




http://i22.tinypic.com/r0unvp.png

I'm more interested in this:

NEU-FONZE has now addressed this to some degree. Would any of the other posters who've spent considerable time and intellectual effort trying to characterize the mechanics of collapse care to weigh in on this? The similarity is undeniable. David B. Benson, einsteen, shagster... is the above a sufficient explanation?

The Landmark tower was 30 stories, 380 feet, and seemed to have a substantially different architecture from WTC1. Most notably the Landmark was destroyed by controlled demolition. I can't think of two more dissimilar cases of high-rises; about the only thing they have in common is they were both buildings that had sustained sufficient damage to cause collapse.

Now, if the similarity in fall rates is not a surprise, but is instead to be expected, why the time spent tweaking this parameter and that over a period of months when the answer is so simple: any building that falls for any reason does so at an acceleration of 0.6g? With the apparent exception of CD instances which, after closer inspection, will reveal some peculiarity that separates them even more from the cases of the WTC1 and Landmark towers, now expected to show similar drop rates.

I'm not trying to exaggerate for dramatic effect or be facetious or coy. I think this deserves some more scholarly commentary before being waved away. At this time, my opinion is that it is simply coincidence, and I have no expectation of seeing the same drop rates in subsequent extractions of CDs. But then, what do I know? I'm just a layman putting a lot of time into getting this data so the associated phenomena can be better understood; all I can do is extract more CDs and put to test the theory of... universal collapse similiarity.

Perhaps we should invite Professor Bazant here. He should have an opinion on mean acceleration of collapsing buildings being centered tightly on 0.6g.

Using poster OneWhiteEye's antenna tower data, WTC 1 slowly sank for about 2.4 seconds, losing about 20 cm in this time. At that point additional buckling occurred and progressive collapse commences. Still I'll be interested in comparing a controlled implosion to WTC 1, just to see.

For that early period, no single hypothesis stands out. The simplest, a constant resistive force, has a resistance only lacking 1.7% of enough to keep the tower standing.

The two best hypotheses for the progressive collapse both have the stretch decreasing with the square of the crushing front speed. One has the resistive growing linearly with the drop; the other has the resistive force growing with the square of the crushing front speed. Both agree with the data within +/- one pixel, approximately, and in the sense of the standard deviation.

However, all the other force and stretch combinations I have have tried are almost as good. I have no objective means of choosing one over another.

This post has been edited by David B. Benson on Oct 27 2007, 07:27 PM

Here is the pre-collapse WTC 1 drop data:

which correctly places collapse t0 time at frame 918, agreeing with poster OneWhiteEye's observations about the video, but was selected automatically by best agreement with previous data.

Fixed a problem and now getting very good fits for all the functions, best for exponential, almost rejectable for constant and strong evidence that the structure was sinking.

This post has been edited by David B. Benson on Oct 27 2007, 09:09 PM

I would argue that it's resistance was decreasing continuously from 101% of that needed to support the tower to 100.00%, and as soon as the resistance dropped below 100.00% to 99.999%, that the building was on the way down at that instant, its acceleration being 0.00001g when the resistive force was 99.999% of that needed to support it.

Not much displacement to notice at those low g's, but that 20cm displacement came from somewhere over the time between impact and that point...

Maybe it'd be more accurate to say that the acceleration became noticeable when the resistive force decreased to 98.3%.

Yes. One of the problems is that we do not know (yet) how to make use of any data before frame 800. I suspect that already by then the antenna tower was tilted about one degree of arc, corresponding to a drop of about 50 cm.

After fixing a problem and rerunning the code, that constant is 1.4%. But this hypothesis is (almost) substantially less likely to explain the data than either an exponentially decreasing force or a linearly decreasing force. Between those two hypotheses there isn't really enough data to choose, but if I had to do so, there is a tiny advantage to the linear hypothesis.

I'll have to run all this on larger data sets before being able to say anything with confidence.

Finally, I'll admit I don't have any particularly strong reasons for just these hypotheses. I'll be happy to include some more if there are suggestions.

This post has been edited by David B. Benson on Oct 27 2007, 09:59 PM