Hardfire: Physics of 9/11

tfk said:
Hey Oz,


Nice to meet 'cha.

Mine's BSMechE, Cornell '74.

Yeoman Project Engr & R&D Engr. (Product Design & Development)...
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Greetings again Tom. University of New South Wales for me - second of the now three unis in Sydney.

All three of your visualisations understood.

The "flips" fit most comfortably with my "gut feelings" - your explanation is an extension of my simple bowling" analogy.

Personally my WTC 9/11 focus has been on the single question "demolition or not?" And I have been confident to conclude "not" by approaching several of the issues from the arse end. So on "far flung girders" the pro demolition case is (broadly) "they could not get there without being ejected into a free fall trajectory with the necessary VH therefore explosives.

However there is no way I can conceive that explosives could throw those lumps. And no CT can tell me how explosives could. So satisfies "no explosives for demolition" but does not explain how those bits got there.

Similarly I have been prepared to pass on the "Jones says there was thermate on site" stuff. So what? The way the collapse occurred there was (a) no need for thermate AND (b) no demonstrable way it could have been used. (Short of a bunch of suicide terrorists going in after the crash, wearing fireproof suits etc etc)

Chandler has helped me on many occasions - his first video (or the first one I came across) is one where he "stabilised" a shaky hand held camera video to demonstrate the "squibs" of the demolition in the "Global Collapse".

Very useful to show what Chandler didn't appear to see - for example the collapse wave continuing inside the outer tube many floors ahead of still standing outer columns. If those outer columns were still standing with nothing behind them how do you get explosives to throw a few bits of column a bit farther than their mates?

So thanks again for the comments

Eric
 
tfk said:
3body,

I think that you'd get a better idea of why the upper block cannot fall to the side if you consider geometry rather than forces.
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Geometry in relation to center of mass of course :D

I'm off to watch the WTC collapse simulator. This should be interesting.
 
psikeyhackr said:
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KIPS is not the weight of the perimeter wall panel It is the PRESSURE, thousand pounds per square inch, that they could withstand. The pressure capacity would be somewhat related to the weight.

I already showed in my two videos that the mass/inertia on every level affects the motion of the building. Both horizontally in the impact and vertically in the collapse. So you don't know enough physics to comprehend that?

psik
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Uh. What?

Kips is a thousand pounds. It's a measurement of weight. Get a dictionary.

Now then, AGAIN! Why does being off by a small amount, or even a LARGE amount on the perimeter panels matter? It's an insignificant percentage of the total building mass!
 
"All data within the model can be changed by the user, enabling open and interactive experimentation."

I assume this only applies to the 22 parameters listed. I'm curious if the simulation can be modified to take into account any tilt in the upper section. The simulation appears to have uniform collisions between the upper and lower sections along all structural components.

I thought that calculations based on the uniform collpase of each floor favoured arrest, even if we assumed the upper section dropped 2 complete floors before again making contact with the lower section. I was surprised that the first run of the simulation showed continuation, at a lower rate, instead of a complete arrest.
 
Kips. Kilo-pounds.

But, weight is really just a unit of force, right? You could convert between pounds and Newtons if you wanted to.
 
3bodyproblem said:
"All data within the model can be changed by the user, enabling open and interactive experimentation."

I assume this only applies to the 22 parameters listed. I'm curious if the simulation can be modified to take into account any tilt in the upper section. The simulation appears to have uniform collisions between the upper and lower sections along all structural components.
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Tilt actually will have very little effect, unless your model is so high-fidelity that it accurately captures the connection failure modes in the steel. This model isn't that good, nor is any other I've heard of. This is an extraordinarily difficult detail.

3bodyproblem said:
I thought that calculations based on the uniform collpase of each floor favoured arrest, even if we assumed the upper section dropped 2 complete floors before again making contact with the lower section. I was surprised that the first run of the simulation showed continuation, at a lower rate, instead of a complete arrest.
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There are numerous assumptions built into the model that favor arrest -- which is fine, provided we declare and understand them. In any event, I've written the author back for clarification. So far he's preferred instead to complain that I work through e-mail rather than post specially on his forum (which I do because I desire a one-on-one discussion free of derails -- just look at what happened in this thread!). Hopefully I'll receive some responses and be able to better understand his setup.
 
Newtons Bit said:
Uh. What?

Kips is a thousand pounds. It's a measurement of weight. Get a dictionary.

Now then, AGAIN! Why does being off by a small amount, or even a LARGE amount on the perimeter panels matter? It's an insignificant percentage of the total building mass!
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I am not talking about it a a percentage of total building mass I am talking about the steel and concrete on each level of the building. The weight of perimeter columns on the 105th level had to be different from what was on the 12th.

kip is used 995 times in 26 documents of the NCSTAR1 report

The very first use that turns up in a Adobe search says:
kip is a force equal to 1,000 pounds - ksi 1,000 pounds per square inch
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That is in NCSTAR 1-1.doc on page 19 in a table of acronymns and abbreviations.

I have the entire report on DVD. I looked it up. Are you happy now?

psik
 
psikeyhackr said:
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I am not talking about it a a percentage of total building mass I am talking about the steel and concrete on each level of the building. The weight of perimeter columns on the 105th level had to be different from what was on the 12th.

kip is used 995 times in 26 documents of the NCSTAR1 report

The very first use that turns up in a Adobe search says:

.
That is in NCSTAR 1-1.doc on page 19 in a table of acronymns and abbreviations.

I have the entire report on DVD. I looked it up. Are you happy now?

psik
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I'm very happy you looked up what the word means. But you still, as of yet, have not answered WHY knowing the EXACT mass is important. Why is it important?

This is the seventh time.
 
ozeco41 said:
Yes ...AND..... Remember some could "fail" that way othersmay fail other ways.... The clue is "they might[most certainly would] be unsteady.
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If all the joints failed, the entire core would be standing as a spire after the collapse front has moved down. At some point, the core columns would become unsteady and might topple over.


Newtons Bit said:
No, they would collapse under their own self-weight. Which is what happened. If you look at photos immediately post collapse you will see a "spire" of core columns that remained. It fell almost immediately after the smoke cleared.
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It's not clear exactly what happened to the spire on 9/11. It appears to have either disintegrated or it just dropped straight down, leaving a cloud of dust that had been covering it. How could a group of columns drop like that without having a section taken away from the bottom?


ozeco41 said:
So the next point is we need to address what you mean by "failure".
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I'm not sure yet what kind of failure you're proposing in your theory, but I would think the most likely way the columns would fail is at the joints, where the ends are connected to each other to make one long core column.


ozeco41 said:
Your perception difficulty seems to be one of scale. The "small upper block" is in reality the totatal structure of 10 or 20 storeys It is a bloody big block. And potentially all that weight is available to strike any single member that blocks the fall.
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Is it true that all the weight is potentially available to strike any member the block falls on? The upper block won't be as structurally sound as it was when it was attached to the lower block. Then when it falls onto the lower block, the force from the impact would make it even more unstable. For all the weight to act as one force, all the bits would have to be firmly connected to a sound structure.


ozeco41 said:
As long as you only add the bits Heiwa gets right which are...
..errr
mmm....
I'll let you pick them. :D
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Some important considerations that the crush-down models seem to skip over:

1. Equal and opposite forces resulting from a collision.

2. Different potential for destruction of primary structure and secondary structure materials.

3. Energy consumed by friction.

4. Stability of lower block, which is still firmly attached to its foundations, in comparison with upper block, which is dangling in mid-air.


Sorry I'm a bit slow at replying. I'm busy with my vegetable plot at the moment. :)
 
bardamu said:
Some important considerations that the crush-down models seem to skip over:

1. Equal and opposite forces resulting from a collision.

2. Different potential for destruction of primary structure and secondary structure materials.

3. Energy consumed by friction.

4. Stability of lower block, which is still firmly attached to its foundations, in comparison with upper block, which is dangling in mid-air.
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Maybe they "seem" to, but they don't, with the possible exception of the second one -- most collapse models assume the primary structure (viz. columns) must buckle or otherwise fail rather than being simply destabilized, pushed to the sides at a much lower energy cost. Proper consideration of 2. means acknoweldging that once the collapse is well underway, the secondary structure (viz. floors) would be much weaker, thereby allowing bracing to disappear and permitting a much lower energy cost failure mode of the primary structure. The crush-down models, again, are excessively conservative in this regard.

Energy consumed by friction goes into deformation of materials. I had thought that the only person who thought these were separate costs was Heiwa. Please don't be like him.
 
psikeyhackr said:
.

kip is used 995 times in 26 documents of the NCSTAR1 report

The very first use that turns up in a Adobe search says:

...

psik
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kip is not the same as ksi. The latter is a unit of pressure, not the former. You would show some style if you could at least acknowledge your error.
 
GlennB said:
kip is not the same as ksi. The latter is a unit of pressure, not the former. You would show some style if you could at least acknowledge your error.
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I acknowledged the error. I don't understand why he started talking about kips in relation to the weight the wheat chex though. It's a 1000 pounds of force and weight is a force but a force is not necessarily a weight. Who talks about weight like that?

psik
 
3bodyproblem said:
lol, cuz if he said "Newtons" you would have thought him arrogant :D
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225f_top_10_list.jpg
 
ozeco41 said:
******** .... The quoted bit is like unto the faeces of a male bovine.



:confused: Gawd this is an interesting forum - you can call each other all the names BUt not use a simple everyday word like B-U-L-L-S-H**

I am (was) a sewage engineer and how do I say **** turd crap poop :confused::boggled:
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OK - Assume - again - you have a steel structure of 111 horizontal elements (floors), each supported by 280+ columns 3.7 m high. This structure is 410.7 m high. Assume you start a big fire at floor 97 and suddenly all 280+ columns above floor 97 disappear and - POUFF - and that upper 14 elements drop down on the 97 lower elements. Then of course floor 98 contacts floor 97.
Let's assume it is a BIG PUNCH. Floor 97 is backed up by 96 elements and floor 98 is backed up by only 13 elements. What happens then?
Well, it is in fact the columns between floors 98 and 99 that will break next because they are the weakest elements adjacent to the BIG PUNCH.
After that floor 99 drops down 3.7 m, another BIG PUNCH occurs and the columns between floors 99 and 100 fail. After total 14 BIG PUNCHES upper section above the fire is gone - resting on top of the 97 intact elements below! Basic physics. Beautifully explained at http://heiwaco.tripod.com/mac5.htm . Happens every time a small part C tries to knock out a big part A.

Or in other words, a steel structure cannot one-way crush down by itself from top down started by a little loose weight up top!
 
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Heiwa said:
Or in other words, a steel structure cannot one-way crush down by itself from top down started by a little loose weight up top!
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Why not comment on the simulator instead of spewing more non-sense? You should check it out, you may owe them a million bucks :D
 
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