WTC 1 & 2. What happened after collapse initiation?

[tsig]

Spring against spring.

Assume two springs 1 and 2!

Spring 1 has length L1 and spring constant C1 and spring 2 has length L2 and spring constant C2.

Spring 1 is fixed at one end and spring 2 is attached to the other end of spring 1.

A force F is applied to the free end of spring 2. What happens?

Evidently both springs compress and a reaction force -F develops at the fixed end of spring 1.

Compression d1 of spring 1 is d1 = F/C1

Compression d2 of spring 2 is d2 = F/C2

The energy E1 required to compress spring 1 is E1 = (d1)² C1/2

The energy E2 required to compress spring 2 is E2 = (d2)² C2/2

The total energy E to compress the two springs is E = E1 + E2

Now release spring 2 from spring 1.

Instead of applying a force to the two springs, spring 2 is now moving with a kinetic energy E and is colliding with the free end of spring 1. We assume a soft collision.

What happens then? Both springs compress as if a force F was applied to them and a reaction force -F develops at fixed end of spring 1.

What happens then? One possibility is that both springs decompress and that spring 2 bounces back! Another is that one of the springs break due to overload. A third possibility is that both springs break simultaneously but it is unlikely. If something breaks it is the weakest link.

What do you think?

Do springs float? Do buildings?

 

[tsig]

I think comparing the towers to giant Slinkys is insane.

Yes but the image of the top of the towers falling and then bouncing up is just incredible. Of course if that unreality actually happened then that would be evidence of conspiracy.

 

[Pardalis]

I think he's confusing inelastic and elastic collisions again.

 

[TheRedWorm]

Seems? Evidently when two bodies (structures) A and B come in contact, the force F of body A on the other body B, produces an opposite reaction force, Fo of body B on body A. Google on Isaac Newton for more info. F = Fo = equilibrium.
Depending on the properties of A and B, F may damage or deform B or Fo may damage or deform A. There are plenty of possibilities but quite easy to analyse what happens after this initiation contact.

After each damage or deformation of A or B you have to redo the analysis, step by step, to see what happens then with the forces involved. Luckily there is always equilibrium to simplify the analysis. Normally some of the new forces that develop after initiation contact produce friction forces, so you have to include those in a complete analysis.

NIST and Bazant suggest without any evidence that A destroys B. NIST suggests that B lacks strain energy to absorb the energy transmitted by A to B without any calculations to back up the suggestion. Bazant suggests that A crushes down B, while A remain intact. Neither has heard about friction!

It seems neither NIST nor Bazant has any knowledge of structural damage analysis (like many participants on this thread). Reason is that very few universities teach the subject. Bazant has written 400+ scientific papers but none about structural damage analysis. He has still a lot to learn.

I on the other hand that have investigated and analysed 100's of steel structural damages due to contacts (ship collisions - also groundings and ships colliding with quays and fixed objects) have some experience. Structural damages occur every day so it is not a new phenomenom! On the contrary.

Some 13 (?) years ago some Japanese made a complete damage analysis of a serious contact A against B using Finite Element Models + plenty of computer capacity. The destructions followed the A+B contact would in reality take 5 seconds, but the analysis split this events in 5000+ sub-events (how the further damages developed and were arrested) and it took the computers three weeks to do the full analysis.

When the analysis was done they actually arranged a real A + B contact and found good agreement between theoretical analysis and the real thing.

Interesting stuff. I wrote a positive review about that project in a serious English engineering monthly journal published by the Royal Institute of Naval Architects in London.

And you can do calculations to back this...assertion up?

lump

 

[GregoryUrich]

Spring against spring.

Assume two springs 1 and 2!

Spring 1 has length L1 and spring constant C1 and spring 2 has length L2 and spring constant C2.

Spring 1 is fixed at one end and spring 2 is attached to the other end of spring 1.

A force F is applied to the free end of spring 2. What happens?

Evidently both springs compress and a reaction force -F develops at the fixed end of spring 1.

Compression d1 of spring 1 is d1 = F/C1

Compression d2 of spring 2 is d2 = F/C2

The energy E1 required to compress spring 1 is E1 = (d1)² C1/2

The energy E2 required to compress spring 2 is E2 = (d2)² C2/2

The total energy E to compress the two springs is E = E1 + E2

Now release spring 2 from spring 1.

Instead of applying a force to the two springs, spring 2 is now moving with a kinetic energy E and is colliding with the free end of spring 1. We assume a soft collision.

What happens then? Both springs compress as if a force F was applied to them and a reaction force -F develops at fixed end of spring 1.

What happens then? One possibility is that both springs decompress and that spring 2 bounces back! Another is that one of the springs break due to overload. A third possibility is that both springs break simultaneously but it is unlikely. If something breaks it is the weakest link.

What do you think?

I think you didn't answer the question.

 

[GregoryUrich]

Oddly enough, Heiwa has already performed this calculation (with gross assumptions in favor of collapse prevention) and determined that the upper floor of the lower block would fail.

He hasn't figured out what that means yet.

Aren't you going to give it a shot? It would be interesting to compare independent solutions.

 

[GregoryUrich]

"Spring is in the air"

In my experience normal springs being extended risk passing their elastic limit, but springs being compressed approach becoming metal tubes and actually gaining in strength as "spring rolls". Springs don't seem to illuminate the issue. But I could easily be talking cobblers. If so, blame it on the ouzo.

Steel columns are quite adequately modeled as linear springs up to their elastic limit.

 

[DGM]

I think you didn't answer the question.

Try not using so many numbers and be more vague. Then he will answer your question.

Remember, Keep it simple for children.

 

[PhantomWolf]

Steel columns are quite adequately modeled as linear springs up to their elastic limit.

Well if the columns of the top section had fallen directly onto the columns of the lower section then there might be a point to it, but since they didn't.....

 

[pomeroo]

At the risk of being a nuisance, I want to keep hammering away at an obvious point. Heiwa doesn't understand--or professes not to understand--why dropping the top third of a building two miles onto the bottom two-thirds destroys the whole structure. In other words, his intuitive sense of reality is defective, demonstrably inferior to that of a child. People like Mackey, RWGuinn, and Newton's Bit, who understand physics and engineering far better than I do, dismiss Heiwa, accurately, as a "zero-force nut" and discuss sophisticated topics that hold more interest for them. They are talking over and past the person they wish to correct, however, as he simply lacks the conceptual grasp of the subject necessary to appreciate their arguments.

Here in a--you should pardon the expression--nutshell is the problem with fantasists in general. A huge hole in their understanding prevents meaningful exchanges with rationalists. The loons insulate themselves from reason and evidence by clinging to a core belief that is massively wrong. That core belief itself is completely unshakable.

For the no-planers, they are hopelessly mired in their pseudoscience that holds that softer substances cannot possibly damage harder ones. They rant ceaselessly about violations of Newton's laws, planes "melding" into buildings, and "indestuctible" structures. Apathoid threw a whole group of crazies into a tizzy--Morgan Reynolds simply ran away--when he asked how a bird can damage a titanium fan blade. They can't even attempt to respond without bringing down their entire house of cards.

And so it is with Heiwa. He tap dances furiously, but he can never acknowledge that his mad assertion, an assertion he made confidently and condescendingly, about the falling third of a building was preposterously wrong. Once he comes to terms with the way the universe actually behaves, everything he has pontificated about for months crumbles.

Before asking him a question that he simply won't get, consider that he maintains that dropping the top third of a building from a great height onto the bottom two-thirds does NOT produce a huge pile of rubble.

 

[Newtons Bit]

Aren't you going to give it a shot? It would be interesting to compare independent solutions.

I did it a long time ago. November of last year to be exact.

 

[Heiwa]

I think you didn't answer the question.

Well, I just provided the relationship between the force F you asked for and the energy input E that you provided, so just fill in the missing numbers yourself.
To simplify you can assume identical spring coefficient C for both springs and why bother with two springs? When in soft, elastic compressive contact the two springs behave as one!
The critical force F due to energy E is then when the spring breaks in one location (and not 1000's of pieces) unless the upper part simply slips of the bottom part due lack of friction.

 

[JihadJane]

Apologies to everyone for my tardy response

Question - what do you mean by "transform ... microscopic dust" ? There is a lot of disinformation out there regarding the average size of the particles generated. If you take your information from 9/11 CT sites you'll almost certainly be misinformed. So - what is your take on the "pulverisation" issue?

Hello.

I'm not sure what you mean by "9/11 CT sites". Most of my information about the dust has come from articles discussing its long-term health effects on rescue workers and New York residents.

e.g. http://discovermagazine.com/2007/oct/the-9-11-cover-up

Having reviewed such articles and read material referred to by posters here I realise I was wrong in believing that the contents of the buildings were transformed into microscopic dust. Large large quantities of very fine dust (much of it, indeed, microscopic) is a more accurate description along with coarse dust and small fragments.

I use the word "transform" because the process by which this occurred is still far from certain, though there are various plausible hypotheses. I doubt that there will ever be enough data available to decide this issue conclusively.

 

[JihadJane]

Originally Posted by JihadJane:
********Without the physical evidence there can never be a conclusive
explanation for the Towers' failure.******

It doesn't mean you can fill the gaps with nonsense.

Do you have physical evidence of CD? No.

You don't define "nonsense" but, in principle, I agree with you and apply yout truism to both sides of the debate.

One side, of course, is massively better resourced to sell its "nonsense" and dress it up as fact, than the other.

A lack of physical evidence means that nothing can be proved. In the context of perhaps the biggest fire/engineering disaster in US history the haphazard removal and destruction of the physical evidence, over the objectons of many experts and relatives of victims, is suspicious behaviour worthy of further investigation.

 

[JihadJane]

Conspiracy?

So you say there is no evidence and that the lack of evidence is proof of conspiracy?

No, I don't say that.

Strangely, though, the lack of evidence supporting the Osama bin Laden conspiracy theory appears to be considered by many as synonymous with proof.

 

[GregoryUrich]

Well if the columns of the top section had fallen directly onto the columns of the lower section then there might be a point to it, but since they didn't.....

I used to think that. The first impacts were most likely column-column although not perfectly coaxial. Calculate the displacement caused by the tilting. It's not as much as you think.

 

[GregoryUrich]

Well, I just provided the relationship between the force F you asked for and the energy input E that you provided, so just fill in the missing numbers yourself.
To simplify you can assume identical spring coefficient C for both springs and why bother with two springs? When in soft, elastic compressive contact the two springs behave as one!
The critical force F due to energy E is then when the spring breaks in one location (and not 1000's of pieces) unless the upper part simply slips of the bottom part due lack of friction.

You still didn't answer the question. I already calculated the force. I'm looking for something to compare to.

 

[JihadJane]

afaics Mackey's #798 responded to your claim about furniture and carpets being pulverised.
Unfortunately many 9/11 "Truthers" have taken certain studies - and the "60 micron average particle size" is a classic - to mean that the whole of WTC1+2 was thus reduced to fine dust. It wasn't. Such a claim is a complete joke. The metal wasn't reduced to dust to any significant degree whatsoever. The concrete was reduced to various sizes, much of which was in the macro range, i.e. gravel-sized upwards. In fact you could argue that the sand-particle size range could be classified this way, in that it will not drift far. Drywalling, insulation, fibrous organic materials etc were pulverised a good deal. Naturally soot particles also drifted on the breeze too.

... For a second time -- what is your take on the "pulverisation" issue ? If you have a strong opinion then what are your sources of information for this?

See my last post to you, above, and my hopefully forthcoming post to R.Mackey, below.

Is there a reason that you missed concrete off your list of "pulverised a good deal" items?

I have never claimed that structural steel was reduced to dust. I was talking about the towers non-metallic contents and components. I think I made this very clear. I cannot answer for what “Truthers" say.

JJ - you are being very cagey and defensive. I and maybe others are trying to get you to come right out and state what you believe.

I was not aware of being "cagey and defensive", though I freely admit to being somewhat strategically pragmatic. I am heavily outnumbered here! Thanks for your observation.

I'll assume that you are asking for my beliefs about the Towers' destruction rather than my broader beliefs about 911. I am undecided though I tend to lean towards the hypotheses that other means besides aeroplanes and fire were employed to bring them down. I don’t see how anything can be proved either way without the destroyed physical evidence. My broader beliefs about 911 being a false flag event, btw, are not dependent on the impact/fire/poor construction/gravity demolition hypotheses being incorrect.

 

[GregoryUrich]

I did it a long time ago. November of last year to be exact.

I think you should try this new approach (inspired by Toke's post a while back). I think you will like it because it avoids Ross's misapplied inelastic collision.

For example: Assume the 3.7m drop is freefall (a=g) and the elastic limit happened to be at a deflection of 3.7m. The average force required to decelerate the top part to a stop would be approximately mg (m=mass of top part). Since the force varies linearly from zero, the force at the elastic limit must be 2mg. However, the top also has weight so the minimum force at the limit must be 3mg.

When I use the actual acceleration and the actual elastic limit, I get 8.5mg which is well beyond any safety factor claimed by anyone.

 

[Heiwa]

Topic is of course what happened after collapse initiation and we all seem to agree energy was released.

NIST suggest that there was lack of strain energy in the remaining structure to absorb it and that global collapse ensued for that simple reason. Friction is ignored.

Bazant in several papers takes a one dimensional approach to prove the same thing; no slipping off sideways displacements that requires 2-D or 3-D, no friction that required at least 2-D, etc, etc. Bazant suggests that a layer of rubble develops soon after initiation that plays an important role but does not explain how energy released produces rubble. And a 1-D layer?

These experts ignore the many tools availble to explain structural damages that have occurred in the past. Quite strange.