Electron microscope analysis of steel spheres from WTC site

[spyderracing]

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To quote it more exactly, the government report says 'and global collapse ensued'. That's it; it describes nothing and it explains nothing. Notice that I am calling for a sequential mechanism.

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How much did a WTC floor weigh?
What is the impulse/momentum generated by a block this weight dropping 3 meters?
How does this compare to the typical load on the steel structure from say the 50 floors it would normally have to support?

Answer these three questions (it's very, very simple physics) and you'll realize that global collapse is indeed inevitable once the first floor goes.

There are legitimate questions to be raised about the collapse but it seems like you've picked the worst possible points. [img]/images/graemlins/blush.gif[/img]

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You have not described a sequential mechanism, or pointed to a source that does describe it.

It would be very interesting if you would actually give that a try. Then we can see if that mechanism matches with what we see on the videotapes and the photographs, with the speed of the collapse, things like amount of thick dust, and so on.

NIST has not dared to do it.

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I don't understand how what he described isn't a sequential mechanism. First floor collapses triggering the next floor to collapse, so on and so forth until all floors have collapsed.

[Nielsio]

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I don't understand how what he described isn't a sequential mechanism. First floor collapses triggering the next floor to collapse, so on and so forth until all floors have collapsed.

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The mechanism ought to involve all major structural elements. For example, one ought to describe what happens with the inner and outer steel structure. When you say that the floors fall on top of each other, then we expect the inner steel structure (40+ massive columns) to remain standing.

Also; if floors fall on floors, where does the energy come from that moves incredible amounts of steel outward?



So the idea is that if we have a detailed account of actions and reactions, then we can start to fit the facts together and see how well it fits (facts include all videographic footage, but also pools of molton metal, micro spheres in the dust, etc, etc). That's how you build a scientific theory that attemps to gain knowledge about the event.

[evil twin]

http://news.bbc.co.uk/1/hi/sci/tech/6987965.stm

Oh and I agree with Phil.

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Firstly, you make no attempt to address the substantive debunkings given by others. Secondly, you post total drivel without the most basic fact checking. Third, you actually hurt the cause of those who care about the real crimes of the government.

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[Phil153]

Nielsio,

The sequential mechanism is blindingly obvious to those who have studied mechanical stress and also understand the energy contained in a large objects moving at velocity.

If you truly wish to understand the phenomena that occurred, I suggest you read these salient points from the journal of TMS, a professional publication that represents a large body of metallurgists and engineers. The important points to understand are in bold:

http://www.tms.org/pubs/journals/JOM...agar-0112.html

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" It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.

The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.
THE COLLAPSE

Nearly every large building has a redundant design that allows for loss of one primary structural member, such as a column. However, when multiple members fail, the shifting loads eventually overstress the adjacent members and the collapse occurs like a row of dominoes falling down.

The perimeter tube design of the WTC was highly redundant. It survived the loss of several exterior columns due to aircraft impact, but the ensuing fire led to other steel failures. Many structural engineers believe that the weak points—the limiting factors on design allowables—were the angle clips that held the floor joists between the columns on the perimeter wall and the core structure (see Figure 5). With a 700 Pa floor design allowable, each floor should have been able to support approximately 1,300 t beyond its own weight. The total weight of each tower was about 500,000 t.

As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour. If it had been free fall, with no restraint, the collapse would have only taken eight seconds and would have impacted at 300 km/h.1 It has been suggested that it was fortunate that the WTC did not tip over onto other buildings surrounding the area. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure. Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a 500,000 t structure has too much inertia to fall in any direction other than nearly straight down.

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This last point should be even clearer when you consider the self containing nature of the steel columns.

[Nielsio]

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http://news.bbc.co.uk/1/hi/sci/tech/6987965.stm

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Well..

This article is nothing but assertions.

Like:

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His calculations suggest the residual capacity of the north and south towers was limited, and that once the collapse was set in motion, it would take only nine seconds for the building to go down.

This is just a little longer than a free-falling coin, dropped from the top of either tower, would take to reach the ground.

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"One thing that confounded engineers was how falling parts of the structure ploughed through undamaged building beneath and brought the towers down so quickly," said Dr Seffen.

The south tower of the World Trade Center collapses, AP
Conspiracy theorists see evidence of a "controlled detonation"
He added that his calculations showed this was a "very ordinary thing to happen" and that no other intervention, such as explosive charges laid inside the building, was needed to explain the behaviour of the buildings.

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So just redefine what happened as 'ordinary' and voila, problem solved.

Note how his blatant contradiction (undamaged massive structure offers litte more resistance than air) isn't addressed in any way.

[evil twin]

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This article is nothing but assertions.

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Of course it is. It's a news story about a paper someone has written. You have to read the actual paper if you want more than that.

[Nielsio]

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This article is nothing but assertions.

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Of course it is. It's a news story about a paper someone has written. You have to read the actual paper if you want more than that.

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If the actual paper contained anything substantial I would expect them at least hinting at it. As it is, this is just a hit-piece.

But that's ok; I didn't actually expect anything else.

[Nielsio]

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This article is nothing but assertions.

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Of course it is. It's a news story about a paper someone has written. You have to read the actual paper if you want more than that.

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Also, why did you link to it if you knew it was just a bunch of blank assertions?

[evil twin]

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Also, why did you link to it if you knew it was just a bunch of blank assertions?

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Without the word "blank", that's what news stories about scientific papers are.

[kerowo]