Evidently I do not quote several pages of unproven observations - just some relevant ones.
No, you (or whoever you might have copied the modified NIST paragraph from) did not edit the text to omit irrelevant portions. You changed the order of sentences, and you removed specific phrases to change the meaning and implications of what remained. Let's look at this again. Here is what you stated in your post:
From NIST report - NISTNCSTAR1-6D chapter 5.2 - we learn:
"The aircraft impacted the north wall of WTC 1 at 8:46 a.m. … between Floor 93 and Floor 98. … The subsequent fires weakened structural subsystems, including the core columns, floors and exterior walls. The core displaced downward … At 100 min (at 10:28:18), the north, east, and west walls at Floor 98 carried 7 percent, 35 percent and 30 percent more gravity load loads … and the south wall and the core carried about 7 percent and 20 percent less loads, respectively., … At 10.28 a.m., 102 min after the aircraft impact, WTC1 began to collapse. … The release of potential energy due to downward movement of the building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse ensued."
And here is the original paragraph from the NIST report:
"The aircraft impacted the north wall of WTC 1 at 8:46 a.m. The aircraft severed exterior columns and floors on the north side of the tower and core columns and floor members between Floor 93 and Floor 98. The subsequent fires weakened structural subsystems, including the core columns, floors and exterior walls. The core displaced downward, the floors sagged, and the south exterior wall bowed inward. At 10.28 a.m., 102 min after the aircraft impact, WTC1 began to collapse.
[from a later page]:
"At 100 min (at 10:28:18), the north, east, and west walls at Floor 98 carried 7 percent, 35 percent and 30 percent more gravity load loads than the state after impact and the south wall and the core carried about 7 percent and 20 percent less loads, respectively."
As before, the blue text is the text that was removed in the process of (you claim) collecting "relevant" passages.
At one point five words are removed to completely change the apparent meaning of the statement. That is not editing for brevity, it is attempted deception. Fortunately such deception cannot succeed, because anyone can compare the modified sentences with the originals in the report. Another removed passage describes the damage from the airplane crash. If you indeed regard that damage as "irrelevant," you are very much mistaken, and obviously so. Severed exterior members, core columns, and floor members are in fact highly relevant to a structural collapse initiated at the same floors where that damage had occurred.
And NIST intentionally leaves 'buckling' vague to mislead the readers.
There is nothing vague about the term. If you didn't understand it correctly that was not NIST's fault. Their documents are technical reports for a technically proficient audience.
NIST suggests that the potential energy of the mass above was released when all columns in the initiation zone simultaneosuly failed.
NIST did not suggest anything of the sort. They describe a progressive failure. Again, anyone can see what NIST actually stated outright (not suggested) by referring to the original report:
Instability started at the center of the south wall and rapidly progessed horizontally toward the sides. As a result of the buckling of the south wall, the south wall was significantly unloaded (Fig 5-3), redistributing its load to the softened core through the hat truss and to the south side of the east and west walls through the spandrels. ... The section of the building above the impact zone tilted to the south (observed at about 8°, Table 5-2) as column instability progressed rapidly from the south wall to the adjacent east and west walls (see Fig. 5-8), resulting in increased gravity load on the core columns. (NISTNCSTAR1-6D. Pg. 324)
And what the amount of potential energy released has to do with the strain energy in the intact structure is beyond me. NIST fails completey to explain what happens with the potential energy after it was released! It becomes kinetic energy ... and then what? An impact? Not seen anaywhere. And this little kinetic energy destroys the whole tower?
If the relationship between the strain energy and the potential energy is indeed beyond you (and I'll take your word on it), then perhaps you should study the subject some more before pronouncing conclusions about it. Just a suggestion.
I would expect it to be arrested (consumed by the 'buckling' of columns) and diverted and absorbed by the intact structure and that the mass above rested on it with some lose parts falling down beside.
Let's suppose that, in some alternate universe, that did indeed happen. Imagine the energy absorbed as strain by buckling columns brought the upper mass to a stop, with the 99th floor pan resting against the 98th floor pan along the south wall, the north wall columns still upright, and the east wall, west wall, and core buckled to reduce their vertical span by (on average) half a story, or 6 feet (more toward the south, less toward the north).
The question is, could this structure possibly stand? I don't know for certain, but it would take real calculations in three dimensions by a real structural engineer to convince me that it could. The top would be tilted 3.3 degrees, causing the south wall columns above the break to no longer align, either in position or angle, with south wall columns below. Instead, these columns (bearing a greater share of the load than normal, because of the tilt) now bear on the 98th floor pan. Due to the tilt, all the columns above and below are now subject to lateral forces. The angle is small so these lateral forces are not large compared to the vertical ones, but the columns were not designed to withstand such lateral forces at all, and they're already buckled and so only have a small fraction of their capacity at this point. Plus, the original airplane impact damage is still there on the remaining floors, and it's still on fire.
In order for it to remain static (now that we've magically brought it to a halt), it's not enough that the
average strength of the remaining members remains above the
average loads on them. Instead, every single member must be able to bear the actual load it receives, individually, without buckling. If any one member is overloaded to the point of buckling, it will buckle, and we no longer have a static situation. That is to say, things will start moving again.
If that's the case, it means that actually, they couldn't have come to a stop as hypothesized in the first place.
I like Gurich's paper about overload caused by the mass above on the structure below.
The mass above is of course a hotch potch of structural items so it easiest just to look at one of them and apply the theory to it, e.g. core column #501
It is an H-beam with two flanges 17x3.5 inch connected by a 2.2x12.6 inch web.
In metric terms the flanges are 430x90 mm and the web is 56x320 mm. The cross area is about 950 cm², i.e. the column is very solid. It weighs 750 kgs/m. It may carry as much as 700 tons transmitted to it from the floors above, i.e. each floor above transmits about 50 tons to the column through bolted connections.
The compressive stress in this core column at floors 94-98 is then abt 736 kgs/cm² or 74 MPa or 30% of the yield stress of the steel. The (smallest) moment of inertia I of this section is about 120 000 cm4 and its radius of gyration is of the order 35 cms. With a free length of 350 cms the slenderness ration is 10! Removing three floors as support and the free length is 1 400 cms and the slenderness ratio is still only 40! The thick steel plates, 56 and 90 mm cannot buckle under any circumstance when the compressive stress is only 30% of yield stress even if the temperature is 500°C.
Again, even if your figures are correct, they are meaningless, because you are comparing average loads against yield stress. That assumes the loads are balanced, equally distributed. But averages mean nothing when determining whether failure occurs. It's like saying that because the average income in the U.S. far exceeds the cost of adequate food, no one in the U.S. goes hungry. Because of the airplane impact damage, which you deliberately omitted all mention of from your NIST quote and later excused that omission as not being among the "relevant" facts, the loads were not normally or equally distributed. Failure begins if the load on even one member exceeds its capacity to withstand. At that point, for further collapse not to occur, you must show that the structure can reach a new configuration of redistributed stresses in which every member -- again, not just the average, and not just one column that you pick out, but every single individual member -- is capable of resisting the load on it without buckling. So far, you have not described such a configuration and proven it stable with real calculations of the forces acting on the individual members.
I strongly suggest you read my essay on progressive failure, here:
http://www.internationalskeptics.com/forums/showthread.php?t=102994. I wrote it with you in mind, because you keep arguing about the impossibility of collapse based on comparing
average loads with
average capacities. Major Tom might also find it useful.
Anyway our humble experts at NIST suggest that a part of this column 'buckles' - probably it bends - in the initiation zone and then disappears (none has been found) so that the upper, top part - 700 tons - most of it floors bolted to it, drops down on the lower part - and hits it with an impact force!
NIST does not suggest that any columns disappeared (obviously). They could not match specific columns to specific as-built positions, for reasons they explained, but nowhere do they state that columns were absent from the rubble pile. Nor do they describe an "impact" (other than the airplane impact) as being a necessary step in collapse initiation.
NIST thus assumes that the upper part of one column hits the lower part of the same column without missing it. What happens then? I would assume that most bolted floor connections of the upper part shear off due to the impact.
No, NIST does not assume that the upper columns hit the lower part without missing it. Greening, Bazant and Zhou assume that, for the sake of evaluating a simplified scenario as biased against collapse as possible. In reality it is impossible, after a 3.3 degree tilt, for all the columns to directly align with columns below. Instead, columns meet floors, and floors cannot resist large loads concentrated into small areas the way columns can -- which makes reaching a new statically stable configuration, once the upper mass starts moving, even more unlikely.
And that should be the end of it. Hostile comments are always welcome as the houris await me in Paradise.
I hope you do not regard my correcting your errors as hostile. I sometimes pay teachers, editors and proofreaders to correct mine, and I never thought they were being hostile when doing so.
Respectfully,
Myriad