Initiation is really off topic here, but if you don't trust NIST's FEA or their narrative, I guess you'll have to do your own. Please do keep us informed if you find anything interesting.
I did propose... not "find" because no one can see inside... including NIST. Whatever the mechanisms that were in play post plane strike until top drop was basically a "heat driven" process. EXPANSION and lateral displacement of column end to end connections.
I have my doubts about fire weakening 41 core columns more or less driving their aggregate capacity below service loads and NOT messing up the much smaller bracing steel sections... which were "above the flames"... Seems to me that flames would more likely "cook" the braces and the slabs in the core than the columns... whatever "cooking" would do.... probably expand the bracing.
I think we know what happens to steel as it heats up. In fact, NIST told us that heated beams pushed a girder 5 or 6 inches in 7 WTC. Why would the same thing not be in play in 1wtc's core?
The answer is of course... It would!
But of course as in the 7wtc example the ....to push.... means something pushed can MOVE ie is unrestrained. And if you could push a column end way less than 5" you could pretty much turn that column line to non performing. A 1" displacement in each axis would reduce the bearing area of column 704 up there... to 3%. That's well in the insufficient bearing area and well before that it would cause web and or flange crippling.
NB the pushing was not at the column to column connections... it was several feet away... above and below where the bracing (and floors) was. UNRESTRAINED END TO END CONNECTIONS with some 1/2" steel splice plates.
If that pushing happened to a column... at floor 96 for example.. there are still 4 - 36' columns above it that are carrying. 3 floors each. With nothing to bear on.... those 4 columns are going to ... without bearing (resistance) begin to drop.. held only by the floors that they HAD been supporting... held by the column end spliced connections which were not designed as hangers... and pulling down on the hat truss which the column had previously been supporting. OOOPS
Would the 4 columns break free at the hat truss? Who knows? Would the slabs around the unsupported column slump down with the unsupported column? (seems so no?) Would the slabs fracture and break free themselves (locally)? Can the hat truss span the new gap which was previously being supported by a column?
But why should only 1 column be displaced from being pushed by expanding braces? It is surrounded by as many as 8 others
x y x
y o y
x y x
The Y's can now move toward the missing / failed and perhaps "dropped" column location O because the fire was widespread and likely cooking up a large amount of the core area on say flr 96.
Well you can see where this is "going"... as long as the heating persists and there is no restraint on one side of the bracing... it expands in that direction and PUSHES... (the columns off alignment)
soon you will have:
x x y x x
x y o y x
y o o o y
x y o y x
x x y x x
5 failed columns ....hangers (o) with damaged slabs.... 8 "exposed" vulnerable to motion
If this mechanism was in play the non performing columns could grow in number
from 1 to 5 to 13... plus the 6 plane destroyed columns and you have 19 of the 47 columns of the center of the core non performing.
Our hat truss is now sweating bullets. It wasn't supposed to be a bridge SPANNING the core was it? It was supposed to spread the antenna loads to more than the 3 columns it was built over. Clever wasn't that? And it provided a nice rigid end plate to join the core and the facade tube at the top. That region was quite robust being 3 stories of mech equipment, tanks, transmitters and so forth.
It seems pretty clear that the "hollowing out" of the core capacity was in the center under the antenna... and lo and behold... this was the first region where the hat truss completely collapsed... and the antenna dropped... with no axial support and the truss "spreading" loads radially from it... right over the "hollowed out core".
++++
It should be noted that the hat truss was working very hard from the moment the plane bashed in the facade and took out 6 core columns (503, 504, 505, 506, 604, & 605). It immediately was "out of balance"... like trying to stand on one leg and carrying a heavy suitcase...Your muscles are trying to move all the load to your one leg on the floor. In the wtc cast the one leg was all the remaining bearing locations for the MAIN trusses... there were 8 of them.
The first core columns to fail during the initiation from "frame heat distortion" were 603, 606, 704, & 705. Now we have 10 of the 47 core columns non performing.
The next sequence of the progression took out columns 703, 706, 803, 804 and perhaps 605 and 607... Now we are up to perhaps 16 non performing columns... 1/3 of the core.. YIKES
The next sequence of failures would be 702, 707, 802, 805, 903, 914, 905. We have now 23 of the core non performing and all the columns below the antenna. 1/2 the core is non performing. We need over 100% reserve capacity to stand. (average reserve capacity for steel frames is under 49% or similar.
THIS is the moment of release... Row 10 is seeing most of the loads from above along with the core perimeter on the east and west side.
The facade damage was more to the West when the plane hit and the opposite side... east on the south facade saw the most increased loads and buckled first as the south side columns saw a rapid momentary load increase leading to buckling and then the entire core structure folded... the antenna dropped inside and the facade shifted and came down no longer in axial alignment with the bottom. The lateral force exerted via the moving slab was so much that facade columns sheared in mid span in some cases and dropped. At the release level facade columns sprung off when they were sheared and some slipped and dropped straight down.
Something like that?
It's a theory anyway... since you asked.... (and MT didn't whisper in my ear)
