Ozeco, we have been looking at WTC1 collapse initiation features for the last 15 pages or so. A bit off topic but it is the next place to look once the OOS model is generally accepted.
A summary of what we have learned so far regarding the initial failure sequence:
Just as Bazant divides the WTC1 collapse into 5 stages in BZ, I do the same but reword the stages slightly:
stage 1) Airplane damage, fuel and fires
stage 2) Visible deformations leading into initial buckling sequence, especially inward bowing (IB) of the south face.
stage 3) Initial buckling sequence (initial lateral propagation of column failure and trajectory over the first 12 ft.
stage 4) Initial collision and resulting trajectory and behavior through subsequent collisions until the conditions necessary for runaway destruction in local OOS regions.
stage 5) Runaway collapse propagation (ROOSD)
We know that stages 2 and 3 are the most important places to look for evidence of CD and they may be the only times where a CD is distinguishable from a natural collapse.
We also know that the NIST did not do any analysis of stage 3, the initial buckling sequence. Their only descriptions of the WTC1 collapse initiation sequence are incorrect:
1-6D, p 312:
Table 5–1. Summary of main events that led to the collapse of WTC 1.
Event Number........ Event
1 .......................Aircraft impact
2 .......................Unloading of core
3 .......................Sagging of floors and floor/wall disconnections
4........................Bowing of the south wall
5 .......................Buckling of south wall and collapse initiation
1-6D, pg 314:
Bowing of South Wall
The exterior columns on the south wall bowed inward as they were subjected to high temperatures, pull-in forces from the floors beginning at 80 min, and additional gravity loads redistributed from the core. Figure 5–6 shows the observed and the estimated inward bowing of the south wall at 97 min after impact (10:23 a.m.). Since no bowing was observed on the south wall at 69 min (9:55 a.m.), as shown in Table 5–2, it is estimated that the south wall began to bow inward at around 80 min when the floors on the south side began to substantially sag. The inward bowing of the south wall increased with time due to
continuing floor sagging and increased temperatures on the south wall as shown in Figs. 4–42 and 5–7. At 97 min (10:23 a.m.), the maximum bowing observed was about 55 in. (see Fig. 5–6).
Buckling of South Wall and Collapse Initiation
With continuously increased bowing, as more columns buckled, the entire width of the south wall buckled inward. Instability started at the center of the south wall and rapidly progressed horizontally toward the sides. As a result of the buckling of the south wall, the south wall 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 onset of this load redistribution can be found in the total column loads in the WTC 1 global model at 100 min in the bottom line of Table 5–3. At 100 min, the north, east, and
west walls at Floor 98 carried about 7 percent, 35 percent, and 30 percent more gravity loads than the state after impact, and the south wall and the core carried about 7 percent and 20 percent less loads, respectively. 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 along the adjacent east and west walls (see Fig. 5–8), resulting in increased gravity load on the core columns. The release of potential energy due to downward movement of building mass above the buckled columns exceeded the strain
energy that could be absorbed by the structure. Global collapse ensued.
1-6draft, p 288, Table 9-5 titled "Observations for WTC1", fifth entry:
and
1-6D, p 312, Table 5-2, last entry
Tower began to collapse – first exterior sign of collapse was at
Floor 98. Rotation of at least 8 degrees to the south occurred before
the building section began to fall vertically under gravity.
1-6draft p 290, figure 9-8 on probable collapse initiation sequence for WTC1:
3. Collapse Initiation
• The inward bowing of the south wall induced column instability, which progressed rapidly horizontally across the entire south face.
• The south wall unloaded and tried to redistribute the loads via the hat truss to the thermally weakened core and via the spandrels to the adjacent east and west walls.
• The entire section of the building above the impact zone began tilting as a rigid block (all four faces; not only the bowed and buckled south face) to the south (at least about 8º) as column instability progressed rapidly from the south wall along the adjacent east and west walls.
• The change in potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could be absorbed by the structure. Global collapse then ensued.
1-6draft, p 294:
Buckling of South Wall and Collapse Initiation
The inward bowing of the south wall increased as the post-buckling strength of bowed columns continued to reduce. The bowed columns increased the loads on the unbuckled columns on the south wall by shear transfer through the spandrels. Consequently instability progressed horizontally, and when it engulfed the entire south wall, it progressed along the east and west walls. Moreover, the unloading of the south wall resulted in further redistribution of gravity loads on the south wall to the east and west walls and to the thermally weakened core via the hat truss. At 100 min, the north, the east, and the west walls at Floor 98 carried about 7 percent, 35 percent, and 30 percent more gravity loads than the state after impact, and the south wall and the core carried about 7 percent and 20 percent less loads, respectively. The section of the building above the impact zone began tilting to the south at least about 8° as column instability progressed rapidly from the south wall along the adjacent east and west walls, as shown in Fig. 9–13. The change in potential energy due to downward movement of building mass above the buckled columns exceeded the strain energy that could have been absorbed by the structure. Global collapse ensued.
1-6draft, p 317:
Finding 26: The WTC 1 building section above the impact and fire area tilted to the south as the structural collapse initiated. The tilt was toward the side of the building that had the long span floors. Video records taken from east and west viewpoints showed that the upper building section tilted to the south. Video records taken from a north viewpoint showed no discernable east or west component in the tilt. A tilt to the south of at least 8 degrees occurred before dust clouds obscured the view and the building section began to fall downwards.
In reality...
1) building features like the antenna and north wall tilted less than 1 degree during the inital failure sequence.
2) all 60+ columns in the west wall failed within a 0.5 second interval. (which makes no sense if the building moved as the NIST described above)
3) forceful ejections appeared out of the 98th floor windows
before any point on the west wall or the antenna began to fall downwards.
http://img690.imageshack.us/img690/9109/femrnew.gif
4) all 47 colre columns have bolted splice connections along the 98th floor about 3 ft above the floor level.
5) overpressure is detected at the 77th floor during the 98th floor column failure sequence as can be seen here:
http://www.youtube.com/user/achimspok?&MMN_position=313:313#p/u/19/acTcwA_YHuA
Just the tip of the iceberg, but a fair summary so far.
) So the contacts will be mainly beam on beam with an order of magnitude less strength than the original axially loaded columns.
) and in one extended debate with a committed conspiracy theorist we identified thermxte cutting of floor joist lower chords as one demolition mechanism which could mimic the type of collapse initiation which happened on 9/11. The logistic improbabilities of that method are pretty obvious. As they are for most others - either pre placed and proofed against early blast off then cook off. Or place after impact by invisible fire suited suicide squads - whilst the fires rage.