NIST measurements of inward bowing at about 10:22:
Time-line of the formation of WTC1 inward bowing along the south wall:
9:58 No fires are visible on the east side of the south perimeter. Only some smoke coming out of a few windows.
9:59 3 large fireballs emerge from the middle and east side of the south perimeter as WTC2 starts to collapse. These locations mark the center of where IB will be visible after a few more minutes. Two clips which highlight the ejections:
10:28 Building collapses. The NIST claims that floor sagging pulled in the south perimeter to the point of failure. The south wall failure overloads the core, causing progressive column failures from south to north over a tilt of 8 degrees.
In reality, all core and perimeter columns have failed with minimal tilt. both the antenna and north wall had tilted less than 1 degree during the entire column failure sequence. All columns have failed by this moment:
The range of tilt during the collapse initiation sequence is determined here
Perhaps the cause of the IB has more to do with the large fireballs that emerge from the center of the IB region only a few minutes before IB was first reported?
NIST mentions the fire ejections briefly:
NCSTAR1-5, Page 15: "Very shortly after the collapse began, fire and smoke were pushed out of the south face of WTC 1, probably due to a pressure pulse transmitted to WTC 1 from the collapsing tower. The most prominent effect was on the 98th floor where flames were pushed out of windows along the west side of the face."
Probably? It is not hard to verify this so why guess? There is smoke coming from the south face around this region and we can see no movement due to the collapsing tower within the smoke. Any wind pulse transmitted from WTC2 to WTC1 would be visible within movement of the veil of smoke covering the south wall of WTC2.
Also, the ejections come from the center and east side as anyone can see, not the west side.
Two Geometric Possibilities for Inward Bowing
NIST has a theory of what caused the IB, and their collapse initiation scenarios for both buildings depends upon it being correct.
The NIST description of WTC1 south wall inward bowing:
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 5â€"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 5â€"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. 4â€"42 and 5â€"7. At 97 min (10:23 a.m.), the maximum bowing observed was about 55 in. (see Fig. 5â€"6).
55 inches of inward bowing (IB) requires about 9 ft of floor sagging. According to the NIST's own description of the event, the floors sagged about 9 ft between 9:06 and 9:23."
9 feet of floor sagging in 17 minutes is what the official story of collapse initiation depends upon. Make sense?
Great visual model of the extent of the sagging required to produce a 55 inch IB is shown by mmmlink:
Even worse, there was no visible fire on the east side of the south face until the 3 large fire ejections appeared at 9:59.
The ill-fated perimeter section in red is where the maximum measured inward bowing is observed only 24 minutes later.
It will be pulled in more than 4 ft in 24 minutes by the famous sagging floor trusses.
Then, that wall will rip the east and west perimeter and the core down while not causing any vertical feature to tilt more than 1 degree from plumb.
Created on 10/15/2010 12:05 PM by admin
Updated on 04/29/2011 10:31 PM by admin