Heiwa: What about WTC 2?
Heiwa:
I know you have tended to focus only on the collapse of WTC 1, but I would ask you to take a moment to consider WTC 2. One of the best videos of the collapse of WTC 2 , (pointed out by poster Einsteen over at PhysOrg) may be seen at:
http://baldur.globalsymmetry.com/fact911/wtc2-corner/911.wtc.2.demolition.north.very.close.mpg
I highly recommend that you watch this video, which shows the collapse of WTC 2 looking at the north face of the building; and when you watch it, pause every half second or so to see exactly what’s happening. The collapse starts at the NE corner of WTC 2 near floor 81-82. What is amazing about this video is that it clearly shows a kink developing at the NE corner (near floor 82); a line of inward folding of the perimeter columns that moves rapidly across the north face as the upper section tilts to the east.
Another interesting feature of the collapse of WTC 2 is that the upper block is already leaning by about 2 degrees before any real movement is discernable. However, about 1 sec into the video rotation of the upper block becomes quite apparent. At 3 sec into the video, or 2 sec into the collapse, the angle of tilt is about 5 degrees and a kink is fully developed across the north face as a line of bowed/failing columns starting at the 82nd floor and ending at the 84th floor, i.e, the kink is NOT horizontal! This also shows that the hinge about which the upper block rotates is located at about the 84th floor. At 4 sec, or 3 sec into the collapse, the tilt is almost 10 degrees and a pronounced misalignment of the columns at floor 82 of the NE corner is clearly seen.
Heiwa, all of these features are NOT what I would expect for a controlled demolition! I doubt very much that a would-be demolitionist would want the upper section of WTC 2 to tilt. Nor could he predict or control the kink that formed in the north face. (And please note that the upper section of WTC 1 also tilted before it dropped.) And also observe that the upper section of WTC 2 was misaligned by over 1 meter as a result of the 10 degree tipping just a few seconds into the collapse. This means that the east face perimeter wall columns BELOW the 82nd floor were pushed outwards by the descending upper block and could NOT resist the collapse. Thus the lower perimeter columns failed by shearing of the bolts and welds, not by compressive buckling.
May I suggest that you read chapter 9 of NIST NCSTAR 1-5A and consider how the collapse of WTC 2 was initiated by the inward bowing of the perimeter columns along the entire east face of the building centered near floors 81 -82. There is also a nice IR image (Figure 9-22) that shows there was considerable heating of the perimeter columns along the entire east face and half way across the north face within 30 minutes of the aircraft impacts. The failure of the heat-weakened east face columns ~ 9:58 precipitated the rotation/collapse of the upper section of WTC 2 and is entirely consistent with what is observed in the video discussed above. And by the way, after about 3.5 seconds of rotation, the hinge at the 84th floor obviously fails and a downward motion of the entire upper block begins. At this point, the rapid buildup of momentum and the pull of gravity ensure the total destruction of the building as described by Bazant, Greening and others …...