The Impact Of Flight 175 Caused World Trade Center 2 To Oscillate As Predicted
The impact of the aircraft into WTC 2 caused the tower to sway back and forth for almost four minutes. The estimated period of oscillation was found to be nearly equal to the calculated first mode period of the undamaged structure, indicating that the overall lateral stiffness of the tower was not affected appreciably by the impact damage. The maximum deflection at the top of the tower was estimated to be more than 1/3 of the drift resulting from the original design wind loads (about 65 in. in the N–S direction) as calculated from the baseline analysis (see Chapter 4). Since the lateral stiffness of the building before and after impact was essentially the same, it can be concluded that the additional stresses in the columns due to this oscillation were roughly 1/3 of the column stresses resulting from the original design wind loads, assuming linear behavior and assuming that the oscillation mode shape and the static deflected shape under design wind loads were identical. The building demonstrated an ability to carry this additional load and therefore, still had reserve capacity. This was confirmed by the structural analysis of the damaged towers reported in NIST NCSTAR 1-6.
http://wtc.nist.gov/NISTNCSTAR1-2.pdf (original link)
Seismic Signal Of Second Impact: 13:02:54 (UTC), 09:02:54 (EDT):
http://s3.amazonaws.com/nasathermalimages/public/video/myers plane strike with copyright.mpg
“period of vibration due to plane crash at 80thfloor.” Port Authority (March 1964), three-page document