Quote:
The working collapse hypothesis has been developed around four phases of the collapse that were
observed in photographic and videographic records: the initiating event, a vertical progression at the east
side of the building, and a horizontal progression from the east to west side of the building, leading to
global collapse.
From an analysis of the observed collapse sequence, the following general sequence of events appears
possible:...........
The working hypothesis, for the collapse of the 47-story WTC 7, if it holds up upon further analysis,
would suggest that it was a classic progressive collapse that included:....
The working hypothesis will be revised and updated as results of ongoing, more comprehensive analyses
become available.
........
There are many possible collapse scenarios that have been postulated in the preceding section. Many of
the scenarios will not produce the observed sequence of global collapse events and can be classified as
unlikely. Likely collapse scenarios will be identified through analyses that test the postulated phases of
collapse against observations. It is equally important to test scenarios that are not predicted to match the
observed data. The testing of the postulated collapse scenarios will be conducted through hand
calculations, simplified nonlinear thermal-structural analysis, and full nonlinear thermal analysis.