Interesting input.
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This information gives the first simple explanation for why the east wall broke as it did.
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In the simplest terms, the green areas are much stiffer inter-welded belts around each MER level.
For the WTC2 east face, the upper wall was pulled in along the spandrels marked as blue lines. This pulled the whole upper wall behind the 75-77 green MER extra-stiff belt.
Please notice that the blue lines are the 2 spandrels immediately above the green belt. If the blue spandrels are pulled inward and downward, due to the much stiffer MER belts the break can be expected along the purple step pattern, just as it is seen in femr's gif (with the exception of 2 panels still attached).
The wall ripped along the upper edge of the 75-77 green belt. This is where the bolted connections end and the welded connections begin.
Therefore, in the simplest terms, the upper wall held together with column-to-column bolt connections was pulled behind the green MER belt that is held together through bolted and welded connections. The whole upper wall fell behind the whole middle wall. The upper edge of the middle wall is the purple step pattern, the lowest row of bolted connections in the upper wall.
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If you look at it this way, the break is right where it will be expected if the upper spandrels are pulled in. Quite orderly and predictable, really.
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Honestly guys, I think it is a truly under-appreciated coincidence that the blue spandrels that pull in are located directly above the lowest step pattern of bolted connections. It is the perfect place to force a break along the purple line.
