This image alone contains both MER perimeter corners, which is over half of the entire 75-77 fl MER west perimeter.
It also contains 2 large curved perimeter sheets (bases marked in yellow and pink) with a line of bent and ripped columns along their lower edges. One sheet is over 9 stories tall and 7 panels wide, which is over 1/3rd of the whole width of the building.
Note there are 2 distinct types of sheets:
1) Rectangular and rigid: MER perimeter sheets
2) Bendable, curved sheets: More flexible standard perimeter sections bolted together as seen sheets marked wioth yellow and pink.
Reconstructed model of the west wall failure line
The 4 large pieces fit within the original wall as shown.
Rip along top of MER panels
NW corner 78th fl spandrel rip
SW corner 78th fl spandrel rip
Reconstruction of wall above floor 78
Slow motion video of the beginning of collapse from the south shows how a mass of perimeter wall just above the MER 75-77th floor region protrudes westward and goes into free-fall.
The video shows a mass falling westward from just above the 80th fl and that the large perimeter sheets leading the fall are up top 9 stories tall, 1/3rd the with of the building and have a rip along their lower edges.
Considering that there is also a rip along the upper edges of the MER corner sheets, it is not unreasonable to expect the two rips to be the upper and lower edges of the same ripping action along the 80th floor.
Rips and breaks along the lower edges of the leading large sheets
The same piece shown in 2 frames from the video:
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Reconstruction of entire MER west perimeter
In addition to the 2 falling MER corner sheets, one other large collection of MER panels was discovered standing erect in the middle of West Street.
3 large MER west face sections
RED: North quarter of MER perimeter: 5 panels, 15 columns wide. Lower break along bolted connections. Upper portion ripped violently just above the 78th floor spandrel:
BLUE: South quarter of the MER perimeter: 6 panels, 18 columns wide, upper and lower edges ripped violently along spandrel plates:
MIDDLE MER PERIMETER:
The final location of the middle MER perimeter section is shown:
the paths all 3 MER west face sheets are drawn as arrows.
Groups of 4, 2 and 2 panels, 24 columns wide. Upper edges broken along bolted connections:
Reconstruction of MER panel movement
This video tracks the trajectories and collisions of the NW corner MER sheet, confirming the path as drawn.
Created on 03/23/2011 11:53 PM by admin
Updated on 04/28/2011 12:24 PM by admin
High res of image 
