WTC7 BUILDING MOVEMENT: INDEPENDENT MAPPING AND MEASUREMENTS OF THE EARLIEST DETECTABLE MOVEMENT THROUGH THE COLLAPSE INITIATION SEQUENCE
The collective visual record of the WTC7 collapse is examined directly and independently of all other sources, groups or individuals. The movement of the structure during the initial column failure sequence is mapped and traced back to the earliest point of detectable movement from multiple angles. Features of the initial failure sequence can be understood as a rapid succession of 7 identifiable events occurring in the following order:
1) Movement Detected from 2 Minutes before Collapse
2) Increase of rocking 6 seconds before visible collapse
3) Ejections and overpressurizations
4) Collapse of the East Penthouse
5) Collective core failure
6) Perimeter response
7) Acceleration downward
Collapse Progression and Rubble Distribution
1) Movement Detected from 2 Minutes before Collapse
The earliest detectable movement leading into the visible collapse process was never recognized in the NIST report. There is nothing within the NIST reports or simulations that can explain this type of movement.
The trace process of the northwest corner using sub-pixel tracing (syntheyes) demonstrated:
This camera angle is called the "camera #3 viewpoint" in the NIST report.
The corner started to rock back and forth at about 90 seconds before visible collapse began.
The blue line indicates the moment when visible collapse first begins (when the east penthouse starts to fall).
The early rocking has never been explained. It has not even been detected outside of the measurements reproduced here.
There most probably never will be any official attempt to explain the earliest rocking motion or to consider how this affects the NIST simulations and explanation of the collapse. This is because it will probably never be acknowledged to exist.
According to the NIST, the earliest motion began with rocking of the northwest corner of the building about 6 seconds before the first visible signs of collapse. This rocking is discussed next.
2) Increase of rocking 6 seconds before visible collapse
About 6 seconds before the collapse first becomes visible the northwest corner starts to rock more intensely. This movement was detected by the NIST and they consider it to be the earliest detectable motion. The first visible movement was the collapse of the east penthouse and is indicated in the graph. Once the east penthouse begins to fall, the rocking becomes even more intense until the whole penthouse starts to fall collectively about 5 seconds later.
This is a model that captures the general relationship between the core falling and the perimeter responding
camera 3
top
This type of core motion is one in which the collapse occurs in 3 stages, as described at this link.
MOVEMENT AS SEEN FROM THE DAN RATHER VIEWPOINT
Coupled reaction between core and perimeter
So how is it possible for the perimeter to drop faster than free fall?
Drop curves for the core, northwest corner and northeast corner compared
The core drops first, followed by the east corner and then the west corner.
Of course, the center of mass of the entire system cannot exceed gravitational acceleration, but the perimeter can.
Core and perimeter were still connected through the floor system. Once the core dropped at gravitational acceleration the core-floor-perimeter could have acted like a spring system. First, the core pulled the perimeter inwards. Secondly, the perimeter failed at a very low elevation and was then pulled downwards by the "floor-springs". The falling core slows down at that same time until the entire system fell as one unit.
Drop rates and velocities of core and perimeter compared
4 points are measured; 3 of the points track east, west, and center of the penthouse and one point tracks the west corner of the building. Downward displacements and corresponding velocities are compared to freefall movement.
The west side of the penthouse begins to follow a freefall trajectory but the acceleration decreases just as the acceleration of the west corner of the building takes off. It is then the west corner that follows or exceeds a freefall trajectory.
It appears that the core was slowed down by the perimeter as the perimeter began a sharp acceleration downward. The core appears to have strained the floors, took down the perimeter, and catapulted the outer shell downward. After this, it appears the whole interconnected unit fell together.
Displacement, velocity and acceleration profiles of the northwest corner from the Dan Rather viewpoint:
Syntheyes tracing the northwest corner Dan Rather viewpoint shown here.
The downward displacement is shown next to the NIST measurements using the camera 3 viewpoint. As described in part 3.3, the NIST made a number of mistakes when measuring downward displacement, velocity and acceleration of a point on the building. The mistakes made are too numerous to reproduce here.
In short, they measured a point on the roofline using the camera 3 viewpoint, but they didn't take account of the perimeter flexure discussed as event #6 and didn't seem to notice that the penthouse movement and perimeter movement cannot be distinguished for their first 4 data points. This is explained in detail in section 2.4.
Multiple methods of extracting downward acceleration from displacement data yield the same trends:
Acceleration of the northwest corner seems to exceed gravitational acceleration for a short period. This may be able to be explained through the perimeter coupling to the core. In this sense the core is literally pulling the perimeter down.
Recall the drop data of multiple points along the roofline presented earlier.
One can see both core (screen wall) and northwest corner movement relative to a free fall trajectory.
COMPARISON OF DOWNWARD ACCELERATION WITH THE MOVEMENT OF A KNOWN DEMOLITION
The Demolition of 1515 Flagler Dr...
The downward displacement of this demolition is compared to the downward displacement of the northwest corner of WTC7.
Also of interest are two different comments made by the owner of WTC7, Larry Silverstein, about the collapse and reconstruction of the building. Within the first clip he states that plans for a new building were beginning to be prepared in April, 2000, over 1 year before the then existing WTC7 actually collapsed:
This next clip highlights comments made by people evacuating the area before the collapse of WTC7:
