Onset of Collapse
The claim is made by AE911Truth that the WTC buildings suddenly and without any warning or visible signs of distress began to fall. Its evidence for this claim is slim. One single account suffices for WTC 7, that of an anonymous person being interviewed moments after 7 had fallen.
The proof of “rapid onset” for the towers is mostly a litany of accounts of explosions heard by people just before or while the towers were falling (which is actually a separate point according to their list). The slideshow then shows videos from select angles showing the collapses starting and continuing, deals with the “piledriver”, and then moves on.
In fact, the towers show plenty of signs of severe structural problems before they collapse. Here is a video of the onset of Tower 2, the first to fall. Notice the perimeter columns being pulled into the building. This deformation is visible well before the columns finally failed, resulting in the collapse of the building.
You may say, “That seems pretty quick!” But this is not fast enough for what AE911Truth needs. It posits the support columns being cut at the same time, instantaneously. The warping of these columns is not happening instantaneously. You can watch the columns slowly bend in as the floor trusses pull them in. That’s not explosive detonation cutting the columns.
Tower 1 also demonstrated these slow deformations before its collapse.
Here in the North Tower, the south side shows these same slow deformations. The grid laid over the picture shows you where the building’s perimeter columns should be. The small white lines show you how far the perimeter columns have been pulled into the building by the floor trusses. The worst of the deformations are happening right where the fires are strongest.
Understand that you are looking at a building a city block wide. That’s a lot of slow deformation happening in that building’s structure.
Building 7 is a different case, because there isn’t as much visual documentation of its structure to go by. Nevertheless, this building’s collapse was not a rapid onset, either.
First off, the “rapid onset” that AE911Truth is talking about is the final descent of the northern perimeter. They show it in all their videos, and the sight of that building suddenly sinking down to nothing is startling. They bank on it.
But at that point the collapse has been going on for over 10 seconds.
The Final Report on Building 7 shows that the collapse started when a support beam on Floor 13 was knocked loose by other beams expanding because of high temperatures from the fires. This started a partial collapse of floors around Column 79, leaving it unsupported over several floors. That column then buckled, setting off a vertical collapse that progressed up to the roof. This caused the east mechanical penthouse to collapse and fall off into the building. This partial collapse removed vital support from the rest of the core columns. They failed from east to west and dragged the rest of the building down with it.
This is when most videos of 7’s collapse begin, when the building begins this final descent. There is no rapid onset here. One piece failing leads to another, and so on through the progressive collapse of Building 7.
Furthermore, the fire department determined that the building was slowly deforming before deciding to pull their men away by 2:00 p.m. From a Firehouse interview with Deputy Chief Peter Hayden:
…also we were pretty sure that 7 World Trade Center would collapse. Early on, we saw a bulge in the southwest corner between floors 10 and 13, and we had put a transit on that and we were pretty sure she was going to collapse. You actually could see there was a visible bulge, it ran up about three floors. It came down about 5 o’clock in the afternoon, but by about 2 o’clock in the afternoon we realized this thing was going to collapse.
Firehouse: Was there heavy fire in there right away?
Hayden: No, not right away, and that’s probably why it stood for so long because it took a while for that fire to develop. It was a heavy body of fire in there and then we didn’t make any attempt to fight it. That was just one of those wars we were just going to lose. We were concerned about the collapse of a 47-story building there. We were worried about additional collapse there of what was remaining standing of the towers and the Marriott, so we started pulling the people back after a couple of hours of surface removal and searches along the surface of the debris. We started to pull guys back because we were concerned for their safety.
Therefore none of the buildings on 9/11 experienced a rapid onset of collapse. The towers had visible deformations to its outer structure well before it fell, and Building 7’s slow deformations are verified by both rigorous computer modeling and fire department officials.
AE911Truth tries to prove its case by selecting certain videos that appear to show a rapid onset. You will never see the warping of Tower perimeter columns in an AE911Truth presentation. You will have to look quickly to find them use a video of 7 that shows the east penthouse falling before the rest of the exterior.