What Demolished Three Of These Skyscrapers?

This slide was added to the January 2008 slideshow.

Crippling Structural Damage, Massive Fires, and Gravity

In this slide, Gage puts up a labeled picture of the WTC complex and the surrounding area, and then asks a simple question. The answer has three parts.

Crippling Structural Damage

Both WTC 1 and 2 had large passenger jets flown into them. 7 World Trade was hit by falling debris from the North Tower. These impacts resulted in terrible damage to their abilities to stand.

What goes up must come down. This is as simple an observation as possible in the physical world. Buildings, especially skyscrapers, are structural systems that manage to delay the "coming down" part as long as possible. Through the various structural pieces, the weight of the building and its contents are supported. Another way of saying this is that the force generated by gravity on the building and its contents is being kept in a state of potentiality by the building's structure.

The energy used to tear these buildings apart was added to them as they were being built. A robust and intact structure kept this energy at bay. But when the structure was damaged, then the building's ability to hold back this energy was severely impeded.

The Twin Towers lost perimeter columns and core columns. Both were needed to help support the gravity forces of the building, and the perimeter columns provided ALL resistance to lateral forces like wind. Because the core was not designed to resist lateral forces, you can see in pictures of the construction that the core never went that far above the rest of the completed building. Too far up and the core could not have stayed vertical.

The Twin Towers also appears to have lost the fireproofing from the structural steel in the explosion that accompanied the impact damage. This was a further assault on the buildings' abilities to resist the stresses being dealt to those buildings.

7 World Trade was a similar building overall to the towers, but it had some highly unusual parts to its structure. It was built over a Con Ed substation and was designed to transfer as little weight to that structure as possible. This shoved the core columns to the south in the building, and a ramp used to access the entire WTC complex shoved the columns to the west.

The structure compensated for this by building a dense network of transfer trusses in the fifth and seventh floor of the building, a "foundation in the sky", as I refer to it.

When structures are compromised the way those three buildings were on 9/11, their ability to redistribute normal and abnormal loads is weakened. This is the first part of our answer.

Massive Fires

In addition to impact damage, the airplanes that hit the Twin Towers sprayed a large quantity of jet fuel all over several floors of the building. This set off huge fires in the building that stretched over entire lengths of floors at times.

Buildings are normally designed to allow for a small office fire that burns from place to place. Fireproofing keeps the steel from heating past the point of weakening, any actual weakening transfers loads to other parts of the building, and as the fire moves, the burnt-out areas cool and return to a stronger state.

But when the fires are as large as the fires in the towers were, and when the fireproofing protecting the steel is gone, then the steel can quickly reach dangerous temperatures. More of the structure becomes compromised.

The structure of the towers actually began to work against itself. The floor structures began to sag under the terrific heat of these fires. This caused them to begin to pull the perimeter columns into the building. The perimeter columns were also being heated, and so they began to deform as well:

Though 7 World Trade wasn't stripped of its fireproofing, those fires were allowed to build unimpeded by any fire suppression effort. We have all heard the tragic stories of the police and firefighters who died in the Tower collapses, which fell before any meaningful fire suppression effort could begin. After those collapses, 7 World Trade was determined to be a lost cause for many reasons and abandoned. One firefighting official called it a "battle we were going to lose," and in the sheer volume of duties in that single day, 7 was written off.

I've no doubt that if the FDNY had been able to concentrate solely on WTC 7 with all its marshaled forces, the building wouldn't have fallen. That was not in the cards dealt to 7 World Trade on 9/11. Instead, the fires would grow until other officials called it a "candle," "fully involved," with "all 47 floors" on fire. And after burning for 7 hours, it finally collapsed.

Gravity

One of the most vivid lessons of 9/11 should be how brutal an opponent the force of gravity is to large buildings.

The tower sections above the impact zone had tremendous masses. Several scholarly papers have shown that once that amount of mass picked up enough momentum, it would have easily destroyed the structure below. Falling just the distance of a single floor would have given those upper sections far more energy than required to tear the building apart. And so they did. Even though the structures both above and below tore apart under this force (crushing down and up), the mass of the upper section remained right there, a pile driver demolishing the towers floor by floor.

What happened to 7 World Trade is very similar to this. The initiating event for its collapse began low in the building. First, the east interior of the building fell after the loss of a single column in that area. The resulting debris falling into the building included a large mechanical penthouse on the roof.

This debris would have torn apart two of the three critical transfer trusses for the west side of the building. This would have allowed the heavy supporting structure in the fifth and seventh floors to slide to the east. This failure would have dragged the rest of the building down behind it, allowing the immense mass of 7 World Trade to crush itself up as it fell.

These Three Elements Demolished These Three Buildings

It was the combination of these three elements that tore down all three of these buildings. Take a single one from the equation, and those buildings would probably still be standing.

This is why you will hear conspiracy theorists pretend that only one of these elements is used in various "official explanations." Alone, none of them could have overwhelmed the towers and Building 7. Together, they explain the collapses easily.

NIST 7 World Trade Hypothesis Not Relying On Damage

Many controlled demolition advocates are making much of the recent statement by NIST that their working hypothesis is based solely on the fires present in the building, and not any damage from the debris of 7 World Trade. This, I believe, is a misunderstanding of what NIST is doing.

In their Interim Report on Building 7 (available here (PDF)), NIST lays out several scenarios as to how the building may have fallen. Some of these make use of an earlier estimation of damage to the building. Later evidence has revealed a better picture of this damage and these scenarios have been invalidated as a result.

It may also prove true that the fires alone (without diesel fuel contributed) prove enough to have destroyed column 79 and taken down the building. If that's the case, then any contribution to the collapses from the damage and diesel fuels may still have been present and contributed to the collapse. Until the Final Report on Building 7 is released, we won't know what NIST means by this. Preliminary rushes to judgment should be avoided.

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