“Tube in a Tube”

The designers coined the term “Tube in a Tube” to describe the buildings’ construction. The design was an innovation of its day. Thick steel columns ran up the middle of the building. This housed the elevators, stairwell, electrical conduits, water, sewer and other services which ran up and down the length of the buildings.

For you to understand the collapse, you will have to remember four main elements.

Core columns
Perimeter columns
Floor Trusses
Fire proofing
The columns of the building normally found evenly spaced out on a given floor became the outer wall of the building. This left large open areas for renting. A good explanation of this can be found on PBS.

Instead of encasing each column in heavy concrete, (normal fire proofing) the designers relied on ‘sprayed on’ fire proofing with a 2 hour rating to protect the load bearing columns and trusses from fire.

Each WTC tower was essentially bolted together like an erector set. Each average floor had 376 5/8″ bolts, 188 Truss seats, 120 ViscoElastic pieces and 120 gusset plates.

Below is a diagram of the truss system with connections.

Trusses connected Perimeter columns to the core. Without this connection neither one could stand alone. Note how the columns are constructed in threes known as column trees. Each column is bolted onto the column beneath and to the tree beside it.

There was a 3 to 4 inch layer of concrete on the average floor. There were reinforced concrete floors in the core as well. Contrary to what some conspiracy theorists say, the core walls were NOT concrete reinforced. This was an error made by a news organization which grew a life of its own.

The fire proofing was sprayed on after the steel went up. This is called “Passive” fire proofing.

Here is a photo of the core sub levels during construction. You can see just how deep below ground level the buildings went.

This type of construction makes a very open floor plan.

There is a big difference between this type of construction and others like the Landmark Towers in Fort Worth, Texas, which is often used as a comparison by conspiracy theorists.

There are large I-Beam columns encased in concrete. Large I-Beams also hold up the floors. The photo below was taken during preparations to demolish the building.

Note the vertical column above still has some concrete around it.

The Windsor Tower in Madrid is similarly built but with a concrete reinforced core added.

Now you have the general idea of the differences in construction between the towers and other high rise buildings. So why did it collapse the way it did?

A major factor was the fire proofing on the impact floors. The impact blew off the fire proofing as in the above PBS special.
Sources: http://www.debunking911.com
I’m hearing a great deal of rhetoric from our “conspiracy theorists”, but little fact. I thought you could debunk anything that disproved 9/11 being a government conspiracy!
Austingirl: Nice try! But once again, no cigar. If you check prior posts from approx. two days ago, I provided the mathmatical calculations that explain the speed at which the buildings pancaked. You are basing your info on “Loose Change” or some other site that simply doesn’t understand the science. If you have a “credible”, “scientific” source, I will be happy to take a look at it.
Austingirl: I visited your recommended site. But when I clicked on their “Resources and References”, there was nothing there. Interesting don’t you think!

And they say we can only cut cops and teachers…

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