Saturday, March 25, 2006

The Case for Controlled Demolition, by Judy Wood, Ph.D


Analysis of Collapse Time
Free-fall from roof "collapse" every 10 floors "collapse" every floor
"collapse" initiated
ahead of collapse wave
Seismic Evidence

How long should it take the WTC towers to collapse?

Page 305 of the 9/11 Commission Report states, "At 9:58:59, the South Tower collapsed in ten seconds, .... The building collapsed into itself, causing a ferocious windstorm and creating a massive debris cloud." (Chapter 9. html, pdf)

The height of the South Tower (WTC2) is 1362 feet, and the height of the North Tower (WTC1) is 1368 feet, which are nearly the same.

Columbia University's Seismology Group recorded seismic events of 10 seconds and 8 seconds in duration, which correspond to the collapses of WTC2 and WTC1, respectively.
Information Based on Seismic Waves recorded at Palisades New York
Seismology Group, Lamont-Doherty Earth Observatory, Columbia University

Event origin time (EDT)
(hours:minutes:seconds)
Magnitude
(equivalent seismic)
Duration
Impact 1 at North Tower 08:46:26±1 0.9 12 seconds
Impact 2 at South Tower 09:02:54±2 0.7 6 seconds
Collapse 1, South Tower 09:59:04±1 2.1 10 seconds
Collapse 2, North Tower 10:28:31±1 2.3 8 seconds
Collapse 3, Building 7 17:20:33±1 0.6 18 seconds
Do these values seem reasonable? Let's calculate a few values we can use as a reference.
For the following, I used the height of WTC1 as 1368 feet and considered each floor to be a height of 12.44 feet. (1368/110 =12.44 ft/floor).
I assumed gravity = 32.2 ft/sec2 or 9.81 m/sec2.

Case 1: Free-fall time of a billiard ball dropped from the roof of WTC1, in a vacuum
Let's consider the minimum time it would take the blue billiard ball to hit the pavement (see below). Start the timer when the ball is dropped from the roof of WTC1. We'll assume this is in a vacuum, with no air resistance.

From the rooftop of WTC1, drop one (dark-blue) billiard ball over the edge. As it falls, it accelerates. If it were in a vacuum, it would hit the pavement, 1368 feet below, in 9.22 seconds, shown by the blue curve in the figure, below. (It will take longer if air resistance is considered, but for simplicity, we'll neglect air resistance.)

(Click on image to enlarge.)

Notice that the billiard ball begins to drop very slowly, then accelerates with the pull of gravity. If in a vacuum, the blue ball will hit the pavement, 1368 ft. below, 9.22 seconds after it is dropped. That is, unless it is propelled by explosives, it will take at least 9.22 seconds to reach the ground (assuming no air resistance).

Let's consider the "Pancake Theory"
According to the pancake theory, one floor fails and falls onto the floor below, causing it to fail and fall on the floor below that one. The "pancake theory" implies that this continues all the way to the ground floor. In the case of both WTC towers, we don't see the floors piled up when the event is all over, but rather a pulverization of the floors throughout the event. So, clearly we cannot assume that the floors stack up like pancakes. Looking at the data, we take the conservative approach that a falling floor initiates the fall of the one below, while itself becoming pulverized.

To illustrate the timing for this domino effect, we will use a sequence of falling billiard balls, where each billiard ball triggers the release of the next billiard ball in the sequence. This assumes pulverization is instantaneous and does not slow down the process. In reality, this pulverization would slow down the "pancake" progression, so longer times would be expected.

Case 2: ‘Progressive Collapse’ in ten-floor intervals
Let’s simulate the floor beams collapsing every 10th floor. This assumes there is no resistance within each 10-floor interval. Refer to the figure below.

The clock starts when the blue ball is dropped from the roof (110th floor). Just as the blue ball passes the 100th floor, the red ball drops from the 100th floor.
When the red ball passes the 90th floor, the orange ball drops from the 90th floor, ... etc. Notice that the red ball (at floor 100) cannot begin moving until the blue ball reaches that level, which is 2.8 seconds after the blue ball begins to drop.

This approximates the "pancaking" theory, assuming that each floor within the "pancaking" (collapsing) interval provides no resistance at all. With this theory, no floor below the "pancake" can begin to move until the progressive collapse has reached that level. For example, there is no reason for the 20th floor to suddenly collapse before it is damaged.

With this model, a minimum of 30.6 seconds is required for the roof to hit the ground. Of course it would take longer if accounting for air resistance. It would take longer if accounting for the structures resistance that allows pulverization.

(Click on image to enlarge.)


Case 3: ‘Progressive Collapse’ in one-floor intervals
Similar to Case 2, above, let's consider a floor-by-floor progressive collapse.
Refer to the figure below:
(Click on image to enlarge.)

Now, let's consider momentum.
Assume that the top 10 floors stay intact as a solid block weight, Block-A. Start the collapse timer when the 100th floor fails. At that instant, assume floors 90-100 miraculously turn to dust and disappear. So, Block-A can drop at free-fall speed until it reaches the 90th floor. After Block-A travels 10 floors, it now has momentum. If all of the momentum is transferred from Block-A to Block-B, the next 10-floor block, Block-A will stop moving, even if there is no resistance for the next block to start moving. If Block-A stops moving, after triggering the next sequence, the mass of Block-A will not arrive in time to transfer momentum to the next "pancaking" between Block-B and Block-C. In other words, the momentum will not be increased as the "collapse" progresses.

Recall the physics demonstration shown below. (I believe everyone who has finished high school has seen one of these momentum demonstrations at some point in their life.)

Note, if some part must stop and then restart its descent every 10 floors, the total collapse time must be more than 10 seconds. Given that the building disintegrated from the top down, it is difficult to believe there could be much momentum to transfer, anyway. Also, consider the energy required to pulverize the 10 floors between each "pancake." After being pulverized, the surface-area/mass is greatly increased and the air resistance becomes significant. I don't believe the pulverized material can contribute any momentum as it "hangs" in the air and floats down at a much-much slower rate than the "collapsing" floors.

Now, let's consider reality.

QUESTIONS:
(1) How likely is it that all supporting structures on a given floor will fail at exactly the same time?
(2) If all supporting structures on a given floor did not fail at the same time, would that portion of the building tip over or fall straight down into its own footprint?
(3) What is the likelihood that supporting structures on every floor would fail at exactly the same time, and that these failures would progress through every floor with perfect symmetry?



Case 4: ‘Progressive Collapse’ at near free-fall speed
Now, consider the chart below.
(Click on image to enlarge.)

Let's say that we want to bring down the entire building in the time it takes for free-fall of the top floor of WTC1. (Use 9.22 seconds as the time it would take the blue ball to drop from the roof to the street below, in a vacuum.) So, If the entire building is to be on the ground in 9.22 seconds, the floors below the "pancaking" must start moving before the "progressive collapse” reaches that floor, below. To illustrate this, use the concept of the billiard balls. If the red ball (dropped from the 100th floor) is to reach the ground at the same time as the blue ball (dropped from the 110th floor), the red ball must be dropped 0.429 seconds after the blue ball is dropped. But, the blue ball will take 2.8 seconds after it is dropped, just to reach the 100th floor in free fall. So, the red ball needs to begin moving 2.4 seconds before the blue ball arrives to "trigger" the red ball's motion. I.e., each of these floors will need a 2.4 second head start. But this creates yet another problem. How can the upper floor be destroyed by slamming into a lower floor if the lower floor has already moved out of the way?

Case 2, above, shows the red ball being dropped just as the blue ball passes that point.

Remember, I'm assuming the building was turning to dust as the collapse progressed, which is essentially what happened.

So, for the building to be collapsed in about 10 seconds, the lower floors would have to start moving before the upper floors could reach them by gravity alone.

Did we see this? I believe it's pretty clear in some of the videos. The "wave" of collapse, progressing down the building, is moving faster than free-fall speed. This would require something like a detonation sequence.

Realizing that, for example, the 40th floor needs to start moving before any of the upper floors have "free-fallen" to that point, why would it start moving? There was no fire there. And, if anything, there is less load on that floor as the upper floors turn to dust.

In the picture (at right), notice that WTC2 is less than half of its original height, yet has no debris that has fallen ahead of the demolition wave.


So, how could the ground rumble for only 8 seconds while WTC1 "disappeared?"

I don't think this part of the building made a thud when it hit the ground.
Perhaps here, the only use of gravity was to get the dust out of the air.

The Case for Controlled Demolition (continued) - Seismographic Evidence
Analysis of Collapse Time
Free-fall from roof "collapse" every 10 floors "collapse" every floor
"collapse" initiated
ahead of collapse wave
Seismic Evidence
Seismic Information
SEISMOLOGICAL OBSERVATION OF IMPACTS AND COLLAPSES AT WORLD TRADE CENTER

Seismology Group
Lamont-Doherty Earth Observatory, Columbia University
Palisades NY 10964
Version of 9/14/01

Seismograph stations in southern New York, northern New Jersey, western Connecticut, and Pennsylvania, operated by the Lamont-Doherty Earth Observatory of Columbia University, recorded the collapse of each of the towers of the World Trade Center on Tuesday morning September 11 and the subsequent collapse of 7 World Trade Center later that afternoon. The closest station, at Palisades, New York, is located 21 miles (34 km) north of lower Manhattan in Rockland County. This station also registered the impacts of the two airliners that crashed into the towers.
The signals generated by the collapsing North and South towers were much larger than those from the two airliner impacts. The signals generated by the collapse of Building 7, however, were smaller than those of the impacts. In addition, many smaller signals were registered at Palisades throughout the rest of the day that may have originated from the further collapse of the Twin Towers and the fall of walls and other debris in the surrounding area.
The Palisades recordings of the Twin Tower collapses were comparable in size to the signals from a small earthquake of seismic magnitude 2.4 that was felt in the east side of Manhattan and in the western parts of Queens earlier this year, on January 17.
The seismic signals from the five events on 11 September differed from a small earthquake in that they were richer in low-frequency energy and poorer in high-frequency energy. These differences can be attributed to the short time duration of the fault rupture responsible for the earthquake as compared to the long and complex collapse of the buildings. The seismic waves from the five World Trade Center events resemble those produced by the collapse of a salt mine south of Rochester, in 1994.
The catastrophic events at the World Trade Center, as might be expected, producedmuch larger seismic effects than the bombing of the World Trade Center in 1993. The seismic effects of the collapses are comparable to the explosions at a gasoline tank farm near Newark on January 7, 1983, which were detected up to 130 miles away.
The seismographic stations are part of the Lamont-Doherty Cooperative Seismographic Network, which is operated in conjunction with several other institutions and is supported by the U.S. Geological Survey under the National Earthquake Hazard Reduction Program. As part of its agreement with the USGS, Lamont-Doherty makes this data available upon request without restriction.
Preliminary measurements made by Lamont-Doherty analysts are summarized in the Table below:

Data from Columbia University Seismology Group
Date Origin
Time (UTC)
Magnitude
(Richter scale)
Time
(EDT)
Dominant
Period
Signal
Duration
Remark
09/11/2001 12:46:26±1
0.9
08:46:26
0.8 sec
12 seconds
first impact
09/11/2001 13:02:54±2
0.7
09:02:54
0.6 sec
6 seconds
second impact
09/11/2001 13:59:04±1
2.1
09:59:04
0.8 sec
10 seconds
first collapse
09/11/2001 14:28:31±1
2.3
10:28:31
0.9 sec
8 seconds
second collapse
09/11/2001 21:20:33±2
0.6
17:20:33
0.7 sec
18 seconds
Building 7 collapse

Location of the World Trade Center is 40.71°N and 74.01°W.

Other seismic information:
Seismograms recorded by LCSN Station PAL (Palisades, NY)
New York Earthquake, 10/27/2001
Seismograms recorded by LCSN Station PAL, 10/27/2001
How long did the ground rumble?

Vibration of the ground following the plane impact of WTC1.


Vibration of the ground at the time of the WTC1 "collapse."
So, if it takes at least 9.22 seconds for the roof to hit the ground, how could the ground quit rumbling after 8 seconds?

==>> Consider the picture below.
I don't think this part of the building made a thud when it hit the ground.
Perhaps here, the only use of gravity was to get the dust out of the air.

There should be pulverizing or pancaking; not both.

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