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9/11
See other 9/11 Articles

Title: Here's another reason the 9/11 fire-mediated collapse theory has to be wrong.
Source: http://www.opednews.com/articles/opedne_joseph_s_070522_oh_y
URL Source: http://www.opednews.com/articles/op ... 522_oh_yeah_2c_here_s_anot.htm
Published: May 23, 2007
Author: Joseph Smith
Post Date: 2007-05-26 07:03:54 by Kamala
Ping List: *9-11*     Subscribe to *9-11*
Keywords: 911
Views: 230
Comments: 13

May 23, 2007 at 10:03:51

Here's another reason the 9/11 fire-mediated collapse theory has to be wrong.

by Joseph Smith Page 1 of 1 page(s)

http://www.opednews.com

The notion that the WTC towers collapsed because fire weakened the steel is laughable.

The fact that other steel-framed, steel-cored buildings have suffered much longer burning, much larger in extent and, demonstrably, hotter fires, and yet never collapsed, shows how difficult it is in practice to bring down one of these buildings from fire.

Apparently, these buildings are robust structures, highly over-built to handle heavy wind loads; and it seems you would need to heat a large volume of steel, uniformly, over a wide cross-sectional area of the structure, to even have a chance of making one collapse in the neat, symmetrical manner witnessed (to the extent it is even, theoretically, possible to do this without resorting to explosives in the first place).

The easiest way to see that these buildings were rigged for demolition is to start by considering the fact that, between the time Flt. 175 hit WTC2 and the time the building collapsed, only 56 minutes had elapsed. And 56 minutes, simply, isn't enough time to develop a fire hot enough, nor large enough in extent, to even have a remote chance of getting enough steel hot enough to be a factor.

The best way to see the absurdity of the fire-mediated collapse theory is to make some simplifying assumptions...and apply some simple math and physics to the problem.

Say, for the sake of argument, that you’re concerned with one floor of the building. Assuming that you have an unlimited supply of readily combustible fuel available (which is, obviously, not true, but let's be generous), and there is no heat loss by convection, conduction or radiation (another ridiculous assumption, but let's give the shills every advantage).

Now, the rate at which the temperature rises on that floor will be determined by the composite thermal mass of the building materials associated with that floor, and the rate at which you can bring in oxygen to burn the fuel. Assuming, say, about 5E5 kg of steel, and about 1.4E6 kg of concrete, per floor (taking internet based numbers at face value), with specific heats of about 450 and 3300 J/kg*C, respectively, simple algebra shows that you would have to release about 3.27E12 Joules of energy to uniformly bring the temperature from ambient up to, say, 700 degrees C (starting to get into the interesting range, but probably still not high enough to cause a collapse).

The problem is that for WTC2, you have to release this huge amount of energy in only 56 minutes. That means you would have to burn somewhere on the order of 30,000 gallons of jet fuel in 56 minutes. That means you would have to supply air to the fire inside the building at a rate somewhere in the neighborhood of 6E5 cubic feet per minute.

That's right, in order to bring the temperature of one floor of a WTC tower from 25 to 700 degrees centigrade, uniformly, in a short 56-minute time frame, you would have to supply about 600,000 cubic feet of air per minute...for each of those 56 minutes. And that’s a ridiculously high number. And even if you did find a way to create such blast furnace like conditions, the fact of the matter is that you would convect a significant portion of the heat away, just like what happens in a fireplace; in order to let fresh air in, you have to let the heated, oxygen-depleted air escape.

If you were lucky, and the process was, say, 50% efficient (meaning the airflow only carried away half your heat), you would need to double everything, which would mean burning 60,000 gallons of jet fuel in 56 minutes, while feeding the fire with over one million cubic feet of air per minute.

By way of the above numbers, the absurdity of the "official" version of events is laid bare for all to see.

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#1. To: nolu_chan (#0)

The author here is being very kind to NIST. It is an interesting article.

So many events have to happen in such a short time in the NIST fantasy.

In the assumed aircraft debris path(depending which one you want to use), 100% of the fireproofing is removed. Then you have fuel poor, ventilation limited, 15 min transient fires that flare up and die down and must migrate to the area of outer girder "bowing". This takes around 60 min in the WTC 1 to reach the south face and 10-15 min in WTC 2 to reach the east face.

So now we are down to a basic office fire that is 40 min for each tower. Also in these time frames, all the cement and gypsum board must be removed from the core so in this time, the core can heat up, cool, then contract. Even thought NIST states their were no combustibles or fuel loading in the core.

In the area of limited "bowing". NIST states that around 30% was severe. That would be around 18 outer collumns. The "bowing" was seen over 2-3 floors.

In the meantime, the trusses have to expand, then contract and sag. In the UL tests, the trusses sagged a few inches, but in the computer models. the sag turns into 40 plus inches.

Let me try and get this straight, first remove all the insulation, then heat up and cool down the core, which in turn, pulls on the trusses which expanded then contracted then sagged, which in turn then pulls on 18 outer girders over a couple of floors, and BINGO, the towers are "poised for probable global collapse.

Its Rube Goldberg meets the game Mouse-Trap.

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-26   7:48:45 ET  Reply   Trace   Private Reply  


#2. To: nolu_chan (#1)

Some more quotes from Dr. Frank Greening:

Ironicall, some try to tell me that molten iron/steel was "to be expected" in the WTC fires - see the reports on the WTC dust by one of LashL's "experts" R. J. Lee. But even R. J. Lee avoids telling us WHY molten iron/steel is to be expected in a jet-fuelled fire. --------------------------------------------------------------------------------

NIST consider the acceleration of the Tower AND the acceleration of the aircraft, and then appear to confuse the two. --------------------------------------------------------------------------------

Quote from NIST 1-5:

"Since the aircraft impact forces were estimated to have been about 100g, NIST assumed there was not enough of the ceiling system in place to provide significant thermal protection."

This is interesting indeed! First quote does say "aircraft impact forces"... But 100g's is NOT a force! It is an acceleration. The force involved depends on the mass....

In NIST NCSTAR 1-5D, pages 43 to 44, NIST calculate the peak force ON THE TOWER from the aircraft impact as 76 x 10^3 kN. This is consistent with an acceleration of 0.25g. (Using F =Ma, we have F = 31 x 10^6 x 0.25 x 9.8 Newtons)

Now an equal and opposite reaction force acts on the aircraft, so again using F = Ma we have 76 x 10^3 kN = 124 x 10^3 x a, from which we calculate that the acceleration OF THE AIRCRAFT was 613 m/s/s or approximately 63 g's.

This appears to be an example of poor editing by NIST! --------------------------------------------------------------------------------

Just to address a few issues about the state of the Twin Towers after the aircraft impacts:

Please check out NCSTAR 1-5D. Here are a few snippets:

"Information regarding the integrity of the ceiling tile systems would be pivotal in assessing the role of the floor truss assemblies in the eventual collapse of the towers. .... Accounts of building occupants (show that) the impact of the airplanes resulted in some dislodging of ceiling tiles and damage to the suspension system. Descriptions of the magnitude of the damage at the observers locations and the spatial extent of the damage were neither quantitative nor comprehensive."

"The concern (of the tests of the ceiling tile system) was for floors just above and below the impact zone, which were not directly damaged by the airplane, but had significant fires after the impact."

The test results showed that all "ceiling systems resisted significant damage up to about 1g applied to the test platform."

NIST's own estimation of the MAXIMUM magnitude of the acceleration caused by the impact of the aircraft was about 0.25g.

Hence we have NIST's own studies showing that the aircraft impacts couldn't do more than dislodge a few ceiling tiles just a couple of floors from the center of the impact! --------------------------------------------------------------------------------

It seems to me that NIST makes an enormous number of assumptions without evidence, something that is frowned upon in science.

Take a look at the following:

Table 12-9 in NCSTAR 1-5G; or Table 5-5 in NCSTAR 1-5F; or Section 2.3.4 in NCSTAR 1-5G; or Figure E-31 in NCSTAR 1-2; or Figure 5-9 in NCSTAR 1-6; or Section 5.2.3 in NCSTAR 1-6.

Then show me the scientific evidence that NIST has for its "loss of thermal insulation" theory. --------------------------------------------------------------------------------

So the REAL question is what melted the iron in the towers. And please note that the iron spheres were quite abundant in the WTC dust. --------------------------------------------------------------------------------

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-26   12:37:14 ET  Reply   Trace   Private Reply  


#3. To: Kamala (#0)

Let me try and get this straight, first remove all the insulation, then heat up and cool down the core, which in turn, pulls on the trusses which expanded then contracted then sagged, which in turn then pulls on 18 outer girders over a couple of floors, and BINGO, the towers are "poised for probable global collapse.

A lot of food for thought here. For the moment I wish to address the above which I believe may be erroneous.

As I see it, the assertion is that the trusses heated and (at first) expanded causing an outward bowing. Upon further heating (not cooling) the trusses lost structural strength and sagged, pulling on the outer girders.

The initial pancake collapse theory held that the bolts failed and the floors dropped. This required thousands of bolts to fail simultaneously for a symmetrical collapse, an unlikely event.

The newer theory addressed this issue by asserting that the bolts and welds held and sagging of the steel caused the floor structure to pull itself loose from its supports.

-----

Another point: While one may conjecture about how all the office furniture burned hot enough to take out the floor trusses, what was in the core that could burn and take out the core columns? It would seem that the fuel would be most limited in the core where the columns were massive.

-----

Another brain dropping: Of what do the "visco-elastic dampers" consist? If there was enough heat generated to wipe out the steel columns, what would happen to visco-elastic dampers when subjected to that heat?

-----

nolu_chan  posted on  2007-05-26   17:57:14 ET  Reply   Trace   Private Reply  


#4. To: nolu_chan (#3)

You are correct. Everything is an assertion or assumed. Also you are correct, the trusses would not contract because of the assumed heating. They would continue from expansion to sagging.

where is the pulling truss force coming from?

How does a sagging truss pull outer collumns?

That is why NIST uses the core shortening to pull the trusses which in turn pull the outer girders.

NIST wants you to believe that this all happened in a very small time frame. 13-15 min for the 1700-1800F transient flare up, then around another 30 min at lower temps.

These dampers were made of something like an oily memory foam. NIST needs to have this intact, along with the floors to the outer girders, for the assumed pulling.

If these melt and disconnect with the bolts, the floors cannot pull.

How does a disconnected floor pull?

A few other tid bits:

One would have to remove around 9 core girders for the tower to collapse.

One would have to remove 5 complete floor systems.

One would have to sever around 60 outer collumns.

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-26   18:55:01 ET  Reply   Trace   Private Reply  


#5. To: Kamala (#4)

One would have to remove around 9 core girders for the tower to collapse.

For WTC-2, the NIST estimates 10 completely severed columns and 1 heavily damaged. The illustration [Figure 3-3 on p. 40/90 or Figure 6-25 on p. 115/165] indicates 22 damaged columns.

WTC-2 was hit significantly lower than WTC-1. The columns were sturdier at the lower elevation.

This particular fairy tale worst possible case scenario is based on the aircraft hitting the building with a head-on trajectory. The video evidence says it ain't so. Even the NIST report must acknowledge that the right engine exited through the northeast corner, and that the landing gear assembly landed near the engine.

The left engine purportedly severed 15 perimeter columns and its debris purportedly severed 9 core columns and heavily damaged another. Color me skeptical. The plane pushed debris to the northeast corner making it highly unlikely that it had any opportunity to sever 9 core columns.

Indeed, considering that the plane did not hit the building head-on, I fail to see how it could have taken out more than 2 to 4 columns in a worst-case scenario.

At page 100/150, NIST asserted for its model that "aircraft-damaged structural components were removed."

NIST hallucinates that 22 core columns were "aircraft-damaged." They are most definitely structural components. It is a lot easier for a computer model to drop a building when one removes up to 22 core columns. It may be a lot easier but it has the disadvantage of being detached from reality.


NIST page 40/90

Figure 3-3. Simulation of aircraft impact damage to the 78th through 83rd floors in WTC 2.

The middle of the left wing hit the 78th floor, severing nine perimeter columns and breaking 19 windows on the south face. The SFRM was stripped from the floor trusses over the same width as the building core. The stripping of insulation from the trusses continued inward across the tenant space and about two thirds of the way into the core. There was no direct core column damage from the debris on this floor. However, the southeast corner core column was so damaged on the 80th floor that it broke at its splices on the 77th and 83rd floors.

There was heavier damage to the 79th floor. The left engine and the inboard section of the left wing shattered a 25 ft wide section of the center of the floor slab all the way to the core of the building and severed 15 perimeter columns. Reaching the building core, the debris severed nine columns, heavily damaged another, and abraded the SFRM from the eastern two thirds of the columns and trusses all the way to the north end of the core.

The damage was most severe on the 80th and 81st floors, hit directly by the fuselage. On the lower floor, a chunk of the floor slab was broken, just above the affected piece of the 79th floor. In addition, a 70 ft deep strip along the east side of the core floor was crushed. The north side floor slab sagged along its eastern end. Ten of the perimeter columns severed on the 79th floor were displaced here also. Within the building core, ten columns were severed, including many that were severed on the 79th floor. The SFRM was stripped not only from the eastern two thirds of the core structural elements, nearly to the north wall, but also from most of the trusses on the east tenant space, all the way to the north facade.

-----

NIST page 41-91

On the 81st floor, the fuselage pulverized a section of the floor 40 ft wide that extended into the southeast comer of the core. The SFRM and gypsum fire protection on the full depth of the east side of the core and in the entire east side of the tenant space was stripped. The structural damage to the core columns was limited to near the southeast corner, but as mentioned above, the impulses felt here caused damage to the key corner column all the way down to the 78th floor. The right engine passed all the way through the 81st floor, exited from the northeast corner, and damaged the roof of a building on Church Street, before coming to rest some 1,500 ft northeast of WTC 2 near the corner of Murray and Church Streets. The right landing gear assembly passed through the 81st floor at the east side of the north face and landed near the engine on the roof of a building on Park Place. (See Figure 1-1 for the street locations relative to the towers.)

The right engine hit the 82nd floor spandrels about 50 ft from the east edge of the building, crushing part of the 82nd floor slab. Along with the inboard section of the right wing, it severed eight to nine perimeter columns, including some to the east of those severed on the lower floors. The wing caused truss damage up to the southeast corner of the core and severed five columns. As on the 81st floor, the fire protection on the east side of the tenant space and the east side of the core was dislodged.

The 83rd floor caught the middle of the starboard wing. The east side floor slab appeared to be dislodged and sagged at least half of the way into the building.

The result of the core column damage was that the building core leaned slightly to the southeast above the impact zone. The tendency of the core to lean was resisted by the floors and the hat truss.

The direct impact of the aircraft was over in about 0.6 s. The structural and insulation damage, summed over all floors, was estimated to be:

The tower swayed more than one foot back and forth in each direction on the impact floors, about one-third the sway under the high winds for which the building was designed. Nonetheless, just like WTC 1 across the Plaza, WTC 2 absorbed the aircraft strike and remained standing.


nolu_chan  posted on  2007-05-27   0:41:37 ET  Reply   Trace   Private Reply  


#6. To: Kamala (#4)

where is the pulling truss force coming from?

NIST? Leslie E. Robertson Associates? Someplace other than nature?

How does a sagging truss pull outer collumns?

Perhaps at a somewhat more downward angle?

That is why NIST uses the core shortening to pull the trusses which in turn pull the outer girders.

NIST wants you to believe that this all happened in a very small time frame. 13-15 min for the 1700-1800F transient flare up, then around another 30 min at lower temps.

They just want to put out B.S. non-studies until people lose interest.

These dampers were made of something like an oily memory foam. NIST needs to have this intact, along with the floors to the outer girders, for the assumed pulling.

If these melt and disconnect with the bolts, the floors cannot pull.

It seems like these would go before the steel. Heating up the material would seem to make it boil or expand or something.

How does a disconnected floor pull?

You adjust the variables. Computers merely crunch numbers. They do as instructed, however mindless the instruction may be. GIGO - garbage in, garbage out.

-----

Other questions:

If there were nothing but vertical downward gravitational force, and minimal resistance from the structure to that force, what force created the explosive force upward, and what force threw a 600,000 lb chunk of metal into another building? Unless there were a very significant resistance by the bottom part of the structure, how was a tremendous horizontal force generated?

Just before collapse, the top of the WTC-2 is seen leaning about 80 to 100 feet over the side. If it did not disintegrate in mid-air, presumably a very large chunk of building fell at free-fall speed. If it is in a debris cloud and does not emerge, it would seem that the building collapse generated a continuous debris cloud downward at free-fall speed.

How were the fires hot enough and severe enough to cause the steel to fail, but not hot enough and severe enough to cause the windows to fail?

If the metal were that hot, why do we not observe it glowing?

Just prior to collapse, the back WTC-7 shows no fires or broken windows.

nolu_chan  posted on  2007-05-27   1:12:15 ET  Reply   Trace   Private Reply  


#7. To: Kamala (#0) (Edited)

And 56 minutes, simply, isn't enough time to develop a fire hot enough, nor large enough in extent, to even have a remote chance of getting enough steel hot enough to be a factor.

Even if 56 minutes were long enough to weaken the steel and cause the upper floors to collapse, there still wouldn't be enough force to bring the whole building down. The upper portion would only fall the distance of one floor, that would not be enough force to cause the whole building to collapse.

If you want to measure someone's real IQ, just present them with these facts and if they still believe the towers came down like the government said they did then you know they aren't too bright. BAC is prime example.

God is always good!
"It was an interesting day." - President Bush, recalling 9/11 [White House, 1/5/02]

RickyJ  posted on  2007-05-27   2:20:22 ET  Reply   Trace   Private Reply  


#8. To: Kamala (#0)

WTF?  posted on  2007-05-27   3:02:55 ET  Reply   Trace   Private Reply  


#9. To: All (#8)

God is always good!
"It was an interesting day." - President Bush, recalling 9/11 [White House, 1/5/02]

RickyJ  posted on  2007-05-27   3:08:53 ET  Reply   Trace   Private Reply  


#10. To: WTF? (#8)

Fantastic clip. Thanks for the post.

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-27   6:03:29 ET  Reply   Trace   Private Reply  


#11. To: nolu_chan (#5) (Edited)

The report is full of contradictions from section to section. NIST had to have more damage in the WTC2 because it fell first. Plainly, the aircraft may have missed the core completely, or at most, damaged 1-3 collumns.

As much as NIST states how important the hat truss was to the wtc, it models simulations without it.

The aircraft was just about crushed on impact by the outer collumns and floors slabs. The time frame was from .02-.03.

WTC1 was a dead, head on middle strike, yet WTC1 has less damage than WTC2. NIST states that only one core collumn could be severed/failed by a direct engine strike. How do they account for all the failed and severed core collumns?

As you have noted, a landing gear exited the south face of WTC1, also a engine, landing gear and also some fuselodge exited WTC2.

In the computer aircraft impact/debris modeling, NIST could never get the simulations to duplicate the exiting of all the aircraft debris. No matter if A, B, C, or D cases were ran. So, all cases were incorrect and did not match real observed events.

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-27   7:26:48 ET  Reply   Trace   Private Reply  


#12. To: Kamala (#11)

The NIST finding requires that the floor end connections held and that the sagging floors remained connected to the columns.

This is directly opposite of the speculation of FEMA which stated, "As catenary action progresses, horizontal framing elements and floor slabs become tensile elements, which can cause failure of end connections (Figure 2-21) and allow supported floors to collapse onto the floors below."

To create a symmetrical downward pancaking, the FEMA solution required that all of the end connections fail simultaneously on each floor. FEMA found, as an actual OBSERVATION, that, "All column end plate bolted connections appeared to fail from the unanticipated out-of-plane bending .... The bolts were observed to exhibit classical tensile fracture in the threaded area."

Regarding the dampers, FEMA found, "Many of the bearing seat brackets and the damper angle connections on the column/spandrel beam plate were completely sheared off.

The NIST solution depends on those same end connections to be so strong that they withstood forces which caused the perimeter columns to bow.


http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm

Federal Building and Fire Safety Investigation of the World Trade Center Disaster

National Institute of Standards and Technology (NIST)

Answers to Frequently Asked Questions

(NIST NCSTAR throughout this document refers to one of the 43 volumes that comprise NIST’s final report on the WTC Towers issued in October 2005. All sections of the report listed in this document are available at http://wtc.nist.gov.)

-----

2. Why did NIST not consider a “controlled demolition” hypothesis with matching computer modeling and explanation as it did for the “pancake theory” hypothesis? A key critique of NIST’s work lies in the complete lack of analysis supporting a “progressive collapse” after the point of collapse initiation and the lack of consideration given to a controlled demolition hypothesis.

* * *

NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns— consisted of a grid of steel “trusses” integrated with a concrete slab; see diagram below). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.


World Trade Center Building Performance Study

FEMA P. 2-24, 2-25

2.2.1.4 Structural Response to Fire Loading

As previously indicated, the impact of the aircraft into WTC 1 substantially degraded the strength of the structure to withstand additional loading and also made the building more susceptible to fire-induced failure. Among the most significant factors:

As fire spread and raised the temperature of structural members, the structure was further stressed and weakened, until it eventually was unable to support its immense weight. Although the specific chain of events that led to the eventual collapse will probably never be identified, the following effects of fire on

-------------------

structures may each have contributed to the collapse in some way. Appendix A presents a more detailed discussion of the structural effects of fire.


FEMA Appendix B

B.3.2 Observations

1. The exterior tree columns were spliced using bolted end plate connections.

2. All column end plate bolted connections appeared to fail from the unanticipated out-of-plane bending of the column tree sections due to either the aircraft impacts or the deformation and buckling of the unbraced columns as the floor system diaphragms were destroyed by the impacts and fires. The bolts were observed to exhibit classical tensile fracture in the threaded area. Most bolts were also bent in the shank. Figure B-1 shows the column end plates and holes with some fractured and bent bolts. No evidence of plastic deformation was observed in the end plates.

3. Column splice requirements in the AISC Specifications (1963) indicated in Section 1.15.8 that "Where compression members bear on bearing plates and where tier-building columns are finished to bear, there shall be sufficient rivets, bolts, or welding to hold all parts securely in place."

-----

B.4 Examples of WTC1 and WTC 2 Connection Capacity

B.4.1 Bolted Column End Plates

Collapse of the WTC towers resulted in failure of many of the bolts in bolted end plate connections as the columns were subjected to large and unanticipated out-of-plane bending. In the majority of cases, the A325 high-strength bolts reached their tensile capacity and failed in the threaded stress area. The example shown in Figure B-7 examines the flexural capacity of the bolted end plate in a column in the impact area where the column plate thickness was 1/4 inch.

The simple moment capacity of the bolt group is 20 to 30 percent of the plastic moment capacity of a column fabricated from steels with a 50 to 100 ksi yield point, assuming no axial load in the columns. The end plates at the columns splice have a 11-3/4-inch x 14-inch cross-section. The columns are subjected to axial load from the dead load acting on the structure. For the as-built structure, the moments acting on the bolted splice are small, because the splices were located at the column inflection points and the resultant of the applied axial load and moment is within the middle third of the 12-inch-deep bearing connection. Assuming an axial stress of 20 ksi in the column, the corresponding axial force acting on the base plate is 280 kips. As the columns lose lateral support and deform out-of-plane from overloading eccentricities and from the thermal effects, the bending moment acting on die column splice does not introduce significant forces into the bolted end plate connection until the eccentricity exceeds 2 inches. As the eccentricity increases, the applied bending moment will exceed the bolt preload stress when the eccentricity reaches approximately 4 inches. Continued deformation will exceed the ultimate moment capacity of the connection and result in instability as the eccentricity approaches 4.5 inches.

It also should be noted that the column splices were staggered midheight at each floor, as was illustrated in Chapter 2. As a result, two-thirds of the perimeter columns were continuous at each floor's midheight elevation. This resulted in staggered failure patterns, as the bolted end plate connections and spandrel beam connections failed during the resulting instability and collapse. The exception to this staggered pattern was the splices at mechanical floors, which were not staggered, and the bolts were supplemented with welds.

[nc note - with the exception of the mechanical floors, the bolts were not supplemented by welds.]

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B.4.3 Floor Truss Seated End Connection at Spandred Beam and Core

* * *

It is probable that, once the 3/8-inch gusset plate fractures, the next lower bound resistance is provided by the bearing capacity of the two 5/8-inch bolts on the beam seat angle. This failure also tore off the ends of the angle even though the tensile capacity of those segments was predicted to be higher.

It should also be noted that each truss top chord provided a horizontal diagonal plate brace (1-1/2 inches x 1/2 inch) to the two adjacent columns. These members were welded to welded bracket plates on each adjacent column/spandrel member, as illustrated in Figure B-10. In this case, it would appear that the diagonal plate braces fractured on their gross section or tore the bracket plate. The component of ultimate strength of the two diagonal plate braces normal to the column/spandrel member is about 85 percent of the tensile capacity of braces, which would be 76 kips.

Many of the bearing seat brackets and the damper angle connections on the column/spandrel beam plate were completely sheared off. Only the weld segments remained on face of the column/spandrel beam plate (Figure B-11). This mode of failure appears to be due to excessive vertical overloads on the floor system. This is in contrast with the fialure mode exhibited in Figure B-9 where the bearing seat bracket has pulled away from the column/spandrel plate, after fracture of the top chord gusset plate.


nolu_chan  posted on  2007-05-27   17:53:51 ET  Reply   Trace   Private Reply  


#13. To: nolu_chan (#12)

Interesting information. The FEMA/BPAT was more honest and truthful in many aspects. The mechanical floors were of a more conventual contruction, much more robust than even the office areas.

Mark

"I was real close to Building 7 when it fell down... That didn't sound like just a building falling down to me while I was running away from it. There's a lot of eyewitness testimony down there of hearing explosions. [..] and the whole time you're hearing "boom, boom, boom, boom, boom." I think I know an explosion when I hear it... — Former NYC Police Officer and 9/11 Rescue Worker Craig Bartmer

Kamala  posted on  2007-05-28   7:25:13 ET  Reply   Trace   Private Reply  


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