The 9-11 THRUTH MOVEMENT deeltje 2

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THE COLLAPSE
Nearly every large building has a redundant design that allows for loss of one primary structural member, such as a column. However, when multiple members fail, the shifting loads eventually overstress the adjacent members and the collapse occurs like a row of dominoes falling down.

The perimeter tube design of the WTC was highly redundant. It survived the loss of several exterior columns due to aircraft impact, but the ensuing fire led to other steel failures. Many structural engineers believe that the weak points—the limiting factors on design allowables—were the angle clips that held the floor joists between the columns on the perimeter wall and the core structure (see Figure 5). With a 700 Pa floor design allowable, each floor should have been able to support approximately 1,300 t beyond its own weight. The total weight of each tower was about 500,000 t.

As the joists on one or two of the most heavily burned floors gave way and the outer box columns began to bow outward, the floors above them also fell. The floor below (with its 1,300 t design capacity) could not support the roughly 45,000 t of ten floors (or more) above crashing down on these angle clips. This started the domino effect that caused the buildings to collapse within ten seconds, hitting bottom with an estimated speed of 200 km per hour. If it had been free fall, with no restraint, the collapse would have only taken eight seconds and would have impacted at 300 km/h.1 It has been suggested that it was fortunate that the WTC did not tip over onto other buildings surrounding the area. There are several points that should be made. First, the building is not solid; it is 95 percent air and, hence, can implode onto itself. Second, there is no lateral load, even the impact of a speeding aircraft, which is sufficient to move the center of gravity one hundred feet to the side such that it is not within the base footprint of the structure. Third, given the near free-fall collapse, there was insufficient time for portions to attain significant lateral velocity. To summarize all of these points, a 500,000 t structure has too much inertia to fall in any direction other than nearly straight down.

WAS THE WTC DEFECTIVELY DESIGNED?
The World Trade Center was not defectively designed. No designer of the WTC anticipated, nor should have anticipated, a 90,000 L Molotov cocktail on one of the building floors. Skyscrapers are designed to support themselves for three hours in a fire even if the sprinkler system fails to operate. This time should be long enough to evacuate the occupants. The WTC towers lasted for one to two hours—less than the design life, but only because the fire fuel load was so large. No normal office fires would fill 4,000 square meters of floor space in the seconds in which the WTC fire developed. Usually, the fire would take up to an hour to spread so uniformly across the width and breadth of the building. This was a very large and rapidly progressing fire (very high heat but not unusually high temperature). Further information about the design of the WTC can be found on the World Wide Web.

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Op vrijdag 11 februari 2005 09:00 schreef Redux het volgende:
Skyscrapers are designed to support themselves for three hours in a fire even if the sprinkler system fails to operate. This time should be long enough to evacuate the occupants. The WTC towers lasted for one to two hours—less than the design life, but only because the fire fuel load was so large. No normal office fires would fill 4,000 square meters of floor space in the seconds in which the WTC fire developed. Usually, the fire would take up to an hour to spread so uniformly across the width and breadth of the building. This was a very large and rapidly progressing fire (very high heat but not unusually high temperature). Further information about the design of the WTC can be found on the World Wide Web.

bron: http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html

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Op vrijdag 11 februari 2005 09:13 schreef YuckFou het volgende:
Ik kan hier niet uit opmaken of het over het eerste of tweede toestel gaat, maar van de tweede is vrijwel de hele fuel load in een grote bal aan de buitenkant van de toren verbrand...teveel imo om daarnaast de hele structuur van het gebouw te verzwakken.

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Op vrijdag 11 februari 2005 09:22 schreef YuckFou het volgende:
geen linkjes en zwaar onderbouwde mening op deze vroege morgen, sorry.
Maar als je naar alle filmpjes kijkt dan lijkt het me duidelijk, het eerste vliegtuig schoot vol de toren in en ontplofde vrijwel geheel binnen in de otren, dat zo'n ding daarvan in stort lijkt me logisch.
Maar die tweede die trek ik niet helemaal, die knalt er op een hoek in, explodeert voor (zo te zien) het grootste gedeelte buiten de toren en toch zakt die toren als eerste in...vreemd....

* YuckFou is nooit te beroerd wat extra kerosine op het conspiracy vuur te gooien

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Op vrijdag 11 februari 2005 09:35 schreef UncleScorp het volgende:
Pretty obvious zou ik zeggen ...

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Steel Structure Nonlinear FEA Simulation Provides
Insight into World Trade Center Collapse.

OVERVIEW

Had the World Trade Center (WTC) collapsed in two hours,there would have been few if any casualties. Which has raised the question: Why did the WTC collapse in just one hour? And what changes can be made to the building code for high-rise buildings and bridges to prevent another occurrence? As part of a research study, funded by Federal Emergency Management Agency (FEMA), researchers from academia, government and private industry investigated the cause of the collapse of WTC building. Dr. Abolhassan Astaneh-Asl, professor of civil and environmental engineering at the University of California, Berkeley, under the Directorate of Engineering of the National Science Foundation (NSF), investigated the collapse of the World Trade Center. He was one of five expert witnesses invited to testify before the Committee on Science of the U.S. House of Representatives at the March 6, 2002 hearing. Learning from 9/11 - Understanding the Collapse of the World Trade Center. Dr. Astaneh-Asl's presentation included a movie of a simulated crash of a passenger aircraft onto a generic steel structure created with MSC.Dytran and MSC.Marc by the MSC.Software nonlinear group.
INVESTIGATION

The collapse of the WTC was caused by a series of very complex events, involving tremendous impact to the structure, fire explosion and resulting heat. Simulation of these events requires an advanced technology to accurately predict the nonlinear impact dynamics, failure and thermal effects. Most civil engineering analysis software is tailored to perform basic static and dynamic analyses in compliance with the building codes which places limitations on its element technology, material models, failure and nonlinearity. Basically, civil engineering analysis software provides linear static, frequency and normal modes (earthquake) analyses of building structures and therefore is unsuitable for simulating the complex events at the WTC. To show the feasibility of simulating such a complex event, MSC.Dytran was selected to analyze the initial impact of a Boeing 747 on to a generic steel structure. MSC.Dytran, which is based on an explicit technology, is very well suited for short duration events such as crashes, impact dynamics and explosions. MSC.Marc was selected for the thermal analysis, because of its powerful heat transfer and thermo-mechanical analysis capabilities. Both MSC.Dytran and MSC.Marc provide nonlinear analysis of many different types of applications and are limited only by the end user system resources.

CREATING THE MODEL

Because of the limited time available to provide an initial analysis, a search of MSC.Software's past projects turned up the public domain geometry of a Boeing 747 with partially meshed wings and engines. MSC.Patran was used to add the fuselage and stiffeners, tail section, flooring and other major components, completing the finite element model of the Boeing 747. Concentrated masses were added in specific locations along the aircraft to represent the cargo, passenger weight distribution and fuel. The total weight of the Boeing 747 was 304,000 kg. 304,000 kg = 670,200 lb. The maximum takeoff weight of a Boeing 747 is 875,000 lb. The maximum takeoff weight of a Boeing 767 is 395,000 lb.

A full mockup of the building was unnecessary, because of time limitations and the fact that the actual structural data had not yet been made available Apparently, Astaneh-Asl still does not have the plans of the WTC. Wouldn't it would be reasonable to give your researchers the basic data needed for their investigations. Therefore, a generic six-story steel structure was constructed with tubular beams and columns. The gravity loading was applied to the entire structure and the dead weight of the building was added through the floorings located on the top-two and bottom-two floors of the structure. Floors were not added to the impact area, which facilitated the study of the failure pattern of both the aircraft and the beam-column connections. The steel-concrete composite floors are responsible for much of the structures resistance/strength against the lateral motion induced by the impact of a plane, so this is surprising. The foundation of the building was rigidly fixed. Approximately 61,000 elements were used to construct the entire model of the building and Boeing 747.

IMPACT SIMULATION

The Boeing 747 was run into a centralized location of the building exterior between the 3rd and 4th floors at 200 m/sec (about 450 mph) at zero degree yaw and pitch angles. When the aircraft crashed into the WTC, the initial impact to the building resulted in massive structural failure and deterioration to both building and the aircraft. Then a fire explosion caused further weakness to the building structure. Concerning the exterior fireballs. Consider, this quote from the Federal Emergency Management Agency report into the collapse of the Twin Towers: Although dramatic, these fireballs did not explode or generate a shock wave. If an explosion or detonation had occurred, the expansion of the burning gasses would have taken place in microseconds, not the 2 seconds observed. Therefore, although there were some overpressures, it is unlikely that the fireballs, being external to the buildings, would have resulted in significant structural damage. In order to visualize the massive rupture and structural failure emanating from the dramatic impact, "contact with erosion" were defined between the Boeing 747 and the steel structure.

The contact technology in MSC.Dytran allows the prediction of severe material failure such as rupture, perforation, cracking and shearing effects. In addition, "single surface contact" was defined for both the building and aircraft to account for buckling of structural beams and columns and the crushing of the internal components of the Boeing 747. The failure criteria of the steel and aluminum material were defined based on their maximum plastic strains. For example, when an element reaches its maximum plastic strain limits it will no longer provide structural strength and is eliminated from the calculation..The analysis showed that the impact of the crash substantially weakened the structure. However, because of redundancy in the structural design, the gravitational load was redistributed on the beams and columns that had not failed. Therefore, the impact of the Boeing 747 on the building by itself did not cause the WTC to collapse. MSC.Dytran supports shared memory parallel capability, allowing the job to be submitted on multiple processors to reduce the CPU time. The impact simulation required 24 hours to complete a 250 millisecond time simulation on an SGI dual processor (300Mhz).

THERMAL SIMULATION

As the Boeing 747 deteriorated, it dispersed approximately 10,000 gallons of fuel inside the WTC, (allowing for fuel consumption during the flight). This was a massive amount of fuel and during the investigation of the WTC, fuel was even found in the elevator shafts and on the first floor. That liquid fuel from the planes was found on the first floor is an obvious lie. It is worth noting that 10,000 gallons of jet fuel could be contained in a cubic tank of side length 11 feet. Ten thousand gallons is the (estimated) quantity of fuel carried by the Boeing 767s which hit the towers (a Boeing 747 has a fuel capacity of 57,285 gallons). Based on the impact simulation created in MSC.Dytran, a heat transfer and thermal stress analysis was performed in MSC.Marc.

The results of the impact simulation were brought into MSC.Patran for post processing, where the rigid floors were converted into deformable shell elements and element properties were associated with the beams, trusses and the floor. The analysis preference was switched to MSC.Marc and a new input file was written based on the deformed building.

It was decided to run a nonlinear conduction/convection/radiation analysis with temperature dependent thermal and mechanical properties for the steel taken from the MSC.Marc database. In the temperature range to which many members were subjected the ultimate stress was reduced by a factor of five. The properties of the concrete were approximated.

Because of time limitations, two strategies were pursued, including radiation on one model and not on the other. Radiation, where the energy travels from one surface to the next, plays a major role. To properly model radiation, it is necessary to compute the proportion of one surface visible from a second surface known as "view factor". Because view factors must be calculated using an implicit procedure in MSC.Marc, it requires a large bandwidth and computing time. Selecting the radiating surfaces was a straightforward procedure because the model was constructed of shell elements instead of beam elements. Because of the complexity of the structural model, the radiation matrix became excessive. The view factor calculation using the Monte Carlo method in MSC.Mentat required 19 hours of processing time. Since this simulation, a new algorithm has been developed that reduces processing time to two hours. The radiation procedure was dropped because of time limitations. However, at the temperatures involved, radiation played an important part and, because of the combustion, modeling of this effect is nontrivial.

Very little information was available regarding the heat source, so it was assumed to be 1500°C, acting in the area of the structure carved out by the plane. This is unbelievable, and shows the thermal modeling to be a complete farce. Let me help out. Kerosine, i.e. jet fuel, burns in air at about 825°C and a reasonably severe office fire (fuel load of 40 kg per square meter) burns at about 750°C. Convective boundary conditions were applied to nearby members in the center of the structure. A thermal analysis using an adaptive time stepping procedure was performed for one hour. It illustrates that the temperatures would have reached over 500°C even on adjacent floors (even if more radiation was included). The thermal analysis required 2,300 seconds on a workstation.The thermal results were then incorporated into MSC.Marc to perform an elastic-plastic dynamic analysis. MSC.Marc used an implicit procedure for this.

While dynamics would normally not be included in this type of analysis, part of the structure obtained from MSC.Dytran was disconnected. In a static analysis, this would normally result in rigid body modes. But gravity loads and the thermal loads were driving this analysis. The thermal stress analysis showed little deflection for the first 30 minutes and then a large plastic strain occurred which resulted in instability. This is reflected in the large plastic strains that are shown in the joists. The model with close to 56,000 shell elements required 12 hours of processing time. While the impact of the crash substantially weakened the structure, the remaining steel beams and columns melted because of the extreme temperatures. This is absolute garbage. Steel melts at about 1500°C. It is clear that the fires could not/did not get much above 825°C (and were almost certainly cooler). Even if we agree that the heat source was 1500°C, the temperature of the surrounding steel would have been well below 1500 degrees. As further evidence of the farcical nature of the thermal modeling, consider that this article estimates that "temperatures would have reached over 500°C" and apparently this is enough to melt steel (1500°C). Also buckling in the trusses was possible, especially after the damaged crossbeams were unable to provide lateral support. As a result, the load could no longer be distributed and the building collapsed.

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While the impact of the crash substantially weakened the structure, the remaining steel beams and columns melted because of the extreme temperatures. This is absolute garbage. Steel melts at about 1500°C. It is clear that the fires could not/did not get much above 825°C (and were almost certainly cooler). Even if we agree that the heat source was 1500°C, the temperature of the surrounding steel would have been well below 1500 degrees. As further evidence of the farcical nature of the thermal modeling, consider that this article estimates that "temperatures would have reached over 500°C" and apparently this is enough to melt steel (1500°C)

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Op vrijdag 11 februari 2005 09:54 schreef iteejer het volgende:
magnifiek

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Op vrijdag 11 februari 2005 09:58
schreef YuckFou het volgende:
While the impact of the crash substantially weakened the structure, the remaining steel beams and columns melted because of the extreme temperatures. This is absolute garbage. Steel melts at about 1500°C. It is clear that the fires could not/did not get much above 825°C (and were almost certainly cooler). Even if we agree that the heat source was 1500°C, the temperature of the surrounding steel would have been well below 1500 degrees. As further evidence of the farcical nature of the thermal modeling, consider that this article estimates that "temperatures would have reached over 500°C" and apparently this is enough to melt steel (1500°C)

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Op vrijdag 11 februari 2005 10:15 schreef UncleScorp het volgende:
Nog een klein voorbeeldje van amerikaanse wetenschap en hun conclusies ...

VS-wetenschappers dienden van de politiek conclusies te veranderen

http://www.hbvl.be/nieuws/wetenschap/default.asp

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Op vrijdag 11 februari 2005 10:15 schreef Redux het volgende:
Ik moet het even opzoeken, maar het is was toch de vloeren die naar beneden kwamen zetten waardoor het hele zaakje instortte? Correct me if im wrong.

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Op vrijdag 11 februari 2005 10:59 schreef YuckFou het volgende:

[..]

Ik vind anders nog steeds dat het gebeurt is d.m.v. controlled explosions