World Trade Center bombing of 1993
In the World Trade Center bombing (February 26, 1993) a car bomb was detonated by Arab Islamist terrorists.
The attack was planned by a group of conspirators including Ramzi Yousef.
They received financing from al-Qaeda member Khaled Shaikh Mohammed, Yousef's uncle, who would later allegedly admit to planning the September 11, 2001 attacks.
Osama bin Laden, declaring: the ruling to kill the Americans and their allies civilians and military - is an individual duty for every Muslim who can do it in any country in which it is possible to do it.
According to interviews by Al-Jazeera as well as United States interrogations of al-Qaeda members Ramzi Binalshibh and Khalid Shaikh Mohammed (captured in 2002 and 2003 respectively), Khalid Mohammed was the instigator and prime organizer of the attacks.They also indicated bin Laden's direct participation.
http://en.wikipedia.org/wiki/Responsibility_for_the_September_11,_2001_attacks
Why Did It Collapse?
Tim Wilkinson, Lecturer in Civil Engineering
The structural integrity of the World Trade Center depends on the closely spaced columns around the perimeter. Lightweight steel trusses...
It appears likely that the impact of the plane crash destroyed a significant number of perimeter columns on several floors of the building, severely weakening the entire system.
as fire raged in the upper floors, the heat would have been gradually affecting the behaviour of the remaining material. As the planes had only recently taken off, the fire would have been initially fuelled by large volumes of jet fuel. strength of the steel drops markedly with prolonged exposure to fire,
Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination. Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards. Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete storey at the level of impact.
Once one storey collapsed all floors above would have begun to fall. The huge mass of falling structure would gain momentum, crushing the structurally intact floors below, resulting in catastrophic failure of the entire structure. While the columns at say level 50 were designed to carry the static load of 50 floors above, once one floor collapsed and the floors above started to fall, the dynamic load of 50 storeys above is very much greater, and the columns were almost instantly destroyed as each floor progressively "pancaked" to the ground.
This section added 14 January 2006
This website generates many queries from people in response to some of the other theories that are put forward relating to the collapse - namely that it was a controlled explosion.
The initial impact/further weakening by fire reasoning is based on uncontestable knowledge about the behaviour of structures in general, and the weakening of steel under fire conditions, plus video footage of the events and examination of the steel afterwards.
The fire wasn't hot enough to melt the steel
There has never been a claim that the steel melted in the fire before the buildings collapsed, however the fire would have been very hot. Even though the steel didnt melt, the type of temperatures in the fire would have roughly halved its strength.
The way the building collapsed must have been caused by explosions
Demolition experts spend weeks inside a derelict building planning an event. Many of the beams are cut through by about 90% so that the explosion only has to break a small bit of steel. In this state the building is highly dangerous, and there is no way such a prepared building could still be running day to day like WTC was.
Why did the building fall so quickly?
The huge dynamic loads due to the very large momentum of the upper floors falling were so great that they smashed through the lower floors very quickly. The columns were not designed to carry these huge loads and they provided little resistance.
The author respects people's right to question theories, but at the present time the author does not believe there is enough evidence for him to change his views on this incident.
http://www.civil.usyd.edu.au/wtc.shtml
In the World Trade Center bombing (February 26, 1993) a car bomb was detonated by Arab Islamist terrorists.
The attack was planned by a group of conspirators including Ramzi Yousef.
They received financing from al-Qaeda member Khaled Shaikh Mohammed, Yousef's uncle, who would later allegedly admit to planning the September 11, 2001 attacks.
Osama bin Laden, declaring: the ruling to kill the Americans and their allies civilians and military - is an individual duty for every Muslim who can do it in any country in which it is possible to do it.
According to interviews by Al-Jazeera as well as United States interrogations of al-Qaeda members Ramzi Binalshibh and Khalid Shaikh Mohammed (captured in 2002 and 2003 respectively), Khalid Mohammed was the instigator and prime organizer of the attacks.They also indicated bin Laden's direct participation.
http://en.wikipedia.org/wiki/Responsibility_for_the_September_11,_2001_attacks
Why Did It Collapse?
Tim Wilkinson, Lecturer in Civil Engineering
The structural integrity of the World Trade Center depends on the closely spaced columns around the perimeter. Lightweight steel trusses...
It appears likely that the impact of the plane crash destroyed a significant number of perimeter columns on several floors of the building, severely weakening the entire system.
as fire raged in the upper floors, the heat would have been gradually affecting the behaviour of the remaining material. As the planes had only recently taken off, the fire would have been initially fuelled by large volumes of jet fuel. strength of the steel drops markedly with prolonged exposure to fire,
Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination. Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards. Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete storey at the level of impact.
Once one storey collapsed all floors above would have begun to fall. The huge mass of falling structure would gain momentum, crushing the structurally intact floors below, resulting in catastrophic failure of the entire structure. While the columns at say level 50 were designed to carry the static load of 50 floors above, once one floor collapsed and the floors above started to fall, the dynamic load of 50 storeys above is very much greater, and the columns were almost instantly destroyed as each floor progressively "pancaked" to the ground.
This section added 14 January 2006
This website generates many queries from people in response to some of the other theories that are put forward relating to the collapse - namely that it was a controlled explosion.
The initial impact/further weakening by fire reasoning is based on uncontestable knowledge about the behaviour of structures in general, and the weakening of steel under fire conditions, plus video footage of the events and examination of the steel afterwards.
The fire wasn't hot enough to melt the steel
There has never been a claim that the steel melted in the fire before the buildings collapsed, however the fire would have been very hot. Even though the steel didnt melt, the type of temperatures in the fire would have roughly halved its strength.
The way the building collapsed must have been caused by explosions
Demolition experts spend weeks inside a derelict building planning an event. Many of the beams are cut through by about 90% so that the explosion only has to break a small bit of steel. In this state the building is highly dangerous, and there is no way such a prepared building could still be running day to day like WTC was.
Why did the building fall so quickly?
The huge dynamic loads due to the very large momentum of the upper floors falling were so great that they smashed through the lower floors very quickly. The columns were not designed to carry these huge loads and they provided little resistance.
The author respects people's right to question theories, but at the present time the author does not believe there is enough evidence for him to change his views on this incident.
http://www.civil.usyd.edu.au/wtc.shtml