1. Structural Impact: When the hijacked airplanes struck the World Trade Center towers, they created massive structural damage. The impacts severed critical load-bearing columns and weakened the steel frames of the buildings. The intense heat from the burning jet fuel further compromised the structural integrity of the steel.
2. Jet Fuel Fires: The aviation fuel carried by the airplanes ignited upon impact, resulting in intense and prolonged fires within the towers. The jet fuel burned at extremely high temperatures, reaching up to 1,832 degrees Fahrenheit (1,000 degrees Celsius). These fires caused the steel support structures to lose their strength and undergo a phenomenon called "creep."
3. Creep: Under sustained high temperatures, steel loses its strength and deforms gradually under constant load. This process is known as creep. The steel columns in the World Trade Center towers began to buckle and sag under the weight of the upper floors due to the intense heat from the fires.
4. Catenary Effect: As the steel columns weakened due to creep and the weight of the upper floors became unmanageable, a domino-like chain reaction occurred. The floors began to sag and deform, creating a catenary effect. The floors above the impact zones progressively failed, transferring their weight to the lower floors, which were not designed to withstand such excessive loads.
5. Pancaking: The progressive failure of the floors led to a phenomenon called "pancaking." As the upper floors collapsed, they fell onto the lower floors, creating a cascading effect. The impact from the falling floors generated enormous forces that caused the entire building to crumble under its own weight. This pancaking effect accelerated the collapse of the towers.
It's important to note that the towers were initially designed to withstand significant wind and seismic forces but not the unique scenario of high-speed airplane impacts and intense fires that occurred on 9/11. The combination of structural damage and extreme heat weakened the steel structures beyond their design limits, resulting in the eventual collapse of the World Trade Center towers.
