how did the twin towers collapse

The Twin Towers collapsed primarily due to the combination of structural damage from the airplane impacts and the intense fires fueled by jet fuel and building contents. The planes damaged key vertical support columns and removed fireproofing, allowing fires to rapidly heat and weaken the steel framework. The heated steel lost strength, causing floor beams to sag and pull inward on the perimeter columns, eventually leading to buckling and collapse of the floors. This progressive failure cascaded downward, causing the towers to collapse mostly straight down. The North Tower was hit near the center and stood longer due to more symmetric damage, while the South Tower was hit lower and off-center, causing earlier collapse. Investigations concluded that the fires' prolonged heating weakened the steel enough to cause the collapses, not melting the steel but reducing its load-bearing capacity. This progressive collapse released gravitational energy, which drove the entire structure's failure.