On September 11, 2001, three steel-framed skyscrapers somehow collapsed.
They all collapsed at freefall speed or greater, building 7 collapsing into its own footprint, and the two towers disintegrating mostly into dust which formed a cloud that enveloped the city.
Douglas Beason Los Alamos discusses directed energy weaponry
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Figure wall. A view over the dome of WFC2 shows the damage to WTC6 in the center of the photo. To the left is the collapsed WTC7. Its debris stack is at least five stories high. To the right of WTC6 is the remaining north wall of WTC1 which leans toward WTC6. Where did the wall go? Where did the top 100 floors of the north wall go? They did not fall on WTC6 or WTC7 because there are no steel wheatchex there. Some of the core of WTC1 remains, but where is the rest of the core? The amount of steel on the ground barely covers the ground.
(Thanks to spooked for this picture.)