In memory of the 2,977 people killed on 11 September 2001, among them 343 firefighters of the FDNY.
This is an interactive engineering model of the North and South Towers of the World Trade Center: the aircraft impacts, the fires, the loss of structural capacity and the progressive collapse. No people are depicted. You can fight the fires, reinforce or remove structural members, change the fire and impact conditions, and see how each change affects whether, when and how the towers fail.
It is a reduced-order model loosely calibrated to the NIST NCSTAR 1 findings. It is meant for exploration, not forensic analysis.
08:45:00EDT
Tools
Water supply
Floor plan
Click a column or cell to inspect it.
Scenario & physics ▸
Launch impact
Challenges
Event log
Simulating…
Controls
Orbit / zoom / pan
Right-drag or left-drag in Inspect mode · wheel · Shift+drag or middle-drag
Space
Play / pause
1–8
Simulation speed
N
Jump to the next event (impact or collapse)
, / .
Rewind 5 min / fast-forward 5 min
X
Toggle the engineering X-ray view (load ratio heatmap)
F1–F4
Cameras: overview, approach of the next impact, South Tower, street level, river
Each tower has 236 perimeter columns and 47 core columns on each of its 110 stories, plus spandrels and floor trusses. Every column segment carries a share of the weight above it. Impact damage, heat (steel loses about half its strength by 600 °C), sagging floors pulling the walls inward, and your interventions all reduce a segment's capacity. When a column fails, its load shifts to its neighbours through the spandrels and to the rest of the structure through the hat truss. If a whole story can no longer carry the weight above it, the upper block drops and crushes the stories below one at a time. The collapse can stop partway if those stories are strong enough.
Fires spread cell by cell across each floor, burn out after about 20 minutes, climb the building through broken windows, and are suppressed by water.