On September 11, 2001, following the four terrorist attacks that shocked the United States, two American Airlines planes hit the World Trade Center causing the collapse of the Twin Towers (WTC1 and WTC2) and Building 7 (WTC7).
Hijacked by an Al Qaeda terrorist group, the first plane crashed at 8:46 a.m. into the North Tower while the second plane crashed at 9:02 a.m. into the South Tower. On that tragic Tuesday, 2900 people died.
In this video, with the support of 3D reconstructions-some of which have never been seen before-we analyze the causes of the collapse from a technical-engineering perspective. We will explain how the Twin Towers fell in less than 10 seconds after the planes hit and why Tower 7 collapsed hours later, despite not being directly hit.
We will examine the doubts, conspiracy theories and the question behind the temperature of the steel. A mini-documentary to retrace what happened.
00:00 - Twin Towers: 3D reconstruction of the impact
02:20 - Features of the Twin Towers: the World Trade Center project
04:06 - Why was steel chosen for their construction?
05:09 - Structure of the Twin Towers
08:11 - Steel behavior under stress: elastic and plastic phases
11:40 - What happens when steel reaches 1000°C?
13:00 - The collapse of the Twin Towers: NIST explanation
16:57 - Structure of World Trade Center Building 7
20:09 - Why did the WTC7 building collapse? The event dynamics