9/11 conspiracy theories debunked: 20 years later, engineering experts explain how the twin towers collapsed

By David Oswald, Senior Lecturer in Construction, RMIT University
Erica Kuligowski, Vice-Chancellor's Senior Research Fellow, RMIT University
Kate Nguyen, Senior Lecturer, ARC DECRA Fellow and Victoria Fellow, RMIT University

The collapse of the World Trade Center has been subject to intense public scrutiny over the 20 years since the centre’s twin towers were struck by aircraft hijacked by terrorists. Both collapsed within two hours of impact, prompting several investigations and spawning a variety of conspiracy theories.

Construction on the World Trade Center 1 (the North Tower) and World Trade Center 2 (the South Tower) began in the 1960s. They were constructed from steel and concrete, using a design that was groundbreaking at the time. Most high-rise buildings since have used a similar structure.

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