A new mathematical explanation of what triggered the catastrophic torsional mode of the Tacoma Narrows Bridge

The spectacular collapse of the Tacoma Narrows Bridge has attracted the attention of engi- neers, physicists, and mathematicians in the last 74 years. There have been many attempts to explain this amazing event, but none is universally accepted. It is however well estab- lished that the main culprit was the unexpected appearance of torsional oscillations. We suggest a mathematical model for the study of the dynamical behavior of suspension bridges which provides a new explanation for the appearance of torsional oscillations dur- ing the Tacoma collapse. We show that internal resonances, which depend on the bridge structure only, are the source of torsional oscillations.