Where this idea comes from· Billah & Scanlan, 1991
The Tacoma Narrows Bridge (1940)
The bridge in Washington State opened on 1 July 1940 and fell into the water on 7 November 1940, in a steady wind of about 40 miles an hour.
One thing to hold: Film of its last hour shows the deck twisting in long waves. The wind didn’t push it over; the twisting fed itself, growing a little with each swing (engineers call this flutter).
Why it matters: Since then, bridge designs are tested in wind tunnels for how they move, not only for how much weight they hold.
What we don’t know: Many textbooks call it simple resonance. Engineers who studied it say that is not the whole story.