42 MPH Wind Tore This Bridge Apart. It Wasn't Resonance

On November 7, 1940, a wind of about 42 mph twisted the brand-new Tacoma Narrows Bridge until it tore itself apart. You've probably been told it was resonance. Engineers who studied it say that's wrong. Engineering Disasters #8 looks under the hood of "Galloping Gertie": why the Narrows was a hard place for a bridge, Eldridge's 25-foot truss vs Moisseiff's 8-foot solid girders, the slender-bridge trend and deflection theory, a deck that bounced in 4 mph winds, Farquharson's wind-tunnel warning, the last morning minute by minute, why the 0.2 Hz twist doesn't match ~1 Hz vortex shedding, torsional flutter (negative damping), why an H-shaped deck twists, the "simply forgotten" lessons, and the 1950 "Sturdy Gertie." Saturday, November 7, 2026 is the 86th anniversary of the collapse. Chapters 0:00 Intro: 42 mph 0:49 A hard place for a bridge 1:19 Two designs 2:13 The slender trend 3:01 Galloping Gertie 3:48 The warning in the wind tunnel 4:33 November 7th, 1940 5:23 The fall 6:04 Was it resonance? 6:44 The numbers don't match 7:23 Torsional flutter 8:17 Why this shape twisted 9:09 Simply forgotten 10:01 Sturdy Gertie 10:58 The lesson 11:30 About this video Sources WSDOT, Tacoma Narrows Bridge history (main page and timeline): https://www.wsdot.wa.gov/TNBhistory/ and https://www.wsdot.wa.gov/TNBhistory/bridge... WSDOT, the 1940 bridge (site, designs, ratios): https://www.wsdot.wa.gov/TNBhistory/1940-b... WSDOT, collapse: https://www.wsdot.wa.gov/TNBhistory/collap... WSDOT, why the bridge failed: https://www.wsdot.wa.gov/TNBhistory/bridge... WSDOT, aftermath and Carmody Board: https://www.wsdot.wa.gov/TNBhistory/bridge... WSDOT, the bridges since 1950: https://www.wsdot.wa.gov/TNBhistory/bridge... WSDOT, weird facts: https://www.wsdot.wa.gov/TNBhistory/weird-... K. Y. Billah & R. H. Scanlan, "Resonance, Tacoma Narrows bridge failure, and undergraduate physics textbooks," American Journal of Physics 59(2), 118-124 (1991): https://doi.org/10.1119/1.16590 (PDF: https://www.ketchum.org/billah/Billah-Scan...) D. Green & W. G. Unruh, "The failure of the Tacoma Bridge: A physical model," American Journal of Physics 74(8), 706-716 (2006): https://doi.org/10.1119/1.2201854 HistoryLink.org, "Tacoma Narrows Bridge collapses on November 7, 1940" (File 5048): https://www.historylink.org/File/5048 HistoryLink.org, Tacoma Narrows Bridge essay (File 21131): https://www.historylink.org/File/21131 Notes: Wind speed (about 42 mph) is the reading reported at the east end; fishermen said it was stronger at the west end. WSDOT pages give the 1950 bridge's truss depth as 33 feet in the text but 25 feet in one table; we use 33 feet. The flutter-onset range (roughly 16 to 30 mph) comes from scale-model tests and is approximate. The violin-bow and swing comparisons are simplified teaching analogies, and the energy bars in the flutter chapter are illustrative, not measured. Illustrations are not to scale. Narration voice is AI-generated; script researched and checked against the sources above. Would you have driven across Galloping Gertie for the thrill?