The Tacoma Narrows Bridge Collapses

A Bridge Comes Apart in the Wind

On November 7, 1940, the Tacoma Narrows Bridge in Washington began twisting violently and collapsed. The bridge had opened only months earlier, carrying road traffic across the Narrows of Puget Sound. It was a slender suspension bridge whose deck had already shown conspicuous motion in winds, earning it a nickname well before its failure. The final movement was different in character from the vertical waves often seen earlier. The roadway twisted, with opposite sides moving in different directions. Film preserved part of the collapse and made it possible to compare the kind of motion witnesses described with the structure visible in the images.

Why the Deck's Shape Mattered

The deck used solid plate girders, and the structure was relatively flexible. Wind moving around a deck can produce forces that depend on how the deck is oriented at that instant. Once the deck twists, those forces can change in a way that feeds further motion. The failure is commonly explained in terms of aeroelastic instability, rather than a simple external beat coinciding with a fixed natural frequency. Real bridges have several possible modes of motion. Their behavior depends on stiffness, damping and aerodynamics acting together. The disaster gave engineers a full-scale example of what could happen when that interaction had not been adequately accounted for.

A Record With More Than One Use

The surviving film is often shown because it makes a large structure look unexpectedly flexible. It can also encourage a viewer to skip over the design and maintenance history. Engineers had recognized troubling motion and tried measures to reduce it. Their efforts show that the issue was known before the final day, even though the ultimate failure was not prevented. The collapse killed no people; a dog left in an abandoned car died. The difference between the human outcome and the scale of structural destruction is important when describing or recreating the event.

What Changed Afterward

Bridge designers paid greater attention to how deck sections behaved in wind, using tests and design changes to improve stability. The replacement bridge opened in 1950 with features that differed from the original design. The collapse did not mean suspension bridges were inherently unsound. It identified a class of behavior that could not be inferred simply by checking whether a bridge could carry its own weight and traffic. A structure could be strong under ordinary static loads and still be vulnerable to motion that increased with the airflow. The November film remains useful because it shows that distinction in a form visible without a calculation.