Galloping Gertie: How the 1940 Tacoma Narrows Collapse Transformed Bridge Engineering

Galloping Gertie: The Tacoma Narrows Bridge Collapse, Nov. 7, 1940

The Tacoma Narrows Bridge, nicknamed "Galloping Gertie," began to oscillate in steady 40 mph (64 km/h) winds on the morning of Nov. 7, 1940. At 11:02 a.m. the center span failed and plunged into Puget Sound. The elegant suspension bridge — opened just months earlier in July 1940 and then the third-longest in the world — had been designed by noted engineer Leon S. Moisseiff, who had also helped design the Golden Gate Bridge.

Early warnings and temporary fixes

From its opening, workers and users noticed unusual motion in the deck and quickly nicknamed the structure "Galloping Gertie." The state toll authority brought in University of Washington engineer F. Bert Farquharson to investigate. Scale models (a 1:200 model 54 ft/16.5 m long and a 1:20 model 8 ft/2.4 m long) and wind-tunnel section tests were used to replicate the behavior.

Several quick fixes were attempted. Engineers installed four hydraulic jacks hoping to act as shock absorbers and added tie-down cables at the approaches; these measures reduced motion near the ends but did not stop midspan movement. One tie-down cable failed during a high-wind event on Nov. 1, and the bridge's motion resumed.

The final minutes

By Nov. 2, modeling indicated the deck began to twist when side gusts struck the span, and Farquharson's team recommended cutting openings in the plate girders or adding wind deflectors. They estimated temporary deflectors could stabilize the span in about 10 days and a full retrofit in around 45 days — but those corrections were not installed before the collapse.

On Nov. 7, copy editor Leonard Coatsworth was driving across with his daughter's three-legged cocker spaniel, Tubby, when the bridge began undulating and then tilting violently. Coatsworth abandoned his car partway across and survived; a photographer, Howard Clifford, later described running across a roadway that seemed to leave him "running in air." A cameraman recorded the dramatic failure. There were no human fatalities; Tubby the dog was the only casualty that day.

"Before I realized it, the tilt from side to side became so violent I lost control of the car..." — Leonard Coatsworth, Tacoma News Tribune

Cause: torsional flutter and self-excited motion

Investigators concluded the collapse was due to torsional flutter, a self-excited aerodynamic instability. After a midspan cable slipped and the span became unbalanced, the deck began to twist. That twisting changed the effective angle at which wind hit the bridge's solid plate girders, allowing the deck to absorb energy from the wind and amplifying motion. Once oscillation synchronized with wind vortices, the twisting became self-sustaining and catastrophic.

The official failure report summarized that the span was too long, the deck too light, and the roadway too narrow to resist aerodynamic forces adequately.

Legacy and changes in design practice

The Tacoma Narrows collapse had profound and lasting effects on bridge engineering. Key changes included:

• Mandatory wind-tunnel testing of three-dimensional scale models for long-span bridges to study aerodynamic behavior before construction.
• Expansion of design theory beyond simple vertical deflection to include torsion, coupled modes of motion, and aeroelastic effects.
• Practical retrofits and design changes to increase torsional stability, as later applied to other major spans such as the Golden Gate Bridge after storms showed vulnerability.

Although the disaster damaged the reputation of the bridge's designer, the engineering lessons learned from "Galloping Gertie" reshaped aerodynamic and structural analysis and made subsequent bridges safer worldwide.

Further reading

Primary sources include the Washington State Department of Transportation investigation and contemporary accounts in the Tacoma News Tribune, as well as later engineering analyses of aeroelastic phenomena such as torsional flutter.