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This Day in History — The Bridge That Galloped to Its Destruction

On this day in 1940

On November 7, 1940, Galloping Gertie twisted itself apart in a roughly 40-mph wind four months after opening. Its only casualty was a spaniel named Tubby.

The Off-Key Bard stands near the shore of Puget Sound on a windy November morning in 1940. Across the water stretches an elegant suspension bridge, its slender roadway hung between two towering steel towers. But something is terribly wrong. The bridge is moving. Not the gentle vibration of passing traffic, but waves that roll along the roadway. Then the motion changes. One side of the deck rises while the other drops, and the bridge begins twisting as though an invisible giant has seized it by both ends.

"The wind is not simply pushing against the bridge. The bridge and the wind have become part of a destructive cycle."

On November 7, 1940, the Tacoma Narrows Bridge collapsed into Puget Sound, four months and seven days after it opened on July 1, 1940. Workers had nicknamed it "Galloping Gertie" because the deck moved so much in the wind. No person died. The only fatality was a dog. The collapse was caught on film, and the footage became one of the best-known pieces of engineering history ever recorded.

A Bridge Built Thin

The Narrows is a deep, fast-moving channel, so a suspension bridge was the practical answer. The state highway department's lead engineer, Clark Eldridge, planned a bridge with 25-foot-deep stiffening trusses. Federal funding conditions brought in Leon Moisseiff, a prominent suspension-bridge designer, who redesigned it with an 8-foot solid plate girder in place of the truss. WSDOT notes that it was only the second suspension bridge to use a solid plate girder, after the Bronx-Whitestone Bridge. The change cut costs and gave the bridge a very graceful look.

The numbers show how slender it was. The main span was 2,800 feet, the third-longest suspension span in the world, behind only the George Washington and Golden Gate bridges. The roadway was 39 feet between the cables. WSDOT puts the width-to-span ratio at about 1:72, compared with 1:47 for the Golden Gate. The bridge cost about $6.4 million and was financed with a Public Works Administration grant and an RFC loan. About 10,000 people attended its dedication on July 1, 1940.

Galloping Gertie

The bridge moved from the start. Workers nicknamed it "Galloping Gertie" during construction, and it kept moving after it opened. In moderate winds, alternate halves of the center span visibly rose and fell several feet.

The state and its engineers tried to stop it. Tie-down cables were attached to the plate girders and anchored to concrete blocks, but they snapped shortly after installation. Diagonal cable stays did not help. Hydraulic buffers were put out of action when their seals were damaged during sandblasting. Professor F. B. Farquharson of the University of Washington began wind tunnel tests on a model. His first studies, finished on November 2, 1940, pointed to the solid stiffening girders as the probable cause. He proposed cutting holes in the girders or adding curved deflectors. The steel for the changes was ordered in early November, but nothing had been installed when the bridge fell.

The Morning of November 7

At 7:30 a.m., the wind at the bridge measured 38 mph, from the southwest, and hit the solid girder broadside. About two hours later it was 42 mph near the east end. Wikipedia and National Geographic both describe sustained winds of roughly 40 mph. It was a strong wind, but nothing like a hurricane.

Farquharson arrived about 9:30 to film and photograph the motion. Around 10:00, Leonard Coatsworth, a news editor at the Tacoma News Tribune, drove onto the span with his daughter's dog, Tubby, in the back seat. At 10:03 the roadway began a twisting motion, and by 10:07 it had become enormous. WSDOT says the deck tilted as much as 28 feet from one side to the other and reached angles up to 45 degrees.

The tilting roadway threw Coatsworth's car against the curb near the east tower. He crawled out and made his way to the toll plaza. Eldridge arrived about 10:15 and warned people to leave. A large piece of concrete fell from the center span around 10:30.

Tubby

At about 10:55, Farquharson tried to rescue Tubby, who was still in the car. The dog bit him. About six minutes later the deck began tearing apart, and Farquharson ran roughly 1,100 feet to the toll plaza as it fell.

At about 11:02 a roughly 600-foot section of the center span broke free and fell 195 feet into the water, and the collapse was complete by 11:10. Tubby and Coatsworth's car went down with it. HistoryLink calls Tubby the only fatality. Coatsworth was later paid $814.40 for his car and its contents.

Barney Elliott filmed the collapse on 16 mm Kodachrome for The Camera Shop. Paramount distributed the footage, and it was added to the National Film Registry in 1998. WSDOT notes that most copies run about 50 percent faster than real time because of a frame-rate error in conversion.

Flutter, Not Resonance

Many physics textbooks have described the collapse as ordinary resonance, with periodic wind gusts matching the bridge's natural frequency until the vibrations became destructive. The American Physical Society explains why that familiar account is misleading. The more important phenomenon was aeroelastic flutter, a self-excited instability in which the bridge's movement altered the surrounding airflow, producing aerodynamic forces that reinforced the movement. As the twisting increased, the interaction between the deck and the wind supplied still more energy, eventually exceeding the structure's ability to resist it. Unlike a simple resonance demonstration, the destructive motion did not require regularly timed gusts of wind.

The precise sequence involved several interacting factors. The Washington State Department of Transportation describes a cable band slipping near the midpoint of the north suspension cable, contributing to the sudden change from vertical waves to torsional motion. Its engineering history also discusses vortex shedding, in which airflow separates around the solid plate girders and forms swirling regions that can influence the bridge's movement. Researchers have continued examining the relative importance of these effects, including the direction of the wind and the bridge's unusually low resistance to twisting. The bridge had survived stronger winds during earlier storms, demonstrating that wind speed alone did not determine whether the destructive instability would develop.

What the Investigation Found

A federal investigation led by engineers Othmar Ammann, Theodore von Kármán, and Glenn B. Woodruff examined the collapse. Their March 1941 findings identified the bridge's excessive flexibility as a fundamental weakness, particularly its inability to resist twisting. The solid plate girders and roadway also behaved aerodynamically, generating lift and drag as wind passed around them. The investigators associated the sudden transition to torsional motion with movement of a cable band near the center of the span, while recognizing that the complete interaction between wind and structure required further study. Rather than assigning responsibility to a single designer, the commission emphasized the need for the engineering profession to understand aerodynamic forces more thoroughly. The collapse helped establish wind-tunnel testing and aerodynamic stability analysis as essential parts of long-span suspension bridge design.

What Came After

The replacement bridge opened on October 14, 1950, after 29 months of construction. It is 5,979 feet long, 40 feet longer than the original, and has more lanes. It reused the original anchorages and tower pedestals. National Geographic calls it "Sturdy Gertie." On July 16, 2007, a second suspension bridge opened for eastbound traffic, and the 1950 bridge was reconfigured to carry westbound traffic only.

The wreck of the 1940 bridge is still on the bottom of the Narrows, in some places more than 200 feet down. Divers report anemones, wolf eels and octopuses living in the twisted girders, and it counts as one of the largest artificial reefs in the Pacific Northwest. The ruins were listed on the National Register of Historic Places on August 31, 1992.

Across the Narrows, steel was spun,
A graceful bridge beneath the sun.
But winds revealed what plans concealed—
And taught the strength that science yields.

The collapse is one of the clearest cases of engineering advancing through failure. The designers built something that met the expectations of the day: strong materials, cables that could carry heavy loads, and an elegant, economical answer to a hard crossing. What they had not fully accounted for was that a long, flexible deck is a dynamic system that interacts with the air around it.

The warning signs were plain. The bridge moved during construction, moved after it opened, and resisted every fix. A strong structure is not the same as a stable one, and a structure has to be designed for the ways it can respond to a force as well as for the force itself.

Sources

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