Introduction
On November 7, 1940, just four months after opening, the Tacoma Narrows Bridge in Washington State dramatically collapsed during a windstorm. The bridge, nicknamed "Galloping Gertie" for its tendency to bounce in the wind, twisted and swayed violently before its center span tore apart and plunged into Puget Sound below.
The collapse was captured on film and has become one of the most famous engineering failures in history. It changed the way engineers design bridges and remains a powerful lesson in the dangers of ignoring aerodynamic forces.
The Bridge
The Tacoma Narrows Bridge was, at the time of its opening, the third-longest suspension bridge in the world, with a main span of 2,800 feet. Its design was revolutionary — the bridge used unusually narrow, solid plate girders instead of the open trusses that were standard for suspension bridges of that era.
Chief engineer Leon Moisseiff designed the bridge to be flexible, believing that a degree of pliability would help it withstand wind forces. The bridge used deep, solid plate girders just 39 feet wide supporting an 80-foot-wide roadway — a ratio of about 1:35, far narrower than typical bridges of the era.
Galloping Gertie
From the day it opened, the bridge was plagued by unusual movement. Even in moderate winds, the bridge would move vertically by several feet. Drivers reported feeling seasick crossing it. Engineers made several attempts to dampen the movement, including installing hydraulic buffers and heavy cables, but the oscillations persisted.
The movement was caused by aeroelastic flutter — a phenomenon where wind creates oscillations in a structure that feed back on themselves, causing the movement to grow rather than dampen. The bridges narrow, solid girders acted like sails, catching the wind and amplifying the motion.
The Collapse
On the morning of November 7, 1940, winds of approximately 40 mph (not extreme by Pacific Northwest standards) caused the bridge to begin oscillating violently. The motion was torsional — the bridge twisted back and forth, with one side rising while the other fell.
The bridge twisted like a ribbon in the wind, its roadway rising and falling in waves more than 28 feet high, before finally tearing itself apart.
Leonard Coatsworth, a journalist for the Tacoma News Tribune, was the last person to drive on the bridge. He described the experience in terrifying detail: "I drove onto the bridge and started across... The bridge was heaving and waving in the most alarming manner... I could feel the bridge swaying... I got out of the car and tried to walk to safety, but the motion of the bridge threw me to the ground."
At approximately 11:00 AM, the center span collapsed into Puget Sound. Remarkably, only one person died — Coatsworths cocker spaniel, Tubby, who was left in the car when Coatsworth abandoned it. Coatsworth could not reach the dog despite multiple attempts.
The Investigation
The collapse was investigated by a board of engineers and scientists. The final report concluded that the bridge failed due to aerodynamic instability caused by its unusual design. The solid plate girders created aerodynamic forces that the bridge could not resist.
Key findings included:
- The bridge was too narrow and flexible for its length
- The solid plate girders trapped wind and created oscillating forces
- Standard engineering practices of the time did not account for aerodynamic effects on bridges
- The design had been approved despite concerns raised by some engineers
The Legacy
The Tacoma Narrows Bridge collapse fundamentally changed bridge engineering. Before this failure, bridge designers primarily considered static loads — the weight of the bridge and traffic. After Galloping Gertie, aerodynamic testing became a standard part of bridge design.
Modern suspension bridges use open trusses instead of solid girders, allowing wind to pass through rather than creating lift. Wind tunnel testing of bridge models is now mandatory for large spans. The replacement Tacoma Narrows Bridge, opened in 1950, was built with these principles and has stood for over 75 years.
Conclusion
The collapse of the Tacoma Narrows Bridge is a powerful reminder that engineering is not just about calculations — it is about understanding the forces of nature and respecting their power. The bridges dramatic failure, captured on film for all to see, became the defining lesson in aerodynamic design for generations of engineers. When nature presents forces that your calculations did not predict, the results can be catastrophic.