The collapse of the Tacoma Narrows Bridge on November 7, 1940, was a dramatic and tragic event, but it also proved to be a watershed moment in structural engineering. Nicknamed “Galloping Gertie” for its unsettling dance in the wind, the bridge’s sudden fall exposed critical flaws in design and understanding of aerodynamics, fundamentally altering how engineers approach bridge construction.
The Rise and Fall of Galloping Gertie
Connecting Tacoma, Washington, and the Kitsap Peninsula, the Tacoma Narrows Bridge opened with fanfare just months before its disastrous end. At the time, it was the third-longest suspension bridge in the world, a testament to the innovative designs of Leon Moisseiff, a renowned bridge engineer who had also contributed to the design of the iconic Golden Gate Bridge.
However, unusual oscillations were noticed almost from the start. Workers gave the bridge the moniker “Galloping Gertie,” and engineer F. Bert Farquharson and his team from the University of Washington were tasked with investigating the problem, acknowledging, “On that night, the bridge began to gallop.” Moisseiff recognized that other bridges he had designed exhibited similar behavior, though with less intensity.
Efforts to Stabilize the Bridge
As Gertie’s oscillations grew more pronounced, engineers scrambled to find a solution. First, four hydraulic jacks were installed to act as shock absorbers, proving ineffective. Then, in an attempt to reduce movement, temporary cables were tied to the ground across the bridge’s span. However, a cable snapped during high winds on November 1st, and the galloping resumed.
Farquharson’s team conducted extensive modeling, creating a 54-foot (16.5 meters) scale model and an 8-foot (2.4 m) section to identify the root cause. Their tests revealed that winds gusting from the sides caused the bridge to twist. They proposed a fix: either drilling holes in the girders or installing deflectors to block the wind. Implementing these changes could have provided enough stability in just 10 days, with a full retrofit taking 45 days.
A Witness to Disaster
Unfortunately, these repairs never came to fruition. On the morning of November 7, Leonard Coatsworth, a copy editor for the Tacoma News Tribune, was driving to a family cottage on the peninsula with his daughter’s three-legged cocker spaniel, Tubby, when the bridge began to sway violently. He called the newspaper, prompting reporter Bert Brintnall and photographer Howard Clifford to witness the disaster firsthand. Coatsworth recounted losing control of his car as the bridge tilted, and Clifford described the road bouncing so dramatically that he was forced to run and sometimes kneel to avoid being left suspended in the air. Clifford was the last person to safely exit the bridge before it collapsed.
The final, catastrophic moment arrived at 11:02 a.m. when a 57-foot (17.5 m) cable snapped, and the central span plunged into the water. Clifford and Brintnall were able to capture the bridge’s fall on camera. Tragically, Tubby the dog did not survive, and he was the sole casualty of the collapse.
From Tragedy to Insight: The Science of Torsional Flutter
The collapse significantly damaged Moisseiff’s reputation, and he passed away just three years later. However, the disaster provided unparalleled opportunities for engineering analysis, leading to groundbreaking discoveries.
A team of experts eventually pinpointed the cause of the collapse as torsional flutter. A crucial factor was the slipping of the midspan cable, which separated into two unequal lengths. This imbalance allowed the bridge to twist, and the twisting altered the wind’s angle relative to the bridge’s main girders. The bridge began to absorb more energy, amplifying the motion. When the twisting synchronized with wind vortices, the motion became self-sustaining.
“In other words, the forces acting on the bridge were no longer caused by wind. The bridge deck’s own motion produced the forces. Engineers call this “self-excited” motion,” as described by the Washington State Department of Transportation (WSDOT).
Ultimately, the bridge was too long, its deck too light, and its roadway too narrow to effectively resist aerodynamic forces. The Tacoma Narrows Bridge collapse served as a harsh but vital lesson, fundamentally changing the approach to bridge design and ushering in a new era of wind engineering and aerodynamic considerations in large-scale structures.
