THE HAGUE, 16 JANUARY 2025. While we use resonance to detect failures in materials, there are some famous examples of the inverse of this, resonance causing a failure. In November 1940, strong winds swept across the Tacoma Narrows Bridge in Washington, setting it into violent motion. What started as a rhythmic sway quickly escalated into a dramatic collapse, tearing the bridge apart. This event, one of the most famous structural failures in history, was caused by our favorite phenomenon, resonance. In this article we’ll explore the science behind the Tacoma Narrows Bridge collapse, and delve deeper into the concept of natural resonance.
What Happened to the Tacoma Narrows Bridge?
The Tacoma Narrows Bridge, nicknamed "Galloping Gertie" due to its frequent swaying, was a suspension bridge completed in 1940. Spanning over two kilometers, it was an engineering marvel of its time. However, its slender, flexible design was vulnerable to aerodynamic forces.
On November 7, 1940, a strong wind gusting at about 65 km/h triggered an oscillation in the bridge. Initially, the structure swayed in a periodic motion, but the wind created vortices around the bridge's deck, amplifying the oscillations through a process called aeroelastic flutter. Aeroelastic flutter is a kind of feedback loop between the airflow around a structure, and the structure’s motion. As the structure moves, it changes the flow of air, which in turn changes the forces acting on the structure, amplifying its motion even more.
This led to the bridge entering a state of resonance, where the external force (the wind) perfectly matched the natural frequency of the bridge. At resonance, even small, consistent forces can cause large oscillations. The wind-induced vibrations increased in magnitude, eventually causing the bridge to twist violently and collapse into the water below. Luckily, everyone survived the collapse.
Understanding Resonance: The Science Behind the Catastrophe
Resonance occurs when an object vibrates at its natural frequency due to an external force matching that frequency. This phenomenon can affect a wide range of structures and systems, from bridges to buildings, and even in everyday situations like a glass shattering when exposed to a high-pitched sound.
When this happens, the vibrations grow larger and more intense, potentially leading to catastrophic failure if the structure cannot handle the stress. In the case of the Tacoma Narrows Bridge, the resonance was triggered by the interplay between the wind and the bridge's natural frequency. The force of the wind was consistent enough to continually push the structure in sync with its vibrations, amplifying the sway until the bridge reached its breaking point.
RESONIKS and the Power of Sound in Structural Testing
At RESONIKS, the principle of resonance is central to what we do. While resonance can lead to catastrophic failures in structures like bridges, it can also be harnessed for positive applications. Our Acoustic Resonance Testing (ART) technology leverages sound waves to detect subtle defects in materials by inducing resonant vibrations and measuring the response. This method allows us to pinpoint weak points or imperfections in materials that traditional testing methods might overlook.
The same sensitivity to vibrations that brought down the Tacoma Narrows Bridge is what makes ART so effective at identifying potential defects before they lead to failures. Our advanced AI-powered systems analyze the resonance behavior of materials, ensuring that structures and components are sound and ready.