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The Tacoma Narrows Bridge was destroyed due to torsional flutter, a sophisticated occurrence where wind velocity and the bridge’s physical characteristics joined to produce a self-sustaining movement.(Image credit: Stillman Fires Collection, Public Domain)ShareShare by:
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Milestone: Demise of the Tacoma Narrows Bridge
Date: 11:02 a.m. local time on Nov. 7, 1940
Where: Tacoma Narrows strait, Puget Sound, Washington
Who: Leonard Coatsworth and others who observed the downfall
The winds were clocking in at 40 mph (64 km/h) across the Tacoma Narrows passage when “Galloping Gertie” started its undulations.
The Tacoma Narrows Bridge, linking Tacoma, Washington, to the Kitsap Peninsula, had been inaugurated with great celebration just a few months prior, in July 1940. The graceful and adaptable construction — at that point, the third-longest suspension bridge across the globe — had been created by globally recognized bridge architect Leon Moisseiff, who contributed to the design of the Golden Gate Bridge as well.
However, from the outset, staff members spotted the bridge’s movement in the breeze, giving it the nickname “Galloping Gertie.”
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“We learned from the opening night of the bridge that an issue was present. That evening, the bridge commenced to buck,” noted F. Bert Farquharson, an engineer at the University of Washington who was employed by the Toll Authority to identify the cause of the movement, according to the Washington Department of Transportation (WSDOT).
A view of Galloping Gertie following its destruction.
When Farquharson’s group got in touch with Moisseiff, he recognized that a couple of his other bridges also exhibited movement, though at a greatly diminished magnitude.
Farquharson’s team ordered a 1:200 scale representation that extended 54 feet (16.5 meters), along with an 8-foot-long (2.4 m) 1:20 scale reproduction of a fraction of the bridge to attempt to determine the problem’s origin. They also made use of a wind tunnel in an effort to simulate the dilemma.
At the same time, the Toll Authority promptly started striving to resolve the matter. Quickly after the bridge was opened, engineers put in place four hydraulic jacks meant to function as shock absorbers, but Gertie kept on moving. In October, the crew connected short-term wires to secure the bridge to the ground across its reach. Even though the tie-down wires lessened the motions toward the edges of the bridge, the middle continued to oscillate vertically. Despite everything, one wire broke off during a spell of high winds on Nov. 1, and the bridge initiated its undulations once more.
On Nov. 2, Farquharson’s group wrapped up their modeling, which demonstrated that the bridge commenced twisting as breezes surged up from the sides. The group put forward either creating openings in the girders or holding back the breeze by using deflectors. They got to work on making corrections. They maintained that, in 10 days, some of those deflectors would have given the bridge ample stability to render it secure, and the comprehensive bridge retrofit would have been finalized in 45 days.
However, they never had the chance to find out if those fixes would be effective. On the morning of Nov. 7, Leonard Coatsworth, a copy editor employed by the Tacoma News Tribune, was heading to his family’s cottage for the summer on the peninsula alongside Tubby, his daughter’s cocker spaniel that had three legs, when the bridge started to rise and fall and sway from one side to the other. He contacted his newspaper, which dispatched reporter Bert Brintnall and staffer Howard Clifford as a photographer.
Leading up to this, Coatsworth indicated that he’d undergone the bridge rising and falling, but the swaying was something new.
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“Before I understood it, the swaying from side to side grew so intense that I lost command of my vehicle and momentarily believed that it would jump the high curb and travel across the bridge’s sidewalk before colliding with the railing,” Coatsworth wrote in a journal entry composed the same day on behalf of the Tacoma News Tribune.
He left the car midway across the structure.
For his share, Clifford turned out to be the last individual to exit the bridge.
“The pavement was bounding up and down, dropping below me and actually causing me to be running with nothing under my feet. It would then bounce upward, forcing me onto my knees. I continued onward for what seemed like a prolonged period, although it likely only lasted a couple of minutes, and finally reached firm land. Bert [Brintnall] was awaiting me there, making me the final person to depart from the bridge,” Clifford recounted in a subsequent story for the newspaper.
A sharp report, akin to the sound of gunfire, resonated when the 57 foot (17.5 m) cable gave way, and at 11:02 a.m., the center section of the bridge plunged into the water. Clifford and Brintnall in conjunction with a cameraman filmed the bridge’s demise.
Tubby the canine did not survive, although he was the sole loss on that specific day.
The devastating breakdown inflicted serious damage to the standing of Moisseiff, who passed away from a cardiac arrest just three years afterward.
Nonetheless, the bridge’s devastation likewise yielded unmatched engineering knowledge.
A team in due course reached the determination that torsional flutter was the trigger for the failure. After a cable at midspan moved, it split into a pair of segments of differing lengths. Consequently, the bridge was then permitted to begin turning. The act of twisting altered the angle at which the wind struck the bridge’s core plate girders, which in turn caused it to soak up more energy, thus amplifying the extent of the movement. At a certain point, the twisting aligned itself with the wind vortex, and the twisting turned into self-perpetuating.
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“To put it differently, the forces applied to the bridge ceased being driven by the wind itself. The bridge deck’s own movement gave rise to the forces. Engineers use the term “self-excited” motion to describe this occurrence,” as stated by the WSDOT.
Overall, the bridge was excessively lengthy, its deck was not heavy enough, and its road surface was excessively narrow to offer adequate protection against aerodynamic forces, as reported in a failure study.
Stemming from the destruction, all engineers now must assess a scaled 3D model of any bridge in a wind tunnel prior to commencement of construction. The destruction likewise brought about a shift to the “deflection theory” — a belief that considered vertical motion in suspension bridges as the sole relevant factor — to integrate other types of movement. What’s more, subsequent to a significant windstorm placing the Golden Gate Bridge in harm’s way back in 1951, the renowned Bay Area landmark was strengthened to boost its “torsional stability.”
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Tia GhoseSocial Links NavigationEditor-in-Chief (Premium)
Tia is the editor-in-chief (premium) and was formerly managing editor and senior writer for Live Science. Her work has appeared in Scientific American, Wired.com, Science News and other outlets. She holds a master’s degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor’s degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.
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