1940 collapse of Tacoma Narrows Bridge
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| 1940 collapse of Tacoma Narrows Bridge | |
|---|---|
| Name | Tacoma Narrows Bridge (1940) |
| Caption | Collapse of the Tacoma Narrows Bridge on November 7, 1940 |
| Location | Tacoma, Washington, Puget Sound |
| Coordinates | 47.2690°N 122.5510°W |
| Opened | July 1, 1940 |
| Collapsed | November 7, 1940 |
| Designer | Leon Moisseiff, Clark Eldridge |
| Builder | Washington Toll Bridge Authority, Pacific Bridge Company |
| Length | 5,939 ft |
| Mainspan | 2,800 ft |
| Type | suspension bridge |
1940 collapse of Tacoma Narrows Bridge The 1940 collapse of the Tacoma Narrows Bridge was a dramatic structural failure of a suspension bridge spanning Admiralty Inlet in Puget Sound near Tacoma, Washington. The bridge, notorious for its torsional oscillations nicknamed "Galloping Gertie", opened in 1940 and collapsed a few months later under wind-induced motion, becoming a landmark event in structural engineering and aerodynamics. The failure involved engineers, designers, academics, and institutions that reshaped standards used by American Society of Civil Engineers, National Advisory Committee for Aeronautics, and subsequent Federal Highway Administration practice.
Background and design
The proposal for a high-capacity crossing connected Tacoma and Vashon Island access routes across Puget Sound and was promoted by local politicians including John D. Spellman advocates and regional planners tied to Pierce County. The commission engaged designers influenced by earlier work of Othmar Ammann on the George Washington Bridge and by the aerodynamic theories of Gustave Eiffel and Isambard Kingdom Brunel. Lead design employed principles from Leon Moisseiff's deflection theory used on the Golden Gate Bridge and the Benjamin Franklin Bridge, with suspension elements similar to those on the Mackinac Bridge concept studies. The narrow plate-girder deck and shallow stiffening trusses were intended to reduce material costs during the Great Depression and align with procurement from fabricators like Bethlehem Steel and contractors such as Kaiser Shipyards affiliates.
Design reviews involved state agencies including the Washington Toll Bridge Authority and consulting firms with links to Harvard University and Massachusetts Institute of Technology faculty who had contacts with researchers at Caltech and the National Bureau of Standards. Critics referenced vibration problems studied by Alexander Graham Bell contemporaries and earlier collapses including the Broughton Suspension Bridge to caution about aeroelasticity and resonance in long-span structures.
Construction and opening
Construction began under the supervision of engineers from Clark Eldridge's office with materials procured through companies like California Steel Company, Union Pacific Railroad logistics, and steelwork subcontracted to firms influenced by John A. Roebling's Sons Company methods. The project employed labor from unions including International Brotherhood of Carpenters and coordination with the Works Progress Administration for local employment. Shipping of cables and erection procedures echoed practices used on the Brooklyn Bridge and on Forth Bridge maintenance programs. The main cables were spun using techniques related to those pioneered by John Augustus Roebling, while the towers drew on structural precedent from Gustave Eiffel-inspired engineers collaborating with the American Institute of Steel Construction.
The bridge officially opened on July 1, 1940, with ceremonies attended by officials from Washington (state) and representatives from Pierce County, drawing observers from academic centers including University of Washington and Stanford University.
Collapse on November 7, 1940
On November 7, 1940, winds near 40 mph from Puget Sound generated large-amplitude torsional oscillations in the center span, culminating in structural failure. Photographers including Harold A. Franklin and film crews from University of Washington and local newspapers captured iconic footage of the deck twisting 90 degrees and the eventual fracture of the deck into pieces that fell into Tacoma Narrows Strait. The collapse engaged rescue and salvage teams from United States Coast Guard, Mason County operators, and salvage contractors linked to Merrill & Ring logistics. No human fatalities occurred among bridge users that day, though a dog named Tubby famously was lost during the event and became part of the public narrative reported by outlets like The Seattle Times and Associated Press.
Witness accounts were documented by engineers from University of Michigan and by observers associated with National Research Council (United States), prompting immediate investigations by agencies including National Advisory Committee for Aeronautics and state highway engineers.
Causes and engineering analysis
Investigations attributed the failure primarily to aeroelastic flutter and torsional resonance induced by steady winds interacting with the bridge's narrow plate-girder deck and shallow stiffening trusses. Researchers from Princeton University, Massachusetts Institute of Technology, and Caltech applied theories of aeroelasticity developed by Theodore von Kármán and Ludwik Silberstein to analyze the oscillatory modes. The bridge's low torsional stiffness meant that wind pressures caused nonlinear oscillations beyond the linear theories of Leon Moisseiff's deflection theory; subsequent modeling used methods from John B. Johnson and experimental data from National Bureau of Standards wind-tunnel tests led by teams connected to Langley Research Center.
Key factors included inadequate aerodynamic shape of the deck compared to later box girder solutions like those on the Severn Bridge, insufficient damping devices compared to later retrofits advocated by Owen D. Young-linked committees, and poor accounting for vortex shedding interactions described earlier in studies by Michael Faraday-inspired fluid dynamicists and contemporary theorists such as Theodore von Kármán. Analyses published in journals associated with American Society of Civil Engineers and the Proceedings of the Royal Society reframed concepts of flutter, resonance, and coupled modes for long-span suspension bridges.
Aftermath and reconstruction
Salvage operations recovered steelwork and anchors involving contractors tied to Puget Sound Naval Shipyard and salvage firms with ties to United States Army Corps of Engineers. Litigation and policy responses involved Washington Toll Bridge Authority and influenced state legislation administered by Washington State Department of Transportation. The failure prompted revisions to design standards by the American Association of State Highway Officials and research funding from National Science Foundation-linked programs supporting aeroelasticity studies at MIT, Princeton, and University of Washington.
A replacement pair of parallel suspension spans was constructed with improved deck cross-sections, deep stiffening trusses, and aerodynamic fairings, designed by engineers consulting with Modjeski and Masters and fabricated by firms including Chicago Bridge & Iron Company. The new span opened in 1950, later widened and supplemented with a parallel span in the 2000s, involving contractors like Fluor Corporation and design input from HDR, Inc..
Legacy and influence on bridge engineering
The collapse significantly advanced understanding within institutions such as American Society of Civil Engineers, National Research Council (United States), and National Advisory Committee for Aeronautics and influenced the curricula at Massachusetts Institute of Technology, Stanford University, and University of California, Berkeley. It catalyzed wind-tunnel testing programs at Langley Research Center and at university facilities like the Boundary Layer Wind Tunnel Laboratory and informed the aerodynamic redesign of later spans including the Severn Bridge, Humber Bridge, and retrofits on bridges by Othmar Ammann and Ralph Modjeski practitioners.
The event entered popular culture through newsreels by Movietone News and Pathé News, academic case studies used by Harvard Business School and engineering ethics courses, and museum exhibits at institutions such as Museum of History & Industry and Tacoma Art Museum. Its lessons on aeroelastic flutter, structural dynamics, and interdisciplinary collaboration between civil engineers and fluid dynamicists continue to shape modern bridge standards promulgated by Federal Highway Administration and codified in manuals by American Association of State Highway and Transportation Officials.