Tacoma Narrows Bridge, 1940: Wind and a Slender Deck
The Tacoma Narrows Bridge collapsed in November 1940, four months after it opened. What the investigators concluded about wind, slenderness and what designers changed.
Civil & Structural · Last reviewed
What happened
The Tacoma Narrows suspension bridge in Washington State opened in July 1940. It moved noticeably in light winds from the start, earning the nickname "Galloping Gertie". On November 7, 1940, in winds of roughly 40 miles per hour, the deck began twisting in a large torsional motion and the main span broke up and fell into the water.
What the investigation found
- The deck was very slender for its length and used shallow solid plate girders rather than an open truss. It was light and flexible, with little resistance to twisting.
- The wind loads were far below what the structure was designed to resist in static terms. The failure was dynamic: wind interacting with the moving deck sustained and amplified the twisting motion (aeroelastic flutter).
- Designers at the time had analyzed wind mainly as a static pressure and had little data on dynamic wind effects on long, slender decks.
What changed
- Wind-tunnel testing of scale bridge models became standard practice for long-span bridges.
- Bridge decks were designed with greater stiffness, often as open trusses or aerodynamically shaped sections.
- Aeroelastic behavior became part of long-span bridge design analysis.
Apply the lesson
- Identify one structure or system where you rely on a static check. What dynamic effect could it ignore?
- List the assumptions in the design that were never tested because they had always worked before.
- Ask what happens if a component behaves well in a quiet test but changes behavior when it moves.
Engineering lesson: a design can satisfy every static check and still fail dynamically. Check how the whole system behaves when it moves.
What came after
The University of Washington Libraries collection documents the whole story of the bridge: its construction, its collapse, the later studies of its aerodynamics and the construction of a second bridge across the Narrows. The photographs, films and documents in that collection are the place to see the original material.
Related tools and labs
Calculators, labs and simulators are part of the All-Access Pass.
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Questions
Was it resonance?
It is often described that way, but the accepted explanation is aeroelastic flutter, where the wind forces depend on the motion of the deck itself. It is a different mechanism from simple resonance with vortex shedding.
Did anyone die?
Reports say no person was lost. The bridge had been closed to traffic when the collapse began.
Was a new bridge built?
Yes. The University of Washington Libraries collection describes the construction of a second bridge spanning the Narrows after the collapse.
Where can I see photographs and film of the collapse?
The University of Washington Libraries Tacoma Narrows Bridge Collection holds photographs, film and documents, and is linked in the sources.
Educational material. Examples use simplified, hypothetical inputs and are not a design, a construction document or professional engineering advice. Confirm requirements with the codes and standards adopted where the work is built and with a licensed engineer.