Civil and Structural Engineering
Tacoma Narrows Bridge
The original Tacoma Narrows Bridge opened across Puget Sound on July 1, 1940, and immediately began swaying so dramatically in wind that it earned the nickname Galloping Gertie and drew sightseers hoping to feel the motion. On November 7, 1940, in a moderate wind of roughly 40 mph, the deck twisted into a violent torsional oscillation and collapsed into the water. No person died; the only casualty was a dog named Tubby, left in an abandoned car. The federal investigation that followed, led by aerodynamicist Theodore von Karman, found the slender, shallow deck was aerodynamically unstable in a way 1930s bridge engineering had not accounted for, and the collapse became the founding case study for aeroelastic design in modern bridge engineering.
- Started
- 1938-11
- Ended
- 1941-03
- Wind speed at collapse
- ~40 mph
- Collapse speed
- Sudden
- Preventability
- High
- Lesson transfer
- Universal
- Last reviewed
- 2026-08-21
Narrative
The story
The ambition
The Tacoma Narrows Bridge was conceived to link the Tacoma peninsula to Gig Harbor across a mile-wide, tidally turbulent strait, replacing a slow ferry crossing with a suspension bridge that would be both a practical crossing and a showpiece of modern engineering. Designer Leon Moisseiff, a leading suspension-bridge engineer of his era, proposed an unusually slender structure: a deck only 8 feet deep supporting a two-lane roadway 39 feet wide across a 2,800-foot center span, a width-to-length ratio of roughly 1 to 72, far narrower relative to its length than earlier suspension bridges. The design used shallow plate girders instead of the deep stiffening trusses common on prior spans, favoring a lighter, more graceful profile and a lower construction cost. Construction began in November 1938 and finished in about 19 months, at a cost of roughly $6.4 million, and the bridge opened to traffic on July 1, 1940.
The rise
From the moment traffic crossed it, the bridge behaved unlike anything drivers had experienced. Even in modest wind, the roadway rose and fell in visible vertical waves, and workers during construction had already nicknamed it Galloping Gertie for the motion. Rather than alarming the public, the sway became an attraction: drivers reported a rolling, fairground sensation crossing the span, and sightseers came from around the region specifically to feel the bridge move underfoot. Engineers on site treated the undulation as a nuisance to be damped rather than a structural danger, because the prevailing engineering assumption of the time was that a suspension bridge's stiffness needed to resist traffic loads and thermal expansion, not aerodynamic forces from wind.
The cracks
Officials and engineers made repeated attempts to tame the motion. Tie-down cables were added to anchor the deck to the shore, and they snapped under the stress. Inclined stay cables and hydraulic buffers followed; the hydraulic dampers were later damaged during sandblasting work and never functioned as intended. University of Washington engineering professor Frederick Farquharson was brought in to study the bridge's behavior and ran wind tunnel tests on a scale model. Just five days before the collapse, Farquharson's tests recommended adding aerodynamic fairings to the sides of the deck to smooth the airflow and reduce the lift and drag forces acting on it. The recommendation had not been implemented when, on the morning of November 7, 1940, a sustained wind from the southwest began building across the Narrows, reaching about 38 mph by 7:30 a.m. and around 40 to 42 mph by mid-morning, well within the range the bridge had weathered many times before without failing.
The collapse
Traffic crossed normally through the morning of November 7 despite the wind, and the bridge shed its usual vertical undulation for a new, more violent motion. Around 10:00 a.m., news editor Leonard Coatsworth drove onto the bridge with his daughter's dog, Tubby, in the back seat. Shortly after 10:00 a.m., a cable band at mid-span on the north main cable slipped, splitting the cable's span into unequal segments, and the deck's motion shifted from vertical waves into a twisting, torsional oscillation, with one side of the roadway rising as the other fell. Coatsworth abandoned his car and crawled to safety on hands and knees as the deck tilted at increasing angles; Farquharson, who was on the bridge observing, tried to retrieve Tubby from the car but the terrified dog bit him and he had to withdraw before the structure gave way. By around 11:00 a.m. chunks of concrete were breaking off the roadway and suspender cables were snapping under the twisting load. At about 11:02 a.m. a roughly 600-foot section of the center span tore free and dropped about 195 feet into Puget Sound, and the rest of the span finished collapsing within minutes. Tubby drowned in Coatsworth's car. No person was killed or seriously injured; the last vehicles had crossed shortly before the torsional motion began, and everyone caught on the bridge as it failed escaped on foot.
The aftermath
The collapse, filmed by local cameraman Barney Elliott and others, became one of the most widely viewed pieces of engineering-disaster footage ever made and turned the bridge into an instant case study. The Public Works Administration financed the crossing and the Washington Toll Bridge Authority reimbursed Coatsworth for his car and its contents, including Tubby, months after the collapse. The Federal Works Agency convened a board of prominent engineers, Othmar Ammann, Theodore von Karman, and Glenn Woodruff, to investigate. Their 1943 report concluded the bridge's failure came from excessive flexibility: its shallow, narrow deck acted like an airfoil under wind loading, generating aerodynamic lift and drag forces that fed the deck's own torsional motion in a self-reinforcing pattern the report distinguished from simple resonance, later described in engineering literature as aeroelastic flutter. A replacement Tacoma Narrows Bridge, built with a deep open stiffening truss and a wider deck to resist twisting, opened at the same crossing in October 1950. The original bridge's remains still lie on the floor of the Narrows, now one of the largest artificial reefs in the world, and the site is listed on the National Register of Historic Places.
The lessons
Galloping Gertie is the case that forced bridge engineering to treat wind as a structural load, not a nuisance. Moisseiff's design was not undersized for traffic or gravity; it met and exceeded the stiffness standards of its day for those forces. What it lacked was any accounting for aerodynamic instability, a phenomenon aircraft designers understood by the 1930s but that had not yet crossed into civil engineering practice. The bridge gave months of visible warning, in the form of dramatic, well-photographed swaying that drew sightseers rather than concern, and the fixes attempted, tie-downs, dampers, stay cables, treated the symptom without addressing why a slender deck acted like a wing in crosswind. Every suspension bridge built since has been evaluated for wind-induced flutter and torsional stability, and wind tunnel testing of scale models became standard practice as a direct result. The case endures in engineering curricula less because the physics is exotic and more because the warning signs were so visible, so public, and so widely dismissed as harmless before they proved otherwise.
Causal timeline
Failure Anatomy
- 1938-11
A slender bridge is designed and built
Leon Moisseiff designed a suspension bridge with an 8-foot-deep, 39-foot-wide deck across a 2,800-foot span, using shallow plate girders rather than deep trusses; construction ran from November 1938 to mid-1940 at a cost of about $6.4 million. [1]
Technical failure - 1940-07-01
Galloping Gertie earns its name
From its July 1, 1940 opening, the deck swayed visibly in wind, drawing sightseers who came to feel the motion; the bridge quickly became known as Galloping Gertie. [2]
Technical failure - 1940-10
Remedial fixes fail to solve the underlying problem
Engineers added tie-down cables, which snapped, plus stay cables and hydraulic dampers, the latter later disabled during sandblasting, none of which corrected the deck's aerodynamic instability. [3]
Technical failurePoor execution - 1940-11-02
A wind tunnel study flags the real cause, too late
Frederick Farquharson's wind tunnel tests on a scale model, completed around November 2, 1940, recommended adding aerodynamic fairings to the deck, a fix never implemented before the collapse five days later. [4]
Information failure - 1940-11-07
The deck twists apart and collapses
On November 7, 1940, in roughly 40 mph wind, a cable band slipped and the deck's motion turned torsional; by about 11:02 a.m. a roughly 600-foot center section tore free and fell into Puget Sound. Tubby, a dog left in an abandoned car, was the only casualty. [5] [6] [7]
Technical failure - 1943
Federal investigation and a redesigned successor
A Federal Works Agency board led by Theodore von Karman, with Othmar Ammann and Glenn Woodruff, found the failure was aerodynamic instability from excessive flexibility, not a construction or material flaw; the replacement bridge, opened in 1950, used a deep open truss deck to resist twisting. [8]
Information failure
Structured analysis
What Went Wrong
Root causes
A deck too slender to resist wind-induced twisting. The bridge's deck was only 8 feet deep and 39 feet wide across a 2,800-foot span, using shallow plate girders instead of deep stiffening trusses, an unprecedented width-to-length ratio that left it aerodynamically unstable in wind. [1]
Aerodynamic instability was not part of 1930s bridge engineering practice. Suspension-bridge design of the era accounted for stiffness against traffic loads and temperature, not for wind acting on the deck as an airfoil, so the flutter risk was not evaluated before construction. [8]
Contributing factors
Remedial fixes addressed symptoms, not the cause. Tie-down cables snapped, added stay cables and hydraulic dampers were installed, and the dampers were later disabled during sandblasting, none of which corrected the deck's underlying aerodynamic shape. [3]
A wind tunnel recommendation arrived too late to act on. Professor Frederick Farquharson's wind tunnel tests, concluded five days before the collapse, recommended aerodynamic fairings to smooth airflow around the deck, but the fairings were never installed. [4]
Immediate trigger
A cable band slipped and the deck's motion turned torsional. On the morning of November 7, 1940, a cable band at mid-span on the north main cable slipped, splitting the cable's span into unequal segments and shifting the deck's oscillation from vertical waves into a self-reinforcing twisting motion that exceeded the structure's capacity. [5]
Visible symptoms
Dramatic swaying from the day the bridge opened. The bridge undulated visibly in wind from its opening in July 1940, earning the nickname Galloping Gertie and drawing sightseers who came specifically to feel the motion while crossing. [2]
Warning signs
Visible vertical oscillation during construction and after opening. Workers observed pronounced up-and-down undulation of the deck during construction, well before the bridge opened to traffic, prompting the Galloping Gertie nickname. [2]
Failed remedial measures. Tie-down cables installed to control the sway snapped under the load, and hydraulic dampers meant to absorb motion were later damaged during sandblasting and never worked as intended. [3]
A wind tunnel study warned the deck needed aerodynamic fairings. Farquharson's scale-model wind tunnel testing, completed five days before the collapse, identified the deck's aerodynamic shape as the problem and recommended fairings to correct it. [4]
Affected groups
Keep reading
Related failures
Evidence
Claims & sources
Every numbered marker in the analysis links to the claim it rests on, and each claim to its sources.
- [1]
The Tacoma Narrows Bridge, designed by Leon Moisseiff, had a deck only 8 feet deep and 39 feet wide across a 2,800-foot center span, a roughly 1:72 width-to-length ratio using shallow plate girders instead of deep stiffening trusses; construction ran from November 1938 to mid-1940 at a cost of about $6.4 million, and it opened July 1, 1940.
- [2]
From its opening, the bridge swayed visibly in wind, earning the nickname Galloping Gertie, and the motion drew sightseers who came to feel the crossing move underfoot.
- [3]
Engineers attempted to control the swaying with tie-down cables, which snapped, and with added stay cables and hydraulic dampers, the dampers later disabled during sandblasting work and never functioning as intended.
- [4]
University of Washington professor Frederick Farquharson conducted wind tunnel tests on a scale model of the bridge that concluded about five days before the collapse and recommended adding aerodynamic fairings to the deck, a fix not implemented before November 7.
- [5]
On the morning of November 7, 1940, shortly after 10:00 a.m., a cable band at mid-span on the north main cable slipped, and the deck's motion shifted from vertical waves into a self-reinforcing torsional oscillation.
- [6]
In wind measured at roughly 38 to 42 mph that morning, the bridge's twisting worsened through the late morning, and at about 11:02 a.m. a roughly 600-foot section of the center span tore free and fell about 195 feet into Puget Sound, with the rest of the span collapsing within minutes.
- [7]
No human died in the collapse; the sole casualty was Tubby, a three-legged Cocker Spaniel left in Leonard Coatsworth's car after he abandoned it and crawled to safety on foot.
- [8]
A Federal Works Agency board of Othmar Ammann, Theodore von Karman, and Glenn Woodruff investigated the collapse and concluded it resulted from excessive flexibility in the deck, which acted aerodynamically like an airfoil and generated self-reinforcing torsional forces under wind loading, a phenomenon distinct from simple resonance and later described as aeroelastic flutter, rather than any construction or material defect.
Moderate Reported explanation Tacoma Narrows Bridge (1940) Tacoma Narrows Bridge history: Lessons from failure
Sources
Tacoma Narrows Bridge (1940)
Wikipedia
Tacoma Narrows Bridge collapses
History.com
Tacoma Narrows Bridge history: Lessons from failure
Washington State Department of Transportation
Tacoma Narrows Bridge history: Collapse
Washington State Department of Transportation
Tacoma Narrows Bridge history: Tubby trivia
Washington State Department of Transportation