We think of large bridges as bastions against the forces of nature, a permanent part of the landscape that connects Point A to Point B. We would never expect a major bridge to fall due to winds, particularly those blowing at less than hurricane force. But in November 1940, the newly opened Tacoma Narrows Bridge outside Tacoma, Washington succumbed to the winds blowing at the rather innocuous speed of about 40-mile-per-hour (64 km/h). The bridge, known now and then as “Galloping Gertie,” did not fall due to the wind’s force, but to the fact that the winds blowing past set up a flutter in the bridge span that caused it to undulate wildly and eventually tear itself apart.
[Image to right: View of Narrows Bridge Photographer James Bashford. Courtesy, Washington State Department of Transportation]
To Cross the Tacoma Narrows
For years, residents and officials desired to build a bridge connecting the Washington State community of Tacoma and the Kitsap Peninsula on the western side of Puget Sound. Tacoma, a thriving industry town since incorporation in 1884, has been a major West Coast port and at one time was the lumber capital of the United States.
The Tacoma Narrows was an obvious location to span the fjord-spattered Puget Sound as the channel here was less than a mile wide. However, the water was deep, over 200 ft (61 m), and tidal currents of over 8.5 mph (14 km/h) swept through the channel four times a day.
The first proposal to cross Puget Sound came from the Northern Pacific Railway at the end of the Nineteenth Century: a railway trestle across the Tacoma Narrows. A trestle/bridge would shorten the land trip from Tacoma to Gig Harbor from 107 miles (171 km) skirting around the Sound via Olympia to 8 miles (13 km). (Today, the new Tacoma Narrows Bridge remains the only bridge crossing of Puget Sound.) The photo below right shows an aerial view of the Tacoma Narrows, where Puget Sound becomes a channel some 4600 feet (1430 m) wide. (Courtesy, Washington State Department of Transportation)
Twenty years later, the Tacoma Chamber of Commerce took up the initiative and consulted with several of the most noted large bridge builders in America including engineers David B Steinman, who later designed the Mackinac Bridge in Michigan, and Joseph B. Strauss, later the chief engineer on the Golden Gate Bridge in California.
In January 1937, the Legislature of Washington State passed a bill that created the Washington State Toll Bridge Authority and gave $25,000 to study the Tacoma County request for a bridge at the Narrows. The bridge concept also received support from the US Navy because of its shipyard in Bremerton and the rising international concerns in the Pacific.
The initial design by Washington State engineer Clark Eldridge called for a conventional suspension bridge design. Its basic features included a center span of 2,600 feet (793 m); 2 side spans of 1,300 feet (396 m) each; trusses and cables 39 feet (11.9 m) center-to-center; and stiffening trusses 25 feet (7.6 m) deep. However, a proposal to build a similar bridge for less money came from Leon Moisseff, a noted bridge designer from New York who had consulted on the Golden Gate Bridge construction. Interestingly, this was the first bridge that Moisseiff largely designed himself.
Eldridge's design; elevation detail, May 23, 1938, Washington State Department of Transportation records
Moisseiff's design proposed a slimmer, more elegant bridge for about a third less money. The side spans became 1,100 feet (335 m) long, and the center span 2,800 feet long (850 m). Instead of the 25-foot (7.6 m) deep truss deck support in Eldridge's design, Moisseiff substituted a solid 8-foot (2.4 m) plate girder support. Moisseiff also reduced the number of bracing struts joining the tower legs to 2 above the deck and 2 below. This design created a much lighter, more flexible bridge, having a center span-to-width ratio of 1 to 72. This ratio was unprecedented, substantially more slim the Golden Gate Bridge's 1 to 47 ratio.
The US Public Works Administration approved most of the funding for the latter design, based on cost, and added a qualification that the State Toll Bridge Authority hire outside consultants for the bridge design. Clark Eldridge later claimed: “We were told we couldn’t have the necessary money without using plans furnished by an eastern firm of engineers, chosen by the money lenders.”
Leon Moisseiff became the consultant hired to design the superstructure (towers, cables, etc.). The firm of Moran & Proctor of New York were chosen the consultants to design the substructure (piers). When the design was completed, Washington State Highway Department engineers balked. They believed Moisseiff's plan was “fundamentally unsound” in that the design made the Narrows Bridge lighter and narrower —a tight 39 ft (11.9 m) wide — than any long bridge ever built. As designed, the Tacoma Narrows Bridge would, at that time, be the third-longest suspension bridge in the world with a main span of 2,800 feet (850 m) — behind the George Washington Bridge in New York and the Golden Gate Bridge near San Francisco.
On September 27, the state opened construction bids. The Pacific Bridge Company won the contract for building the Tacoma Narrows Bridge. Bethlehem Steel Company supplied the steel, and John A. Roebling Sons Company of New York, builders of the Brooklyn Bridge, supplied the cable wire. The design consultants, Moisseiff’s firm and Moran & Proctor, divided the standard architect fee. The construction began officially on 25 November 1938 but local residents remember the actual start day as 23 November.
Moisseff had published an important research paper with Fred Leinhard of the Port of New York Authority in 1933 that looked at the extension of the deflection theory of Austrian engineer Josef Melan to include horizontal bending of a bridge under wind forces. Applying this work to the Tacoma Narrows design, Moisseff recommended that his original bridge design should be stiffened and made wider, but these alterations were turned down, apparently due to the added cost.
As a result, the Tacoma Narrow Bridge was a very narrow bridge (two lanes) for its length and thus insufficiently rigid. Thus, when the winds blew broadside to the bridge, the roadbed would move easily, and the bridge earned its “Galloping Gertie” moniker during construction. Even in light to moderate winds, the bridge would heave and send the center span roadbed rising and falling several feet every four or five seconds.
[Image to right: View of 1940 Narrows Bridge, looking west from the Tacoma side. Note tie-down cables attached to side span in foreground. Photographer James Bashford. Courtesy, Washington State Department of Transportation]
Since the oscillations began during the construction phase, several measures were incorporated to reduce them. The Washington Toll Bridge Authority retained Professor Frederick Burt Farquharson of the University of Washington to study the situation and recommend solutions. Farquharson and his students built scale models of the bridge and tested them in a wind tunnel. They reported the results of the initial assessment on 2 November 1940, but before they could be implemented, disaster struck.
The Tacoma Narrow Bridge officially opened to traffic on 1 July 1940. Washington Governor Clarence D. Martin conducted the ribbon-cutting ceremonies. Then, the Governor paid the first toll and his car sped across the bridge.
The Narrows Bridge, called the “baby brother” of the Golden Gate Bridge, was constructed to withstand winds of 120 mph (193 km/h), which, calculations showed would cause a 20-foot (6.1 m) deflection, or sideways movement, of the bridge deck. And indeed, in its brief lifetime, it weathered several strong storms.
“The Bridge is About To Go”
While all suspension bridges do sway in the wind to some degree, the Tacoma Narrows Bridge moved even in light winds of 3-4 mph (5-6 km/h), a rippling of the roadway flowed in waves of 2-3 feet (0.6-0.9 m), and occasionally as large as 5 ft (1.5 m), from one end of the center span to the other. Interestingly, strong winds often had no effect on the bridge. The motions of the bridge deck were felt by those crossing the bridge. In fact, motorists often crossed during such galloping events as if it were an amusement park ride, some travelling long distances to “take the ride”. Drivers reported instances when cars in front of them disappeared in the trough of the roadbed wave while they were rising on the crest. The motion was described by reporters and others as the bounce, the ripple, a gallop, a wave, an undulation, and rising and falling like a roller coaster.
Soon the newspapers had adopted the nickname “Galloping Gertie,” but it likely originated with the bridge construction workers, (The name actually had been applied to the first large suspension bridge, then the longest in the world at 900 ft, which spanned the Ohio River at Wheeling West Virginia. This Wheeling Bridge collapsed in a windstorm in 1854.)
During the early morning of 7 November 1940, southwest winds were blowing down the Narrows at 35-45 mph (56-72 km/h), hitting the bridge broadside and causing the center bridge span to undulate by 3-4 ft (0.9-1.2 m). The winds were generated by a low pressure system that was located off Vancouver Island to the north. (Weather map to right for 7 pm, 7 November1940, courtesy, NOAA Central Library Data Imaging Project ).
At 8:30 AM, Clark Eldridge, project engineer for the Washington State Toll Bridge Authority, drove across the bridge, noticing only “typical” undulations. Professor Farquharson arrived an hour later. Having heard about the motions, he had come to take motion pictures and still photos of the movements for his studies. Winfield Brown, a student at the University of Puget Sound, walked onto the bridge to get “a thrill for a dime” (the pedestrian toll).
Just before 10 AM, a delivery van owned by Rapid Transfer Company passed through the tollbooth heading west. It was followed by Leonard Coatsworth, a news editor for the Tacoma News Tribune heading to the family cottage on the Kitsap Peninsula with his daughter’s dog. Not long thereafter, the nature of the movements changed. The rhythmic rise and fall were now joined by a twisting of the roadbed, which increased to as much as 45 degrees in each direction, and the undulations rose from 5 ft to 28 ft (1.5 to 8.5 m).
The delivery van had almost reached the West Tower when the company’s partners Ruby Jacox and Walter Hagen jumped from the vehicle moments before it tipped over in the bridge’s twisting. They clung to the curb where the movement was less. “Chunks of the concrete actually burst out of the bridge deck as it swayed, groaned and buckled,” recalled Jacox, They were eventually rescued when workman, J. K. Smith and W. H. Kreiger, painting at the East Tower backed their truck out to them. (Smith and Kreiger had abandoned the tower when the noise of the bridge’s motion rose to frightening levels.)
Eldridge received a phone call at his office (a mile from the bridge) to “come and look at the bridge, that it was about to go.” Returning, he ventured out observing that “The main span was rolling wildly. The deck was tipping from the horizontal to an angle approaching forty-five degrees. The entire main span appeared to be twisting about a neutral point at the center of the span in somewhat the manner of a corkscrew.”
10:03 a.m. first section of concrete from roadway splashes into the Narrows below Galloping Gertie.
Courtesy, Washington State Department of Transportation
Brown had crossed to the tower opposite and was returning when suddenly he was thrown flat. He recalled “Time after time I was thrown completely over the railing. When I tried to get up, I was knocked flat again. Chunks of concrete were breaking up and rolling around. The knees were torn out of my pants, and my knees were cut and torn. During the worst parts, the bridge turned so far that I could see the Coast Guard boat [the cutter Atlanta] in the water beneath.”
Coatsworth had passed the East Tower then the twisting motion tossed his car into the curb. He crawled through an open window onto the roadway and struggled toward the tower about 150 yards (137 m) away. He later reported “Around me I could hear concrete cracking. I started back to the car to get the dog, but was thrown before I could reach it. The car itself began to slide from side to side on the roadway. I decided the bridge was breaking up and my only hope was to get back to shore.”
“On hands and knees most of the time, I crawled 500 yards [458 m] or more to the towers . . . . My breath was coming in gasps; my knees were raw and bleeding, my hands bruised and swollen from gripping the concrete curb . . . . Toward the last, I risked rising to my feet and running a few yards at a time.”
He and Brown stumbled to the tollbooth where Coatsworth informed the attendant that his dog remained in the car and then phoned the Tacoma News Tribune office, which dispatched photographer Howard Clifford and reporter Bert Brintnall.
Movie clip showing the collapse of the Tacoma Narrows Bridge, looking westward, 7 November 1940 Cinematographer Barney Elliott, owner of The Camera Shop
Farquharson continued to shot movies of the wild bridge movements from near the East Tower. He was soon joined by Clifford, Brintnall, and freelance photographer James Bashford whom the News Tribune had contacted. Another cameraman, Barney Elliott from The Camera Shop also stood on the bridge shooting the event. Clifford attempted to get to Coatsworth’s car to save Tubby but had to turn back. “I saw the span buckle and start to break in the center. I pressed the camera trigger and started to run, he recalled. … Behind me I heard rumblings and explosive sounds which scared the daylights out of me.”
Farquharson would later make it out to Coatsworth’s car, but the terrified black spaniel bit him and would not leave the car. Farquharson retreated to the East Tower minutes before the first section collapsed.
The Washington State Police had quickly closed the bridge to all traffic when the movements became violent, allowing only Farquharson and reporters to venture out onto the bridge. At around 10:30 AM, a floor panel from the center span dropped into the water below. As the roadbed broke up, a rain of concrete splashed into the waters of Puget Sound, 195 ft (59 m) below. Just after 11 AM, a 600-ft (183 m) span of the western end, twisted free, flipped and plunged into the Sound, its splash sending water 100 feet (30 m) into the air. Farquharson said the snapping suspender cables sounded like gunshots, flying into the air “like fishing lines.”
Engineers who had rushed to the scene hoped that the span’s wild motions would diminish once the first span broke free, but the twisting and turning continued until nine minutes after 11 am when the remaining sections tore free and plummeted into the Sound. The 1100-ft (336 m) side spans dropped 60 feet (18.3 m) then rebounded, finally coming to rest with a 30-ft (9.2 m) sag. The center span disappeared into the deep waters below.
Collapse of Center Span of Tacoma Narrows Bridge, Extract from film by Barney Elliott, The Camera Shop
In minutes — by 11:10 AM — the great bridge was no more. The falling center span carried Coatsworth’s car and the doomed Tubby with it — neither the car nor his body were ever recovered. Tubby was the only serious casualty of the collapse, though those caught on the bridge deck suffered major scraps to their knees and body as they struggled to safety.
Remembering the experience, Winfield Brown would later remark, “I’ve been on plenty of roller coasters, but the worst was nothing compared to this.”
In the days following, the US Federal Works Agency established a commission to study the bridge’s collapse. The panel included the renowned physicist Theodore von Karman and was known as the Carmody Board. Their findings did not place the blame on a definitive cause but suggested possible reasons:
The principal cause of the Narrows Bridge's failure was its flexibility;
The solid plate girder and deck acted like an airfoil, thus creating drag and lift; and
Aerodynamic forces involved were little understood. Design engineers need to test all suspension bridge designs thoroughly using models in a wind tunnel.
The Board refused to lay blame on any individual; instead, it laid responsibility on the entire engineering profession. Clark Eldridge had a different opinion and bluntly laid blame on Moisseiff and the consulting firm of Moran and Proctor for building the bridge too thin.
The failure of the bridge happened when never-before-seen twisting modes, called torsional vibration mode, occurred under wind speeds at 40 miles per hour (64 km/h). Specifically, it was the second torsional mode, which occurred when the midpoint of the bridge remained motionless while the two segments of the bridge connected to the midpoint twisted in opposite directions. (see video for an example) Such vibrations were believed to be caused by aeroelastic fluttering. Fluttering arises when independent displacements and/or rotations of structural elements become coupled in an unstable oscillation driven by the wind. This neutralizes the natural damping of the structure. Such motions amplify, increase in magnitude, with time as the wind puts more energy into the system. The wind speed causing such flutter is called the flutter velocity, which may occur a relatively low wind speeds with steady flow. A bridge’s design must ensure that the flutter velocity is higher than the peak wind speed to be experienced at the site.
Once these fluttering motions have begun, the amplitude eventually increases beyond the strength of some vital part of the structure: in this case, the suspender cables whose failure initiates complete failure of the bridge’s integrity.
Even after over half a century, the full explanation of the failure has not been conclusively determined though many explanations have been put forward.
Following the collapse, it was decided that the bridge could not be repaired, and a new one was eventually built on the same site although its construction was largely delayed by World War II. Bethlehem Pacific Coast Steel Corporation and John A. Roebling Sons Company won the construction contracts for the replacement and construction of the new bridge began in June 1948. The new Tacoma Narrows Bridge, wider (four lanes of traffic), heavier, and stronger than its predecessor opened in 1950, Locals nickname this one “Sturdy Gertie.”
The New Tacoma Narrows Bridge
Courtesy, Washington State Department of Transportation
The steel from the much of the bridge was salvaged and recycled for use during the American the war effort. The remains of the highway deck of the old suspension bridge still lie in deep water, acting as a large artificial reef, which creates a wildlife haven from the swift tidal currents. In 1992, the remains of the 1940 Narrows Bridge were placed on the National Register of Historic Places.
Barney Elliott, owner of The Camera Shop recorded the collapse of the bridge on film. It shows Leonard Coatsworth leaving the bridge after exiting his car. In 1998, the Library of Congress selected The Tacoma Narrows Bridge Collapse for preservation in the United States National Film Registry as being culturally, historically, or aesthetically significant. Though shot in color, most copies in circulation are in black and white since the newsreels of the day only used 35 mm black and white.
The Tacoma Narrow Bridge was not the only one to experience some degree of excessive motion. The Golden Gate Bridge, New York’s Bronx-Whitestone Bridge, and Maine’s Deer Isle Bridge also demonstrated the alarming tendency to undulate in the wind. All were retrofitted with extra cables and/or stiffening devices to eliminate or reduce such tendencies.
The event led to bridge design engineers to incorporate aerodynamics in their design and testing, which included the use of wind tunnels and scale models of the bridge and surrounding terrain. This has led to the development of design equations and mathematical models that can be used in determining wind loads on bridges and other structures.