How Washington’s most infamous bridge failure helped engineers prevent more
On this episode of Mossback's Northwest, Knute Berger looks back at what Puget Sound learned from the Tacoma Narrows bridge disaster.
The Puget Sound region has always posed a challenge for transportation. We’ve gotten around by canoe, schooner, steamers, ferries and, in the era of the automobile, road bridges of various kinds. But some of those bridges have proved problematic.
The classic example is the most notorious bridge failure in the history of the Pacific Northwest: The collapse in 1940 of a brand new suspension bridge nicknamed “Galloping Gertie.” But that wasn’t the only bridge failure in the region.
In the early 1950s, the state seriously considered building bridges or floating underwater tunnels that would crisscross the region. They imagined a veritable highway grid laid over and circling Central Puget Sound so you could drive directly from downtown Seattle to Bremerton or Port Orchard via Bainbridge or Vashon islands.
We’ve also built and lost floating bridges, a label that seems like a contradiction in terms — car-carrying bridges that float? Generally, floating bridges have served us well, but not without problems. The Hood Canal floating bridge sank in a storm in 1979, and the old I-90 floating bridge across Lake Washington to Mercer Island did the same over Thanksgiving weekend in 1990. In both cases, open hatches in the pontoons allowed water to slosh in, contributing to the disasters. No one was killed in either case.
The most epic bridge failure in American history — certainly the most spectacular caught on film — occurred at the Tacoma Narrows in 1940. It was then that the brand-new Tacoma Narrows suspension bridge, which connected the mainland with the Olympic Peninsula at the narrowest point between the two land masses, collapsed in a matter of hours just four months after opening.
The bridge had been controversial from the start. Some questioned the need for it: Would there really be enough traffic to warrant it? Others saw it as a boondoggle that would benefit only Tacoma.
The decision was to build a comparatively narrow two-lane suspension bridge with some financing help from the federal government. Rather than the usual open trusses, solid steel would support the bridge deck.
Shortly after the bridge’s opening in July 1940, drivers noticed an up and down motion of the roadway in the wind — even to the point where you could lose sight of cars on the other end of the bridge as it undulated. The roller-coaster effect gave rise to the bridge’s Galloping Gertie nickname.
On Nov. 7, 1940, as 42 mph winds funneled through the Narrows, the bridge began to move ominously. The two ends of the bridge weren’t only moving up and down — they began moving in opposite directions, twisting the deck like a corkscrew.
A man who fled from the bucking bridge said the roadway twisted so much—nearly 45 degrees — that while fleeing the bridge deck he could see the Sound below when the deck turned to the side. A newspaper editor from the Tacoma News Tribune, Leonard Coatsworth, abandoned his car on the span and crawled back to safety. When Gertie collapsed, the only fatality was his daughter’s small three-legged spaniel, Tubby, who was trapped in the vehicle and fell with the bridge to the bottom of the Sound.
After the fiasco came the finger-pointing. The bridge designers blamed the government. Consulting engineers blamed the designers. No one had thought to take aerodynamics into account — especially for such a narrow, light bridge.
A larger, stronger bridge was eventually built, but because of World War II it was delayed until 1950. In 1951 the new span was hit with 75 mph winds and it did just fine. It got the nickname “Sturdy Gertie.”
This resilience was in part a result of the Galloping Gertie disaster's legacy. Engineers at the University of Washington tested new Narrows bridge designs in a wind tunnel, which had never before been done for suspension bridges. That resulted in designs that could withstand the wind and not set the bridge into a self-destructive galloping motion. The professor in charge of testing, F.B. “Bert” Farquharson, had witnessed the original collapse and was responsible for filming what some have exaggeratingly described as “the Pearl Harbor of engineering.”
There are now two bridges over the Narrows: Sturdy Gertie and a new toll bridge opened in 2007. The wreckage of first Narrows bridge still lies on the sea bottom and has been placed on the National Register of Historic Places.
By the way, Farquharson and his team were also responsible for wind-tunnel testing another steel structure you might have heard of: The Space Needle, a tower that stands in part because of lessons learned from Galloping Gertie.