In a wind tunnel, a research tool that allows studying and understanding the impact of air movement on solid objects, in southwestern Ontario, Canada, a team made up of the world’s best experts in bridge aerodynamics and acoustics studies a full-scale model of the railing of the Golden Gate Bridge in San Francisco. Experts have been hired to solve the mysterious problem of a strange buzzing sound that has been emanating from the iconic bridge for a year and has come to unhinge some neighbors.
The sound, which is only heard on windy days, has been compared to a “ghostly harmonica”, “singing monks” and a “hissing kazoo”.
The strange hum has become a mythical element of the San Francisco aural landscape. Amateur detectives have roamed the city streets tracing the origin of the sound and an electronic music producer claims to have mixed it into a soundtrack that recreates existential terror. Some fans call it a “reassuring” song. For others it is “creepy” or “unbearable”. One woman has simply attributed it to “aliens.”
“I can imagine a similar sound used to torture prisoners,” said one of the neighbors affected by the annoying noise, through the social media application NextDoor. Love it or hate it, the engineering team will announce their strategy to end the noise, a spokesperson reported.
In June 2020, neighbors began to complain about the noise. Shortly after, the officials of the entity that manages the bridge began an investigation, puzzled. They monitored the sound and even used instruments to measure the vibrations of the hum, finding that it often emits a frequency of 440 hertz, which matches the musical note la. As one Nextdoor user points out, it could be used to “tune the oboe.”
More resistant to strong winds
Experts have concluded that the buzzing occurs when strong city winds hit a set of newly installed bridge railing slats from a slightly offset angle, either slightly north or south of the usual westerly winds.
“After exhaustively studying this phenomenon, we have concluded that the sound comes from the new railings that we have installed on the west side, which are more aerodynamic,” says the spokesman for the entity that manages the bridge, Paolo Cosulich-Schwartz.
“This facility is part of a redevelopment of the Golden Gate designed to protect the bridge for future generations by allowing it to withstand sustained high winds of up to 100 miles per hour.” In this sense, he explains that the new railings are thinner than those installed on the west side. In fact, they were installed to prevent the bridge from having the same end as the ill-fated Tacoma Narrows Bridge, in Washington, which began to sway violently in the wind and collapsed in 1940, shortly after its construction. That stretch, nicknamed “Gallopin ‘Gertie,” has become a classic engineering school lesson on how not to build a bridge.
“So this was a must-see project,” says Cosulich-Schwartz of the Golden Gate Highway and Transit District, to justify last year’s wind resistance reform, costing 10 million euros. “With the impacts of climate change, leading to more severe weather events, it was even more urgent to complete it as soon as possible.”
A study done by the agency in 2013 showed that the maximum sustained wind speed for which the bridge was built was 111 kilometers per hour. In its 84-year history, it has already been briefly closed three times by winds of between 111 and 120 km / h in 1951, 1982 and 1983. In none of the three cases was it damaged.
So the bridge engineers thought that the new thinner slats would allow the bridge to withstand sustained winds of 100 miles per hour, which the study estimated would only occur every 10,000 years. They just didn’t predict that the slats would create such a cacophony in normal years.
Warren Blier, a veteran scientist with the National Weather Service, says sustained winds of 100 miles per hour would only occur in the event of a tornado, hurricane or tropical storm. And none of them have ever been known or anticipated to pass near San Francisco. “It seems highly unlikely to me,” says Blier, who acknowledges that his job is usually to predict the weather seven days in advance, not for the next 10,000 years. “In the history of the state, no hurricane has reached the coast of Northern California.”
Not everyone wants the noise to go away
Meanwhile, bridge engineers are determined to find a solution to the drone. At RWDI engineering, an hour west of Toronto, a life-size model of a 10-foot section of the new railing has been built in a wind tunnel the size of a convention center conference room. Engineers are subjecting it to gusts of various wind speeds and testing modifications to see if they can silence the hum. The same company tested a model of the entire bridge in an earlier phaseBut apparently no one realized that hum would be such a serious problem.
“We will share more information on a possible solution this summer,” said Cosulich-Schwartz. “We understand that some neighbors find the sound annoying. We want to be good neighbors. So we hope to calm residents’ ears with a solution.”
But, in this famous city full of opinions, not everyone wants the buzz to go away. A local blogger has elaborated a playlist of ambient sounds from the Golden Gate to help your listeners on those sleepless nights where sound is missing.
“I like the sound,” says West San Francisco resident Brianne Howell who recorded a video with the hum of the bridge on one of his usual walks along the coast. “It reminds me of the creepy sound in a movie when something scary is going to happen. I think it’s kind of sad to end it.”
Translated by Emma Reverter.