Whether you're charmed or perturbed by the loud hum coming from the Golden Gate Bridge on windy days, it's likely going to get fixed next year.
Way back in June 2020, amid some seasonal winds, Bay Area residents starting to emerge from three months of strict lockdown heard a bizarre new sound emanating across the Bay from the Golden Gate Bridge. This "singing" or "humming" is now a regular occurrence when the winds are right, all because of some safety slats installed in the bridge's railing that act like a colossal harmonica.
It's an ethereal, steady, monotone little song that the bridge puts out, and for some it adds a little more magic to the picturesque Golden Gate and the entrance to our grand Bay.
It's a bit more alarming and distracting when you're actually driving, biking, or walking on the bridge, and engineers have been trying to come up with a fix for the last eighteen months. (They claim that these sounds were not produced when they originally tested the new, narrower slats.)
The new slats, a critical mass of which had been installed by early June 2020, were meant to make the suspension bridge more aerodynamic and less prone to "catastrophic aerodynamic instability" up to 100-mph winds. The worst example of such instability is the infamous Tacoma Narrows Bridge collapse, which was caused by rhythmic fluttering and buckling that occurred in 40-mph winds.
Now, as the bridge district announced this week, a plan has emerged to fix the Golden Gate's sound problem. Bridge engineers, in consultation with acoustics and aerodynamics experts, tried multiple fixes for the problem, but the solution they settled on involves "the installation of thin, u-shaped aluminum clips attached to both edges of all 12,000 vertical slats on the newly installed west railing. The clips, which are just 1/8 of an inch thick, will cover the edge of every slat from top to bottom and will include a thin rubber sleeve underneath to dampen vibrations that contribute to the sounds."
They provided a top-down illustration for some clarity, with the top of each slate in orange.
The clips, then, will all be painted International Orange to match the existing slats, "making them invisible to most Bridge users," the district says.
If you want to nerd out on the sound mechanics that produce the distinctive tone, you can delve deeper via this six-page staff report that is getting presented to the bridge's board this week. Engineers found that "The high-frequency tone of approximately 1.1 kHz was recorded when the wind direction was at an angle of less than 80 degrees to the railing and with no significant change in frequency relative to changes in wind speeds," and, "The onset of the high-frequency tone was recorded at a wind tunnel wind speed of approximately 27 miles per hour."
The bridge's engineers say that the fix for the slats will cost $450,000 in fabrication expenses, and will reduce the loudness of the bridge's hum by 75%. And, they say, installation can occur by bridge maintenance workers as part of their regular work, which won't impact the district's budget.
The project to install these new clips on every west-side slat is expected to be complete by late 2022.
Photo: Benoit Debaix