The Hidden Life of Bridges

Portland and Hawthorne Bridge

I often find myself contemplating the effects of a Cascadia Subduction Zone earthquake while on my weekly stroll across Portland’s Hawthorne Bridge. Mostly, I think about how badly it would suck if the quake began while I was in the middle of the span. Consider the stresses that the bridge would have to endure during the 4+ minutes of shaking expected in a major event; shaking that will likely be severe enough to throw people off the ground as the land rolls in waves in response to the snap of the Cascadia fault system. Would the bridge survive such an event? Would *I* survive it? How about the motorists, or the bridge operator in their high perch above the lift system? I find it remarkable that we can expect any feat of engineering to withstand such forces.

What I rarely consider, however, are the stresses and strain that our bridges feel day-by-day and moment-to-moment as they carry heavy vehicle traffic and are expected to lift and move to accommodate the passage of watercraft underneath their spans.

On Friday I was stopped short in my walk across the bridge to the east bank. There was a strange noise emanating from the bridge; A louder than usual sound of metal resonating with the passage of vehicles and the jarring squeak of I-beams and girders bending under stress. I was momentarily worried until I noticed that the sound that seemed like it should be coming from below me, was actually being projected from above. I glanced up to see a speaker system mounted on the tower. Next to it hung a banner that read “The Hidden Life of Bridges.”

The enhanced soundscape was one element of an art installation that’s part of Portland’s annual Time Based Art festival. The artists, Tim DuRoche and Ed Purver, highlighted the Morrison and Hawthorne bridges in their work with the intention of bringing some public attention to the marvels that are our public works infrastructure and to the daily lives and passions of those people who keep them safe and operating. The imagery and sound that they’ve managed to capture in this project are quite remarkable, in my opinion, and are summed up beautifully in this video from the Morrison bridge project.

Under the Morrison Bridge from Ed Purver on Vimeo.

There’s a live component to this art installation, too. At this link you can listen to the live, modestly sound filtered, “music” of the Hawthorne Bridge as cars, cyclists, and pedestrians cross the Willamette River. Overlying the music of the bridge are short biographies of and interviews with the bridge operators. The project will only be running through October 9th, so take a listen now before the installation is dismantled. I hope that the videos, at least, will remain available for a long time to come.

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