Although Seattle is not a city plagued by earthquakes, its position on the waterfront of the Pacific Northwest makes it vulnerable to a big quake, especially given its population. City planners taking this into consideration are building a new ‘flexible’ bridge along the city’s shoreline that could help keep key roadways open for traffic in the event of a major quake. When it opens next spring, the bridge could be the first earthquake-proof roadway of its kind in the entire world.
The fate of the Alaskan Way Viaduct has been a topic of many a heated debate in Seattle for years. Currently, a project is underway to replace part of the aging elevated road with a tunnel. The above-ground portion of the road, though, will be comprised of an exit ramp that utilizes new technology to protect it from collapsing during even a very strong earthquake. Memory-retaining metal rods (called “Shape Memory Alloy” rebar) and a bendable concrete composite will help the bridge sustain quakes and then return to its original shape, according to the Washington State Department of Transportation.
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The department says this bridge will be the first in the world to employ the new building technology. While it’s impossible to guarantee that any man-made structure can be earthquake-proof, especially since the magnitude of Seattle’s next big earthquake is unpredictable, builders are aiming for the next best thing: a flexible bridge that can absorb earthquake forces, rather than be destroyed by them. Seattle’s new flexible exit ramp bridge will be the first real-world application of materials that the Earthquake Engineering Lab at the University of Nevada, Reno has been researching for 15 years. In testing, bridge columns using the new building technology have withstood magnitude 7.5 earthquakes and then returned to their original shape.
The exit under construction will guide drivers from northbound State Route 99 onto South Dearborn Street, which leads into the heart of the downtown district. The ramp sits immediately west of the city’s sports stadiums, a spot seismologists have predicted would be particularly vulnerable in the event of a large earthquake. Construction on the flexible bridge began in September 2016 and the new exit ramp is expected to be open next spring.
Images via WSDOT/Flickr