US plans first bridge that can bend its way through an earthquake

The Washington State Department of Transportation (WSDOT) is planning to earthquake-proof a Seattle bridge by making it from flexible materials.

Nobody wants an earthquake, but this bridge will be important to study when the next quake hits– WSDOT

The bridge in question is the State Route 99 exit ramp in Seattle, and it will be the first real-world test of 15 years of research inside the Earthquake Engineering Lab of the University of Nevada, Reno. It will use "super-elastic metals and bendable composites" such as shape-memory alloys, bendable concrete and titanium to keep the bridge operational after a quake.

The frames of the bridge are built to bend and twist, but always return to their eyeglass shape. Large-diameter nickel-titanium rods engineered for bridge construction behave much the same way, but on a larger scale.   

The bendable concrete also moves with the memory-retaining rebar in the column. This engineered composite contains tiny synthetic fibers that keep concrete shear to a minimum when it moves.

The columns that were built in the university’s labs were able to return to their original shape after an earthquake measuring 7.5 on the Richter Scale.

The specialised materials that will be used in the bridge are up to 90 times more expensive than standard steel and concrete. The Federal Highway Administration gave the go-ahead for this small-scale real-world test, and a federal grant paid for much of the additional costs.

Tom Baker, bridge and structures engineer for WSDOT, said: "This is potentially a giant leap forward. We design for no collapse, but in the future, we could be designing for no damage and be able to keep bridges open to emergency vehicles, commerce and the public after a strong quake.

"We’re testing this cutting-edge technology in a real-live lab now. We’ll examine how it performs with heavy traffic volumes, rain, freezing and thawing cycles and evaluate where we go from here."

The Inhabitat website says although Seattle is not as vulnerable to earthquakes as Los Angeles "its position on the waterfront of the Pacific Northwest makes it vulnerable to a big quake".

The off-ramp is currently under construction and scheduled for completion in spring 2017. It is being dug by tunnel boring machine Bertha.

As WSDOT note: "Nobody wants an earthquake, but this bridge will be important to study when the next quake hits."

Image via WSDOT

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  1. ! Seattle is no stranger to earthquakes so that the newer buildings did withstand the last quake without any structural failures while the much older ones did have! It only follows that the same quake resistant standards ought to likewise apply to bridges! However are not quake resistant bridge span mountings already long since in use? It then follows that bendable spans will make it possible for these mountings to be retained in place during a severe earthquake! However the ultimate test is , even with all this newest technology newly installed : Could any traffic on such a bridge not just as easily be flung off the bridge due to the force of the quake?!

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