BRIDGE CONSTRUCTION: New Seattle bridge designed to withstand earthquakes

The bridge has flexible joints with reinforcing bars that can snap back into place once tremors cease

Bridge Construction News KING-TV (Seattle) November 15, 2016
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Image source: KING-TV (Seattle)

A new bridge that will carry traffic from State Route 99 into Seattle is designed to survive earthquakes and seismic shocks.


The bridge will take traffic from northbound State Route 99 off and into the city. As drivers cross it, they will not see any significant difference between this bridge and any one of hundreds of new concrete structures built around the United States.


This bridge is made largely of the same materials, such as concrete, rebar and pre-stressed concrete beams holding up the road deck. However, on this bridge, it is the connective tissue, the joints, where the quakeproofing comes in. The joints are designed to be flexible. Reinforcing bars made from a special metal alloy will hold their shape, snapping back to their original position when the stress and movement of the earthquake are over.


The idea is to do what other bridges do not: lose the structural integrity of concrete that holds up the bridge. That ability for a bridge to hold itself together can depend on the degree of shaking, and if strong enough it, can crumble and lose its ability to support the road above.


The new bridge design is intended to go back into service immediately after a post-quake inspection.


The expectation is that the new bridge, if widely adopted, would show earthquake resilience, not only the ability to ride out the quake, by allowing the economy and society to recover far more quickly.


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