Sunday, August 12, 2012

Niigata, Japan's Bridges: Yonahime Bridge on Route 8

August 2007 (37.3168 Degrees, 138.4348 Degrees) Yonahime Bridge
This is a 120 m long through truss arch, crossing over a narrow canyon south of Kashiwazaki. We saw a landslide scarp on the uphill side of this bridge, but since the bridge is founded on piles, it was probably strong shaking that caused it to rack during the earthquake.

When we visited the bridge (on Aug. 4th) we saw many of its members had buckled and some of its connections were damaged along with its bearings.  Still, the bridge remained in service (jacked up and sitting on metal boxes), which shouldn’t be a problem unless another strong earthquake occurs. This very common bridge type is sensitive to shaking, because the struts and bracing can’t resist compression. A deck arch bridge immediately to the north was undamaged by the earthquake.  

It might be possible to redesign the Yonahime and other tied arch bridges for large earthquakes by supporting it on isolation bearings.  Certainly, these fixed bearings, which we saw damaged on several of the longer span bridges, are a lot of trouble to replace.
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Niigata, Japan's Bridges: Yonahime Bridge on Route 8 by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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