Ibaraki, Japan's Bridges: Kouzaki Bridges across the Tonegawa (2)

June 2011 (35.9105 Degrees 140.396 Degrees) Kouzaki Bridges

A few months after the Great Tohoku Earthquake, Professor Fujino at the University of Tokyo took me to see some of the bridges in Ibaraki Prefecture. I thought the rivers running through Tokyo were green oases until we drove into Ibaraki.

The Tonegawa was an ancient river that constantly flooded Tokyo until it was finally diverted east through Chiba Prefecture into the Pacific. After the recent earthquake (and the Fukushima nuclear power plant disaster) carp caught in the river were found to have increased amounts of radioactive cesium.

The Kouzaki Roadway Bridge is a long steel girder bridge that includes three tied arch spans on single column bents with hammerhead caps over the Tonegawa River. The arch spans are 48.8m, 49.2m, 48.8m and the approach spans are 79.2m. There is a parallel steel girder pedestrian bridge. Both bridges were built in 1967.

The roadway bridge was retrofitted quite recently with concrete casings around the columns and dampers, restrainers, and shear keys around the bent caps. During the earthquake, the site experienced liquefaction that damaged the piles, caused considerable movement of the spans, and cracks and spalls to the restrainer connections. The bridge was closed in May (two months after the earthquake) so it could be repaired. It is thought that the retrofit prevented unseating during the earthquake.

Ibaraki, Japan's Bridges: Kouzaki Bridges across the Tonegawa (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.