Eleven small cracks in the Seto Ohashi Bridge linking Honshu and Shikoku remain unrepaired since being found by Honshu-Shikoku Bridge Expressway Co. in 2009, company officials said Tuesday.
The highway-railway bridge consisting of seven metal sub bridges linking Kurashiki in Okayama Prefecture and Sakaide in Kagawa Prefecture opened in 1988 and will mark its 25th anniversary Wednesday.
The fatigue cracks measuring around 5 mm in length were found on the highway layer of the Iwakurojima and Hitsuishijima section in Sakaide in October 2009.
Because repairing the cracks is difficult due to train services running below the highway layer, the cracks have been painted to prevent rust.
The expressway company plans to coordinate with the railway operator, Shikoku Railway Co., to repair the cracks, the officials said.
"Metallic fatigue had been taken into account for the railway layer expected to accommodate bullet trains, but not for the highway portion," said Yozo Fujino, a University of Tokyo professor well versed in the bridge's structure.
"The cracks are not a threat to the fail-safe structure," he said. "If the bridge is to be maintained for 50 to 100 years, however, more detailed checks may have to be conducted."