Structural Strategy for Risk Mitigation of Bridges Subjected to Earthquake-Induced Ground Deformation

At 21:26 on April 14, 2016, an earthquake of JMA magnitude 6.5 with its epicenter in the Kumamoto region of Kumamoto Prefecture occurred, with a JMA seismic intensity of 7 observed in Mashiki Town. At 1:25 on April 16, an earthquake of JMA magnitude 7.3 also occurred. Strong tremors occurred over a wide area mainly in Kumamoto Prefecture, including tremors with JMA seismic intensity of 7 observed again in Nishihara Village and Mashiki Town, causing tremendous damage. This series of seismic activity resulted in damage to numerous road structures, including the collapse of Aso-Ohashi located in front of the site of a large-scale slope failure, the destruction of the National Route 57 road, damage to bridges and tunnels on the Prefectural Route 28 Kumamoto-Takamori Line, and the collapse of a bridge spanning Kyushu Expressway. This paper introduces some technical measures to reduce a risk of the loss of function in bridges subjected to the ground deformation induced by an earthquake, with practical examples of restoration projects for three road bridges, namely Tawarayama-Ohashi, Aso-Choyo-Ohashi, and Aso-Ohashi which were damaged by the effect of the ground deformation due to the 2016 Kumamoto earthquake.