The authors propose an evaluation methodology that incorporates epistemic uncertainty under the conditions of insufficient knowledge and data in the fragility evaluation of structures subjected to fault displacement. In developing the optimal evaluation model, the authors analyzed the damage case of Shih-Gang Dam in Taiwan and summarized the key issues in the fragility evaluation of structures subjected to fault displacement. Based on the summary, we conducted a reproduction analysis using a model that can evaluate both the overall and local behaviors and confirmed the validity of the optimal evaluation model.

In 2017, the gate of the bottom outlet at the Susobana Dam in Nagano Prefecture became inoperable during flood control due to sediment and submerged wood debris that reached the level of the bottom outlet. This accident is an unacceptable risk for the function of the dam, and it is necessary to identify the causes and take countermeasures to prevent recurrence, including at other dams. In this study, a fault tree for gate inoperability due to sediment and submerged wood debris was developed for the high-pressure roller gate of the bottom outlet, which does not design for the passage of sediment and submerged wood debris. Furthermore, we organized each risk factor systematically and quantitatively.