Seismic Fragility of Concrete Gravity Dams with Spatial Variation of Angle of Friction: Case Study

Concrete gravity dams are essential infrastructure components and because of earlier design practices, they may be vulnerable to future earthquake events. Therefore, their vulnerability is important to characterize, particularly given the large societal consequences of dam failure. Seismic fragility curves allow a rational safety and vulnerability assessment of existing structures under earthquake hazards offering statements of the conditional probability of reaching a limit state. This paper evaluates the seismic fragility of a case study concrete dam located in northeastern Quebec, improving on existing approaches by including spatial variation of the angle of friction and offering insights regarding the significance of modeling parameters, importance of spatial variation, and overall vulnerability of the dam to two failure modes. Finite-element techniques are used to model the dam system and to fully account for dam-reservoir-foundation interactions. Uncertainties in the ground motions and modeling parameters are included and propagated using a sampling technique. The fragility curves are developed using nonlinear time-history analysis, and the uncertainty related to the spatial variation of the angle of friction is included in the fragility analysis through the incorporation of random fields modeling. The study reveals that this additional source of uncertainty has a slight effect on the fragility of the dam and is mainly critical when severe damage levels are considered. (C) 2015 American Society of Civil Engineers.