An accurate and realistic definition of the structural response of concrete dams to earthquakes requires advanced numerical analysis methods capable of modeling the dynamic interaction between the dam and the foundation rock, so as to remove as much as possible the acknowledged excessive conservativeness of the results obtained using simplified approaches.
The seismic wave propagation model we used was initially developed for two-dimensional cases and then extended to three-dimensional cases; by delimiting the foundation with artificial contours that allow seismic waves to enter (through the application of equivalent forces) and scattering waves (caused by the presence of the dam-reservoir system) to exit, this model can reproduce, within the calculation domain, the same behavior that would be obtained with an unlimited foundation.
In-depth studies were conducted on the three-dimensional foundation domains with canyons, which are necessary to optimize models in real cases: an approach based on orthotropic elements was assessed to model absorbent contours, and proved to be a valid alternative to the approach based on infinite elements, allowing for the use of calculation codes featuring orthotropic (linear) elasticity and Rayleigh damping options. The possibility of reducing calculation times (without compromising the quality of the results) by using a sparser horizontal subdivision near the lateral contours of the foundation was examined; a deconvolution technique was tested, aimed at best reproducing the seismic motion assigned to the free surface.
The model was then used to create two case studies on three-dimensional dam-reservoir-foundation systems. The first involved a large concrete arch dam in California (USA) for which experimental data recorded during a weak earthquake were available; the results of the model were compared with the measurements, so as to check their reliability for use in real cases. The second case study concerned a large Italian concrete arch dam located in a high seismic hazard area, and confirmed the excessive conservativeness of traditional analysis approaches compared to the proposed model.
Finally, a methodology was identified to integrate seismic risk assessments of concrete dams into tools for estimating the resilience of the electrical system.