ABSTRACT
To accurately and realistically define the response of concrete dams to earthquakes it is often necessary to carry out complex FEM (Finite Element Method) analyses able to consider the three-dimensionality of the problem, the semi-unbounded size of the foundation, the non-linear behaviour of the system and the dynamic interactions of the dam with the foundation and the reservoir. An advanced approach to deal with dam-foundation seismic interaction was recently implemented and tested with the objective of appropriately simulating the propagation of seismic waves in a realistic massed foundation, considering its semi-unbounded extent. The approach, indicated by the acronym SAM-4D (Seismic Advanced Model for Dams), was developed by RSE to overcome the main deficiencies (above all the excessive conservativeness of the results) of traditional and simplified methods. Artificial non-reflecting (or absorbing) boundaries are used to delimit the semi-unbounded foundation and effective earthquake forces, computed with reference to the elastic wave vertical propagation theory, provide the seismic motion: the method can be adopted within the framework of FEM codes able to address all the above-mentioned complexities and allows to reduce the recognized excessive conservativity of the results obtained with simplified traditional approaches (e.g. the massless approach). Pre-processing software tools were developed to automate the calculation and the assignment of the effective earthquake forces to be applied to the artificial boundaries of the foundation. The method, including the pre-processing tools, was validated using theoretical and numerical solutions available in technical literature. Three case studies of dam-reservoir-foundation systems (one 2D case and two 3D cases) were carried out, allowing to verify the reliability of the method for real applications and to highlight the strong conservativity of the traditional analysis approaches with respect to the proposed method.
