Abstract : Influence of hydrodynamic interaction on the dynamic behavior of dams is reduced to two dimensions; the material behavior is assumed to be linearly elastic. For analysis in the frequency domain, the system is considered as two substructures: (1) the dam as a finite element system and (2) the reservoir's fluid as a continuum of infinite length upstream governed by the wave equation. The displacements of the dam including hydrodynamic effects are expressed in linear combination of the modes of vibration of the dam with the reservoir empty. The analysis produces exact results if all modes of vibration are included; however it effectively produces excellent results by considering only the first few modes, thus drastically reducing the number of unknowns. Numerical results for complex frequency responses and responses to earthquake ground motions show: (1) hydrodynamic interaction and compressibility of water must be considered to obtain accurate results for the periods of vibration and response to earthquakes, (2) water in the reservoir significantly increases the lateral displacements from earthquake motion; however, the stresses may not increase, depending on the ground motion frequency characteristics, and (3) compared to many classes of structures, the vertical component of ground motion is more important in the response of gravity dams.
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