Natural Frequencies and Mode Shapes of Various Configurations of Concrete Arch Dams

The monitoring of the dynamic behaviour of concrete dams is an important aspect in their safety evaluation. Dynamic properties (i.e. mode shapes and natural frequencies) provide useful information on the operational behaviour of dams. In this study, the influence of the curvature (single or double), valley characteristics (narrow or wide, U or V) and classification of arch dams (thin, medium-thick and thick) on the dynamic behaviour of these dams was investigated through numerical models. The mode shape sequence was not affected by the curvature, however it was affected by the system stiffness and added mass (water level) for some configurations. The natural frequencies were generally higher for double curvature arch dams, than single curvature arch dams. The first mode shape for all V-shaped valley types was a symmetric mode followed by an antisymmetric mode. Whilst for the U-shaped valley types, the first and second mode varied between symmetric and anti-symmetric modes for different arch classifications. Based on the observations presented in this paper, the site shape, arch type, arch thickness class influence the dynamic behaviour of concrete arch dams together with the stiffness and water level. An accurate representation of these parameters is critical when performing dynamic analysis of these structures.