Investigating the Effect of Intensity and Location of Damage on Modal Characteristics in Concrete Arch Dams

Dams are among the most important and largest engineering structures used to supply potable and agricultural water and hydro-power as well as prevent seasonal floods. Human experience has shown that when damage occurs in these megastructures, there are irreversible financial, environmental, and fatal losses. Therefore, the issue of safety and proper performance of dams is of vital importance both in terms of designing new structures or health monitoring of the old structures. This subject is of more particular importance in the case of concrete arch dams, since in the absence of identification of small and minor damages, with the growth and spread of structural damages, a general failure may occur in these infrastructures with considerable human and financial losses. Nevertheless, concrete arch dams have been less broadly considered in the investigation, and most of the researches have included simple structures with a low-degree-of-freedom. Therefore, the main objective of this paper is to study the effects of structural damages (including the intensity and location) on the modal properties of these engineering systems. For this purpose, the modal characteristics of the structure, such as the natural frequencies and the shape-modes, are initially computed using finite element model on a concrete arch dam. Considering different scenarios for damage including, nine different locations (on different vertical and horizontal locations) are chosen. The modal characteristics of the system would be then determined before and after the occurrence of damage. In the presented research, the effects of damages at three levels of arch dam body on the modal parameters of the system are investigated. The comparison of the structural modal parameters of the intact and damaged states shows that first, the natural frequencies of the system have lower sensitivity than mode-shapes of the system, and also the damages to the top and middle are more effective than the corner zones on the modal features of the arc-dam body.