| To assess the structural safety of existing dams, the effects of deterioration due to aging or damage that might occur caused by unusual loads such as large earthquakes should be adequately considered. However, it is not easy to identify their location, extent and degree. This paper discusses a method focusing on the change of vibration characteristics of a dam body to be applied to the primary diagnosis of structural soundness of existing dams. Firstly, the effect of internal deterioration or damage on the natural frequencies of concrete gravity dams is estimated by using numerical analysis. Such analysis is required to evaluate the soundness of existing dams without a set of long-term measurement data on vibration characteristics. As a result of analyses assuming several types of horizontal cracks along lift joints, their effect on natural frequencies of a dam body varies depending on the location, depth and continuity of cracks. Secondly, the applicability of the method focusing on the change of natural frequencies of a dam body is discussed referring to the results of numerical analyses and microtremor measurements performed at actual gravity dams. Natural frequencies were affected by reservoir water level and perhaps also by temperature. To evaluate the structural soundness of existing dams, these factors should be adequately distinguished from the effect of deterioration or damage. Lastly, future prospects for improving these studies to assess the safety and risk of existing dams is also discussed |
