Vertical Crack Identification of Arch Dam under Underwater Explosion Based on Mode Transition

The failure process of concrete arch dam subjected to underwater explosion has been the research hotspot in recent years, however, there is a lack of an effective method to identify the crack in dam body. To solve this problem, the crack identification of arch dam caused by underwater explosions has been studied in this paper. Firstly, an analysis method to identify the vertical crack in dam body is proposed, according to a comparison of the modal characteristics of the arch dam with and without crack. Secondly, the reliability of the proposed method is verified by a small-scale arch dam that cracking along the crown beam attacked by foundation explosion. The modal change of the dam induced by cracking is captured in both experiment and numerical simulation. Thirdly, this method is applied to analyze the influence of vertical crack on the modal of a 240 m high arch dam. Some findings need be noted as follows: vertical cracks lead to modal transition of arch dam of two adjacent dense modes, such as orders between 4 and 5, 7 and 8, and 11 and 12 respectively in this case, the ratio of modal transition is 6.04% in the first 8 modes and it is 14.1% in the first 12 modes; The effect of cracks on the mode of arch dam is related to the spatial position of the vibration mode peak, the nearer the two are, the more significant the change in that order of mode is. This finding indicates that the vertical cracks may lead to mode transition or mode loss of arch dams, it should be considered that the change of arch-cantilever system vibration mode sequence in the identification of the crack of arch dam caused by underwater explosion.