No abstract

The existing seismic design codes for hydraulic structures have not yet required to consider the impact of strong aftershocks on the secondary damage caused by the dam. However, the actual earthquake damage indicates that the impact of strong aftershocks cannot be ignored. In order to study the seismic safety of concrete gravity dam subjected to strong earthquakes, this paper constructs a constitutive model that reasonably reflects the dynamic damage evolution process of dam concrete based on damage mechanics theory. According to the similarity of concrete and rock material, the concrete damage model is extended to the rock mass material. Based on this, taking the gravity dam as an example, the overall damage mechanics model of the dam body and the dam foundation is established. According to the characteristics of the dam site and the characteristics of ground motion, the artificial seismic wave with time-frequency non-stationary characteristics is synthesized considering the attenuation law of ground motion duration and intensity envelope function. The effects of main shock and strong aftershock on the whole damage of gravity dam are studied. The results show that the strong aftershock after the main shock has different cumulative effects on the overall damage and plastic strain of the gravity dam. The gravity dam will further expand in the damaged area when subjected to strong aftershocks. The cumulative effect of the aftershock on the damage and plastic strain of the foundation is more significant than that of the dam. Therefore, it is necessary to consider the plastic damage of the dam and the dam foundation in the seismic analysis of the dam.

The traditional linear elastic and Drucker–Prager (DP) models cannot truly reflect the strong nonlinear characteristics of the concrete and rock foundation of the dam under earthquake. Therefore, for comprehensive evaluation of the cumulative damage of the gravity dam structure caused by aftershock, the dynamic damage of the dam body concrete is analyzed by many scholars through the plastic damage mechanics method, but there is little research on rock material at the dam foundation with the method utilized; thus, the simulation of the whole dynamic damage evolution is worthy of investigation of the dam body and dam foundation. According to the randomness of ground motion, the transcendental probability (P) is introduced to express the statistical characteristics of aftershock intensity, and a new method for constructing main-aftershock sequences of ground motion is proposed in this paper. And then, the law of the damage evolution and energy characteristics of the concrete gravity dam under the combined action of the main shock and aftershock sequences is studied. The results are shown as follows: the smaller aftershocks do not cause further damage to the dam; as the aftershock intensity increases, the energy characteristics of the dam body and foundation have shown different changing rules; when the ratio of peak aftershock acceleration to peak main shock acceleration (∇PGA) approximately equals 0.68, the aftershock will cause larger secondary damage to the dam.

No abstract

Strong earthquake cases of concrete gravity dams show that the foundation damage has an important influence on the seismic response and damage characteristics of the dam body. Compared with non-pulse ground motions, pulse-like near-fault ground motions have a wider response spectrum sensitive zone, which will cause more modes of the structure to respond, resulting in more serious damage to the structure. In order to study the real dynamic damage characteristics of concrete gravity dams under the action of near-fault ground motions, this paper takes Koyna gravity dam as the object and establishes a multi-coupling simulation model that can reasonably reflect the dynamic damage evolution process of dam concrete and foundation rock mass. A total of 12 near-fault ground motion records with three types of rupture directivity pulse, fling-step pulse and non-pulse are selected, deep research on the overall damage evolution law of concrete gravity dams. Considering the additional influence of different earthquake mechanisms, different site types and other factors on the study, the selected ground motion records are from the same seismic events (Chi-Chi), the same direction but different stations. The results show that the foundation of the concretes gravity dam often get damaged before the dam body under the action of strong earthquakes. Compared with the near-fault non-pulse ground motion, the structural damage of the gravity dam under the action of the near-fault directivity pulse ground motion is significantly increased, and causes greater damage and displacement response to the dam body. The near-fault fling-step pulse ground motion has the least impact on the dynamic response of the gravity dam structure.