The Seismic Safety Analysis Of Concrete Gravity Dam

The recent decades are the rapid development period of our country’s hydroelectric power exploitation. Several world-class hydraulic projects are constructing or to be constructed in the southwest area of our country, which, however, is the earthquake-prone area. Therefore, the buildings’seismic safety is highly concerned in many projects. As for gravity dam, its upper area usually has violent reactions in an earthquake. So this area is one of the whole dam’s seismic weak positions, and should be studied in detail. In the same time, the computer technique has gained a great development, making the problem-solving capabilities of numerical analysis technique, especially the finite element method, improve a lot. These numerical methods are widely used in the area of science. In this paper, a series of research on the seismic safety of concrete gravity dams’upper area are done, by using some numerical methods, such as the finite element method.etc. The main contents are as follows:(1).A gravity dam’s finite element model is built, and a nonlinear dynamic time-history analysis is done to the dam to get its every moment’s stress field during the earthquake. Then a search program is written according to the genetic algorithm method to search the critical slip surfaces in the dam’s upper area’s stress fields at every moment. Finally, the most dangerous slip surface as well as its safety factor can be determined, and the safety of the dam’s upper area can be evaluated.(2).The Extended Finite Element Method (XFEM), an effective crack analysis method, is used to study the initial crack’s propagation process in an earthquake at the grade change point of a gravity dams’downstream surface. So, the crack’s final pattern can be obtained. The influences of the initial crack’s lengths and dip angles on its propagation are studied further. According to the results, the crack’s propagation in the dam has a very obvious brittle nature. Both the initial crack’s length and dip angles can affect its later propagation to some extant. But, the crack’s final general pattern is mainly determined by the dam’s stress field in the earthquake.(3).A straight horizontal penetrating crack is supposed to be at the gravity dam’s upper area, which divide the dam into two blocks. Then, two different methods are used to compute the upper block’s slipping displacement in the earthquake. One of the methods is the finite element contact method, and the other is the Newmark sliding block method combined with FEM’s elastic time-history analysis. The two methods’characteristic and applicable conditions are discussed, and the results gained by them are compared in detail. According to the results, the dam in such a badly damaged condition still contains some seismic capacity, and both of the methods applied in this paper can be used to analysis this kind of questions. Generally speaking, while the FEM contact method has higher precision and better adaptability, the Newmark sliding block method is easier, and can generate good results under some proper conditions. So the Newmark method can be used to approximately compute the slipping displacement of the destroyed dam’s upper block in an earthquake, and when the more precise results are required, some advanced methods, such as the contact method or discrete element method, can be used further.