The Analyses Of Seismic Response Of High Concrete Dam-Compressible Water-Sediment-Foundation Systems

During an earthquake, the additional hydrodynamic pressures exerted on the face of dams will be produced, the knowledge on which is essential for the anti-seismic design of new dams and the assessment of earthquake safety of existing dams. The analyses of the hydrodynamic pressures and its effects on the dam are a very complex question, that to be solved needs a complete model of seismic response analysis of dam-compressible water-sediment-foundation system. The model involves the dynamic responses of solid medium, two-phase porous elastic medium, fluid medium, and the dynamic interactions among of them. At the same time, the cases of complex media and complex geometrical shapes near dams and the wave propagation out of the semi-infinite foundation should be considered, too. Therefore, an effective numerical method must be provided for the dynamic analyses of this large complex system. FEM-BEM is often believed to be adequate for modeling this question. BEM is usually suitable to analyzing the wave propagation problems in the frequency domain. It seems unable to show its efficiency to the analyses in the time domain, especially to nonlinear problems. The combination method of the explicit finite element method and the transmitting boundary has the advantages in the analyses of large freedom degrees because of its uncoupling characteristic, although it may loss some computing accuracy. It is more important that this method can conveniently deal with the problems with the non-uniform and non-linear cases. In the dissertation, the comprehensive analyses are carried out in the following three aspects. The development of numerical methods and the some referenced conclusions for practical engineering are achieved.1.Studies on the explicit finite element method in the time domainIn the dissertation, the two kinds of calculation formulations of the explicit finite element method for the analyses of dynamic response of solid media with general damping are proposed. Comparing with the existing methods, the one method has advantage in stability; the another has advantage of simple integration formula. The two explicit calculation formulations for analyzing the dynamic response of compressible fluid and two-phase porous elastic medium and for analyzing the dynamic interaction among them are also provided in the same idea. An explicit calculation method in the time domain for the analyses of earthquake responses of structure-compressible water-sediment-foundationsystems is proposed by combining the explicit finite element method with the multi-transmitting artificial boundary for simulating of the energy radiation in the infinite foundation, and the corresponding calculation program are also developed. In this method, the dynamic interactions among structure, compressible water, sediment and foundation are considered strictly and the sediment can be modeled as two-phase poroelastic medium, single-phase solid or single-phase fluid easily. Because it is needless to solve simultaneous equations, the method can reduce computing efforts largely. It is more important that the method can conveniently deal with the non-uniform and non-linear problems, such as the joints in the dam body, the uneven conformations in the foundation, etc.2. Analyses of seismic response of gravity damsAn explicit calculation method in the time domain for analyzing the seismic responses of gravity dam-compressible water-sediment-foundation systems is proposed by combining the explicit finite element method with the multi-transmitting artificial boundary. By using this method, the effects of compressible water and sediment on the dynamic pressure responses exerting on dam face and the seismic responses of dams are studied in the three cases of rigid dam-rigid foundation, flexible dam-rigid foundation and flexible dam-flexible foundation. To verify the validity of the numerical method, a model experimental is carried out on a shaking table. The following conclusions regarding the effects of compressible water, sediment, flexible foundation on...