Research On Key Issues Of Performance-based Seismic Design Of High Dams

Performance-based seismic design for high concrete dam has been started in the domestic. Some of the key issues in this field such as calculating parameters, analysis methods and evaluation methods are studied in order to improve the framework of PBSD. The study includes:1. A method based on Hilbert-Huang transform (HHT) is introduced in the parameter identification of a model arch dam. To overcome the mode mixing, band-pass filters are applied to the original acceleration data first and the results are used for further analysis. Investigation to the process of damage demonstrates that character frequency decreases with the development of damage, but the corresponding damping ratio increases.2. On the basis of gathering field test data of concrete arch dam at home and abroad, the regularities and influential factors of characteristic frequency and damping ratio are summarized.3. The modal parameters such as frequency, modal shape and damping ratio of Ertan arch dam are obtained through identification of the dam response under five different seismic excitations. The FEM model of Ertan arch dam is developed considering the accordance of frequency identified and computed.4. Reference to the damping ratio values got from field test, strong motion analysis and shaking table test, it is proposed the time-history analysis of concrete arch dam should employ a damping equivalent to a 3-5 percent viscous damping ratio at linear elastic analysis. However, in situation where a moderate level of nonlinear behavior such as joint opening and cracking is predicted by a linear analysis, a higher damping ratio of 7-10 percent could be used to account somewhat for the energy loss due to nonlinear behavior.5. A procedure to account the uncertainty of seismic response assessment due to the uncertainty in the characteristics of ground motions is presented. The mean annual probability of exceedance of gravity dam is calculated from a series of deterministic response analysis with three loading intensity level. At the end, the effects of various simplifying assumptions made in SAC/FEMA procedure are evaluated and discussed. It is concluded that more attention should be paied on the assumption about variation of dispersion.6. The basic framework of seismic safety evaluation of concrete dam is proposed. The framework contains the whole process of response spectrum analysis, linear elastic time-history analysis, nonlinear time-history analysis and the post-earthquake stability analysis. As an engineering application, the seismic safety evaluation of Jin'anqiao RCC gravity dam at OBE, MDE and MCE is assessed based on the framework.