Study On Nonlinear Seismic Response Of Concrete Dams

Several large concrete dams are going to be build in china, the seismic safety evaluation is a very importment factor. In this paper, several problems about nonlinear analysis of concrete dams are discussed:Adaptive Spectrogram Method of Joint Time-Frequency Analysis is used to study the non-stationary properties of seismic ground motions. The parameters of frequency-dependent modulating function are obtained statistically based on the adaptive spectrogram analysis of seismic records of San Femado earthquake. Both mathematical models of uniform modulation random process and evolutionary random process are used to generate artificial seismic acceleration. The dynamic response analysis of a 300 meters high arch dam subjected to the artificial seismic excitations is studied and compared to predict the effect of non-stationary seismic motion. The calculation results show that the non-stationary frequency property of seismic ground motion has great effects on the dynamic response of nonlinear structure.A strain-driven formalism is adopted, improving the algorithmic efficiency as much as required for the analysis of large scale problems to become feasible. The non-linear seismic response of 300 meters high arch dam is presented using the proposed damage model and the distribution of strain-rate, tensile damage and compressive damage are analyzed and compared. And it is shown that the strain rates caused by seismic loading are different on the dam and have significant effects on the dynamic response of arch damsThe mass-less base model and viscous boundary base model are still the most wildly applied approximate methods for easiness though many approaches have been proposed for the seismic response analysis of soil-structure system. But there are some problems in the application of mass-less base model. In this paper, detailed formula for the soil-structure dynamic interaction analysis is derived, the concept and the application criteria of mass-less base model and viscous boundary base model is clarified and numerical examples are used to testify the correctness.The dynamic response analysis of high arch dam are intensely affected by the computational model, concrete strain-stress relationship and seismic input mechanism. In this paper, the seismic response analysis of a high arch dam is performed, in which the nonlinear concrete material is modeled by strain rate-dependant damage constitutive relationship and the nonlinear contact of joints is simulated by Direct Stiffness method based on the Lagrange Multiplier. The studies show that the nonlinear concrete model has great effects on the dynamic open displacement of contraction joints subjected to intense earthquake because of the nonlinear softening and local damage and cracking. This is very important to the performance of the water-tight in contraction joints. Based on the strain rate-dependant damage constitutive model, the dynamic response and damage characteristics are studied for arch dam model with and without simulating the opening-closing effects of joints. The analysis show that arch dam model without modeling contraction joints can give reasonable dynamic response results based on the nonlinear concrete model.