Research On Dynamical System's Reliability For Concrete Gravity Dam

To meet the enormous energy demands, several concrete gravity dams are being constructed in earthquake regions of Southwestern China. The reservoir capacities of these projects reach several billion cubic meters, and most of these projects build in strong earthquake regions. Once the dams are failure, it will bring very serious results. A strong earthquake is therefore a great challenge to dynamic reliability design for concrete gravity dams. Therefore it is necessary to systematic analyze dynamic reliability for concrete gravity dams. For this purpose, by means of synthesizing artificial seismic wave and other loads and setting for artificial boundary condition, finite element method(FEM) based numerical calculations were adopted to make dynamic analysis for the elastic-plastic damage process, failure mode and dynamic reliability of conerete gravity dam. Moreover, it made deeply study on evaluation methods for dam-break risk. The results offer important reference to engineering designers and.anti-seismic design. The major contributions are summarized as follow:(1) Single-point and spatial correlation artificial seismic wave synthesis methods were improved based on genetic algorithm and wavelet theory respectively. Initial single-point artificial seismic wave synthesis was optimized by wavelet theory. The iteration processes were optimized by genetic algorithm for single-point and spatial correlation artificial seismic wave synthesis. The result showed that the deviation between calculational and objective response spectrum was smaller by this paper's method than conventional method.(2)An improved viscous-spring artificial boundary condition was proposed based on conventional transmitting and viscous-spring artificial boundary condition in order to eliminate influence of the lateral displacement on structure-foundation interface. Another artificial boundary condition was proposed based on damping-solvent extraction method in order to make damping-solvent extraction method easily used in finite element method(FEM) based numerical calculations.(3) Infinite element method (IEM) was adopted to simulate the influence of infinite foundation to concrete gravity dam, and then elasto-plastic damage constitutive relations model was adopted to simulate the damage process of dam. Moreover, damage distribution and dynamic response of concrete gravity dam were analyzed. By using Hsieh-Ting-Chen four-parameter yield function that could reflect the different strength characteristics of concrete in tension and compression, a damage constitutive model for concrete was proposed based on the energy dissipation principle. It had the same damage evolution law under tension and compression load and it was good for determining stress-strain constitutive and damage characteristic in complex stress state. (4) A new method was proposed based on perturbation theory and pseudo excitation method in order to make the probability analysis for the damage distribution of concrete gravity dam. The expected value, variance and probability of damage of concrete gravity dam were obtained by numerical calculation, and then astringency of this modal was examined.(5)Based on pseudo-excitation method, the probability characteristics of element stress in failure path were calculated. The conditional failure probability of elements in failure path was obtained by method of dummy variable. Through leading into markoff process theory, failure probability of failure path was obtained. And then calculation method for reliability of series model was adopted to calculate systematic reliability of concrete gravity dam.(6) Singular value decomposition(SVD) and weighted regression methods were adopted to improve response surface method. And a new modal was established to calculate checking point. The number of sample points and iteration times was decreased significantly by using the method above, so this method could be applied to analyze the reliability of large structures such as concrete gravity dam and so on.(7) Aiming at random and fuzzy characteristic of deep sliding surface, probability reasoning theory was adopted to analyze the fuzzy reliability for deep sliding stability of dam foundation.(8) The width of breach was deduced through the anti-slide failure probability of dam head, upstream broken-line sloping surface and foundation surface, and then relationship between volume of dam-break floods and time was calculated. Moreover, the losses of lives and property were obtained. A risk evaluation model was established based on system dynamics and grey theory to evaluate the dam-break losses. By decomposing the related indexes and confirming membership degree with the optimized method, another risk evaluation model was proposed based on fuzzy theory. And then this modal was applied to bijie region to to examine the correctness.