Seismic Risk Analysis Of Concrete Gravity Dams

Focus on sustainable development and the western development strategy, the construction of quite a few high dams are in progress in the southwestern region. In consideration of the importance of the dam aseismic safety for the strong earthquake zone, in-depth research for the seismic fragility and the seismic risk assessment of the concrete dams are conducted in this paper. Based on considering the influence of concrete heterogeneity, the damage process and failure modes of concrete gravity dams are studied with uncertain material properties and ground motion input, according to which different evaluation criteria of the seismic damage levels are generalized and the methods of the seismic fragility analysis and risk evaluation are initially established. As an engineering application, it is applied to study the seismic risk assessment of Jinanqiao gravity dam and Fengman dam. The contents of the paper include the following three aspects:(1) Concrete is inhomogeneous in mesoscopic level, which will have a significant impact on the damage process of the dam. But now it is difficult to simulate the seismic damage process of the dam with micromechanics. Therefore, based on the macro homogeneous assumption, the random distribution of the material properties is introduced to reflect the influence of the mesoscopic inhomogeneity approximately in this paper. As is known that concrete is quasi-brittle, elastic damage constitutive equations together with maximum tensile stress and Mohr-Coulomb Principle are employed to simulate the nonlinearity of concrete. The concrete dam is discretized into approximate dense units so that the possibility of cracking in different parts of the dam is same. On this basis, the seismic damage process of Jinanqiao dam and Fengman dam is further investigated respectively.(2) Seismic fragility analysis can describe the probabilities of structural damage caused by different levels of earthquakes. It is one of three issues (seismic hazard analysis, seismic fragility analysis and seismic loss assessment) of seismic risk analysis. The method of seismic fragility analysis in this paper is based on considering the influence of concrete heterogeneity, uncertain material properties and ground motion input. On this basis, seismic damage index of the dam are generalized and fragility curves of the dam are obtained. Also, the seismic fragility analysis of Jinanqiao dam and Fengman dam is investigated respectively. This research is helpful to optimize seismic design, reinforcement and maintenance measures of the dam, but also provide an effective way for seismic risk assessment. (3)Seismic risk analysis of concrete gravity dam is to discuss the possibility of the dam subjected to a certain level of earthquake in operation period, and the probability of some earthquake disaster and social consequence during the earthquake. In this paper, the probability distribution of ground motion's parameters is got by seismic hazard analysis, and the model of seismic risk assessment is founded associated with seismic damage evaluation criteria and fragility analysis which has given. As an engineering application of the method, the risk probabilities of different seismic damage of Jiananqiao dam and Fengman dam are obtained.