Seismic Fragility Analysis And Safety Risk Assessment Of High Arch Dams

With the development of hydroelectric energy,the number of high concrete dams over 200-m height is increasing in Southwest China.High seismic intensity is one of the significant problems that influence the safety of high concrete dams.If the high concrete dams suffer earthquake damage,the consequences are catastrophic.Therefore,the seismic safety of high concrete dams is a widely-concerned issue.Based on these backgrounds,this thesis focuses on the seismic safety evaluationof high concrete dams,and the main contents are concluded as follows.1.A seismic fragility analysis model of Dagangshan arch dam is established,which takes into account the radiation damping of foundation,the opening of contraction joints,and the nonlinear damage of dam concrete.The dam elastic modulus,tensile strength of concrete,damping ratio,and foundation elastic modulus are chosen as the uncertainty analysis parameter,and 5 sample parameter combinations are obtained through Latin hypercube(LHC)sampling.8 actual seismic ground motion records are chosen as seismic input,and the seismic records are scaled to 0.1g-1.0g.Based on the existed criteria for the classification of damage state,three seismic damage levels,slight damage,moderate damage,and severe damage,are proposed.The volumetric yield ratio and the maximum relative dynamic displacements that trend to dowmstream and upstream are counted and analyzed.2.The direct fitting method and probability distribution method are used to drawn the seismic fragility curves of Dagangshan arch dam.According to the curves obtained by the two methods,it is obvious that the probability of severe damage is zero in the design earthquake,and less than 7% in the check earthquake.In addition,the fragility probability of joint opening exceeds 50 mm is analyzed and compared with that corresponding to severe damage level.The results show that the joint opening exceeds 50 mm should be considered in parallel with the severe damage.3.Based on the existing assessment methods,the method for seismic safety risk assessment of high concrete dams is proposed,which consists of seismic hazard analysis,seismic fragility analysis,and earthquake losses analysis.The analysis methods of the loss of life,social and environmental impacts,and economic loss are detailly analyzed according to damage levels.Based on the results of seismic hazard and fragility analysis,the earthquake losses and the risk levels are evaluated by F-N curves.Finally,the integrated risk level of high concrete dams is divided into low risk,moderate risk,high risk,and extreme risk according to the risk levels of losses.