Probability Evaluation Of Seismic Safety Of Concrete Gravity Dam Under Random Earthquake

Hydropower resources are abundant in southwest and Northwest China,but strong earthquakes occur frequently in this area,so it is difficult to avoid hydropower project site selection.Earthquake loads will cause different degrees of damage to concrete gravity dams.Therefore,it is of great significance to study the seismic safety of concrete gravity dams.The seismic vulnerability and reliability analysis of structures can predict the probability of damage at all levels of the dam-dam foundation system under different levels of loads.It is an important method for structural safety analysis and evaluation.In this paper,the load and structural parameters are double random in the dynamic reliability analysis of the concrete gravity dam;the comprehensive damage index is obtained during the vulnerability analysis,and the comprehensive damage level of the concrete gravity dam is divided.The main research contents are as follows:(1)Applying the theory of random vibration to simulate the vibration input of the concrete gravity dam base and the seismic response of the dam body as a Gaussian stable random process.The random dynamic response of the concrete gravity dam body is obtained through the finite element random seismic dynamic analysis,and the results can better reflect the seismic response characteristics of the structure;based on the JC method,the reliability of the deep anti-sliding stability of an actual concrete gravity dam with double slopes is analyzed and established Random structure dynamic deep anti-sliding stability function function,it can be known that the deep anti-sliding stability of an actual concrete gravity dam with double slopes meets the stability requirements of concrete gravity dam.(2)Select the riverward displacement of the dam crest relative to the dam heel as the response index of seismic perform ance,apply the random vibration theory,determine the limit state function based on the response surface method,and refer to the definition based on the riverward displacement of the dam crest relative to the dam heel.The limit state limit of the structure is obtained by applying the JC method to obtain the reliability probability and failure probability under different damage levels of the structure.Orthogonal test is used to analyze the parameter sensitivity of the uncertain factors in the reliability analysis,and the failure probability of reaching the severe damage level is calculated,and the seismic deformation reliability index during the design base period is obtained.The comparison with the code shows that the dam basically meets the requirements Standard design requirements,the project is biased towards safety.(3)Taking the vertical displacement of the concrete gravity dam crest relative to the heel of the dam,the overall damage index,and the cumulative sliding displacement of the dam base surface as a single response index,nonlinear dynamic time history analysis is used to obtain the comprehensive damage index of the dam according to the efficiency coefficient method.The four-level seismic damage classification standard of the comprehensive damage index and the corresponding performance level are given,and the seismic vulnerability curves of concrete gravity dams based on a single response index and the comprehensive damage index are comparatively studied.The results show that the use of comprehensive damage index for vulnerability assessment can adapt to changes in the intensity of ground motions,comprehensively and objectively estimate the probability of various levels of damage to the dam structure under different earthquake intensities,and then design the seismic safety of concrete gravity dam structures.Earthquake disaster prediction and risk analysis provide reference.