Analysis And Early Warning Study Of Arch Dam Crack Based On Extended Finite Element

For large-volume concrete structures such as arch dams and gravity dams,cracks are one of the main structural diseases and will affect the safe operation of structures to varying degrees.Analysis of crack evolution law,evaluation of crack stability and monitoring of crack operation state are one of the main problems to be solved in the operation management of modern large-scale water conservancy and hydropower projects.The traditional finite element crack propagation analysis is subject to the influence of the grid and there are many difficulties.The extended finite element method(XFEM)introduces the reinforcement function on the basis of the traditional finite element,which can simulate the deformation discontinuity problem when the grid is unchanged.Therefore,it has a great advantage in crack propagation analysis.In this paper,the extended finite element method is systematically studied,and the numerical model of gravity arch dam crack is established by using ABAQUS software.The influence of crack propagation on the dam’s self-weight,hydrostatic pressure,temperature load and other unfavorable load combinations and its variation law are investigated.The analysis results are combined with the crack monitoring data to establish a hybrid monitoring model for crack deformation of arch dams.Based on the small probability method,the critical value of crack opening is determined to judge and predict the crack propagation.The main research contents of the thesis include:(1)The basic principles of fracture mechanics and extended finite element method are studied.Abaqus software is used to analyze two kinds of three-dimensional initial crack plates.The numerical results of stress intensity factors are compared with analytical solutions.The results show that the error between the two is small,and the crack propagation stress changes accord with the relevant fracture theory,which proves the effectiveness of the extended finite element method for solving the crack problem.(2)Establishing the extended finite element calculation model of concrete gravity arch dam with vertical cracks,and studying the crack propagation law of arch dam under various unfavorable load combinations.The results show that the crack will expand when the temperature drops,and then stabilize.It can be seen that the temperature drop is the main reason leading to the expansion of cracks;when the cracks in the arch crown beam of the dam body expand,the stress concentration phenomenon occurs in the crack tip part,and the tensile stress value suddenly drops and rises when the crack expands,which changes the big The internal stress distribution of the dam has a great influence on the overall force of the dam.(3)Based on the statistical model,the water pressure and temperature components are simulated by the extended finite element method,and the hybrid monitoring model of crack opening is established.Based on the small probability method,the annual maximum value of crack opening is statistically analyzed and obtained.The critical opening degree under the confidence degree α;the three-level early warning interval of crack propagation is divided by the confidence interval method,and the crack hybrid monitoring model and the critical opening value are combined to provide early warning of crack propagation to ensure dam safety.