Analysis And Evaluation Of Structural Safety Of Concrete Arch Dams With Cracks

As a form of highly indeterminate structure,arch dam can withstand large loads due to their special shape and mechanical characteristics.However,owing to various factors during operation,the dam body inevitably produces cracks.Although the cracked portion can change the stress distribution area within the arch dam body through stress redistribution,it still has a certain impact on the overall structural safety of the arch dam.In this case,it is very necessary to study the structural safety risk assessment of arch dams with cracks in order to grasp their safety patterns and provide some help and reference for decision makers.This paper takes a gravity arch dam as the research object and conducts research on the material parameter variation and safety risk level evaluation of arch dam with crack.The research content and conclusion obtained of this article is as follows:(1)Based on the statistics of the literature on the foundation size of the model and the comparison of the statistical results,the initial assumption for the foundation size of the finite element model is determined.The bedrock is considered as a homogeneous and isotropic elastic material,and the dam body is selected as an elastic-plastic constitutive model which is based on the D-P yield criterion.The foundation size of the finite element model is determined by numerical simulation as having a thickness of 3H,a width of 2.5H for the left and right banks,an upstream length of 3.5H,and a downstream length of 4H.The dam body grid adopts hexahedron elements,and the dam crest is divided into four layers of grid along the arch thickness direction.As the elevation gradually decreases,the number of grid layers gradually increases,until it reaches the 12 layers of grid at the dam bottom.The grid size along the arch beam direction basically matches the size in the arch thickness direction,and the number of grid layers is 36.Subsequently,the rationality of the finite element model was verified by applying water load to the model,and comparing finite element calculations with monitoring data.(2)The concrete crack simulation model is studied,and the cohesive element in the cohesive force model is determined to simulate the crack which is based on the engineering practice as well as the advantages and disadvantages of each model.Based on the depth of horizontal crack at 105m elevation on the downstream surface of an arch dam,the influence on stress,displacement,and natural vibration of the dam is studied.This horizontal crack has an impact on the displacement along the river above the elevation of 105m,as well as on the stress near the crack.During the continuous penetration of horizontal crack through the dam body,both the displacement along the river and the third principal stress increase,and the natural vibration frequency of the dam body tends to decrease,with little impact on the vibration mode of the dam body.(3)Based on the zonal model of the dam with cracks,the variable material parameters were selected,at the same time,the influence of the material parameters variation on the dam body was studied for the crack elements and various areas of the dam concrete.The influence of concrete and crack material parameter variations on the dam body was studied using a MIV-BP neural network model based on the sparrow optimization algorithm.For the vicinity of cracks,the presence of cracks can cause an increase in stress and displacement in that area,so the elastic modulus and tensile strength of the crack area need to be given special attention.At the same time,the elastic modulus and Poisson’s ratio in the middle and lower parts of the dam body require special attention due to their large MIV values.For the non crack periphery,the elastic modulus and Poisson’s ratio of the entire dam body,the elastic modulus and tensile strength of the crack location,and the cohesion outside the dam crest area d ue to its high MIV value need to be paid attention to.(4)Based on the overload method,the overload safety of seamless arch dams and arch dam with downstream 105m elevation horizontal crack has been determined to be between 5.1 and 5.4.The existence of cracks only has a significant impact on the surrounding areas,and has a relatively small impact on non crack surrounding areas.The safety degree of overload to a certain extent reflects the safety and stability of the entire dam body.The impact of cracks on the entire dam body is reflected in the relatively small degree of overload safety.In this paper,various theoretical methods such as Latin hypercube sampling,MIV-BP neural network model based on sparrow optimization are comprehensively used to establish a finite element calculation model,determine the form of crack simulation,and study the impact of material parameter variations of crack elements and dam elements on the dam body based on the zoning of arch dams with cracks,Finally,safety evaluation will be conducted on the seamless arch dam and the jointed arch dam in order to provide certain reference and technical support for the follow-up monitoring of the arch dam.