Study On The Mechanism Of Strong Earthquake Failure Of Concrete Gravity Dams Considering Material Tensile And Compression Damage

Considering that the seismic safety of high dams is the most important problem in dam design,and the dynamic response of concrete gravity dams under strong earthquakes is affected by many factors,which is necessary to consider comprehensively in order to make the numerical analysis of seismic response closer to the real working behavior of concrete dams.Based on the existing seismic response analysis system of concrete gravity dam-reservoir-foundation systems,this paper focuses on the study of the influence of tensile and compressive damage on the strong earthquake response and failure process of the dam considering the key factors including infinite foundation radiation damping effect,uneven ground motion input of dam-foundation and dam-reservoir hydrodynamic interaction under seismic action.This paper analyzes and compares the differences in failure process,failure mechanism and the impact on the evaluation of the ultimate seismic capacity of the dam when the elastic-plastic damage model and the contact model with initial strength are used to simulate the seismic damage model of the slope part of the gravity dam head,which provides support for the demonstration of the next development direction of the dam-foundation system seismic response analysis system,the main research contents and conclusions are as follows:(1)The explicit integration algorithm in time domain for wave equation of concrete dam,visco-elastic artificial boundary for simulating radiation damping effect of infinite foundation,equivalent earthquake load for simulating earthquake input,Westergaard additional mass method for simulating dynamic water pressure,tensile damage constitutive model and dynamic contact force model of dam concrete in this study are described case study.(2)For concrete gravity dam,the non-linear analysis of material damage is carried out,and the concrete plastic damage model is adopted.According to the situation that the original dam damage analysis only considers the concrete tensile damage,the concrete tensile and compression cycle damage constitutive model is given,and the numerical analysis of the strong earthquake response of the gravity dam considering the concrete tensile and compression damage is carried out,with the emphasis on the dam concrete under the earthquake action The damage evolution process and damage development characteristics of compression damage,and through the analysis of the damage development process under different earthquake overload conditions,to analyze and compare the influence of concrete constitutive model considering only tensile damage and simultaneously tensile and compression damage on the evaluation of ultimate seismic capacity of concrete gravity dam.According to the calculation and analysis,under the condition of multi axial stress,the tensile and compressive damage may occur in the same place.Because the compressive constitutive relation of concrete shows the characteristics of ductile material with strengthening property,and the equivalent effect variation value corresponding to the ultimate stress is large,the development of the compressive damage is slow in the degree and scope,so the strong earthquake damage pole of the gravity dam based on the criterion of head damage penetration is very slow,the limit state is mainly controlled by tensile damage.At the same time,there is no significant difference between the ultimate seismic capacity and the overall response considering tensile and compression damage and only tensile damage.(3)The failure process,failure mechanism and the change of displacement difference at the upstream and downstream nodes before and after transfixion of the concrete gravity dam with plastic damage model and dynamic contact force model are discussed respectively.Based on the constitutive relation,the difference of damage evolution process between the two models and its influence on the evaluation of ultimate seismic capacity are analyzed.The results show that the failure of the damage model is related to whether the maximum principal stress exceeds the tensile strength,and the direction of damage propagation is not limited,while the fracture surface of the contact model is mainly judged by the normal force and the tangential force,so the fracture of the damage model is earlier than that of the contact model,but the damage model enters into the softening section after the damage,rather than the immediate loss of bearing capacity.In addition,the damage element near the penetration part of the dam head will also consume part of energy,so the cracking process of the damage model is slower than that of the contact model.If based on the crack penetration of the dam head,the ultimate seismic capacity given by the contact model is slightly lower.Therefore,it is suggested that the contact model can be used for the RCC dam with a clear level of the head,but not for the RCC dam without a clear level of the head.In the case of layer,it is suggested to use the damage model when the calculation scale,time and other conditions allow.