Nonlinear Earthquake Response Analysis Of Concrete Gravity Dam Based On Damage Mechanics

In order to evaluate the seismic performance, study the failure mechanism and modes for concrete dam, it is necessary to use the concrete constitutive model Which is able to model the nonlinear characteristics of strength and deformation of concrete. The plastic damage constitutive model based on damage theory can simulate the whole destruction process from the initiation and propagation of smeared cracks to final failure. In this paper, based on the plastic-damage model proposed by Lee and Fenves and related algorithms, we developed the code to simulate the damage process of concrete gravity dams subjected to static and cyclic earthquake excitation. Meantime, we try to solve the numerical problems, such as divergence of algorithm, excess of plastic tensile strain, spurious mesh dependence result from strain soften. The detail content was summarized as follows:(1) In order to deal with the problems in case of large damage, such as excessive increase in plastic strain, not properly simulating the phenomenon of stiffness degradation and recovery during a large crack opening, closing and reopening process and divergence of algorithm, according to the previous studies, a critical tensile plastic-damage variable was defined to correct stiffness degradation variable and prevent excessive, so that the propagation of damage zones gradually can be traced accurately.(2) For the strain softening phenomena in the constitutive model, a viscoplastic regularized technique was used to transfer this plastic damage model into the rate-dependent viscoplastic damage one so as to reduce mesh dependence of numerical results. Finally, the damage process of a concrete specimen and Koyna gravity dam subjected to static and dynamic loading was analysed by numerical algorithm based on this plastic damage model.(3) Verify the rationality of the model and validity of codes by some numerical examples. For concrete specimen, the damage evolution process under different loading was simulated respectively, such as uniaxial tension and compression, biaxial tension and compression, cyclic tension and compression and so on. The nonlinear analysis for damage process of Koyna gravity dam subjected to earthquake excitation was carried out by considering the damping matrix obtained and rate dependent viscoplastic damage model. The HHT-a algorithm was applied to the time discretization of dynamic equilibrium equation.Comparing with experimental data, numerical results had shown that the plastic model had a good performance to simulate the different stress-strain relationships between tension and compression of concrete material under uniaxial loading, the degradation effects of damage on elastic stiffness and strength, the recovery of stiffness after cracks close and improvement of compressive strength under biaxial compression. The numerical results had proven the capability of this plastic damage model in concrete structure nonlinear response analysis, it can be used to provide technical support for concrete dam design, reinforce and safety evaluation.