A RATE-DEPENDENT ISOTROPIC DAMAGE MODEL FOR THE SEISMIC ANALYSIS OF CONCRETE DAMS

In this paper a rate-dependent isotropic damage model developed for th e numerical analysis of concrete darns subjected to seismic excitation is presented. The model is shown to incorporate two features essentia l for seismic analysis: stiffness degradation and stiffness recovery u pon load reversals and strain-rate sensitivity. The issue of mesh obje ctivity is addressed using the concept of the 'characteristic length' of the fracture zone, to show that both the softening modulus and the fluidity parameter must depend on it to provide consistent results as the computational mesh is refined. Some aspects of the numerical imple mentation of the model are also treated, to show that the model can be easily incorporated in any standard non-linear finite element code. T he application of the proposed model to the seismic analysis of a larg e gravity concrete dam shows that the structural response may vary sig nificantly in terms of the development of damage. The inclusion of rat e sensitivity is able to reproduce the experimental observation that t he tensile peak strength of concrete can be increased up to 50 percent for the range of strain rates that appear in a structural safety anal ysis of a dam subjected to severe seismic actions.