DYNAMIC DAMAGE OF CONCRETE GRAVITY DAMS UNDER EARTHQUAKE EXCITATION

A new plastic-damage constitutive model for cyclic loading of concrete has been developed for the seismic analysis of concrete dams based on plastic-damage theory. Damage variable is used as an internal variable, which is included in the Drucker-Prager yield function. Stiffness degradation induced by material damage is considered in the model. The plastic strain rate is obtained according to the nonassociative flow rule. Damage evolution is determined by effective plastic strain. The crack opening/closing behavior is modeled as elastic stiffness recovery during elastic unloading from a tensile state to a compressive state. The main steps of the algorithm for the internal variable and nonlinear dynamic equation are presented in the paper. The plastic-damage model is used to evaluate the response of Koyna dam, and maximum damage distributions at different time are given in the analysis. The analysis shows that there occur two localized large tensile damages, one is at the change of downstream slope, and the other is at upper region of the bottom. Crack failure is formed from the downstream at the change of slope to upper of the dam at last. The evolution of damage is consistent with the observed cracking in the dam.