عنوان مقاله [English]
Generally Rayleigh damping assumes a specified damping ratio for the structure during the dynamic analysis. Although this assumption is accepted in analysis and design of structures, there is some distance from the experimental results showing that the damping ratio depends on the stress amplitude. In this paper, the damping ratio for each element is a function of its principal stress and its value is determined utilizing a proposed algorithm named as element developed energy dissipation algorithm (EDEDA). The proposed algorithm is implemented into a finite element-based code, which is able to simulate nonlinear behavior of mass concrete utilizing the smeared crack approach. In this regard, due to stress redistribution during the nonlinear time history analysis, we have a new concept, which is the damping ratio redistribution so that when the stress value in each element is changed, the relevant damping value is updated. Analyzing a typical concrete gravity dam (Pine Flat dam), two usual methods in Rayleigh damping approach which are stiffness proportional damping and mass/stiffness proportional damping are considered rigorously. In addition, the brittle damping approach is utilized in the proposed algorithm, where the damping contribution of a cracked element is eliminated from the computing procedure. It is found that when the damping redistribution is taken into account, the damping ratio in each element is updated at each time step corresponding to the principal stress. This algorithm leads to more real results in the considered gravity dam so that during low level of seismic excitation, the response of the structure is less in comparison with the traditional method and raising the excitation level lead to higher damping affecting the crest displacement. In addition, the stiffness proportional damping leads to crack profiles in the neck region of the dam body showing more correspondence in comparison with the results obtained from the models with mass/stiffness proportional damping.