Avaliação de modelos reológicos para concreto submetido a reação álcali-agregado baseada em análise numérica de amortecimento

Abstract

Structural parameters can be elucidative as to the effects of the Alkali-Aggregate Reaction (AAR) in concrete, being the elastic and viscous components of this material, under such pathology, obtained by analysis of the vibrational spectrum at the resonant frequency of longitudinal dynamic stresses. The parameters found in the resonance tested concrete beams are: damping, loss factor and modulus of elasticity. These parameters come from the data analysis of the tests in the frequency domain (amplitude vs. frequency), where equivalence between viscous damping and hysteresis is employed. In obtaining the loss fator and damping is used for curve fitting the least squares method, with error minimization between the experimental curve data and those of the theoretical resonance curve in the frequency spectrum. The resonant frequency used in the analyzes is identified by comparing the theoretical natural frequency with the frequencies obtained in the tests, and the behavioral adherence of the frequency response function of the tests with the theoretical is fundamental. Among the parameters derived from the resonance analysis, damping is a key point in a numerical approach suggested to evaluate rheological models, to be adopted in the prediction of the effects of AAR on concrete over time, where damping is frequency dependent in the consideration of the global damping matrix, defined as a linear combination of global mass and stiffness matrices (Rayleigh damping), thus it is possible to determine values for mechanical parameters of elements such as spring and damper, which can be associated in various ways in the composition of rheological models, making it possible to predict nondestructively the evolution and behavior of global parameters and fractions of the concrete.