Inverse Estimation Method of Stress-Strain Curve in Non-Homogeneous Concrete Specimen Based on High-speed Sensitivity Calculation by Space-Time Alternating Optimization

Abstract

In direct tensile test of concrete, bending moment and strain gradient occurs due to heterogeneity, which degrades the estimation accuracy of tensile stress-strain curve. This paper creates new estimation method of tensile stress-strain curve under the condition of bending moment and strain gradient. This new method uses data assimilation method and can individually estimate stress-strain curves, which are different by place. In the new method, block universe model is assumed in data assimilation. The block universe model is characterized by four-dimensional space, which consists x-y-z space and time flow. The space and time direction in block universe counterparts to the update of displacement and elastoplastic matrix respectively in FEM analysis. In block universe model, simulation parameters are assimilated in space and time directional alternately like EM algorithm and ADDM. In the space directional assimilation, the sensitivity of elastoplastic matrix’s constant factor is used in sequential data assimilation method. Then, node displacement in specimen is assimilated by using gradient decent method. In the time directional assimilation, simulation parameters of stress-strain-curve are perturbated and the influence of the perturbation to inner variables is predicted. Then, elastoplastic matrix is assimilated. By using this new method, the simulation parameters assimilated to observation data and the stress-strain curves were individually estimated.