Analysis of the early age behavior for concrete structure with enhanced microplane model

Abstract

In this dissertation, experimental tests and numerical analyses were performed to investigate the early age behavior of concrete structures. Relating to the material properties of early age concrete, experiments for autogenous shrinkage, basic creep, and tensile stress-strain relations, which are important influencing factors on early age behavior, were carried out. The experimental results show that autogenous shrinkage is not nonlinearly dependent on applied stress and stress-free autogenous shrinkage should be separated from the basic creep test results to obtain the basic creep model for prediction of concrete creep deformation in numerical stress analysis, for example, thermal stress analysis and crack control problems. Furthermore, from the tensile cracking propagation test for early age concrete, tensile stress-strain relations for early age concrete were obtained and corresponding fracture characteristics such as $CTOD_c$ and $K_k$ were obtained. In relation to the material model of concrete, microplane model was adopted in this study. To improve the existing microplane model to describe the early age behavior, nonlinear regression analyses were performed with tensile and compressive test results for early age concrete. Material parameters in enhanced microplane model are analyzed based on the degree of hydration concept, and an age-dependent microplane model is developed. Analysis results show that existing microplane model M4 is not suitable for early age compressive behavior and to resolve that problem, an additional nonlinear function should be multiplied by the existing negative deviatoric boundary of M4. In addition, a parameter E in compression develops in linear fashion with the degree of hydration as the concrete age increases and a parameter E in tension develops faster than that in compression. The evolution of E in the developed microplane model follows the trend of strength development with increasing age. In relation to tensile behavior of...