In designing for repairing or managing maintenance for RC structures with damage due to shrinkage, there is a need for a powerful analytical system to evaluate the mechanical behaviors of RC structures under arbitrary circumstances. The purpose of this research is to propose and then to verify the applicability of an analytical method, which aims to predict the stiffness of RC members with damage due to shrinkage. This analysis is made possible by considering the damage condition in terms of moisture transport and change in volume. The proposed method couples analytical model of micro-scale material level with the one of structural level. Computational code named DuCOM itself is an integrated analytical model which calculates time-dependent properties of concrete, such as free shrinkage strain, strength, moisture profile and phase balance with the inputs of the concrete’s constitutive materials properties and the ambient conditions. The 2D code named WCOMD calculates the mechanical responses of RC structures under loading by using constitutive laws, i.e., interaction of multi-directional cracking, stress-transferring mechanism, bond of reinforced concrete. By inputting the thermo-hydro analytical result of shrinkage strain into the structural analysis, it becomes possible to consider the damage of RC members together with its other mechanical parameters in the structural analysis.
The applicability of the proposed model as stated above was verified by comparing analytical results with experimental ones in multiple views. There are two stages in the analysis, the first one is at material level, using DuCOM to calculate the free shrinkage strain of the concrete, and the second stage is at structural level, using WCOMD to predict the stiffness of the RC specimens. Therefore, experiments at both levels were conducted. In the experiment verifying the reliability of shrinkage strain results, experimental data showed good agreement with analytical results by DuCOM. In the experiments for verifying stiffness prediction, RC beams used for the loading test were cured and later exposed to drying conditions in order to induce cracks by shrinkage. After that, loading test and tensile loading test were conducted to investigate the effect of drying shrinkage on the mechanical responses of the RC beams. According to experimental results of loading test, the stiffness in pre-yielding zone until the yielding point is found to be lower than the case where shrinkage strain is no longer considered. This degradation in stiffness was also well predicted by the proposed analytical model.
The proposed model was examined through systematically arranged cases of damaged RC behaviors, and practically successful results were earned. In conclusion, by considering damage conditions in terms of moisture transport and change in volume, the proposed model was proved to be able to give reliable analytical prediction of the stiffness of RC members with damage due to shrinkage.