Beton ve betonarme elemanların büzüşme mekanizmasının deneysel ve sayısal olarak incelenmesi

Concrete shrinkage is a long-term process causing a reduction in the volume of a concrete member. In the majority of the concrete models, shrinkage is considered as a uniform unrestrained shortening through the longest dimension, but in reality, due to the existence of aggregates and reinforcing bars, which restrains the shrinkage deformations, a non-homogeneous strain distribution occurs within the member. In order to measure such non-homogeneous deformations on an entire surface, digital image correlation (DIC) method is a good candidate. In the conventional DIC method, high-speed video cameras are utilized, but their measurement sensitivity may not be sufficient to detect shrinkage induced deformations in the order of m. Thus, a novel DIC based measurement method for measuring drying shrinkage deformation on concrete surfaces is proposed that utilizes high-resolution images acquired by DSLR cameras. The validity of the proposed method is first tested on three different experimental studies. Then, shrinkage deformations of several concrete beams with and without reinforcement under free and restrained boundary conditions are measured with the proposed method for two months at a new experimental set-up designed for such experiments. This way, non-homogeneous strain distribution on the entire surface due to aggregates and reinforcing bars are obtained. In order to numerically mimic the shrinkage behavior of plain and reinforced concrete members, a new mesoscale modeling and calibration approach is also developed that is based on overlapping lattice method. The validity of this new approach is tested by comparing the numerical results with the DIC measurements of the shrinkage experiments. Numerical results demonstrate that the proposed numerical approach has the capability of modeling shrinkage deformations of plain and reinforced concrete members.