Determination of the design principles of high performance reinforced concrete members by analytical and experimental approach

In this study, a new method has been proposed for the capacity calculation of single reinforced concrete beams under bending load. Unlike the existing models, the proposed method was developed using fracture mechanics principles. First, the shape functions frequently used in fracture mechanics were simplified numerically and three design coefficients varying depending on the normalized crack length were formulated. Then, depending on the dimensionless behavior parameters, an empirical equation giving a normalized crack size was experimentally obtained. For this purpose, the effect of three different concrete strengths, three different tensile reinforcement ratios and three different steel fiber contents on the behavior of 27 reinforced concrete beams was investigated experimentally. It has been observed that the parameters examined have a direct effect on the critical crack length of the beams and in this way affect their bending capacities. Using the experimental capacities of a total of 68 single reinforced concrete beams compiled from various studies in the literature, a comparison was made between the proposed method and the frequently used ACI bearing strength method. The absolute errors obtained with the proposed method and the ACI model were found to be %8,7 and %9,5, respectively. The theoretical result obtained with the proposed method of a total of 49 reinforced concrete beams came closer to the experimental result. Two-dimensional finite element analysis of the tested experimental elements was made and compared with the experimental results. For this reason, the finite element program (LDA) was developed within the scope of the thesis study. The finite element model, developed with the acceptance of plane stress and isotropic continuous damage models, calculates a set of linear equations in each analysis step by using the secant slope starting from the origin of the material model. In this way, frequently encountered convergence problems were eliminated with this program. A significant similarity was observed between the experimentally obtained load-vertical deformation behavior and the behavior obtained with the developed finite element program.