Investigation of the stress-strain state of a section by a numerical experiment

For approbation of theoretical positions, in the matrix of external rigidity, calculation of elements through unit displacements to determine the stress-strain state of the section of a reinforced concrete element with pure bending in the stage before cracking, taking into account the effect of unloading the middle zone, due to different deformation of concrete during tension and compression, numerical experiment with the aim of: checking the possibility of revealing the internal static indeterminacy of the stress-strain state of the section; determination of the deformed state of the section as a whole and its middle zone and the distribution of normal stresses along the height of the section at various levels of exposure to the bending moment. When performing the experiment, the qualitative and quantitative trajectories of the centers of the instantaneous rotation of the section were solved; deformation of the center of gravity of the compressed and stretched faces of the section; distribution of stresses in the section and its middle zone, where the fibers are first compressed, and then partially or completely unloaded with the transition to tension; changes in the position of the centers of the general rotation; the position of the neutral axis in terms of stresses during loading; the value of the bending moment during cracking and the impact on these factors of the class of concrete and the class of reinforcement. The numerical experiment was carried out for a reinforced concrete element of a rectangular section with a single reinforcement. The results of the experiment confirmed the theoretical developments that allow revealing the internal static indeterminacy of the section and determining the stress-strain state of the section, taking into account the zones, due to the different elastic-plastic deformability of the effect of unloading in compression and tension.