Analytical model of deformation of reinforced concrete columns based on fracture mechanics

When conducting seismic calculations of reinforced concrete buildings and structures, it is quite important to use nonlinear models of structural performance, including those taking into account the overcritical operation in the fracture stage. The application of such models is especially important if the structures have an initial damage from fire or corrosion, as well as mechanical damage caused by force factors. The purpose of this study is to develop an analytical model of the deformation of eccentrically compressed reinforced concrete columns considering the stage of failure, which includes such processes as spelling of the protective layer, loss of stability of compressed reinforcement, and softening of confined concrete after reaching the design resistance. The existing models describing hysteresis behavior of reinforced concrete structures under low-cycle loading have been reviewed. The models have been analyzed in terms of considering the defining monotone curves, which are the boundaries of cyclic deformation. The model proposed in the research is constructed by analyzing the stages of the stress-strain state of a reinforced concrete column. At each stage, formulas are found for determining moment and curvature by solving equations of equilibrium of internal forces. Calculations based on the obtained model for a particular reinforced concrete column are carried out, monotonous diagrams are obtained, and a conclusion about the significant influence of the level of axial load on the character of deformation is made. On the basis of the obtained model, the construction of hysteresis diagrams under low-cycle loading is expected in the future.