Geometric criterion of bearing capacity loss of steel-reinforced concrete rods

The article presents a mathematical model of the deformation process of short steel-concrete rods and a geometric criterion for the loss of bearing capacity. It studies the behavior of steel-concrete elements under the action of a short-term compressive load using laboratory samples made from steel pipes with a concrete core. The article presents the diagrams of longitudinal deformation based on experimental data, as well as an engineering model that makes it possible to obtain the P - ∆ dependence for tubular concrete elements by scaling a known diagram for a steel pipe. It also estimates the contribution of a concrete core to the operation of a composite section. The article proposes a piecewise monotonically increasing function that analytically describes the deformation of composite rods. It presents a geometric criterion for the loss of bearing capacity with a monotonously increasing deformation curve, which makes it possible to uniquely determine the critical value of the longitudinal force. The result of the research can be incorporated into the algorithm of operation of software and computing complexes used in the automated calculation and design of structures and structural systems.