Theoretical substantiation of some issues arising in the calculation of compressed reinforced concrete building structures

The problem hidden inside the calculation of compressed reinforced concrete columns in accordance with the requirements of SP 63.13330.2018 “SNiP 52-01–2003 Concrete and reinforced concrete structures. The main provisions” regarding the calculation of the conditional critical force. Despite the fact that concrete, which is part of reinforced concrete, is an elastic–viscoplastic building material, which has physical nonlinearity and nonlinear creep even at low loading levels (from about 20% of the prismatic strength of concrete), the calculation of compressed columns is based on postulates and formulas applicable to absolutely elastic rods that are loaded they work according to Hooke’s law.It is revealed that the conditional critical force used for reinforced concrete columns is the critical Eulerian force, designed to calculate rods made of absolutely elastic material for stability during longitudinal bending, as evidenced by solving the problem of stability of an elastic rod pivotally supported at the ends, loaded with a longitudinal compressive force.This solution is the basis for the calculation of reinforced concrete columns for stability. Formulas are derived by which, when calculating columns according to an undeformed scheme, the effect of deflection on their bearing capacity is taken into account.It is shown how the eccentricity of the longitudinal force applied to the column is taken into account, and the assumptions that apply in this case are given. It was revealed that when determining the conditional critical force according to SP 63.13330.2018, the stress–strain diagram normalized by SP 159.1325800.2014 “Reinforced concrete superstructures of highway bridges. Calculation rules”, is not taken into account. These provisions confirm the need for further investigation of the identified problem.