Justification of the technical condition boundaries of structures based on the limit state method

Abstract

This article examines the theoretical prerequisites for establishing quantitative limits for the technical condition of reinforced concrete structures (limited serviceability and emergency), expressed as fractions of the design bearing capacity. It is noted that current regulatory documents, including GOST 31937, lack direct recommendations on the permissible reduction in bearing capacity due to defects. The results of a summary of experimental data are presented, confirming the presence of a safety margin of up to 30% and a deformability margin of up to 50%, provided that regulatory design requirements are met. An analytical justification for the technical condition limits is provided based on a comparison of the calculated bending moment according to SP 63.13330 and the ultimate actual moment achieved with full realization of the curvilinear stress diagram in the compressed zone of concrete. A ratio in the range of 0.7–0.77 was obtained for a rectangular diagram and 0.55–0.77 for a triangular diagram. An analysis is provided of the reserves incorporated in the reliability factors for materials, operating conditions, and responsibility, as well as the performance characteristics of bending reinforced concrete elements in the ultimate limit state. Practical limit values were proposed: 0.9 for a limited serviceability condition (a 10% reduction in bearing capacity from the design value); and 0.75 for an emergency condition (a 25% reduction), which is consistent with the analysis of experimental and theoretical data.