Reinforced concrete structures (RCS) operating under the natural conditions of the Far North are subjected to alternating freezing and thawing. The impact of freezing–thawing cycles (FTC) leads to the degradation not only of the strength but also of the deformation properties (DP) of concrete. In the current design standards for RCS, the DP of concrete and reinforcement are specified as average statistical values. This study investigates the influence of the variability of concrete’s deformation properties on the reliability of the load-bearing capacity of flexural reinforced concrete elements before and after exposure to FTC. It was shown that considering the variability of concrete’s deformation characteristics at reinforcement ratios up to 1% under alternating temperature conditions has practically no effect on the load-bearing capacity, while at reinforcement ratios close to the limiting values it leads to its reduction. In addition, recommendations were provided for the design of flexural reinforced concrete elements under alternating temperature conditions.

Keywords: freeze-thaw cycle, statistical regularities of resistance, flexure, reinforced concrete, ultimate deformation of concrete, assurance

In the current regulatory documents on the design of reinforced concrete structures, a number of conditional assumptions and limitations are adopted, taking into account the specific nature of the resistance of structural elements and simplifying the calculation. One of these assumptions is the assignment of the deformation properties of concrete as average statistical values, which, along with strength characteristics, determine the stress–strain diagrams of the material.
The influence of concrete freezing–thawing cycles (FTC) leads to the degradation of its deformation and strength properties. The failure mode of a flexural reinforced concrete element (plastic or brittle) depends on the strength and deformation characteristics of the concrete and reinforcement, as well as on the reinforcement ratio.
This study examines the statistical patterns of the ultimate reinforcement ratio and the limiting relative height of the compressed concrete zone under alternating freezing–thawing conditions. The analysis of the statistical regularities of the parameters used and their functional relationships confirms their significant variability and, as a consequence, the possible fluctuations (reduction) of the design reliability level of flexural reinforced concrete structures.
Modeling the variability of the strength of flexural reinforced concrete elements under FTC using statistically representative data on the kinetics of the physical and structural parameters of concrete confirms a sharp decrease in reliability and indicates the need for additional targeted research in this field.

Keywords: freezing–thawing cycles, statistical patterns of resistance, reinforced concrete, ultimate concrete strains, reliability of the limiting relative height of the compressed concrete zone, reliability of the ultimate reinforcement ratio