Probabilistic Time-Variant Flexural Capacity Model and Flexural Bearing Fragility for Reinforced Concrete Beams under Steel Reinforcement Corrosion Induced by Concrete Carbonation

Abstract Steel reinforcement corrosion induced by concrete carbonation is the main reason for the degradation of the load-bearing capacity of reinforced concrete (RC) structures exposed to the atmospheric environment in urban areas. A probabilistic framework is proposed in this paper for the analysis of the time-variant flexural capacity and flexural bearing fragility, with respect to the RC structure subjected to concrete carbonation conditions. Based on constructed probabilistic models for concrete carbonation, reinforcement corrosion, and material damage, considering multiple types of influencing factors and uncertainties, the probabilistic time-variant flexural capacity model is proposed. The acceleration effect on the corrosion rate of the steel reinforcement caused by cover cracking is considered, as well as the deterioration effect on the bonding strength. The construction of the analysis approach for the flexural bearing fragility emphasizes epistemic uncertainties reflected by random model parameters. The proposed models and approach are applied to the flexural bearing fragility analysis of a sample RC beam to show the validity and effectiveness of the methods. The results show that the corrosion behavior obviously affects the mean value, uncertainty level, and probabilistic distribution of the flexural capacity. The cover cracking effect influences both the statistical properties and the distribution type of the flexural capacity, and brings a significant decrease in the reliability indexes. Moreover, the corrosion behavior also changes the sensitivity levels of the design parameters and the importance of the arrangement of the random variables. The uncertainties inside the concrete carbonation depth model and corrosion current density model both contribute to the epistemic uncertainty in the fragility analysis.