Time-dependent reliability of corrosion-affected RC beams—Part 1: Estimation of time-dependent strengths and associated variability

The structural deterioration of reinforced concrete (RC) structures due to reinforcement corrosion is a major worldwide problem. Damages to RC structures due to reinforcement corrosion manifest in the form of expansion, cracking and eventual spalling of the cover concrete; thereby resulting in serviceability and durability degradation of such structures. In addition to loss of cover, RC structure may suffer structural damages due to loss of reinforcement cross-sectional area, and loss of bond between corroded reinforcement and surrounding cracked concrete, sometimes to the extent that the structural failure becomes inevitable. This paper forms the first part of a study which addresses time-dependent reliability analyses of RC beams affected by reinforcement corrosion. In this paper initially the predictive models are presented for the quantitative assessment of time-dependent damages in RC beams, recognized as loss of mass and cross-sectional area of reinforcing bar, loss of concrete section owing to the peeling of cover concrete, and loss of bond between corroded reinforcement and surrounding cracked concrete. Then these models have been used to present analytical formulations for evaluating time-dependent flexural and shear strengths of corroded RC beams, based on the standard composite mechanics expressions for RC sections. Further by considering variability in the identified basic variables that could affect the time-dependent strengths of corrosion-affected RC beams, the estimation of statistical descriptions for the time-dependent strengths is presented for a typical simply supported RC beam. The statistical descriptions, i.e., mean and coefficient of variation (c.o.v.) for the time-dependent strengths are presented for two limit states: (a) flexural failure, and (b) shear failure. The other two parts of the reliability study present the estimation of time-dependent failure probability for the considered RC beam by utilizing the information provided on probabilistic descriptions of time-dependent strengths in this paper. The effects of time to corrosion initiation and its variability on the failure probability of the considered RC beam have also been discussed.