Probabilistic Evaluation of Service Life of Reinforced Concrete Beam Element in Marine Environment

Chloride-induced rebar corrosion is one of the main causes of premature deterioration of reinforced concrete (RC) structures in marine environment. This study aims to develop a probabilistic model to assess the service life of RC beam subjected to chloride-induced corrosion attack. Concrete block specimens containing steel bars are prepared and subjected to accelerated corrosion test. As the corrosion-induced mass loss of steel bars reaches different levels ranging from 0% to 30%, the tests are terminated. The steel bars are taken out of the concrete block, cleaned with a sand blaster, and then scanned with a 3D laser scanner at intervals of 1.0 mm. The distribution of the residual cross-sectional areas of the steel bars is determined. A pitting factor R which is the ratio of the average to the minimum cross-sectional area of corroded steel bars is introduced to describe spatial variation of pitting corrosion along the length of steel bars. Probabilistic analysis shows that the pitting index R can be fitted with Gumbel distribution function very well, and the parameters of Gumbel distribution of pitting factor increase linearly as a function of corrosion-induced area loss. The probabilistic distribution function of pitting factor is then employed to analyze the probability of failure of a RC beam as a function of its service life. The RC beam has a span of 5500 mm and it is divided into 11 elements with a length of 500 mm. The failure occurs as the actual load effects exceed the resistance of any of the eleven beam elements. Based on Monte Carlo simulation, the probability of failure of this RC beam increases from 0.06% to 17.02% and the reliability index decreases from 3.24 to 0.95 after 50 years of exposure to chloride-induced corrosion attack.