Safety analysis of reinforced concrete beams subjected to reinforcement corrosion: probabilistic approach considering torsion, reinforcement anchorage and the service ultimate states

Abstract

Nowadays, reinforced concrete structures are among the most used in the world because of its relatively low cost, strength and ease of obtaining various forms. In low environmental aggressive places, in general, such structures have great durability. However, in aggressive environments, such as large industrial cities and / or coastal regions, the durability of such structures can be strongly affected by chemical attack. Among the most frequent pathological processes in reinforced concrete structures, reinforcement corrosion by chloride ion diffusion is the main factor in the loss of durability. Corrosion is a complex physical-chemical process influenced by several parameters, which are hard to control due to the difficulty of its modeling. Allied to this feature, various parameters of corrosion have large uncertainties inherent to their values, making it even harder to realistic representation of the phenomenon. In this context, purely deterministic analyzes are not able to properly represent the process, requiring the use of probabilistic models for such representation. Based on this, this work presents the study of corrosion of reinforcement, from reliability theory as applied to the durability of beams under torsion moment, anchorage loss and changes in the displacement field for checking the serviceability limit state. The representation of mechanical models is made considering the equilibrium equations and design of ABNT NBR 6118: 2014 coupled to the FORM for reliability analysis. Corrosion is assessed via Fick's law for determining the corrosion start time and Faraday's law for determining the loss of reinforcement by the development of corrosion. The loss of resistance over time after the initiation of corrosion, are evaluated to determine failure probabilities related to the states and limits adopted subsequent verification of safety and durability of structures after the onset of corrosion. At the end of the paper we propose a simplified procedure for the optimal determination of concrete cover and the water-cement factor in order to maintain the durability of the structure.