Probability-based durability design of reinforced concrete structures

Structural ageing may cause the strength and stiffness of any reinforced or prestressed concrete structure to deteriorate in time, particularly if the operating environment is aggressive. Among the most potentially damaging mechanisms of attack are corrosion of the reinforcing steel, and deterioration of concrete due to chloride penetration and carbonation. Because of deterioration, the safety of the structural system decreases in time, with respect to the level of reliability estimated at the time of design. In this paper, an example of a performance-based durability design is illustrated and exemplified with specific reference to a prestressed concrete bridge beam: the approach is applied to the assessment of the current reliability of existing structures. More specifically, a probabilistic model of time of onset of corrosion of reinforcement is derived, taking into account different model of carbonation of concrete cover and chloride penetration. The probability distribution of the time of onset of corrosion once coupled with a model of corrosion propagation allows to assess the evolution in time of the probability of failure of the structural component, and to derive its expected lifetime