A probabilistic methodology to assess the reliability of deteriorating structural elements

A probabilistic procedure for the analysis of current and future reliability of existing structural systems is proposed: they are assumed subject to deterioration over time, due to the exposure to an aggressive environment as well as to the effects of wear during ordinary service, of improper use and maintenance and of extreme accidental events. The assumption is made that the structural elements deteriorate because of the effects of two different sets of phenomena: the first, denoted by ageing, manifest their effects on a substantially continuous basis during the structural lifetime; the others, denoted by shocks, have effects that superimpose only occasionally to the first ones. The evolution of the structural damage due to deterioration through ageing and shocks is derived as the solution of an Itô stochastic differential equation, and then used to assess the time-dependent reliability of the deteriorating structural element. In this paper the probabilistic procedure is presented and illustrated with reference to a realistic example: a reinforced concrete shear wall located in a nuclear power plant and subject to deterioration due to expansive aggregate reactions and to exposure to earthquake loading.