Time-variant redundancy and failure times of deteriorating concrete structures considering multiple limit states

Structural redundancy and load redistribution capacity are desirable features to ensure suitable system performance under accidental actions and extreme events. For deteriorating structures, these features must be evaluated over time to account for the modification of the redistribution mechanisms due to damage processes. In particular, the identification of the local failure modes and prediction of their occurrence in time is necessary in order to maintain a suitable level of system performance and to avoid collapse. In fact, repairable local failures can be considered as a warning of damage propagation and possible occurrence of more severe and not repairable failures. In this paper, failure loads and failure times of concrete structures exposed to corrosion are investigated and life-cycle performance indicators, related to redundancy and elapsed times between sequential failures, are proposed. The effects of the damage process on the structural performance are evaluated based on a methodology for life-cycle assessment of concrete structures exposed to diffusive attack from environmental aggressive agents. The uncertainties involved are taken into account. The proposed approach is illustrated using two applicative examples: a reinforced concrete frame building and a reinforced concrete bridge deck under corrosion. The results demonstrate that both failure loads and failure times can provide relevant information to plan maintenance actions and repair interventions on deteriorating structures in order to ensure suitable levels of structural performance and functionality during their entire life-cycle.