Redundancy and Robustness, or When Is Redundancy Redundant?

The redundancy of a structure refers to the extent of degradation the structure can suffer without losing some specified elements of its functionality. However, because future structural degradation is unknown during design and analysis, it is evident that structural redundancy is related to robustness against uncertainty. This paper proposes a quantitative and widely applicable concept of strong redundancy and shows its relation to the info-gap robustness of the structure. In particular, one of this paper’s propositions establishes general conditions in which the strong redundancy is equivalent to the robustness. This paper also defines a concept of weak redundancy and presents propositions that relate it to the strong redundancy and the robustness. Results are illustrated with several heuristic and engineering examples.