Redundancy of Structural Systems in the Context of Structural Safety

Abstract

Redundancy has long been regarded as a desirable property in ensuring the safety of structural systems. Nevertheless, it should be remarked that there is, as yet, neither a uniform theory of structural redundancy nor any widely agreed definitions. With the aim of incorporating redundancy into safety decision-making, the present article concentrates on the essentials of redundancy as well as its significance within the wider context of structural safety. First, it explains three terms associated with redundancy, including static indeterminacy, alternative load paths and, meanwhile, clarifies their interdependence. Secondly, different levels of structural safety (i.e. reliability and robustness) are investigated from a broader perspective, in which reliability refers to the pristine or intact state of a structure, whereas robustness corresponds to local damage states. Based on the two distinct levels, it is argued herein that the existence of redundancy assists in: (1) enhancing the safety margin/reliability of a structure in its intact state; and (2) mitigating the sensitivity/vulnerability of the structure to localised damage under an accidental situation. Thirdly, it classifies major aspects of ensuring redundant structures, taking into account various stages they are involved in. Further, essential means of designing for redundancy are discussed which can readily be integrated into safety decision-making. A hypothetical structural system is employed for illustrative purpose, indicating that the aforementioned means can be treated within the reliability and robustness frame. Based on this study, some recommendations are presented and areas of further research indicated.