Conceptual and Analytical Differences between Resiliency and Reliability for Seismic Hazards

A distinction is made between the reliability of a structural system and its resilience. The former is generally measured probabilistically, evaluated by means of computer algorithms capable of handling multiple failure modes, and forms the basis of design codes. Resilience must incorporate the time history of performance following significant disturbance, include imprecise definitions and evaluations, and reflect the effects of system performance (physical, economic, social and political) on the community served. Reliability analysis, including code calibration, has generally been the purview of structural engineering risk professionals. Resilience, on the other hand, should integrate community input on the degree of inconvenience and time trajectory of recovery, even incorporating concepts of sustainability. Resilience must often use generalized uncertainty, including fuzzy logic, to transform societal goals into metrics, and recognize sensitivity to sources of uncertainty in terms of acceptance of diminished performance. At a minimum, this requires keeping epistemic and aleatory uncertainty separate.