Uncertainty in Structural Engineering

Structural engineering design is replete with uncertainties, some of which are obvious and some of which many engineers may never have considered. This paper is an examination of the uncertainties facing structural engineers and the ways that engineers have developed to handle those uncertainties. Uncertainty can be separated into two categories: Aleatory, related to luck or chance, and epistemic, related to knowledge. This breakdown has an impact on how we handle the various types of uncertainty. Uncertainty has a range of sources; we consider five broad sources: time, statistical limits, model limits, randomness, and human error. These five sources will be examined using examples from structural engineering, particularly with respect to the allowable stress design and LRFD code formats. Some uncertainties are explicitly dealt with in design codes, some are dealt with through quality control measures, and some are dealt with in implicit ways that we often do not think much about, e.g., heuristics. Design codes can deal with uncertainties caused by randomness, statistical limits, some aspects of time, and modeling. Other uncertainties such as human error must be dealt with using quality control methods, such as peer reviews and construction inspection. DOI: 10.1061/ ASCE 1084-068