Model uncertainty in structural reliability

Structural reliability analysis is based on idealized limit state models. The level of sophistication of the models is, on the one hand, kept suitably simple in order to have mathematical operability. On the other hand, the models are believed to be reasonably predictive with respect to real failures. In order that the reliability analysis can serve as a decision tool in real life decisions in structural design, it is necessary to include elements for subjective assessment of model uncertainty information in the reliability model itself. The paper discusses how this can be done in a rational and philosophically satisfying way without losing the general level of operational simplicity of the limit state models. The philosophy and the mathematical arguments of the paper support the rules of dealing with model uncertainty that are introduced on an intuitive basis in recent international safety code recommendations.