Quantitative deterministic versus probability analyses based on a safety margin criterion

This paper proposes a new criterion called the ratio of safety margin (RSM) for use in the areas of the global factor of safety, reliability and limit states analyses with reference to their respective allowable criteria. An equation for calculating RSM based on the reliability index is formulated. Efforts for proving the applicability of this criterion include a theoretical demonstration in a simple one-variable case; an investigation on a test problem involving two random variables, followed by a slope stability study on a 156 m high embankment dam and an illustrative example presented in a EuroCode 7 guidebook. Calculation of the ratios of safety margin in the three areas provides a quantitative way to accommodate the analytical results within the same theoretical framework and makes the outcomes mutually comparable and supportive, which is much more enlightening than that would be the case by considering only one of them. Calculating RSMs for reliability and limit states methods has also helped solve the key issue concerning the uniqueness of the partial factors calibrated from a particular ‘target case’.