Target reliability of civil engineering structures

The structural reliability recommended in Eurocodes and other international documents vary within a broad range, while the reference to the failure consequences and design working life is mentioned only very vaguely. In some cases the target reliability indexes are indicated for one or two reference periods (in Eurocodes for 1 year and 50 years), however no explicit link to the design working life is usually provided. This article attempts to clarify the relationship between the target reliability levels, failure consequences, the design working life and the discount rate. The theoretical study based on probabilistic optimization is supplemented by recommendations useful for code makers and required by practicing engineers. It appears that the optimum reliability indices depend primarily on the ratio of the cost of structural failure to the cost per unit of structural parameter, and less significantly on the design working life and on the discount rate. (paper)