Specification of the Target Reliability Level

The target reliability levels recommended in national and international documents vary within a broad range, while the reference to relevant costs and failure consequences is mentioned only very vaguely. In some documents the target reliability index β is indicated for one or two reference periods (1 year and 50 years) without providing any link to the design working life. This contribution attempts to clarify the relationship between the target reliability levels, construction costs, failure consequences, reference period, the design working life and the discount rate. The theoretical study based on probabilistic optimization is supplemented by recommendations useful for code developers and practicing engineers. It appears that the optimal reliability level depends primarily on the construction costs, failure costs, and relative cost for improving structural safety, and less significantly on the discount rate and the time to failure.