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The required reliability levels recommended in national and international documents for new and existing structures vary within a broad range, while the reference to relevant costs and failure consequences is mentioned only very vaguely. This contribution attempts to clarify the relationship between the reliability levels required for existing structures, construction costs, failure consequences, reference period, the design working life and the discount rate. The theoretical study is based on probabilistic optimization of the total costs taking into account construction value including historical and artistic value, obsolescence of existing structures, discount rate and time to failure. However, historical and artistic values of some heritage structures are often difficult to assess in monetary units and then the expert judgements are to be utilized. 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.
artistic values, discount rate, heritage structures, optimization, reliability, total costs
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