A rational way of determine
the acceptable reliability level for an existing structure is presented along
with practical values and examples. The approach is based on the statistical
decision theory, and it is not required that the reliability for design of a
new bridge necessarily shall be used for an existing bridge. The paper is
focusing on road bridges and emphasis is put on the use of economical values
for construction and repair that is relevant to this type of structures. It is
demonstrated that assuming that the design practice is optimal the social
failure costs associated with road bridges are very high. Various repair costs
and failure costs are analysed and it is found that only a rather small
decrease in structural reliability of a road bridge should be allowed before
repair is initiated.