Abstract: The a-s-N curve expressed by characteristic stress of structural details is presented. Then the ( a K ,N K ) data under constant loading are transformed into the ( a K ,t K ) data under spectrum loading by using Goodman diagram and Miner's rule,and equivalent initial flaw size (EIFS) distribution parameters are obtained by the ( a K ,t K ) data.Finally,the probability of crack exceedance and structural damage degree are calculated and the durability analysis is completed.

Key words: durability, distribution parameters systems, crack