An evaluation model of ascertaining critical fatigue members was established based on mechanical character of members of box girder of long span bridge,and a method to assess critical fatigue members was provided based on extensive information including structural finite element analysis,strain monitoring results,member classification system and close manual inspect reports.

Farther,the method how to partition every one of these four constituents into members and how to choose the representational form of every kind of member based on key member for durability is proposed.

It is concluded that the structural sensitivity analysis method is the most applicable method comparing with other methods, but some key issues, such as applicable expression of load combination, identification and rating rules for the key components and sensitive components, and so on, need to be properly solved.