Reliability-Based Bridge Life Assessment

Fatigue considerations have usually entered design codes as a secondary consideration and often under the guise of serviceability limits. Most engineers felt if the maximum stress ranges remained below the endurance limit, then fatigue would not be a problem. Two main issues have arisen where codes, such as highway bridge codes, need to further consider fatigue. These are: 1) the random stress spectra, which means there is a significant likelihood that some stress ranges will exceed the endurance limit and, 2) the need to respond to the issue of evaluation of remaining safe life of the structure. In both cases, realistic assessments of the true stress ranges must be used in both fatigue life design and evaluation. This paper concentrates on the evaluation or assessment of existing structures and the definition and determination of safe remaining life. The application is to steel highway bridges but other structures may be evaluated in a similar manner.