Abstract
This paper focuses on estimating the fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a probabilistic approach on the basis of a bilinear stress life (i.e., the
S-N
approach). The current AASHTO
S-N
approach uses a single
S-N
line for predicting the fatigue life. However, because of the variation of actual applied live-load stress cycles, this approach very often results in a severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overestimated. To improve fatigue life estimation, a bilinear
S-N
approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process. In this approach, the equivalent stress range is computed by using two
S-N
slopes and several probability density functions associated with stress ranges. These probabilistic functions are determined on the basis of stress-range bin histograms from long-term monitoring. An existing bridge that is expected to experience finite fatigue life is used to illustrate the application of the proposed approach.