Estimation of Fatigue Parameters and Life Prediction for Orthotropic Steel Deck Based on Reverse Markov Theory

Orthotropic steel deck (OSD) is a widely used lightweight steel structure known for its high load-bearing capacity. However, it is susceptible to cracking, particularly in locations that exhibit structural degradation. In this paper, the reverse Markov method is adopted to identify material parameters and predict the fatigue life of rib-to-rib welds with longitudinal rib-embedded segments in OSD. The structural damage is categorized into five states based on the crack depth, and its state probability distribution and state transfer probability matrix are determined by combining the crack characteristics and service life. This enables the prediction of the crack propagation process during the service life. Then the material parameters C and m can be calculated by substituting the annual crack growth into Paris’ law and combining it with the S-N curve. To illustrate the application of the method, a case study was conducted on the steel box girder of the Xihoumen Bridge. The results indicate that parameter C follows a lognormal distribution with a mean value of 1.90×10−9 MPa−3·m−1/2, while parameter m is determined as 3. Compared with the S-N curve obtained from the test, the calculated S-N curve indicates a fatigue life of approximately 43 years for the welding detail, which aligns much better with the actual performance.