Risk-based fatigue assessment of orthotropic steel decks

The orthotropic steel deck (OSD) shows notable superiorities in bridge applications but is highly prone to fatigue cracking due to the use of massive welded connections, especially in the rib-to-deck (RD) connection. This study presents a risk-based approach to planning different management strategies for OSDs under fatigue, which is supported by the integrated fatigue assessment coupling test data, in-situ measurements and probabilistic simulations. RD connections are focused on since they account for the longest welding length, i.e., about 50 times the total bridge length. The probability-stress-life (P-S-N) curve is first derived for RD connections from fatigue test data. Meanwhile, a condition-based probabilistic model of vehicle loads is constructed using the site-measured data. The load model is then implemented with numerical simulations in a sampling-based manner to derive fatigue stress spectra of different fatigue-critical RD connections. Based on the derived P-S-N curve and stress spectra, the fatigue deterioration of RD connections is assessed in a probabilistic form. Moreover, the failure assessment diagram (FAD) is derived for OSDs considering the serviceability, in accordance with the estimation of associated consequences. Based on the probabilistic estimation, the risk assessment is carried out for the OSD by combining the probability of failure and associated consequences.