Fatigue Life Evaluation for Deck-Rib Welding Details of Orthotropic Steel Deck Integrating Mean Stress Effects

The early fatigue cracking of orthotropic steel decks has been a long-standing problem for heavy traffic regions of China's long-span bridges. However, the actual fatigue life is much lower than the fatigue life calculated by fatigue design codes. In this study, a modified full range S-N curve, the M-S-N method, is proposed to evaluate welded joint fatigue life, considering mean stress, which is based on metal fatigue theory. As an example, a combined shell-solid finite-element model of a segmental bridge is first built for the Jiangyin Bridge to obtain the real stress, integrating welding residual stress and vehicle load stress. The fatigue life is then calculated and compared in order to consider the influence of different vehicle loads and deck-plate thicknesses. The calculation results show that the fatigue life of the deck-rib welded joint in the Jiangyin Yangtze River Bridge decreases nonlinear at a staggering rate with the increase in vehicle load. Under the condition of severe overload heavy vehicles, the Jiangyin Bridge fatigue life is only 2.17 years according to the M-S-N method, which matches practical situations. Deck-rib fatigue life obviously increases with the increase in deck thickness. The current steel bridge deck design with a 16-mm-thick plate is not safe under heavy traffic conditions.