Fatigue Assessment for Deck-Rib Welded Joints of Orthotropic Steel Deck Using a Simplified Nodal Force Structural Stress Approach

The fatigue cracking of orthotropic steel deck (OSD) has long been a problem of bridge structures. It is meaningful to assess bridge fatigue life using an appropriate method. In this paper, a simplified nodal force structural stress approach aiming at the deck-rib welded joints in OSD is first proposed. The accuracy and mesh sensitivity of the calculation results by the proposed approach are investigated. Then, based on the experimental results of OSD, the effectiveness of the master S-N curve in nonultrahigh cycle fatigue region is verified. The slop and knee point of the S-N curve in ultrahigh cycle fatigue region are analyzed. Finally, an actual bridge model composed of both large-scale shell elements and small-scale solid elements is established. The influences of vehicle axle weight and deck thickness are investigated using the simplified nodal force structural stress approach. The results show that: when the mesh is uniformly divided and the stress does not change obviously along the weld direction, the simplified nodal force approach should be adopted. The proposed approach is simple, accurate, and less sensitive to meshing. It is recommended that 20-node reduced integration elements with a mesh size of 0.25 times the plate thickness should be used to limit the error to less than 1%. In a nonultrahigh cycle region (N <= 5 x 10(6)), the 95% guarantee rate master S-N curve can be used to evaluate the bridge fatigue life. The results of actual bridge analysis based on the Jiangyin Yangtze River Bridge show that under standard vehicles the results calculated by different ultrahigh cycle master S-N curves (N > 5 x 10(6)) are significantly different. The fatigue life increases with the increasing of the slope under the same knee point, but decreases with the increasing of the number of cycles at the knee point under the same slope. When the vehicle is overweight by 50%, the fatigue life is only approximately 10 years. The fatigue life prolongs significantly with the increasing of deck thickness so that it should be at least 14 mm to avoid fatigue failure during the design period.