Fatigue assessment of U-rib full penetration welded joints based on local methods

Experimental and numerical methods were used to carry out fatigue assessment of double-sided full penetration U-rib welded joints with different deck thicknesses in Orthotropic Bridge Decks (OBD). The local stress field analysis was conducted by the finite element method. S-N curves for different thicknesses can be obtained based on fatigue test results. The Nominal Stress (NS) method, the Effective Notch Stress (ENS) method, and the Theory of Critical Distances (TCD) were applied to estimate the fatigue life. The feasibility of these three approaches was validated by fatigue test results. The results show that two types of fatigue crack initiation sites (inner and outer weld toes) and typical smooth and rough regions are found. The maximum principal stress decreases by about 30% when the deck thickness increasing from 14 mm to 18 mm, while the fatigue life increases by 6-11 times for different stress ranges. The stress concentration factors (SCFs) for U ribs with 14 mm, 16 mm, and 18 mm deck thicknesses are 2.71, 3.16, and 3.15, respectively. Double-sided U ribs welded joints with thicker decks have better fatigue performance. All predicted results using the NS method and the ENS method are greater than the FAT71 and FAT225 fatigue curves, respectively. The Point Method (PM) and Line Method (LM) in the form of TCD are found to be successful in predicting the fatigue life and recommended to fatigue assessment for double -sided welded U-ribs.