Fatigue experiment and assessment of butt-welded joints in steel structures considering misalignment and weld geometry effects

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This study investigates the fatigue behavior of butt-welded joints considering the effects of misalignments and weld geometries. Fourteen specimens were fabricated with varied assembly root gaps and axial eccentricities, and they were subjected to cyclic tensile loading with constant amplitude. Misalignments (both axial and angular) and weld geometries (including weld toe radius, flank angle, weld reinforcement height, and width) were measured using a 3D optical scanning system and subsequently used for fatigue evaluation in terms of fatigue crack locations and fatigue strength. The fatigue test results indicate a noticeable decrease in nominal stress fatigue strength as the assembled axial eccentricities increase, regardless of the assembled root gaps. However, the correlation between assembled root gaps and fatigue strength is not clear, as a larger assembled root gap corresponds to a flatter weld reinforcement on one hand and an increase in angular misalignment on the other hand. Several stress magnification factor (SMF) and stress concentration factor (SCF) formulae available in the literature are employed to characterize the combined effects of misalignment and weld geometries. The investigation results indicate that misalignments and weld geometries both play critical roles in the fatigue behavior of butt-welded joints. The combination of Remes and Varsta's SCF formula with Luo et al.'s SMF formula is the most recommended method due to its accuracy and robustness regarding the evaluation of both the fatigue crack locations and fatigue life in the investigated butt-welded joints.