Fatigue behavior of load-carrying fillet welded cruciform joints with plates of different thickness

Load-carrying fillet welded joints in welded steel structures are extensively used for connecting the structural members. Typical fatigue cracks have been observed at the welded joints such as secondary structural members of steel bridges. The object of this research is to clarify the influence of the difference in plate thickness on the fatigue behavior of load-carrying fillet welded cruciform joints. Fatigue tests were carried out on the joints with plate of different thickness. The main plate thickness was 9, 14 or 25 mm and the cross plate thickness was 6 or 14 mm. Fatigue crack propagation and strength analyses using fracture mechanics were also performed on the joints with various plate thickness. The tested specimens indicates that the fatigue cracks are initiated and propagated almost along extended line of non-penetration weld line regardless of the main plate and the cross plate thickness. The experimental and the analytical results show that the larger the difference of thickness in each main plate is, the lower the fatigue strength is, when the cross plate thickness is smaller than that of the main plate.