Fatigue lifetime assessment of tube-to-flange arc-welded steel joints with reinforcement ribs under constant and variable amplitude multiaxial fatigue loadings according to the peak stress method

Welded reinforcements are a widespread solution when increasing the stiffness and load bearing capacity of engineering structures is of primary interest, particularly under in-service cyclic loadings which require a fatigue durability assessment. However, experimental fatigue data available in the literature and the number of classified details reported in Standards and Recommendations are limited. On top of that, the fatigue strength assessment of large-scale reinforced welded structures generally involves complex geometries and variable amplitude multiaxial loadings. In this framework, local approaches for the fatigue assessment of reinforced welded structures are applicable without limitations in the complexity of geometries or loading conditions. In this investigation, the fatigue strength of complex Square Hollow Section (SHS) tube-to-flange arc-welded joints with reinforcement ribs of S355 structural steel has been experimentally investigated under constant and variable amplitude pure bending, pure torsion and in-phase as well as out-of-phase combined bending and torsion loadings. The number of cycles to break-through has been adopted as a failure criterion and the cracking behaviour of the tested specimens has been also investigated. Afterwards, the Peak Stress Method (PSM) has been successfully adopted to assess the fatigue strength of the welded reinforcement ribs joining the tube and flange