Fatigue strength of tubular welded connections in offshore floating platforms

Abstract The work reported in the present paper is part of a European research program aimed at developing a hybrid tension‐leg floating platform, suitable for combined offshore wind and wave energy exploitation. Eight (8) fatigue tests on welded tubular joint specimens are performed, which represent the full penetration brace‐to‐cylindrical column welded connections of the project prototype structure. The large‐diameter columns are reinforced internally with a grid of longitudinal and transverse stiffeners fillet welded to the shell. The specimens are approximately 1/6‐scale physical models made of S355 grade steel, and subjected to cyclic loading under constant load amplitude histories. The brace‐to‐cylinder welds are semiautomatic, and high‐frequency mechanical impact treatment is applied in four specimens. The experiments are supported by post‐fracture metallographic examination and finite element analyses. The results indicate two locations for fatigue crack initiation: brace‐to‐cylinder crown and cylinder‐to‐stiffener connection.