Fatigue Strength Curve for Tubular Joints of Offshore Structures under Dynamic Loading

Abstract

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

Assessment of Dynamic Effects of Wave Loads in Fatigue Analysis for Fixed Steel Offshore Structures

“…Therefore, the wind fatigue damage cannot be ignored because of the damage combination, even though the wave-induced fatigue damage is much bigger than the wind fatigue damage. In Siriwardane et al [11], fatigue lives are calculated and compared with the conventional approach. The proposed curve can be directly applied to any tubular joint in seawater without having additional CF tests, which is an advantage.…”