Development of a methodology to estimate fatigue damage in tubular joints of jackets due to direct wave loads in splash zone

Wave induced hydrodynamic loads among various environmental loads hold prominence while designing offshore structures. The cyclic and non-linear character of such loads eventually generates structural fatigue leading to failure, terming the span as fatigue life. The instances of attaining members’ maximum load substantially differ than the instance of structural global load maxima as represented by aggregating loads on members in traditional method of fatigue life analysis. This paper recommends an alternate approach of elemental and cyclical time discretized method owing to more realistic fatigue life estimations. A MATLAB programme has been developed comprising of wave phase angles and instances corresponding to maximum hydrodynamic load on each member, structural redistributive analysis considering quasi-statics, joint configuration recognition, parametric SCF assessments (globally accepted semi-empirical standard explicit equations), and interpreting SN curves for steel tubular joints (API RP 2A 21st Ed. - WJ), evaluating cumulative damage by Miner’s rule and estimating fatigue life of the joints’ interfaces. The proposed analysis has been simulated using a numerical model example, enabling a better understanding of significant prediction differences than of the conventional method. Its applicability in offshore industry could instrument in avoiding fatigue life underestimation (uneconomic) or overestimation (structural failure) lead towards safe and economic designs.