A fatigue damage evaluation using local damage parameters for an offshore structure | Proceedings of the Institution of Civil Engineers - Maritime Engineering
In the fatigue design of offshore structures are normally used the waves and wind fatigue loading. Currently, fatigue analyses for fatigue damage accumulation assessment of this type of structure are based on S-N curves for welded structural components, hot-spot stress approach, and Palmgren-Miner law, according to design codes. Fatigue analyses of design codes and/or recommended practices are supported by global structural analysis. In this paper, a global-local fatigue methodology applied to an offshore jacket-type platform using a local approach through the notch strain damage parameter is proposed. The local approach is based on Neuber's rule combining with the Ramberg-Osgood description. Then, Coffin-Manson strain-life relation together with the Palmgren-Miner linear damage rule are used to evaluating the fatigue damage accumulation for the critical tubular welded joint. For the application of the Neuber's rule, the stress concentration factor values are calculated, according to Efthymiou's analytical equations, for the connection under consideration. This proposed methodology is compared with the simplified fatigue analysis presented in DNVGL-RP-C203 recommendations. These analyses are performed using wave loads from the scatter diagram collected in the North Sea, which were computed through the 5th Stokes order wave theory and Morrison formula.
