Fatigue in Offshore Steel Structures

Fatigue strength and fatigue life of offshore steel structures is studied. The project is a continuation of a large common Nordic research programme "Fatigue under Spectrum Loading and in Corrosive Environment", carried out over a 5-year period with participation of all Nordic countries.
In the experimental part of the investigation, test series with 4 different types of test specimens, including full-scale tubular joints, have been carried through. Test series with different types of stochastic loading, which are considered realistic in relation to offshore structures, have been carried through, together with reference test series with constant amplitude loading. A total of about 350 fatigue tests on plate test specimens and 9 tests on double-T full-scale tubular joints have been carried out.
For both the tubular joints and the plate test specimens, the fatigue life has been determined theoretically by use of fracture mechanics.
The results, which have been obtained in both the experimental and the theoretical part of the investigation, show that the design criteria based on Miner's rule, which are normally used in the design against fatigue for offshore structures may give rather unconservative results.