| At present, semi-submersible drilling platform is widely in ocean engineering due to its outstanding capability in terms of hydrodynamics, mobility, ability of withstanding hazard wind and harsh wave. Semi platform of new generation is free from fatigue failure of kinds of tubular components for it has simple geometry configuration and doesn't contain any complex tubular joints. Therefore, global strength analysis becomes the key factor to guarantee structure integrity due to big span in both longitudinal and transverse direction. While fatigue assessment of critical joints which connect main components of platform cannot be ignored for fatigue analysis of these joints can provide rational suggestion for structure optimization of critical joints. Taking a six-generation Semi platform, analysis procedures of global strength and fatigue strength are presented. In additional, global strength analysis, wave load sensitivity of critical joints and fatigue assessment of critical joints are carried out which can provide rational suggestion for structure design and structure optimization of aimed Semi platform.The main research work is as follows:1) First of all, method of global strength assessment is summarized.2) Design wave method and FEM are adopted to analyze global strength of aimed platform and then study the principle of analysis load case selection, key factor which place key role in global strength.3) Thirdly, wave load sensitivity of critical joints is carried out. 4) Finally, fatigue life of critical joints is evaluated with S-N curve and spectral-based method for linear load. Moreover, key short term wave conditions which have significant effect on fatigue life of key joints are obtained. And what mentioned above provide reference for design of similar Semi platform.
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