| With the development of deep water oil exploration technology, platform of great performance appeared one by one. As the second generation of Spar platform, Truss Spar played an important role in offshore oil exploration with its good motion and economic performance. With the acceleration of offshore oil industry development of China, design for offshore structures similar to the Spar platform will be gradually increased. Due to the importance of structural strength analysis in the design, it's necessary to establish an efficient strength analysis method.Objective to a Truss Spar platform, by simplifying and dividing the structure into substructures, defining parameters of the substructures in detail, a parametric modeling program is developed based on AN SYS. The hydrodynamic model and finite element model are established through parametric modeling program by matching the relevant parameters of the target Truss Spar platform, replacing local joints substructure with refined FE model, the hybrid FE model is obtained. The first order wave force is calculated based on potential theory and Morison formula, low frequency drift force is calculated by Newman's approximation based on the mean wave drift force coefficients calculated by far-field method, and the wind and current load are calculated according to the formula recommended by the practice. For the drift wave excitation frequency close to the natural frequency of Truss Spar, the motion response is analyzed in frequency domain, extreme response of pitch and roll, tension of the mooring lines are obtained through the analysis with consideration of the wind, wave and current load combination with return period of 100 years in South China Sea area. Design wave parameters are determined by spectral analysis method, with all the design loads, global structural strength analysis of refine mixed finite element model is completed through ANSYS according to strength criteria recommended by ABS standard.
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