A kind of direct strength analysis method of semi-submersible platform structures is presented in this paper. With the differences in shape of pontoon, column and beam being considered, the method of accumulative chord length cubic parameter spline function combined with analytic expression is adopted to generate the mesh of platform wet surface. The hydrodynamic coefficients of the platform are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for platforms with low forward speed. The equations of platform motions are established and solved in frequency domain, and the responses of wave-induced loads on the platforms are calculated. According to the mesh of hydrodynamic computation, the fluid dynamic pressure field of platform wet surface is built, and the pressure loads on shell elements in the finite element model of the structure are calculated by the interpolation method. The calculation conditions and loads in the finite element analysis (FEA) of the platform structures are determined according to the design wave analysis approach. A computer program based on this method has been developed, and a calculation example of semi-submersible platform is illustrated. Analysis results show that this method is a satisfying approach for wave load computation and direct strength analysis of the semi-submersible platforms.

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