The researches of the anti-collision characters of a semi-submersible column and its capability of surviving in severe sea state after collision accident are completed in the paper. Three collision cases are designed. A 5000 ton vessel hits the semi-submersible column in transversal, longitudinal and oblique direction. Numerical simulation technique is used to do the analysis, and anti-collision characters of the semi-submersible column are summarized by the curves of collision force vs. penetration, the energy absorption proportion and structural damages. It can be pointed out that the column show a distinctive character when the contact surface is large at the beginning of the collision. There is no rupture of outer shell, which means the column can sustain such kind of collision. Taking advantage of the direct calculation method with finite element models, the global strength of the semi-submersible is verified to assess the influence of structure damage by the collision on the semi’s survival capability in severe sea state. The structure damage caused by the collision is taken into consideration in the FE models. The code SESAM is used to do the calculation through the design wave method. Several assumptions are made to realize the comparison between collision cases. It is found that the collision influence is restricted within the scope of structural components around the collision zone. The collision damage caused by the hitting of 5000 ton vessel will not bring a serious threat to the global strength capability of the semi-submersible.

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