The proper determination of this paper is to study the ultimate strength and postbuckling behavior for complicated stiffened deck girders of offshore platforms. Normally, offshore platforms are designed with reinforcing stiffeners on box deck girder.

The box deck of column stabilized platform will be simulated with FEM software ABAQUS. Linear eigenvalue analysis is firstly applied to introduce the initial imperfection into the structure. Then the non-linear postbuckling analysis for the box deck girder will illustrate ultimate strength and the failure mode under axial load after collapse. The ways how the stiffeners, eigenmode and imperfections influence the ultimate capacity will also be analyzed.

Comparing variable elements affecting the structural strength, the work shows the offshore box deck girder section from the engineering project in this paper is quite robust to the axial compression. For this kind of robust design, such as the box deck girder, the eigenmode selection and amplitude of imperfection will exert slight effects on the ultimate strength, but the severe imperfections will accelerate the local buckling. Stiffeners design will exert dramatic influence on the ultimate strength and postbuckling behaviors. And the work to find the optimum balance among structural strength variable load and allowable imperfections seems to be very promising in engineering. The conclusions provide a more clear insight into the further optimization of the offshore square structure design.

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