This study introduces a large offshore cofferdam installed by suction, unlike conventional ones such as a sheet-pile type, and proposes an effective suction cap for the cofferdam. In structural design view of the cofferdam, there are several critical issues due to its large size. This study conducted structural analyses of stiffened caps for large offshore suction cofferdam using fully nonlinear finite element models, and analyzed changes in behaviors of the cap due to stiffener arrangements to provide design insights. For finite element models, the diameter and the thickness of the suction cap (circular plate only) are 20m and 0.07m, respectively. Suction pressure on the cap was assumed to be 100kPa, all parts of the cofferdam except the cap are considered as boundary conditions. By investigating conventional suction anchors, several stiffener arrangement patterns on the cap of suction cofferdam were derived, and each arrangement was estimated by comparing stress and deformation of the cap. Also, reaction distributions on the edge of the cap were investigated to analyze effects of the stiffener arrangement on the interface behaviors between cap and cofferdam.

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