The self-elevating drilling units are widely used in the offshore industry for oil and gas exploration. The drill floor structure is the main part of the drilling package for a self-elevating drilling unit due to its key function. Its structural strength checking is of great significance on account of the special structure features and the complex combined loading conditions it suffers. The sufficient structural strength of the drill floor is the base and guarantee for safe drilling and extraction.

The finite element method was applied to calculate the structural strength of the drill floor directly considering different load cases which was the combination of environmental loads, permanent loads, variable function loads, and reaction forces from structures and equipments. Total forty load cases were set in the finite element analysis. A detailed finite element model without simplification of the drill floor was built correctly so that it can show the accurate stiffness of the real structure. Based on this model, the design method and the design criterion of the drill floor were described in detail. The environmental loads were calculated according to ABS MODU rules. The influence of the direction of the environmental loads on the drill floor were studied and concluded. Since the drill floor was not just welding with the cantilever beam, the boundary conditions were also particularly introduced owning to the complex connection between them.

After finite element analysis and calculation, the stress distribution of the whole drill floor which includes the main girders and derrick supports were obtained. The locations with high stress were found so those places should be paid more attention. The curves which show the stress variation according to the environment loading direction were drawn and their characteristics were found. The load case and the load which have the main effect on drill floor structure were found. As a result, the suggestions for design improvement were put forward for the structural design, and the finite element analysis was run again to test and verify the design improvement.

This paper can provide meaningful guidance for the future design of the drill floor.

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