SYSTEM DESIGN OF FLOATING OFFSHORE STRUCTURES

An extended incremental load method has been developed to derive the most probable failure path for continuous plated structures such as the assembly of stiffened rectangular and cylindrical cross-sections used in Tension Leg Platforms (TLPs) and Semi-Submersibles. The method allows for load redistribution as structural components strain beyond their maximum loads so that a system of elastoplastic moments develops in sufficient cross-sections to form a failure mechanism for the whole structural system under a variety of possible combined loads. Sensitivity studies show, for any given level of safety, the economic importance of reducing the uncertainties associated with component strength modeling and with post-ultimate behavior characteristics. The results of several such parametric studies lead to important conclusions relating to the adoption of a systems approach coupled also to component behavior for economic design, and for in-service reassessments of such structures.