Ultimate Strength Design of Racks for Jack-Up Units

Abstract

The subject of paper discusses an approach taken in evaluating the load acting on racks for jack-up units (the jack load) together with its computed results. The fracture test of a full-scale rack for a jack-up unit and a finite-element elastic stress analysis for this rack were also conducted. These results led to new design criteria for the ultimate strength design method of racks for jack-up units, when exposed to a combination of loads including stormy conditions. Typically, the ultimate strength of the racks was evaluated on the assumption that the cross section of the rack tooth plastically collapses at its root. During this investigation, it was shown, however, that the ultimate strength of the racks needs to be evaluated also on the premise that the rack tooth is subject to shear fracture caused by its mating pinion tooth.