This paper compares two approaches for the estimation of long-term response of wave load effects on offshore structures. These approaches are applied to estimate the extreme value of the cross section interaction ratio of a tubular component of the bracing system of a semisubmersible platform. The tubular component is subjected to axial loads and bending moments due to static loads and wave effects. The iteration ratio in the ultimate limit state is defined by applying design criteria derived from API RP-2A LRFD [6]. The approaches are also applied to estimate the long-term response of a single degree of freedom system due to wave actions.
The first approach is based on the proposals of Videiro and Moan [3]. The results of the first approach are compared with a new model of long-term response estimation, based on the up-crossing rate distribution of the response process.
