Modelling of jack-up response for fatigue under simulated service conditions

Abstract

Abstract Service loading of jack-ups is mainly due to wave and wind action with variable amplitude and frequency content. As jack-ups are used in deeper waters for long-term deployment, fatigue has become an important consideration both at the design stage and during maintenance for structural integrity assessment procedures. Jack-ups are more dynamically sensitive structures when compared with conventional fixed platforms. This means that the effects of dynamics and structural response become more important and must be adequately modelled to obtain realistic and representative results for the simulated service load sequences which are required to study the fatigue performance. This paper covers the relevant analytical and experimental procedure adopted at University College London to ensure that realistic results of the kind mentioned above were obtained during a study on variable amplitude corrosion fatigue (VACF) of a typical weldable high-strength steel (SE702). It looks at the influences on fatigue resistance of welded tubular joints used in the construction of a typical jack-up platform. Great emphasis is placed on how the relevant factors which affect the fatigue performance of these welded tubular joints are modelled to produce a jack-up standard load history (JOSH). These factors especially include wave loading, structural dynamic response and the effect of corrosion under cathodic protection conditions.