Deterministic and spectral fatigue analysis of the Additional Living Quarter platform in the North Field Bravo

Fixed offshore platforms, especially jacket type platforms, are the most common offshore structures used for oil & gas industry in the Persian Gulf due to its shallow water depths. Sea waves are cyclic loads and have random nature. Thus, the cyclic sea wave forces lead to fatigue damages in jacket’s joints. There are different methods to investigate the fatigue life of jackets such as deterministic method and spectral method. In this thesis, three kinds of assessment methods have been used to estimate the fatigue life of a living quarter jacket platform, at North Field Bravo (Persian Gulf): the static-based deterministic fatigue, the dynamic deterministic fatigue and the spectral fatigue. First, the jacket and the topside have been modelled by Bentley SACS software, then by applying wave cases and analyzing the critical joints under cyclic forces, hot spot stresses have been obtained, and the fatigue damage has been calculated. By using the deterministic analyses, either with the static-based or the dynamic-based, the structure has turned out to be verified, showing comparable results. Instead, with the spectral fatigue approach, many joints have shown a low fatigue life, which has led to a redesign of some structural details.