Study on Ultimate Capacity of Offshore Jacket Platforms Considering the Effects of General and Local Buckling of the Elements

The ultimate capacity of offshore structures including jacket type offshore platforms is used to achieve structural performance levels and determine their ductility. Accurate estimation of this parameter is of great importance. Formation of fatigue cracks at the joints, corrosion of members, environmental loads and damages caused by accidental dynamic loads such as impacts of vessels and floating bodies will result in change of the ultimate capacity of these structures over time of their life. These cases should be considered in calculating the ultimate capacity of the offshore platforms at any given time of their life. However, accurate modeling of the global and local buckling of compression members is important at any time of calculating the ultimate capacity. Buckling modes and deformations due to local buckling will be considered, if the compressive braces are modeled by Shell or Solid elements and the imperfections are applied. The purpose of this paper is to achieve the correct compressive behavior of compression members. ABAQUS finite element computer software is used for this purpose. The buckling envelope derives from Marshall Strut theory defines the post-buckling damaged elasticity model and the hysteretic loop response. Finally, by using this modified behavior in Frame elements, the effects of local buckling in compressive braces can be considered.