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

The accurate estimation of the ultimate capacity of offshore structures, including jacket-type fixed platforms, is of great importance in order to achieve the structural performance levels and determine its ductility. The formation of fatigue cracks in joints, corrosion in members, damages caused by design environmental loads and damages due to stochastic dynamic loads such as the ship impact, will change the ultimate capacity of these structures during lifetime; which should be considered in evaluation of the ultimate capacity of the platforms at any point in time. However, the necessity of proper modeling of global and local buckling of compression members in estimation of the ultimate capacity is important in all these time periods. If compressive braces are modeled using 3-D Shell or Solid elements, deformations caused by local buckling will be investigated if imperfections are applied in necessary cases. However, in this article, using Abaqus finite element software, the estimation of the correct compressive bearing curve of 1-D Beam elements and investigation of the accuracy of this modeling based on Marshall's theory using Frame elements have been discussed. Thus, this modified behavior will also consider local buckling effects in compressive braces. Having this local buckling behavior is very important in the accurate determination of the structural capacity and as a result the correct estimation of RSR.