Collapse analysis of steel jacket structures for offshore oil exploitation

This work describes the formulation of finite-element based numerical methods for global nonlinear collapse analyses of three-dimensional steel framed structures. Particular emphasis is dedicated to the reassessment and determination of residual strength of steel jackets that support offshore oil exploitation platforms. Two main aspects are considered: (1) the formulation for a three-dimensional geometric and material nonlinear frame element, and (2) the implementation of specialized techniques for the solution of the nonlinear problem. The formulation of the element combines a co-rotational approach to represent geometric nonlinearities, providing an accurate treatment of finite rotations, with the plastic hinge approach to represent material nonlinearities. The stiffness reduction due to yielding is performed through a smooth degradation, following a parabolic function. Effects of strain hardening, geometric imperfections and residual stresses are modeled in an efficient manner. In order to determine the full nonlinear equilibrium path and allow the correct determination of the collapse load, the solution strategies consider specialized “continuation” techniques such as the Arc-Length and the Generalized Displacement Control methods. Case studies are presented in order to demonstrate the accuracy, efficiency, and suitability of the implemented methods and techniques.