Development of a Simplified Beam Model for Tubular Joints in Jacket Structures

Jacket structures are extensively used to support heavy-weight offshore infrastructure systems. Hence, reliable simulations and designs are vital to facilitate the safe extraction of offshore energy sources, accommodating the gradual transition to green energies. The tubular members of a typical jacket structure, i.e., braces and chords, are usually simulated by either shell or beam elements. However, the latter typically disregard local flexibility contributions at the point of connection that may lead to an overestimated stiffness of the joint. As reported in the literature, the local deformations in the beam models are not negligible, influencing both the static and dynamic performance of the joint and thereby the entire jacket structure. The present paper introduces a simplified method applying a standard beam element in order to account for the joint flexibility providing a low-dimensional finite element model for jacket structures. To this end, a differential evolution optimization algorithm is applied, considering modal parameters as the objective function. The procedure results in obtaining the geometrical and mechanical properties of the simplified beam element introduced herein to model the tubular joints. The investigation of several case studies with different joint types verifies the effectiveness and the application range of the introduced element in modal and static analyses.