Damage detection in offshore jacket platforms with limited modal information using the Damage Submatrices Method

The development of methods for damage detection for offshore jacket platforms is useful to prevent structural damage. In this work a methodology for damage identification is applied using the Damage Submatrices Method. The method determines the indicators of damage in terms of stiffness degradation, which allows the identification of damage from changes in structural stiffness values by comparing the baseline (or intact) and damaged conditions. A rectangular system of linear equations was solved to determine damage submatrices that contain information of structural damage associated with each structural element. Singular value decomposition was applied to these submatrices to determine the so-called damage indicators. The stiffness matrix was reconstructed based on limited modal data, using the first three mode shapes of the structure. Finally, results of the proposed method are shown using to a numerical case study of one offshore jacket platform. Several scenarios of damage are considered, and three sensitivity analyses were carried out as well, in order to compare the robustness of the method, which take into account: 1) the variation of the damage severity; 2) the combinations of the first three mode shapes of the platform; and 3) the noise influence in the modal displacements determination.