Damage detection in offshore platform structures from limited modal data

• Structural damage localization and quantification with limited modal data is developed.
• Slave DoFs iterative updating procedure (SDUP) is proposed to incorporate the spatially-incomplete mode shapes.
• Modal frequencies and mode shapes are not required to be paired.
• The damage assessment method performs well under mild noise environment.
• Noise has a larger effect on horizontal members than that of slanted brace or vertical columns.

Development of efficient global damage detection techniques for offshore structures is of great importance. The present paper applies the iterative modal strain energy (IMSE) method to locate and quantify the damage for three dimensional frame structures, when limited, spatially incomplete modal data are available. One theoretical development is a new procedure to directly incorporate the spatially-incomplete mode shapes in the algorithm, where slave degrees of freedom iterative updating procedure (SDUP) is developed for evaluating the damage indicator and damage severity. The merits of this new method are that both the modal frequencies and spatially incomplete mode shapes can be used. Also, the modal frequencies do not need to pair the mode shapes one by one. To demonstrate the feasibility and effectiveness of the developed algorithm, numerical studies are conducted for a 3D offshore platform based on data generated from finite element models. Numerical results demonstrate that the present method is effective for the damage assessment of a 3D frame structures when limited, spatially incomplete modal data are available. After considering more practical factors, it is expected to be more applicable in structural damage assessment.