Offshore Platform Structural Damage Identification Versus Robustness

The assessment of existing offshore steel jacket structures for use beyond their initial life requires a proper design of an inspection plan aimed to constantly check-up the integrity of the structural elements. In most cases the visual inspection of structural members or joints is hard to perform and evermore economically demanding. To this aim, within the framework of the Structural Health Monitoring, and taking into account that a damage originates changes in stiffness that are reflected in changes in main frequencies, a dynamic monitoring system able to evaluate the structural frequencies can be used as a sound indicator for major damage of the structure. The capability and limitations of a structural monitoring system as effective instrument to check-up the presence of a member failure are discussed in the paper through the discussion of a specific case study taking into account robustness and damage tolerance indicators. A proposal for possible improvements of the actual monitoring system is eventually reported.