Damage Detection for Offshore Platforms Based on Modal Redundancy Index of Damaged Member

According to the phenomenon that global damage detection of jacket platform is influenced by structure redundancy of damaged member, the concept of modal redundancy index (MRI) of damaged member is proposed. Through numerical simulation by means of mode strain energy method, the way that MRI of damaged members in different types and positions changed was studied, as well as the relationship between MRI and global damage detection. The numerical simulation result demonstrated that when MRI of pile element is less than 2.1×103, damage can be detected; when MRI of slanted brace element is less than 1.5×105, damage can be detected; when MRI of horizontal brace element is more than 5.8×105, damage cannot be detected. Therefore MRI can be a reference index in engineering application of global damage detection of offshore platforms.