Studies On Damage Detection For Offshore Platform Based On Vibration Response

Large-scale civil engineering structures (for example, offshore platform structures) are prone to be damaged during their service lives, caused by various environmental loads. Therefore the occurrence of damage during the life of an offshore structure is unavoidable. Thus, techniques for nondestructive damage detection of large structures based on vibration response are essential to ensure safety. The developed nondestructive damage detection method based on vibration response in large-scale structures was validated by physical model test. And the thesis focuses on the following tasks.The first issue is to study the modal parameters based on vibration response utilizing the Natural Excitation Technique (NExT) and the Eigensystem Realization Algorithm (ERA). An offshore platform was modeled by Finite Element (FE) Method, of which the analytical modal parameters were obtained by modal analysis. Eigensystem Realization Algorithm (ERA) is applied to identify the modal parameters of the field testing under ambient excitation. According to the comparison results, the Natural Excitation Technique (NExT) and the Eigensystem Realization Algorithm (ERA) were shown to be effective for the structural modal parameters identification. The second issue is to study the damage detection method based on the modal strain energy, introducing the damage index of modal strain energy radio. Numerical example of an offshore platform was performed to prove the validity of this method.Several damage scenarios including damaged diagonal braces without and with the mass change of the deck of the structure are simulated. Numerical results indicate that this damage detection method can detect the diagonal damage(s) using the first two...