A stiffness-based method for damage detection in 3-D offshore jacket platforms using inverse vibration problem (IVP) technique

Abstract

More attention has been paid to Damage detection in offshore jacket platforms (OJP) because of repair and maintenance issues. Damage detection using modal data from a few sensors is one of the main important subjects that researchers have paid attention to it. The inverse Vibration Problem (IVP) technique does not need modal data in all nodes of OJP but first modal data in different levels of platform and principal degrees of freedom could be sufficient. Since the complex structural model becomes a reduced shear building by implementing this technique, there must be a reduced equivalent stiffness matrix for the healthy structure to make the comparison for damage detection. This paper deals with the formulation and implementation of IVP technique in corporation of the proper method for calculation of equivalent level stiffness. The proper method was selected based on a comparison of modal data obtained from full and reduced models using comparison tools like the MAC coefficient. Also, damage detection in a typical OJP model under a specific damage scenario was investigated numerically and experimentally and the results show the reliable performance of the methodology. A damage detection flowchart is suggested to detect damage location properly. It is developed mainly based on geometrical couplings in OJP structure in damaged conditions and the method leads to damage location exactly and maximum error in damage prediction is obtained at about 12%.