Mehdi Alavinezhad - Department of Marine Industries, Science and Research Branch, Islamic Azad University, Tehran, Iran
Madjid Ghodsi Hassanabad - Department of Marine Industries, Science and Research Branch, Islamic Azad University, Tehran, Iran
Mohammad Javad Ketabdari - Department of Maritime Engineering, Amirkabir University of Technology, Tehran, Iran.
Masood Nekooei - Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

As one of the most important components of an offshore oil and gas complex, Catwalk (access bridge) provides support for equipment and act as a passage for staff. Therefore, any damage in this structure may result in casualties as well as financial and environmental losses. Hence, identifying the location and severity of damage in these structures is of a great importance. As a common SHM method, modal strain energy uses the changes in the dynamic properties of the structure for identifying the damage location and severity. Considering natural frequencies in the process of the damage localization is one of modifications that has been successfully applied to this method. In order to show the robustness of this method for identifying damages in real class offshore structures with a large number of elements, the improved modal strain energy (IMSE) method is applied for damage localization and quantification in the access bridge of Foroozan platform in the Persian Gulf. The results showed that the IMSE damage index is more accurate than the original Stubbs index. Both the single and multiple damages were predicted with a good accuracy with this method. However, the method was more accurate in locating the damages in horizontal elements as well as the elements far from the supports of the structure.

Offshore complex, Catwalk, Damage identification, Improved modal strain energy, Stubbs index