Seismic performance evaluation of fixed steel jacket platforms retrofitted with Buckling Restrained Braces

In recent years there have been significant developments in seismic retrofit of building structures. For steel off-shore jacket structures, however, researches on the seismic performance evaluation and retrofit are relatively rare. In this study, the advantages of using Buckling-Restrained Braces (BRBs) in offshore jacket structures and its effect on the seismic performance of the platform are highlighted. The potential failure mechanisms of the structures using both normal braces and BRBs under seismic loads were investigated first. Pushover analyses of fixed jacket offshore platforms comprising the most common types of the platforms in practice were conducted. In those model structures, two different schemes of BRB retrofitting were utilized and compared with the normal bracing case. After that, an example for the seismic assessment of an existing 8 legged service platform located in the Gulf of Thailand was investigated. The model was designed based on loads according to the environmental conditions in Gulf of Thailand. Different retrofitting schemes using normal braces were investigated to improve the seismic performance of the structure and the results were compared with the results of the seismic retrofit using BRBs. The analysis results showed that the seismic performances of the jacket structures were greatly improved when bracing members were replaced with BRBs compared to the case with using normal bracing. Numerical results revealed that the plastic hinges were more uniformly distributed over the structures in case of retrofit using BRB, while they were concentrated at the top of the structures when normal bracings were used.