Seismic Performance Evaluation and Retrofit of Fixed Jacket Offshore Platform Structures

Abstract

In this study the seismic performances of the fixed-base jacket structures with various bracing configurations were evaluated by nonlinear static and dynamic methods, and the effects of various retrofit schemes were compared. It was observed that the conventional retrofit methods of increasing member size were somewhat effective in increasing the strength of fixed steel jacket platform structures but were not so effective in increasing ductility. However, the ductility of the structures retrofitted with buckling-restrained braces turned out to be increased significantly. In the structures with conventional bracing, plastic hinges or buckling generally occurred at the upper half of the jacket structures. On the contrary, they were more uniformly distributed along the structure height in the structure retrofitted using buckling restrained braces. The capacity curves obtained from incremental dynamic analysis generally corresponded well with those obtained from nonlinear static analysis using a lateral load pattern proportional to the first mode shape of the jacket structure.