Effects of redundancy in bracing systems on the fragility curve development of steel jacket offshore platform

Abstract

Steel jacket offshore platforms are typically employed for use in shallow to moderate water depths. During platform operations, there have been some historical accidents completely damaging the diagonal members of the bracing systems due to explosions, fire accidents and dropped objects. Different locations of damaged bracings demonstrate different levels of risk for safety and integrity of the structures. This research illustrates the effects of redundancy in the bracing systems for steel jacket offshore platforms. Assessments have been carried out using the nonlinear pushover analysis method and formations of nonlinear hinges of different members were noted. Redundancy in different positions has been considered to investigate the consequences. Reserve strength ratio (RSR) and damage strength ratio (DSR) of the global structure were also evaluated to understand the importance of different local members. From the collapse data of local failures, fragility curves for the global structures were estimated. The results demonstrated that the position of damage can be a great concern which affects the overall performance of the structures.