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 shallow to moderate water depth. During the platform operation, there are some historical accidents of the complete damages for the diagonal members of the bracing systems owing to explosion, fire and dropped objects. The different locations of damages in bracing members demonstrate different levels of risk for safety and integrity of the structures. This present research studies the effects of redundancy in the bracing systems for steel jacket offshore platforms. The assessments have been carried out by nonlinear pushover analysis method and formation of nonlinear hinges of different members were noted. Redundancy in different positions has been considered to investigate the consequences. Reserve strength ration, 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 curve for the global structure was estimated. The results demonstrated that position of damage can be a great concern which affects the overall performance of the structures.