Strength Analysis of Topside Supports on FPSO Hull

Abstract

Abstract

This paper is performed to determine strength and endurance capacity of topside supports and underlying hull structure on Floating Production Storage Offloading (FPSO) platform. Support stools shall be installed on every intersection between longitudinal bulkheads and transverse frames.

Strictly, the analysis is relevant to topside supports and hull structure in the mid-ship area away from the moon-pool, but modification of the results to be representative for the moon-pool area is performed with respect to fatigue calculations has been done.

The results indicate satisfactory fatigue lives of the topside support connections (bracket toes) to the main deck. However, fatigue problems may occur at the ending of the pillar flanges above the main deck. Re-design of the pillars to meet the Det Norske Veritas (DNV) fatigue requirements will be performed during the detailed design of the topside structure.

For the Ultimate Limit State (ULS) load case, local buckling must be expected in certain areas of both the longitudinal bulkhead at 6.24 m of centreline and the inner side bulkhead. However, sufficient strength of the structure has been documented based on considerations of modified force flow due to this buckling. Thus, no modifications of the supporting hull are found necessary due to buckling.

The results show that no modifications of the hull structure should be necessary in order to fulfil the requirements in accordance with DNV Rules. However, the topside support stools shall be re-designed in order to fulfil the requirements of minimum twenty years fatigue life.

Keywords: Fatigue damage, buckling, FPSO platforms, hull topside interface