Structural reliability analysis of FPSOs towards a rational design procedure.
This report presents the structural reliability analysis of the hull girder ultimate strength for
the ship shaped FPSO Triton. The ultimate strength of the hull girder was calculated using a
component approach, where the behaviour of the hull is evaluated based on the behaviour of
the single structural components. Three collapse conditions were investigated; failure
initiated by plate compression, failure initiated by stiffener tension and failure initiated by
Only vertical bending moment has been considered and the hull girder loads are divided into
stillwater and wave induced components. The two loading components have been considered
independent and Ferry Borges - Castenheta load combination method has been applied to
obtain load combination factors for the Full Load, Partial Load (50 % loaded) and Ballast
The distributions of the extreme values of the vertical wave bending moments (VWBM)
were calculated, based on linear strip theory and a long-term formulation. The vertical
mooring forces are small and they were considered to have an insignificant influence on the
bending moment response.
The reliability analysis was carried out using a SORM analysis. Annual reliability indices (ß)
and probabilities of failures were calculated for hogging and sagging conditions. The
calculated ß values were higher than the annual reliability indices proposed in DNV
Classification Notes 30.6 for serious failures in redundant structures. This indicates that the
design is safe and reliable for operation in this particular location.