Reliability analysis of suction caissons for moored structures under parameter uncertainties

• Uncertainty in reliability index of caissons assessed using first order formulation.
• Uncertain parameters in the statistical models of mooring loads are considered.
• Uncertain parameter in the suction caisson capacity model is considered.
• Predictive reliability estimated in terms of statistics of the reliability index.
• Case study of suction caissons subjected to catenary and taut-leg mooring loading.

A study is performed to assess the effect of parameter uncertainties on the uncertainty of the reliability index of suction caissons for moored structures under extreme sea conditions. Uncertain parameters in the statistical model of the maximum dynamic tension of the mooring lines and in the suction caisson capacity model are considered. A first-order approach is used to express the mean and the variance of the reliability index of suction caissons in terms of the mean values of the uncertain parameters, and in terms of the sensitivity vector and the covariance matrix of the uncertain parameters, respectively. The predictive reliability of the suction caisson is estimated as a function of the mean and variance of the reliability index. Suction caissons in normally consolidated clay subjected to loading from catenary and taut-leg mooring lines of an FPSO structure under extreme sea conditions in the Gulf of Mexico are considered for the study. The results show the relative influence of parameter uncertainties on the uncertainty of the suction caisson reliability index.