Statistical properties of bulk carrier residual strength

Time-variant residual strength of bulk carriers under corrosion wastage is investigated by Monte Carlo simulation. A new formulation of the incremental-iterative approach is presented to account for instantaneous neutral axis rotation, in case of asymmetrical damage conditions. Relevant incidence on hull girder residual strength is preliminarily studied. Hence, two main aspects are investigated: the former regards the correlation among input variables, commonly assumed as uncorrelated in classical procedures. In this respect, three correlation models are considered: no correlation, full correlation, and full correlation among variables belonging to the same group of compartments. Subsequently, a z-test is performed and the hull girder residual strength probability density functions are determined for both sagging and hogging conditions, as when correlation exists, Lindeberg-Feller Central Limit Theorem cannot be applied. Three damage scenarios are analysed, according to the last requirements of Harmonized Common Structural Rules for Bulk Carriers and Oil Tankers, assuming as reference case the bulk carrier section scheme, proposed in the last ISSC Report. Finally, the residual strength factor distribution vs. time is determined, together with relevant lower/upper bound values, with certain non-exceedance probability level, that in turn depends on correlation among corrosion wastages of all structural members.