Time-variant reliability analysis of novel deck and bottom panels

There has been an increasing interest in using reliability based approaches in ship structural design. The methods and numerical tools presently available to solve structural reliability problems are capable of representing in a rational manner the uncertainties involved in the design of structures and their consequences on the safety level. With these methods, the uncertainties in the design variables involved in a given strength requirement can be rationally quantified through probabilistic models. As a result, the probability of failure, or the probability of violation of the strength requirement can be computed and used as the safety measure. The objective of the present paper is to use novel longitudinals of Y-stiffener profiles instead of the conventional T-stiffeners profile in double hull oil tanker's bottom and deck panels under axial compressive loads considering the structural degradation due to corrosion effects. The Y-stiffener profile is a fabricated section and simply can be produced by attaching the lower end the conventional stiffener's web to the top of the hat part. The Y-stiffener utilizes the advantages of having more effective plate that allows increasing the stiffener spacing, which in turn drops the required number of stiffeners. Time variant reliability analyses were performed using VaP (Variable Processor) software via applying the Second Order Reliability Method (SORM) for both conventional and novel Y-stiffener profiles. The ultimate strength and the applied load formulations were derived based on the International Association of Classification Societies Common Structural Rules (IACS-CSR) for oil tankers. With the Y-stiffeners, a significant improvement in the panel's safety level was achieved in comparison with the conventional profiles in terms of providing higher safety index, larger safety index to weight ratio over the vessel entire lifetime and more structural weight saving.