Partial Safety Factors Assessment for Double Hull Tankers Following the New Common Structural Rules

Abstract

The partial safety factors are calculated for three double hull tankers of different size, designed according to the new IACS Common Structural Rules and based on load models estimated from the rule design values. The ultimate strength is calculated using progressive collapse method based on the net scantlings +50% of the corrosion addition, tnet+50, and applying the failure modes defined in the new rules defined in the Common Structural Rules. For one of the tankers the load models are calculated based on the actual load manual data. The still water bending moment is calculated for full load condition and the wave bending moment is based on direct calculations of wave induced load, determining the extreme value. The calculated loads are compared with the rule design values. Another load modeling based on the rule design values is calculated. The reliability and partial safety factors are calculated for both cases to show how the load models affect the values of partial safety factors. Sensitivity analysis is made to study the importance of the variables. The reliability of the three takers is calculated based on the rule design values and the corresponding partial safety factors are assessed. To achieve a certain pre defined level of reliability, a design modification factor is applied to the deck plating to adjust the ultimate strength. The loads are assumed to remain unchanged by the design modification factor.