Study on ultimate strength reliability and partial safety factor calibration for CSR ships under new IACS Rec. 34 Rev. 2 wave environment

Objectives This study investigates the impact of the new ocean wave data, IACS Rec. 34 Rev. 2 (released in 2022), on the hull girder ultimate strength reliability and partial safety factors. Methods A database of 36 CSR sample ships was established to fit the extreme wave bending moment prediction formulas under the new ocean wave environment. A hull girder reliability analysis method tailored for the updated wave environment was developed, utilizing the Improved First-Order Second-Moment (IFOSM) method to calculate and compare the failure probabilities (Pf) under both the original and revised wave environment. Concurrently, the partial safety factor for vertical wave bending moment (γW) was optimized. Results The average failure probability of the sample ships under Rev. 2 decreased by 5×10-4 compared to the original environment. At the target reliability level, the average variation rates of partial safety factors for vertical wave bending moment was -10.13%, respectively. The optimized value of γW for all sample ships in both sagging and hogging conditions was determined to be 1.054.Conclusions The research findings provide a quantitative technical basis for the update of ship structural design standards and relevant calibrations under the new ocean wave environment.