Study on the unequivalence between stiffness loss and strength loss of damaged hull girder

Abstract

Hull girder damage degree identification by dynamic parameter change mainly solves the stiffness loss, while ship safety assessment mainly aims at strength loss issues. In this paper, a novel method is proposed to calculate strength loss based on stiffness loss. Section modulus is taken as the strength index to reveal that the stiffness loss of hull girder after damage is not always equivalent to its strength loss, and the theory for unequivalence between stiffness loss and strength loss (UNSS) is validated by 13 common cross sections. A simplified hull section is taken as the research object to verify the theory by different damage cases. Finally, the strength loss correction formulas based on stiffness loss under different damage conditions are summarized by the proportional relationship derived from neutral axis shift and stiffness loss. Results show that the shift of neutral axis is the main reason for UNSS. Different damage conditions will show different UNSS characteristics. The new method concluded for calculating the strength loss of hull girder can help check the hull girder strength.