Objectives  Such ship hull structures as inner bottom plates always bear complex loads involving the longitudinal bending stress and transverse in-plane stress transferred from the ship's side plates under water pressure. Additionally, the cracks that are likely to occur in welded joints and local stress concentration areas degrade the load bearing capacity of ship plates, so it is very important to assess the ultimate strength of cracked plates under biaxial compression.

  Methods  First, the qualitative expression of the residual ultimate strength of cracked hull plates is deduced in theory. Next, the factors that influence residual ultimate strength are investigated by carrying out a series of Finite Element Analyses, including the length and inclined angle of the crack, aspect ratio and slenderness ratio of ship plate, and ratio between transverse and longitudinal in-plane stress, and an approach for the effective projected length of an inclined crack is obtained. Based on the numerical results, a simple empirical formula is proposed to calculate the residual ultimate strength of central cracked hull plates under biaxial compression.

  Results  According to a relative error analysis, the caculated results has higher accuracy by the proposed formula,

  Conclusions  whick can be used to accurately calculate the longitudinal ultimate strength of inner bottom plates.