Ultimate strength assessment of hull girders considering elastic shakedown based on Smith's method

The simplified progressive collapse method, Smith's method, for hull girders is one of the important methods for assessing the ultimate strengths of hull girders. The calculation accuracy primarily depends on the average stress–average strain relationship of the hull-stiffened plates. The vessel experiences cyclic bending moments during navigation due to waves, which lead to in-plane tensile–compressive loadings on the stiffened plates; thus, it is necessary to consider the elastic shakedown characteristics of the stiffened plates under cyclic loading. A novel average stress–average strain relationship for hull-stiffened plates considering the elastic shakedown limit state was developed by combining the nonlinear finite element method with beam–column theory. Furthermore, the obtained average stress–average strain relationship was introduced into Smith's method to evaluate the ultimate strengths of four hull girders and a scaled test model considering the elastic shakedown limit state. The results showed that the developed average stress–average strain relationship could accurately describe the elastic shakedown characteristics of hull-stiffened plates. Smith's method developed based on the above relationship could also effectively evaluate the ultimate strengths of hull girders under an elastic shakedown limit state. •Pioneering proposal of the average stress-average strain relationship for stiffened plates based on elastic shakedown state.•Smith's method procedure for the ultimate strength of hull girders under elastic shakedown state is innovatively developed.•Ultimate strength of four hull girders and a test model were calculated by Smith's method considering elastic shakedown..