Objectives  In view of the fact that the structural performance assessment method of the internal-pressure-resistant square cabin is not clear and the general specifications for naval ships are not fully applicable, the stress analysis method and strength assessment criteria applicable to the internal-pressure-resistant square cabin are studied.

  Methods  Based on the theory of elasticity, the two yield criteria Mises and Tresca commonly applied in ASME BPVC were analyzed. According to the principle of safety, Tresca was determined to be the analysis criterion applicable to the internal-pressure-resistant square cabin. By taking the bulkhead grillage as the basic unit, the stress classification of the internal-pressure-resistant square cabin was carried out based on ASME BPVC, and four typical assessment locations were obtained: the center of the plate panel, the midpoint of the short side of the plate panel, the midpoint of the long side of the plate panel, and the corner of the plate panel. In order to reduce the amount of engineering calculation, the theoretical formula and numerical calculation method of stress components for plate element finite element analysis were proposed based on the stress linearization theory, and the solid finite element model of grillage was established for comparing the difference between the structural assessment results of two models.

  Results  Compared with the accurate results of the solid element model, the error of plate element stress analysis result is basically about 3%, and the results of plate elements are generally larger. Considering the safety conservative assessment principle of ships and nuclear structures, it can be considered that the strength assessment method of internal-pressure-resistant square cabins based on the plate element finite element model and ASME BPVC meets the engineering requirements.

  Conclusions  This study can provide a reference for the stress analysis and strength assessment of the internal-pressure-resistant square cabin, and is of great significance for tackling the technical bottleneck faced by the ships using nuclear power plants.