Effect of reinforcement on buckling and ultimate strength of perforated plates

•A series of numerical studies were carried out to analyze the buckling and ultimate strengths of reinforced perforated plates.•The ultimate buckling strength of the carling stiffener method, doubling method, and face-plating method was investigated.•Design formulae for calculating the ultimate strength of perforated plates were developed.•The optimum reinforcement method for perforated plates according to the loading conditions was proposed.

Cutouts are widely used in ships and offshore structures. These cutouts are used mainly for inspection, and they may be fitted for various purposes, including passing pipes and weight reduction. In general, plates with cutouts (perforated plates) are given high importance at the structural design stage because they can reduce the structural strength. In this regard, local reinforced perforated plates are used in shipyards to satisfy buckling and ultimate strength requirements, but quantitative evaluations of the reinforced perforated plates have not yet been carried out. To mitigate the decrease in the strength of perforated plates, the Carling, face-plating, and doubling stiffening methods have been adopted with the goal of increasing both the buckling and ultimate strengths. In particular, the Carling stiffener has been partially adopted at holes typically found in shipyards (e.g., access holes, lightening holes), but no standard methodologies or recommendations are available for the use of this stiffener. In the present study, a series of numerical studies were undertaken to analyze the buckling and ultimate strengths for various stiffening methods (Carling, face-plating, and doubling) and loading conditions (axial compression and in-plane edge shear loading). An optimal reinforcement method was determined by comparing stiffened weights and ultimate strengths of the three methods. Finally, a design formula for calculating the ultimate strength of a perforated plate was developed on the basis of over 144 cases of finite element analysis.