Numerical and Experimental Analyses of Ultimate Longitudinal Strength of a Small-Scale Hull Box Girder

Hull girder ultimate strength is an essential parameter for the ship's structural design. Numerous research studies have been done about hull girder bending. However, few experimental tests have been carried out due to the fabrication cost, the difficulty of monitoring loads, and mapping surfaces of models on large- and medium-scale. This paper conducted a four-point bending test of a small-scale hull box girder. The dimensions of the box girder model are defined from geometric slenderness ratios representing a double bottom panel at the midship of a typical Suezmax tanker. Numerical finite element models are developed, where the friction coefficient between the model and its supports is determined based on experimental correlation. The numerical models with different initial imperfection distributions are considered to perform ultimate strength analyses. Initial imperfections implemented in the models are based on least-squares regression of the geometric imperfections measured from the experimental models. Strain gauges were installed at the upper panel and obtained measurements compared with local numerical strains. Both experimental and numerical models showed that the upper panel of the box girder presented initial structural failure in the plating between stiffeners, which evolved to the stiffeners, following the expected buckling sequence of a reinforced panel. IACS formulation and direct methods have been employed to evaluate the ultimate bending moment. A correlation between the theoretical and experimental results indicates that the IACS formulation better predicts the ultimate bending moment, with the additional advantage of estimating the curvature. This paper also provides methodology and parameters for future studies of the ultimate strength of ship panels with different slenderness ratios.