Ultimate strength of AL-6XN stainless steel plates and box columns under axial compression and shear loads

The strength limit state is one of the primary limit states that must be considered in the design of an advanced unidirectional double hull ship structure. In this study, the strength of double-hull ship structure made of AL-6XN nonmagnetic stainless steel was investigated. The AL-6XN alloy is an isotropic material and has a highly nonlinear stress-strain curve, without a well defined yield plateau. The investigation included the analytical study of strength of plates subjected to axial compression and combined axial compression and shear, and the experimental and analytical studies of the strength of cellular box columns subjected to axial compression and combined axial compression and shear.; The analytical studies on plates and box columns involved nonlinear finite element analysis, including both material and geometric nonlinearities. The local instability of the component plates was investigated using the finite element method program ABAQUS. The effects of welding residual stress, initial out-of-flatness, and boundary conditions were examined in detail. The ultimate strength from the nonlinear analysis was compared with predictions from empirical formulas used in ship structural design.; For the experimental study, large scale single cell and triple cell box columns simulating components of double hull ship structures were tested under axial compression and combined axial compression and shear loading conditions. The specimens showed excellent ductility and the dominant failure was instability of the component plates. The specimen behavior was analyzed by the finite element method, including measured material properties, residual stresses and initial out-of-flatness. The predicted maximum loads were in close agreement with the experimental maximum loads. The analyses also provided fairly good predictions of the local plate deformations and strains in the test specimens.; The experimental study was supplemented with a parametric study on general box column configurations. Compression-Shear interaction diagrams of various box column sections were developed. The analytical results from box column finite element models were compared with those from plate models. A method of predicting box column strength, assuming that each component plate contributed to overall stub-column curve was proposed. Comparisons with experimental results showed reasonably close predictions by the proposed method, compared to those from other methods.