Generalized closed-form formulae for characterizing the ultimate strength envelope of ship stiffened panels subjected to combined biaxial compression and lateral pressure

Semi-analytical formula derived from numerical or experimental data is universally recognized as a powerful approach in the ultimate limit state (ULS) design of ship structures. However, it is extremely challenging to formulate a unified equation with excellent accuracy, applicability and practicality for characterizing the ultimate strength envelope of ship stiffened panels under combined biaxial compression and lateral pressure using conventional regression techniques. To address this drawback, this paper proposes a novel strategy mainly involving an equivalent sequential loading approach and artificial intelligence method. The FE model and new loading approach are validated based on the reported experimental data and classical proportional loading approach. Then, traditional implicit interaction relationship of the ultimate strength of stiffened panels under biaxial compression is decoupled by using the new loading method. Afterward, ABAQUS non-linear finite element analysis (FEA) incorporated with a Python code is conducted extensively. Influences of the plate aspect ratio, plate slenderness ratio, column slenderness ratio, transverse/longitudinal load and lateral pressure on the longitudinal/transverse ultimate strength (LUS or TUS) are comprehensively examined. In total, 4009 and 2813 datasets are numerically generated to develop two artificial neural network (ANN) models. The derived explicit formulae used to predict the LUS and TUS both reveal positive agreements with FE results (R = 0.993 and 0.999 for the two test sets), and they are eventually implemented in two user-friendly graphical interface tools. Performance of the proposed generalized closed-form formulae is further verified by using the reported experimental data, empirical formulae and numerical results of other scholars. The proposed formulae can effectively address the ultimate strength assessment of stiffened panels under different load combinations, including pure longitudinal/transverse compression, combined longitudinal/transverse compression & lateral pressure, as well as combined biaxial compression & lateral pressure.