An advanced design diagram of stiffened plate subjected to combined in-plane and lateral loads considering initial deflection effects

•The proposed design method, incorporating design curves and empirical formulas, provides a higher safety margin for stiffened plates under limit lateral pressure (Qlim), indicating the need for further consideration of span effects in load capacity.•Location and initial deflection shapes greatly impact the limit state analysis of stiffened plates, affecting the predictive ultimate strength under longitudinal compression and combined loads.•Stiffened plates with stiffener web local buckling-shaped deflections (wb) show lower ultimate strengths compared to traditional stiffener sideways deflection (wos), emphasising the significance of wb in realistic welding conditions. This study presents an advanced methodology for stiffened plates subjected to combined in-plane longitudinal compression and lateral loads. The proposed methodology is based on comprehensive numerical parametric analyses, and it utilises newly developed design curves for the lateral pressure limit and tailored empirical formulae for stiffened plates to increase the precision of ship structural designs. Plate–stiffener combination (PSC) members are used for the limit state analysis, which introduces various positions and initial deflection shapes specific to the PSC models. Local buckling-shaped deflections of the stiffener web are also incorporated into the analysis, which closely mirrors the real-world welding conditions of stiffened plates and provides deeper insight into their load-bearing capacities. These findings highlight the importance of accurately selecting the positions and initial deflections of stiffeners in PSC-based analyses to ensure that structural predictions are safe and reliable. The proposed method is grounded in conservative PSC models and represents a significant advancement in ship structural design in terms of safety and practicality. This research introduces a novel design methodology for stiffened plates subjected to combined longitudinal compression and lateral loads, leveraging comprehensive numerical parametric analyses. Central to this approach is the newly developed design curves for limit lateral pressure (Qlim) and empirical formulas tailored for stiffened plates, enhancing the precision in ship structural design. A distinctive feature of this study is the utilisation of plate-stiffener combination (PSC) members in the limit state analysis, meticulously considering various locations and initial deflection shapes specific to PSC models. A critical innovation