Ultimate Buckling Limit State Assessments of Perforated Panels in Medium-Range Merchant Ships Based on Updated Classification Rules and Nonlinear Finite Element Analysis

Merchant vessels often feature numerous perforations in their web frames. To enhance the buckling resistance of these perforated panels, it is customary to install local reinforcements around the openings. This research introduces a novel approach that segments perforated panels into separated unstiffened panels (SUPs) and applies recently updated classification rules for buckling strength assessment, supplemented by inelastic FEA. This research aims to show a case study on how to reduce shipbuilding expenses by conducting a quantitative analysis of the buckling strength of such panels. The study treated perforated panels as separated unstiffened panels (SUPs) in accordance with Common Structural Rules (CSR). The authors examined web frames from various types of carriers, including those for liquefied petroleum gas, containers, products, and crude oil. They gathered data on dimensions, materials, and applied loads for 96 SUPs in total. To assess the buckling strength of these SUPs, IACS rules, eigenvalue finite element analysis (FEA), and inelastic FEA were employed. We performed element size convergence analyses on a square unstiffened panel with simple support on all four edges, ultimately deciding on a 10 mm element size for both eigenvalue and inelastic FEAs. Additionally, inelastic FEAs were performed on the rectangular, unstiffened panels with various aspect ratios, and it was decided to use the average level of initial imperfection for the inelastic FEAs. The SUPs under investigation were classified into Method A and Method B based on CSR recommendations. The ultimate buckling strengths of the categorized SUPs were evaluated by CSR and inelastic FEA. CSR rules provided more conservative ultimate buckling strengths for SUPs corresponding to Method A, while inelastic FEA did for SUPs that were classified into Method B. On the other hand, the inelastic FEAs and CSR rules provided similar ultimate buckling strengths for SUPs requiring Method B. The eigenvalue FEA confirmed that Method B can be an alternative method to inelastic FEA and CSR rules. Significant cost savings were demonstrated by selectively applying CSR and inelastic FEAs for SUPs requiring Method A. The originality of this work lies in its application of the latest classification rule logic, detailed finite element validation using real ship data, and a cost-benefit analysis of reinforcement strategies.