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Publications
Li, Sh., Paik, J.K., Guedes Soares, C., Georgiadis, D. and Kyun Kim, D. (2025), Effect of plate-stiffener combination modelling uncertainty on ship hull girder ultimate strength reliability in vertical bending, Ocean Engineering, Vol. 340, 122226.
Vertical bending moment, resulting from uneven weight distribution, buoyancy, and dynamic wave forces, is a primary load component influencing ship hull structures. In extreme conditions, excessive bending can exceed a hull girder's ultimate strength, potentially causing catastrophic failure, commonly referred to as "breaking of its back." Assessing the ultimate capacity of ship hull girders is therefore critical for modern safety design practices. Hull structures, typically composed of stiffened plates, are often simplified into assemblies of "plate-stiffener combination" (PSC) models for efficient performance evaluation. These models approximate the behaviour of continuous stiffened plated structures under specific loads, making them a widely used approach for hull girder capacity analysis. While PSC models are effective for evaluating vertical bending moments, uncertainties arise due to variations in configurations, stress-strain relationships, or load-shortening curves. These factors influence local failures of plating, stiffener webs, and stiffener flanges, as well as their interactions. This paper quantifies the modelling uncertainties in PSC-based analyses of ultimate strength and reliability of ship hull structures. Based on multiple empirical formulae and 63 representative structural configurations, the derived uncertainty factor ?for PSC elements follows a log-normal distribution with a logarithmic mean of 0.087 and standard deviation of 0.1. A new formulation of limit state function is introduced to accommodate these uncertainties. The proposed approach is demonstrated through illustrative examples involving an ultra-large container ship and the Dow’s frigate. It was found that the inclusion of PSC elements’ modelling uncertainty represents a considerable reduction in reliability index ranging from 2.5% to 15%. The proposed framework provides a practical method for embedding strength modelling uncertainty into ultimate strength-based reliability assessments.
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