Standard structural assessments of ship hulls include the evaluation of the elastic structural response. Elastic analysis neglects extreme and unpredicted loadings, which can produce catastrophic outcomes, such as the loss of the ship’s ultimate strength. Moreover, hull elements are considered unaffected by age-related degradation. Therefore, this study models and quantifies the effect of corrosion-induced structural degradation on the ultimate strength of a high-tensile-steel (HTS) cargo ship using progressive collapse and nonlinear finite element methods. Uniform and pitting corrosion are modeled through selected scenarios, which hull elements might encounter during exploitation, producing a total of 148 calculation models. The findings show that corrosion-induced degradation can significantly decrease the ultimate strength of the hull (up to 30% for the most severe scenarios assessed). Furthermore, ultimate strength decreases almost proportionally to the amount of wastage considered. It was found that stiffener corrosion has a significant effect on the total ultimate strength. This study’s aim is to emphasize the vast importance of including ultimate strength along with ageing effects in industry-standard structural assessments of large HTS ship structures, designed to last for several decades whilst exposed to excessive and unpredicted bending moments.

Due to the sudden nature of hull girder collapse caused by extreme loadings, the ultimate strength of ships, i.e., ultimate capacity, has to be evaluated. Ultimate strength analysis procedures have already been provided within the rules of the classification societies for sea-going ships. However, rules for inland vessels are not fully addressing the issue. In addition, literature data on the ultimate strength of inland vessels are almost negligible, which is alarming, considering the frequency of grounding and overloading events in inland navigation. Moreover, inland vessels' structural elements are prone to buckling due to their slender plates. In order to evaluate ultimate strength, an inland waterway (IW) barge is chosen for progressive collapse analysis (PCA) employment. PCA has demonstrated that the buckling collapse of structural elements vastly governs a vessel's ultimate capacity. Results show the extent of the safety zone between the actual loss of the ultimate capacity and the linear-elastic behavior of the structure.

This paper assesses the structural integrity of atypical superstructures mounted on the decks of two sister sea-going tankers under extreme load conditions. Namely, each tanker features a pair of deckhouses which are welded onto the existing deck structure girders, exposing them directly to harsh environmental loads. These deckhouses, designed as ‘ad hoc’ solutions resembling land-based structures with similar applications, serve as storage for ballast water treatment systems, added due to insufficient internal technical space within the existing ship structure. Given the lack of fully developed regulations for assessing the structural integrity of novel and atypical ship structures, classification rules typically require a direct structural assessment to ensure their structural integrity. Therefore, this study uses the finite element method to analyse extreme design load scenarios faced by these structures, including seawater loads from waves, wind loads, accelerations due to ship motions, and static loads from the structures’ and internal equipment weights. Besides identifying critical areas, the findings reveal that the initially proposed deckhouse structures failed to meet the criteria for certain scantling arrangements and demonstrate how variations in scantlings affect the overall structural response. Based on these insights, general recommendations for modifying the deckhouse structure are proposed.