Plate panels of ships and floating offshore structures are likely subjected to cyclic loads arising from waves at sea. Depending on sea states, e.g., whipping in harsh sea states, the maximum amplitude of the cyclic loads may reach over 70% of ultimate loads. Of concerns is how the cyclic loads will affect the ultimate strength compared to a case of monotonically increasing loads. The aim of this paper is to experimentally investigate the ultimate strength characteristics of a steel stiffened plate structure under cyclic axial-compressive loading. A full-scale collapse testing in association with bottom structures of an as-built 1,900 TEU containership was conducted. It is concluded that the effects of cyclic loading on the ultimate compressive strength of steel stiffened plate structures are small as far as fatigue damages are not suffered due to the small number of load cycles. Details of the test database are documented, which will be useful to validate computational models for the ultimate strength analysis.

As a sequel to another paper of the authors on welding-induced initial deformations [1], this paper aims to obtain a direct measurement database of welding-induced residual stresses in a full-scale steel stiffened plate structure and also to study the applicability of computational models to predict them. A full-scale steel stiffened plate structure in association with plate panels in bottom structures of an as-built containership carrying 1,900 TEU was fabricated using exactly the same welding technology as used in today's shipbuilding industry. The X-ray diffraction method was employed to measure the residual stress distributions in the plating. In addition to simple formula estimations, computational models using the three-dimensional thermo-elastic-plastic finite element method were applied to predict the residual stress distributions. A comparison between full-scale measurements, numerical predictions and simple formula estimations was made. Details of the full-scale measurements are documented as they can be useful to validate the computational models formulated by other researchers.

This paper is a sequel to the authors' earlier article (Paik et al. 2020a, Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading, Structures,

This paper presents a new methodology to determine the design values of wave-induced hull girder loads acting on ships. The method is based on probabilistic approaches associated with selected scenarios that represent possible events in terms of the ship's functionality, operation and environment. As illustrative examples, the method is used to determine the design values of wave-induced vertical bending moments for as-built ships (a VLCC class tanker, a 9,300 TEU containership and a 22,000 TEU containership) and a hypothetical 25,000 TEU containership. The probabilities of exceedance for wave loads acting on ships are discussed in association with the design load values determined from classification society rules. It is found that both the class rule method and the present method are in good agreement for the considered example ships. The present methodology can of course be applied to determine other components of design wave loads such as horizontal bending moments and torsional moments.

The aim of the present paper is to investigate the ultimate strength characteristics of as-built ultra-large containership hull structures under combined vertical bending and torsional moments with varying the ship size. The intelligent supersize finite element method (ISFEM) is employed for the ultimate hull girder strength analyses. A total of three as-built containerships carrying 9,300 TEU, 13,000 TEU, and 22,000 TEU are studied. Based on the computations, ultimate strength interaction relationships of containership hull girders under combined vertical bending and torsional moments are also formulated by a curve fitting. Insights and structural design recommendations obtained from the study are summarized, which will be useful to not only enhance the ultimate limit state capacity of containership hull structures in existing sizes but also achieve the robust structural design of ultra-larger containerships which have never been built before.