Assessing the collapse behavior of stiffened plate structures is an essential issue in predicting the ultimate strength of ships. The design of large structures requires an efficient approach to obtain results for several design variants within a reasonable period of time. Despite recent developments in computer technology, elasto-plastic large deflection analyses with Finite Element Analysis (FEA) are too time consuming for large structures. The Idealized Structural Unit Method (ISUM) proposed by Ueda and Rashed (1984) is one framework for implementing a faster model for collapse analysis, which is used in this paper. In ISUM, the elements are significantly larger than in FEA. Material and geometrical non-linearities are idealized and included in the formulation of the ISUM elements. Larger elements mean fewer nodes and fewer degrees of freedom to solve for. Therefore, calculation times for ISUM are much shorter than for FEA. The stiffened plate is one of the basic structural elements in ships. Not only the ultimate strength of individual stiffened plates, but also their post-ultimate strength behavior has to be accurately predicted to analyze the collapse behavior of ship structures as a whole. Yao et al. (1997b,2001) showed that under thrust in stiffener direction (hereafter longitudinal thrust) plastic deformation localizes in a part of the plating whereas the rest of the plate unloads. This phenomenon strongly influences the post-ultimate strength behavior of plates and stiffened plates and has to be considered in ISUM. For the plate panel, several idealized plate elements exist. The Simple Dynamical Model by Yao et al. (1993,1997a) consists of Elastic Large Deflection Analysis (ELDA) and Rigid Plastic Mechanism Analysis (RPMA). It has been successfully applied to plate panels, Yao et al. (2001), and in combination with beam-column elements also to stiffened plates, Fujikubo et al. (1998). As the plating is divided into several elements to all of which the Simple Dynamical Model is applied independently, this approach can cope with localized plastic deformation. However, the applicability of the model is limited to purely longitudinal thrust. The original ISUM rectangular plate element, Ueda et al. (1984), and an improved element, Ueda et al. (1993), are applicable to combined loads; they are based on the effective width concept. However, the original element cannot accurately predict the decrease in load-carrying capacity beyond ultimate strength. The improved element has better accuracy in this prediction, but its formulation is rather complicated and makes it difficult to apply this element, to stiffened plates. Another ISUM rectangular plate element that treats its internal lateral panel deflection as additional degree of freedom has been proposed, Masaoka et al. (1998). The lateral deflection of the plate is approximated by its elastic eigenmode throughout the collapse behavior. This element is applicable to combined loads and its formulation is less complicated than that of the previous element. However, the approach of using elastic eigenmodes of plates does not give good results for stiffened plates, ISSC (2000), because overall bending deformation of the stiffener and localization of plastic deformation cannot be considered. In the present paper, a new ISUM stiffened plate model that can cope with local panel buckling, stiffener buckling and localization of plastic deformation is proposed. To consider the buckling/collapse behavior of stiffener and plate panel including their interaction accurately, stiffeners and panels are modeled individually by beam-column elements and plate elements. The concept of using the internal lateral deflection as degree of freedom, Masaoka et al. (1998), is employed for the plate element, but several features of the element are reformulated. The new ISUM model is also applicable to stiffened plates under biaxial thrust, Fujikubo and Kaeding (2000, 2002). However, in this paper only the case of longitudinal thrust is considered. First, the characteristic collapse modes of stiffened plates under longitudinal thrust are studied by clasto-plastic large deflection analyses with FEA. The new ISUM model is formulated taking these characteristics into account. Several examples demonstrate the applicability and accuracy of the new method. Finally, the proposed model is applied to assess the collapse behavior of box girder specimens. The numerical results agree well with experiments.


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    Titel :

    Idealized structural unit method for collapse analyses of stiffened plate structures


    Weitere Titelangaben:

    Idealisiertes Struktureinheit-Verfahren (ISUM) für Bruchfestigkeitsanalysen von versteiften Plattenstrukturen


    Beteiligte:
    Kaeding, P. (Autor:in) / Fujikubo, M. (Autor:in)

    Erschienen in:

    Erscheinungsdatum :

    2003


    Format / Umfang :

    11 Seiten, 14 Bilder, 3 Tabellen, 19 Quellen



    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch





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