Influence of Shape of Initial Deflection upon Compressive Ultimate Strength of Long Rectangular Plates(Welding Mechanics, Strength & Design)

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In general, the deck plate of a box girder such as ship hull is subjected to inplane tensile and/or compressive load due to longitudinal bending. The deck plate is a main strength member of a box girder, and is stiffened by stiffeners and girders in the longitudinal and transverse directions to prevent overall buckling under compressive load. When the strength of a deck plate is considered, the plate elements subdivided by stiffeners and girders play an important role, and the accurate evaluation of their compressive strength is necessary, taking into account of the effect of welding deflection and residual stresses. In this paper, the compressive ultimate strength of a long rectangular plate with initial deflection is theorectically investigated, and the following main conclusions are obtained. (1) The simple formulae are proposed to calculate the conservative compressive ultimate strength of a long rectangular plate with welding initial deflection and residual stresses. (2) The mode of initial deflection due to welding is measured on 33 deck panels of a bulk carrier and a pure car carrier, and the coefficients of components of series functions to express initial deflection are calculated. (3) The characteristic of elastic-plastic large deflection behavior of a long rectangular plate with initial deflection may be described as follows: In case of thin plate, only one component mode of the initial deflection is amplified and becomes stable as the deflection increases. This component mode is not necessarily the one at buckling and is influential upon ultimate strength. This component is usually pretty smaller than the maximum initial deflection. In case of thick plate, a certain portion of the plate, where the largest curvature of the initial deflection is located, is decisive to progress of plastification which leads to collapse. Then, the maximum curvature of the initial deflection is decisive rather than the maximum deflection. Concerning plate of medium thickness, the mode of the initial deflection may change as the deflection increases. In this process, progress of plastification may be accelerated or decelerated by interaction among the component modes. This phenomena makes lower or higher the ultimate strength. (4) Based on the characteristic, Deflection method and Curvature method are proposed to predict the compressive ultimate strength of thin plate and thick plate, respectively. It is confirmed that these methods predict the ultimate strengths accurately in comparison with calculated ones. (5) The in-plane rigidity of the plate decreases as the load increases, since the compressive load is not supported at the central portion of the plate due to the effect of large deflection in the case of thin plate, while it is due to the effect of plastification by bending in the case of thick plate.
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Influence of Shape of Initial Deflection upon Compressive Ultimate Strength of Long Rectangular Plates(Welding Mechanics, Strength & Design)

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