自動車専用運搬船のラッキング変形に対する強度

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In the conventional thin walled beam theory, transverse sections of a beam are assumed being stiffened rigidly by frames and bulkheads, and our main concerns are longitudinal stresses caused by bending and torsion. On the contrary, considering the beam structure with weak transverse members, which is the case for the hull girder of a pure car carrier, its transverse section sometimes deforms significantly by the shearing effect so-called racking. Based upon an equivalent truss idealization of shell plating, the hull girder is analyzed as a three-dimensional framed structure. We examine the effects of the structural patterns of large openings of the transverse bulkheads by numerical calculations and experiments. It is found that the racking deformation is effectively restrained by the bulkhead with a diagonal pattern of plating. Numerical values of racking angle are in fairly good agreement with experiments. Cracking failures caused by racking deformation of the transverse sections are sometimes found at the intersections of transverse girders and frames, and also at the corner of an opening in a partial bulkhead. Having calculated the stress concentration factors at the round intersections of the transverse girders and frames by the finite element method, the depth of the girder and the radius of the round intersection are properly determined in such a manner that the maximum local stresses are within the allowable levels. Numerical computations are carried out for an actual car/container carrier, whose bulkheads have large openings for the purpose of the vehicle access on decks. The racking load is derived along the line of Classification Notes by D_nV, and we assume the rolling angle of 27 degrees under the fully loaded condition. Strength of the intersections of the transverse girders and the local deformation of the openings at the partial bulkhead sections are found to be very sensitive to the racking deformation of the hull girder.
社団法人日本船舶海洋工学会の論文

自動車専用運搬船のラッキング変形に対する強度

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