Progressive Collapse Behavior of Ship Hull and Efficient Method of Its Analysis

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An efficient method of progressive collapse analysis of ship structural members and systems was pursued in this study from two different aspects, one is the extension of Idealized Structural Unit Method (ISUM) and the other is the application of dynamic explicit method to quasi-static Finite Element Analysis (FEA). In ISUM, the structure is discretized into possible largest elements and the nonlinear behavior of such elements due to yielding and large deflection is idealized by appropriate shape functions and yielding criteria. The degree of freedom to solve for is therefore significantly reduced compared to FEA, resulting inthe reduction of computational efforts and time. The major achievements in this study can be summarized as follows:(1) ISUM rectangular plate element was extended so that the lateral pressure can be considered as well as the thrust loads. It was also made possible to consider the effect of welding residual stresses both in plate and in stiffener. The progressive co … More llapse analysis of a ship cross section under pure bending was performed, and a good accuracy and an efficiency of ISUM were demonstrated. CPU time required for ISUM was about 1/70 of that for FEA.(2) ISUM girder element for the progressive collapse analysis of double hull structure was developed. The effect of cutouts in the floor or girder can be considered by appropriately selecting integration points for the calculation of stiffness matrices. The progressive collapse analysis of a double bottom structure subjected to uniform lateral pressure showed the efficient and accurate applicability of the proposed ISUM model. CPU time required for ISUM was about 1/70-1/100 of that for FEA.(3) The loading condition necessary for the quasi-static FEA using dynamic explicit approach was discussed. It was shown that the condition is given as a function of natural period corresponding to the natural vibration mode resembling the buckling mode.(4) Cyclic bending test of a box-girder specimen was performed to investigate the cyclic collapse behavior including the initiation of a low cycle fatigue cracking after panel buckling. A comparison between test and ISUM analysis exhibited the satisfactory accuracy of ISUM analysis. Less