Ultimate Hull Girder Strength under Longitudinal Bending

1. 研究了加筋钢板在推力作用下加筋的最佳建模方法。结果表明，无论是用解析法还是有限元法分析连续加筋板的倒塌行为时，加筋腹板应采用板模型，加筋翼缘应采用梁柱模型，以获得准确有效的结果。为了研究底部结构的倒塌行为和强度，开发了一种简单而有效的方法来模拟加筋板在侧向压力和推力载荷联合作用下的倒塌行为。通过与有限元分析结果的比较，验证了该方法的合理性。将该方法应用于计算机程序中，模拟了船体梁在纵向弯曲作用下的渐进垮塌行为。结果表明，船底侧压力和舷板侧压力对船体梁强度的影响较小。采用有限元法进行了一系列弹塑性大挠度分析，模拟研究了某舱底圆的连续破坏行为。在计算结果的基础上，建立了一个简单的动力模型来模拟舱底圆的倒塌行为。将该模型应用于计算机程序中，模拟了船体梁在纵向弯曲作用下的连续倒塌行为。结果表明，考虑大圆的屈曲效应时，船体梁的极限强度基本相同，但超过极限梁强度的承载力略有不同。提出了考虑剪力引起的截面翘曲对船体连续倒塌行为和船体梁极限强度影响的新方法。结果表明，当船体弯曲受压侧的翘曲法向应力变为压应力时，船体梁的极限强度最大降低15%。理想结构单元法（ISUM）单元是一种新开发的单元，能够对船体梁进行纵向弯曲的倒塌分析。在本研究项目中，尚未进行崩塌分析。然而，这种新单元与梁柱单元相结合，并准确地模拟了加筋板在压缩中的倒塌行为。该单元在船体梁倒塌分析中的应用仍然是一个未来的任务。评估了各种设计因素对船体梁极限强度的敏感性。利用这些灵敏度，对四艘现有船只进行了可靠性分析。得出的结论是，这些船是足够安全的，不会折断船体的大梁。建议在不同的设计阶段采用不同的方法来评估船体梁的极限强度。在详细分析中，推荐采用精确推导出加筋板单元平均应力-平均应变关系的Smith方法作为评估船体梁极限强度的最佳方法。少

1. The best modelling method of stiffener in the stiffened plating under thrust was investigated. It was found that the stiffener web should be modelled by a plate whereas stiffener flange should be modelled by a beam-column to obtain accurate results efficiently when the collapse behaviour of cotinuous stiffened plating is analysed either by the analytical method or the FEM.2. To investigate the collapse behaviour and strength of bottom structure, a simple but effective method was developed which enables to simulate the collapse behaviour of stiffened plating subjected to combined lateral pressure and thrust loads. The rationality of this method was confirmed by comparing the calculated results by this method with those by the FEM analysis. This method was implemented into the computer code to simulate progressive collpse behaviour of a ship hull girder subjected to longitudinal bending. It was confirmed that the influence of lateral pressure on ship bottom and side shell plating on t … More he ultimate hull girder strength is rather small.3. Performing a series of elastoplastic large deflection analysis by the FEM, progressive collapse behaviour of a bilge circle was simulated and investigated. On the basis of the calculated results, a simple dynamical model was developed to simulate collapse behaviour of bilge circle. This model was implemented into the computer code to simulate progressive collapse behaviour of a ship hull girder subjected to longitudinal bending. It was confirmed that the ultimate hull girder strength is almost the same but the capacity beyond the ultimate hull girder strength is a little different when the buckling effect of a bolge circle is accounted.4. New method was developed to account for the influence of warping of the cross-section produced by shear force on the progressive collapse behaviour and the ultimate hull girder strength. It was found that the ultimate hull girder strength is reduced by 15% at maximum when the normal stress by warping becomes compressive at the compression side of the hull girder bending.5. The plate ISUM (Idealised Structural Unit Method) element was newly developed which enables to perform collapse analysis of a ship hull girder subjected to longitudinal bending. In this research project, collapse analysis was not yet performed. However, this new element was combined with beam-column elements and the collapse behaviour of a stiffened plate in compression was accurately simulated. The application of this elements to hull girder collapse analysis remains as a future task.6. Sensitivities of various design factors on the ultimate hull girder strength were evaluated. Using these sensitivities, reliability analysis was performed on four existing vessels. It was concluded that these vessels are safe enough against breaking of their hull girder.7. It can be recommended that different method should be applied according to the stage of design to evaluate the ultimate hull girder strength. For the detailed analysis, the Smith's method using accuately derived average stress-average strain relationships of stiffened plate element was recommended as the best method to evaluate ultimate hull girder strength of a ship hull girder. Less