Abstract
This study examined the hull girder strength of intact and damaged ships by adopting the incremental-iterative method for progressive collapse analysis, which was extended to the general case of the unsymmetrical bending of beams with an arbitrary cross-section. The sources of an unsymmetrical loading, including rotation of the loading plane and section asymmetry caused by structural damage, are described. A fast and robust procedure is presented to determine the translation and rotation of the instantaneous neutral axis at each curvature increment when applying Smith’s progressive collapse analysis method. A series of analyses were conducted on a double hull VLCC and a bulk carrier, considering various loading plane angles and damage conditions. The decrease in ultimate strength and the influences of rotation of the instantaneous neutral axis and ship heeling are discussed. The proposed method can be used for a rapid and rational assessment of the hull girder strength under adverse conditions.
Highlights
Fast and robust methods are needed to design ship hulls to withstand extreme wave-induced bending moments under both intact and damaged conditions
Parunov et al [23] reported that IACS-CSR applies a fixed reduction of 10% on the ultimate strength of a hull girder with collision damage when predicting it with the incremental-iterative method without considering the rotation of the neutral axis
To apply Smith’s method to unsymmetrical bending, the position of the instantaneous neutral axis (INA) at any incremental curvature should be defined with two parameters
Summary
Fast and robust methods are needed to design ship hulls to withstand extreme wave-induced bending moments under both intact and damaged conditions. Parunov et al [23] reported that IACS-CSR applies a fixed reduction of 10% on the ultimate strength of a hull girder with collision damage when predicting it with the incremental-iterative method without considering the rotation of the neutral axis. This prescribed reduction ratio is not fully justified, and more research on this topic will be needed to develop the appropriate guidelines for ultimate strength assessments under adverse conditions. A systematic examination of the influence of rotation of the neutral axis under various loading and damage conditions is presented for the case of a double-hull oil tanker and a bulk carrier
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