Ultimate Longitudinal Strength of a Suezmax Tanker Ship Under Sagging Condition Using FEA and the IACS Method

Ultimate longitudinal strength at the midships of the hull girder is an essential parameter for the ship’s structural design. International Association of the Classification Societies (IACS) has adopted the Common Structural Rules (CSR) for bulk carriers and tankers, which specify the requirement associated with the ultimate bending moment of the hull girder structure, providing recommendations for the calculation. The first method is a single-step procedure for calculating ultimate bending under sagging conditions, and the second is an incremental, iterative method. This paper analyzes a typical Suezmax ship using a single-step procedure proposed by IACS and a correlation with the numerical bending analysis of a ship section by nonlinear FEA using shell elements. The procedure for building the mesh of the upper deck in both methods is based on assembling individual deformed plates to simulate the initial imperfections. The deformed plates are provided from a previous buckling analysis. Different levels of plate deformations are analyzed using Smith’s initial imperfection equations. The numerical model is analyzed using the Abaqus software, and Python script is employed to build the upper panel. The results showed a correlation between the FEA and the IACS recommendations.