Time-variant ultimate strength reliability assessment of ship hulls considering corrosion and fatigue

Ship structures suffer various types of damage while in service. Age-related structural degradations, such as corrosion and fatigue cracks, are considered major types of damage. The purpose of this work is to propose a methodology to assess the time-variant ultimate strength of ship hull girder under the degradation of these damages, to provide a procedure to quickly perform reliability analysis of aging ship hulls, and to develop a more rational renewal and repair schemes that not only consider the maximum allowable corrosion wastage and critical crack size criteria, but also take into account the hull ultimate strength.; Mathematical models for predicting corrosion as a function of ship age are reviewed and compared based on sets of real vessel corrosion measurements. Fatigue cracking mechanism is also analyzed in this work. A crack size prediction model as a function of ship age is presented. Extensive numerical studies are carried out to investigate the ultimate strength reduction of unstiffened plates and stiffened panels that are wasted due to pit corrosion. The effect of fatigue cracks on tensile and compressive ultimate strength of unstiffened plates and stiffened panels are also analyzed by the finite element method. Empirical equations are developed to estimate the ultimate strength of unstiffened plates and stiffened panels with pit corrosion or fatigue crack damage based on the finite element analysis results. Using these equations, a modified simple formulation is proposed to predict the ultimate strength of the entire ship hull girder considering these age-related degradations.; Time-dependent reliability procedure of a double hull tanker is presented as an example with consideration given to the effects of corrosion and fatigue crack damage on ultimate strength and reliability. It is expected that the methodologies and procedures developed in the present study will provide a useful tool for assessing time-variant ultimate strength and reliability of aging ship hulls.