Numerical Research On Residual Ultimate Strength Of Ship’s Hull Structures With Cracking Defects

Due to the rough sea conditions,there are many maritime accidents happened in the last decades,causing huge loss of human property.And lessons from these ship accidents stimulate domestic and foreign researchers to pay attention to the safety of ship structures.Ultimate strength of ship structures represents the maximum load-carrying capacity of a ship,and the ship will collapse after exceeding the ultimate strength.Therefore,the ultimate strength assessment of ship structures is an important indicator to guarantee the safety of ship structures.On the other hand,ship structures are inevitable to suffer various kinds of damages and defects during their lifetime in service.In addition to corrosion,as a common defect of ship structures,cracking defect can cause local stress concentration,which is considered to have a significant effect on the buckling and ultimate strength behaviors of ship structural members and reduce the load-carrying capacity.This may lead to the collapse of ship structures when external loads acting on the ship structures are still lower than the ultimate design loads.Therefore,it is of great importance to predict the residual ultimate strength of the ship’s structural members with cracking defects to avoid catastrophic failure of structures in ship’s lifetime cycle.In this regard,this thesis carries out comprehensively numerical analysis of residual ultimate strength of ship’s hull structures with cracking defects,and the following works and contributions has been made in this thesis:(1)Investigation methods and progress of ultimate strength of ship structures have been reviewed thoroughly,also the research on residual ultimate strength of structural members with cracking defects has been summarized in details,and the importance of considering the effect of ultimate strength reduction due to cracking defect has been elaborated.(2)The effect of welding-induced initial imperfections(including the shape of initial deflection,the magnitude of initial deflection and the level of residual stress)on the collapse behavior of cracked plate is investigated thoroughly,by using numerical method in which the welding-induced initial imperfections are simulated properly.(3)Numerical analyses on the residual ultimate strength of cracked steel plates under longitudinal compression are conducted,in which the crack length,crack location and crack angle are varied in a systematical way to check their effect on collapse behavior of cracked plates.Based on the numerical results derived,simple empirical formula as a function of crack projected length are proposed to predict the ultimate strength of plate with a central inclined crack under longitudinal compression.(4)Numerical studies on the residual ultimate strength of cracked stiffened plates subjected to uniaxial compression are performed,in which four different types of cracked stiffened plate models are considered.Some parameters,including plate thickness,crack length and crack location,are changed during the numerical simulations in order to examine their influence on ultimate strength characteristics of cracked stiffened plates under uniaxial compression.(5)The effect of cracking defects on the ultimate strength of open box girders subjected to torsion,vertical bending moment and the combination of these two loading components is investigated numerically.Three types of cracks are taking into account in the numerical calculations,and main parameters including crack length,crack location and crack angle are varied.