Study On Residual Strength Of Cracked Ship Structures Under Combined Loadings

Ship hull structures such as inner bottom plates always bear complex loadings involving the longitudinal bending stress,transverse in-plane stress transferred from ship side plates under water pressure and uniform pressure of goods.Additionally,cracks which are prone to occur in welded joints and local stress concentration areas would degrade the load bearing capacity of ship plates seriously.So it's very important to assess the ultimate strength of cracked ship structures under combined loadings.Modified formulas used to calculate ultimate strength of cracked stiffened panels under combined loadings are proposed based on Perry-Robertson formula and equation proposed by Paik,considering the effects of combine loadings and crack damage on the effective breadth of panel under longitudinal compression.Firstly,closed form equations are deduced to calculate the effective breadth of panel under combine loadings based on Karman equations.Then,the factors that bring influences on residual ultimate strength of cracked panels were investigated by carrying out series of finite element analyses and simple empirical formula is proposed to calculate the residual ultimate strength of central cracked ship plate under biaxial compression based on the numerical results.After that,modified formulas to assess residual ultimate strength of cracked stiffened panels are deduced.Comparisons of values calculated by modified formulas,finite element method and experiments are conducted.Finally,ultimate strength of cracked box girders is studied,and an empirical formula is proposed to assess ultimate bending strength of cracked box girder when its cracked edge under tension,which could be taken as lower limits.