Study On Calculation Method Of Ultimate Strength Degradation Of Ship Hull Considering Maintenance And Renovation Effects

It is crucial important to estimate the ultimate strength of structuresduring the design, manufacture and service of ships. Ultimate strength ofship hull structure is the largest ability to resist the collapse of the wholeship structure. During the service of ships, without consideringmaintenance and other factors, the ultimate strength of the ship hullstructure is gradually degrading. This is mainly because of the hullstructure affected by damage factors, like corrosion, fatigue and so on.During the operating period, damages caused by corrosion and fatiguereduce the ultimate strength of hull structure gradually. Obviously, theultimate strength of ship hull structure is a time dependent issue. So it isnecessary to study the ship’s ultimate strength considering thetime-varying effects.This paper firstly studied the ultimate strength calculations of theship hull structures without considering damages through non-linear finiteelement method and the Smith method. When using nonlinear finiteelement method to calculate the ultimate strength of the ship hull, wemaitly discuss the influence of material nonlinearity on the calculationresults. Compared with the finite element method, Smith method candescribe the collapse of the hull structure model correctly and is relativelysave time, and more reliable when calculate the ultimate strength of thehull. The effect of corrosion damage and fatigue crack damage factors onthe ultimate strength can be quantified with Smith method. Then, thispaper studied corrosion damage and fatigue damage of the ship structures. Through adding the new calculation module of corrosion and fatigue, theprogram made by this paper can calculate the ship hull ultimate strengthin its life cycle and get the time-varying curve of ultimate strength.The results demonstrate that the material nonlinearity factor has littleeffect on the ultimate strength of ships, then, we can use the idealelastoplastic curve to analysis the strength of ship hull structural. It helpssave calculating time and avoids the complex process of materialproperties tests. In addition, the software developed in this paper not onlycan calculate ultimate strength of simple box girder, but also can calculatethe ultimate strength of large civilian vessels and warships, so we can getthe ultimate strength degradation curve of the ship hull structures in itswhole life. Therefore we can make reasonable maintenance strategy toensure the safety of the hull. The method of calculating ship hull ultimatestrength in its life cycle is validated with test data and FEM results. Theresults show the present method has good applicability and applicationprospects.