Study On Assessment Methods Of Ultimate Strength Of Steel Components With Corrosion Damage

Corrosion damage makes the ultimate strength of the components severely reduced,seriously threatening the safety of the marine structure.As a kind of corrosion,pitting corrosion has received more and more attention.Accurate evaluation of the ultimate strength of steel components with pitting damage is a necessary prerequisite for the maintenance of ship and marine engineering structures.In this paper,the finite-element analysis method was used to study the ultimate strength reduction rules for plates and stiffened panels,subjected to random pitting damage,with different aspect ratios(?)and slenderness ratios(?)of plate,and slenderness ratios of stiffener(?)and corrosion volume ratios(DOV).The BP neural network was used to evaluate and predict the ultimate strength.The formula for calculating the ultimate strength reduction factor of the pitting damage plate and the stiffened panel was obtained,which provided the basis for the ultimate strength assessment and prediction of the pitting damage component.The specific work and main results are described as follows:(1)Numerical calculation models of the plates and stiffened panels with random pitting damage were established,and compared with models in the existing literature to verify the correctness of the models.(2)Based on simulation analysis,the effect of random nature of pitting on the ultimate strength of pitting plates was studied.The obtained results show that with the increase of the corrosion volume ratio(DOV),the effect of random nature of pitting corrosion increases,and the pitting corrosion with uniform distribution pattern overestimates the ultimate strength of the pitted structure.(3)The effect of various influencing factors(????DOV)on the ultimate strength of plates under uniaxial compression was studied.The results show that at the same degree of corrosion,the strength of the pitting plate deteriorates more seriously with the increase of the aspect ratio;the plate with small slenderness ratio has severe strength degradation and thick plates cause more severe degradation than other plates.(4)The effect of various influencing factors(??????DOV)on the ultimate strength of stiffened panels under uniaxial compression was studied.The results show that on the same model conditions,the stiffened panel with small aspect ratio and small slenderness ratio of the plate has severe strength degradation;the relation of ultimate strength reduction with slenderness ratio of the stiffener shows the characteristics as an extreme function with the most serious strength reduction at ? = 0.7;the ultimate strength decreases linearly as the corrosion volume ratio increases.(5)A BP neural network model was constructed to fit the calculation formula between the ultimate strength reduction factor and the influential factors thanks to its strong nonlinear fitting capabilities.This formula was used to evaluate and predict the ultimate strength of plates and stiffened panels with random pitting damage.Comparing with the existing ultimate strength evaluation method of the pitted damage components,the relative error of the ultimate strength reduction factor calculated in this paper and the ultimate strength reduction factor calculated in the literature is less than 10%,which verifies the feasibility of the evaluation method in this paper.(6)The orthogonal experiment design method was used to simplify the scale of learning and training samples of the BP network model and reduce the amount of calculation of the finite element model.The error of network prediction after using the orthogonal experiment is slightly larger than that based on all the sample data,but it still has the good evaluation accuracy of the ultimate strength of the pitted plate and the stiffened panel(the maximum relative error is less than 5%).