Mechanical Properties Deterioration Assessment Of Random Pitting Steel Tube Members Using Numerical Method

The spatial structure is applied at a higher and higher frequency due to its flexibility of structural form and beauty of structural shape.Corrosion will deteriorate the mechanical performance of the spatial structure to a certain degree after the structure comes to use.Compared with other types of corrosion,pitting corrosion is the most server one,which is particularly harmful to the safety of the structure.At the same time,steel tubes are the main component of spatial structures.Considering the two points aforementioned,it is of profound significance to study the mechanical properties deterioration of randomly-pitting-corroded steel tube.Based on the statistic rule of actual corrosion,this paper establishes the finite element model of randomly-pitting-corroded steel tube and analyzes its mechanical properties deterioration under axial tension,axial compression and shear force.Furthermore,a practical calculation method for the deterioration of corresponding mechanical properties is also proposed.The main contents and conclusions of this paper are as drawn:1.According to the statistic law of actual corrosion,a numerical model of randomly-pitting-corroded steel tube is established.In the numerical model,parameters e.g.shapes of the pits,sizes of the pits,positions of the pits,are considered.The parameters of the numerical model of randomly-pitting-corroded steel tube are obtained by random sampling in Matlab.At last,a finite element model of randomly-pitting-corroded steel tube is formulated on the platform of ANSYS after the data converted into APDL language.2.The deterioration of elastic modulus,yield strength,and ultimate strength of randomly-pittingcorroded tubes under axial pressure is studied.The results demonstrate that it is unsafe to adopt the uniform pitting corrosion to simulate pitting corrosion.The maximum section loss rate can be used to evaluate the yield strength deterioration and ultimate strength deterioration of randomly-pitting-corroded tubes.And the corrosion rate can be used to evaluate the elastic modulus deterioration of randomly-pitting-corroded tubes.Then the relationship between corrosion rate and maximum section loss rate is discovered by data fitting.Finally,three simplified equations for ultimate strength,yield strength and elastic modulus are proposed based on the aforementioned relationship and the time-varying models of the corrosion rate.3.The deterioration of elastic modulus and buckling load of randomly-pitting-corroded tubes under axial pressure is studied.And the method to analysis the deterioration of the buckling of randomly-pittingcorroded tubes is proposed.It is deduced that the elastic modulus deterioration of randomly-pitting-corroded tubes under axial pressure is the same as axial tension.It also can be concluded that corrosion rate can be used to evaluate the deterioration of elastic buckling load and elastoplastic buckling load,and the normalized slenderness ratio can be used to evaluate the deterioration of plastic buckling load.Considering the formulae of stability design in the steel structure design specification,a simplified design formula for the stability of randomly-pitting-corroded tubes under axial compression is proposed.4.The deterioration of shear modulus and shear strength of randomly-pitting-corroded tubes under shear force is studied.The results demonstrate that it is unsafe to adopt the uniform pitting corrosion to simulate pitting corrosion.The maximum section loss rate can be used to evaluate the shear strength deterioration of randomly-pitting-corroded tubes.And the corrosion rate can be used to evaluate the shear modulus deterioration of randomly-pitting-corroded tubes.Then the relationship between corrosion rate and maximum section loss rate is discovered by data fitting.Finally,two simplified equations for shear modulus and shear strength are proposed based on the aforementioned relationship and the time-varying models of the corrosion rate.The novelties of this paper:1.A simple numerical model of randomly-pitting-corroded tube is formulated.The finite element model of randomly-pitting-corroded steel tube is put forward based on actual corrosion.2.The method for analyzing the mechanical properties deterioration of randomly-pitting-corroded steel tubes is proposed based on the steel tubes finite element model subjected to random pitting corrosion.