Experimental Study On Axial Force Test Of Non-uniform Pitting Grid Structure Members Based On Frequency Method

The large-span grid structure is widely used in wet and highly corrosive environments such as industrial plants.Health testing of grid structures that have been in a corrosive environment for a long time is a hot spot.Non-uniform pitting often occurs in grid structures in highly corrosive environments.In the past,the axial section of the rods with different corrosion degrees was simplified.The influence of corrosion factors on the axial force of the rod is not considered.The effect of pitting on the structure of the grid is much greater than that of uniform corrosion.Pitting causes stress concentration on the surface of the rod,When the stress in other parts is much less than the yield stress,The crater position stress has reached yielding,Uneven deformation of the surface of the rod reduces the plastic properties and load bearing capacity of the rod.The intrinsic relationship between the axial force of the rods with different degrees of corrosion and the corrosion factors directly affects the accuracy of the axial force detection.In this study,the effect of pitting on the natural frequency of the members of the grid structure is analyzed based on the frequency method by the combination of single-rod test and single-pole numerical simulation.By considering the diameter,depth,position,number,and section form of the etch pit on the rod,the influence of the parameters on the rod frequency under different axial forces is considered.Analyze the influence of the pit on the natural frequency of the rod;By analyzing the correlation between the parameters of the crater and the frequency of the member,the influence degree of different factors of the crater on the frequency of the member is determined.The calculation relationship between the axial force and the natural frequency suitable for the non-uniform pitting grid member is fitted by a large number of experimental data.Through the ultimate bearing capacity test of the pitting rods,the influence law and influence degree of the parameters of the pits on the ultimate bearing capacity of the members are analyzed.The accuracy of the law obtained by the single-bar test is verified by the non-uniform pitting grid scale model test;The accuracy of the above fitting formula is further tested by the grid scale model test data.And correct the fitting formula,The formula for calculating the axial force of the non-uniform pitting grid structure based on the frequency method is fitted.The results show that the etch pit has a greater influence on the frequency of the grid structure members.The influence of different parameters of the pit on the frequencyof the rod and the degree of influence are different.Compared with the accuracy of calculating the axial force of the grid member by equal section reduction,it is more accurate to calculate the axial force of the grid structure rod which is pitting by the fitting formula.Therefore,this study can provide accurate basic data for the analysis of the mechanical performance of corroded grid structures.At the same time,it can reveal the potential safety hazards of the in-service network and make preventive measures in advance.This fitting formula can provide a reliable and novel method for the axial force test of non-uniform pitting grid members and the health detection of in-service grids.