Experimental Research On Axial Force Testing Of Space Truss Structures Based On Wavelet Analysis Frequency Method

The accurate identification of the axial force or stress of the structural bars of the space grid structure in service is one of the problems to be solved in structural health monitoring.At present,there are obvious defects in several common methods of axial force measurement in engineering,such as magnetic flux method mainly used in bridge cable force detection;strain gauge test method is greatly affected by the test environment,and it is difficult to ensure the accuracy of the traditional embedding method after many years.In view of the mature application of frequency method in cable force detection of bridges and its advantages of nondestructive and convenient,it is a new choice to use frequency method to test the axial force of members of space truss structures.However,due to the differences in material properties,length,mechanical properties and restraint conditions between the two methods,the theoretical formula of frequency method for space truss members must be deduced again.In addition,the actual test signal is inevitably noisy due to the influence of surrounding environment and electromagnetic interference.Therefore,how to improve the accuracy of frequency method to measure the axial force of bar has become one of the hot issues in current research.Based on this,this Research uses the combination of wavelet analysis and frequency method to reduce the noise of the test signal in advance to improve the extraction accuracy of the vibration frequency information of the bar,and then uses frequency method theory to identify the bar axial force,so as to achieve the purpose of improving the accuracy of the bar axial force measurement of the grid structure.Firstly,the wavelet analysis method is used to de-noise the simulated noisy vibration signals of the truss members.By comparing the de-noising effect of the signals,the wavelet analysis de-noising method suitable for the axial force test of the truss members is selected,and the suitable wavelet basis function,wavelet threshold function,wavelet threshold estimation method and wavelet decomposition layer are determined.Secondly,through the single-bar and multi-bar model test of grid structure,it is verified that the method of wavelet analysis de-noising can effectively improve the frequency extraction accuracy of the acceleration response signal of the bar,which proves the effectiveness of this method.Then,the length,section area,restraint form and axial force of the bar which may affect the vibration frequency of the bar in the identification of the axial force are compared and analyzed.On this basis,the calculation formulas based on various factors are fitted by the measured data of single and multi-bar tests,and the relationship between the calculated frequency,the measured frequency and the fitting frequency is analyzed and compared.Finally,the influence of different bar constraints,tension and compression conditions on the vibration frequency is further studiedthrough the scale model test of space truss structure;and the number of bar constraints at both ends affecting the vibration frequency of the bar is taken as a parameter to further optimize the fitting formula,in order to obtain an effective formula for measuring the axial force of the bar of space truss structure,and verify the frequency method based on wavelet analysis.Feasibility of testing the axial force of members of space truss structure.The results show that the pre-noise reduction of the vibration signal by wavelet analysis can improve the accuracy of the natural frequency extraction of the member.The length,cross-section area,restraint form and axial force of the bars will have different effects on the frequency of the bars.The theoretical vibration frequency of the bars calculated from the theoretical calculation alone is more erroneous than the measured data of the bars.According to the revised formula of fitting measured data,the effect of bar restraint is further optimized,which shows good applicability in the measurement of bar axial force in grid scale model.This study provides a non-destructive and non-destructive testing and evaluation method for the health detection of grid structures in practical engineering,which takes into account the length of members,section area,restraint form,axial force of members and other engineering variables.The paper has 50 pictures,23 tables,and 60 references.