Now take the ratio of the elastic modulus of the equivalent rod element of the joint bolt loose damage to the elastic modulus corresponding to the intact structure as the stiffness reduction coefficient, ie: G=Ewanhao-EtiaoEwanhao@100%(2) where Ewanhao is intact The elastic modulus of the equivalent rod unit of the bolt joint node, Etiao is the elastic modulus of the equivalent rod unit with the looseness of the joint bolt, then the size of G can reflect the degree of looseness of the bolt of the flange joint node. Indicates the relationship between actual damage and G. In A(B) of G, A represents the number of damaged bolts, and B represents the degree of looseness.
Strain Modal Theory and Strain Mode Acquisition The definition of strain mode difference vector is known by St. Venan's principle. Strain is sensitive to local damage. Considering that the strain mode of the corresponding structural displacement mode is the inherent dynamic characteristics of the structure, the position and extent of the structural damage can be determined by comparing the strain mode changes (strain mode difference vector) of the intact structure and the damaged structure. If the strain mode difference vector is defined as: vj=7d, j-7s, j(3), 7d, j is the j-th order strain modal vector of the rod end of the damage structure of the damage structure, 7s, j is The j-th order strain modal vector of the rod end corresponding to the intact structure. Then, in the case of a reasonable arrangement of strain modal points, it can be used as a symptom of structural damage diagnosis.
The strain mode is obtained according to the definition of strain mode. <4>:<=B5(4) In the vibration analysis of the transmission tower-line system, the first-order mode of the structure is often along the direction of the transmission line. Portrait. In order to eliminate the nonlinear influence of the transmission tower-line system to the greatest extent, it is better to use the first-order frequency and the longitudinal excitation along the transmission tower-line system to obtain the strain response at each position of the strain mode under the resonant excitation. A force sensor is arranged at the end of the connection between the transmission line and the tower structure to obtain the force of the transmission line to the transmission tower, and the force is applied to the finite element model of the tower structure to obtain the strain response 71 corresponding to the position of the strain mode; 70 is subtracted from 71, and normalized on this basis, the true strain mode of the transmission tower structure which eliminates the nonlinear coupling effect of the tower is obtained.
The establishment of the strain mode library for loose bolt damage of the node bolts is to obtain the strain mode corresponding to the various bolt loose joints of the transmission tower structure, and the bolt looseness damage is equivalent to the bending stiffness of the rod end section of the equivalent rod. On the basis of the following, the strain modal pattern library of the loose bolt damage of the transmission tower structure can be established as follows: Firstly, according to the equivalent method of loosening damage of the structural joint bolts in section 1.1, the damage under different degrees of bolt loosening damage can be obtained. The amount of identification (ie, the reduction factor of the equivalent beam element elastic modulus), and combination of them, establish a transmission tower damage model corresponding to various damage locations and degrees.
Fuzzy pattern recognition of node bolt looseness damage Based on the above improved fuzzy pattern recognition method, the specific steps of fuzzy pattern recognition of node bolt looseness damage are as follows: First, the strain mode of the actual damaged structure is measured, and the strain of the intact structure is obtained. The modal difference is calculated and its fuzzy subset on the strain mode difference domain is calculated. Then, using the improved fuzzy pattern recognition method, the structural damage pattern closest to the fuzzy subset with the strain mode difference of the actual structure is obtained. Finally, the position and extent of the actual structural joint bolt damage are obtained according to the obtained structural damage mode.
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