Research On Grid Structure Damage Identification Combined With Modal Strain Energy Decomposition Method And Wavelet Packet Energy Index

Countries all over the world attach great importance to the research of large-span spatial structures.The research development level of this structural system is one of the important indicators to measure the development level of building science and technology in a country.Large-span spatial structures that have been in service for a long time face great risks,and there is currently no reliable and practical method for safety assessment of such structures.The timely establishment of structural damage identification and health monitoring systems for large-span spatial structures can not only provide timely information on the operation status of the structure,so that people can repair and strengthen the structure in time,but also predict the service life of the structure based on the current state of the structure.This technical means provides guarantee for the safety performance of the structure and escorts the sound operation of the structure.This paper takes the large-span space grid structure as the research object,and uses the modal strain energy decomposition and its expansion method to conduct damage identification research.First,the theory of the element modal strain energy method is enriched,and the applicability of the element modal strain energy change rate in the damage identification of spatial structures is discussed,and the modal strain energy decomposition method is applied to the damage identification of the grid structure.When the unit is slightly damaged,the wavelet packet decomposition is used for secondary recognition,and the DS theory is used to integrate the recognition results of the two methods.The main work and conclusions of the paper are as follows.（1）The rationality of using the undamaged stiffness matrix of the element to replace the element stiffness matrix after structural damage in the principle of the element modal strain energy change rate is proved,and an example is used to illustrate the effect of the element modal strain energy change rate on a plane truss structure.Some problems in damage location.（2）Using the secondary development function of ABAQUS and using Python language to develop a script program that is convenient for extracting the stiffness matrix and mass matrix of the structure.And use MATLAB to compile the corresponding series of programs for space coordinate conversion,element stiffness matrix decomposition,modal strain energy calculation,etc.,which establishes the basis of program calculation for the theory.（3）The research on structural damage identification based on the rate of change of element modal strain energy has been rich in research results from beams to twodimensional slab structures,and the research results of three-dimensional structures based on the rate of change of element modal strain energy are rarely seen.On the basis of summarizing the relevant research results at home and abroad,the applicability of the element modal strain energy change rate method to the three-dimensional structure damage identification is discussed.A numerical example is used to illustrate the use of the element modal strain energy change rate index for the three-dimensional structure.Damage location is inappropriate.（4）Based on the successful application of the modal strain energy decomposition method in the damage identification of offshore platforms,using this method in the damage identification of the grid structure,a systematic identification program was compiled,and the damage identification ability was investigated with a calculation example.This method is feasible to locate the damage position of the grid structure,and the recognition result is better.（5）In view of the poor recognition effect of the modal strain energy decomposition method when small damage occurs in the element,this paper uses the wavelet packet energy method to further identify the suspected damaged elements selected by the modal strain energy decomposition method,and proves this method It is effective and feasible.Under multi-damage conditions,this paper proposes the idea of using wavelet packet energy change indicators to perform multi-level identification of units under multidamage conditions.Based on the analysis of a grid structure,the method is effective and feasible.（6）Based on the information fusion theory,the DS evidence theory is used to fuse the two damage identification results of the modal strain energy decomposition method and the wavelet packet decomposition method.This method solves the poor recognition effect of the modal strain energy decomposition method when the element is slightly damaged The damage identification theory of space grid structure was developed.