Research On Fuzzy System For Damage Identification Of Grid Structure Based On Modal

In recent years,with the rapid development of economy,large-span grid structure is widely used in domestic key projects and large industrial buildings due to its various advantages.In the process of grid structure in service,there will be bolt damage,member deformation and other damage affecting the safety of the structure,which is not easy to be found.If the damage is not treated in time,it is bound to cause the overall collapse of the building structure and endanger people’s personal safety and property safety.Therefore,it is necessary to detect the damage of the large grid structure in service every other period of time.In this paper,based on the current research results in the field of structural damage,a damage identification method of grid structure based on the combination of frequency change square ratio method and fuzzy reasoning method is proposed.Firstly,the square ratio vector of frequency change of all members in the grid structure is calculated.The actual square ratio vector of frequency change is calculated by ANSYS simulation of the damage of members.According to the modal confidence criterion,whether there is a strong correlation between the two vectors is judged,so as to identify the damaged members.Then,the fuzzy inference system based on frequency parameters and the fuzzy inference system based on vibration mode parameters are constructed respectively.The damage degree of the members in the asymmetric position of the structure is identified by the fuzzy inference method based on frequency parameters,and the damage state of the members in the symmetric position is identified by the fuzzy inference method based on vibration mode parameters.In this paper,the numerical simulation and experimental analysis of grid structure are carried out.In the part of numerical simulation,firstly,the modal analysis of the grid structure is carried out by using ANSYS software.The damage of the bar is simulated by reducing the elastic modulus of the bar,and the corresponding frequency and mode information are extracted;Then,the frequency and mode data are processed to obtain the square ratio vector of frequency change and the fuzzy rules of fuzzy inference system;Finally,the fuzzy inference system based on frequency parameters and vibration mode parameters is established through the fuzzy logic toolbox of MATLAB,and applied to the damage identification of grid structure.In order to verify its effectiveness,the damage conditions of single member at three different positions of top chord,web member and bottom chord are set respectively.In the test part,the force hammer is used to excite the excitation points of the grid structure,and the response signals of the structure are collected by sensors.Then the modal parameters of the structure are obtained directly through the modal analysis section of DASP software.The first-order vibration mode data and the first six order frequencies of the structure are extracted as the measured values in the process of structural damage identification,The damage detection method proposed in this paper is used to analyze the set working conditions.Through the numerical simulation and experimental analysis,it can be seen that the damage location can be accurately determined by using the square ratio vector of frequency variation to calculate the correlation,but the damage degree can not be determined;The fuzzy inference system based on frequency parameters can accurately determine the approximate damage degree of members;The fuzzy inference system based on modal parameters can effectively identify the damage state of bars in symmetrical position.The first step is preliminary damage location,the second step is damage degree determination,and the third step is accurate damage location.The three steps complement each other.The damage identification of grid structure is carried out,and the identification result is good.