Structural Health Monitoring And Response Analysis Of Transmission Tower Under Typhoon Excitations

Structural health monitoring is of great significance for the theoretical research and engineering application on damage assessment and active control of civil engineering structures.Due to the complex shape of engineering structures,it is tough to conduct experimental modal analysis and the artificial excitation is difficult to implement,therefore the excitation signal can not be effectively measured.The theory and technology of identifying structural modal parameters based on traditional input and output signals are difficult to be applied in large-scale engineering structures.However,the modal parameter identification method of civil engineering structures under environmental excitation,which does not need the known inputs as preconditions but only processes and calculates the output signals,has been widely used in engineering fields.In this paper,a random subspace modal parameter identification method based on output data is expatiated in detail.This method uses space projection theory to eliminate the noise signals unrelated to the response data and has good anti-noise abilities.Taking an electric transmission line in service in Guangdong Province as the engineering background,ANSYS finite element simulation software was used to establish the finite element model of the tension-resistant section.The generating fluctuation wind speed is applied to the model to conduct wind-induced dynamic response analysis,and stochastic subspace method is used to compile MATLAB program to identify the modal parameters of the dynamic response of the simulation transmission tower.Results were compared with the finite element results and the reliability of the program was verified.A nonlinear static collapse analysis was completed by applying wind loads to the model and continuously adjusting the wind speed,and then the influence of the unfavorable wind attack angle mentioned in the specification was studied.Through numerical simulation,the number of the transmission tower in the tension-resistant section which collapsed first and its initial failure location were determined.According to the information of stress nephogram and vibration modes,the layout plans for strain and acceleration sensors were designed,and then a complete health monitoring system was built.The structural health monitoring system installed on the transmission tower completely recorded the data of nearby wind field and tower vibration response during the landing of Typhoon Khanun.Through orthogonal decomposition of the time history data of the wind speeds,along-line direction and vertical-line direction wind speeds were obtained,respectively.The wind spectrum,turbulence integral scale,gust factor and turbulence intensity in two directions were calculated,and the variations of acceleration responses under different wind speeds were also calculated.The compiled random subspace method was used to study the measured data,then the frequencies and damping ratios of the towers were identified.It can be seen from the identification results that the frequency identification results under different wind speed excitations in the direction of the longitudinal and the vertical line are basically unchanged.It shows that the structure of the transmission tower did not cause obvious damage during the typhoon Khanun registration.