| Transmission tower would suffer from serious vibration problem under fluid wind loads,earthquake loads and some loads caused by extreme weather conditions.It is of important theoretical significance to adopt modern technical method for the research of the natural vibration feature and dynamic response and it would process a good prospect of engineering application.In this paper,the research uses technical routine of combination by experimental research and theoretical analysis.The vibration measurement technique of the transmission tower,force on the key tower element,damage identification and some other problems are studied on a typical 2D-J1-27 type tension angle tower.The main achievements are listed as follows:1)Strain modal analysis methodology for the transmission tower is studied.Based on the spatial deformation mechanical relation of one dimensional element,a new strain modal analysis method which is suitable for the transmission tower is proposed,and the method is used to analyze the strain modal distribution characteristics of the transmission tower.2)Transmission tower optimal strain gauges placement and analysis of dynamic strain measurement are studied.Based on strain modal analysis method,Effective Independence method is extended to the issues of strain gauge placement for the transmission tower.An optimal strain gauge placement methodology is proposed for the dynamic measurement of the transmission tower.The new proposed method is used to gain effective arrangement for the placement of strain gauges for the transmission tower.The strain modal of the transmission tower is tested and analyzed.The result shows that the selected test points are sound and they have stronger signal-to-noise ratio,and the strain distribution condition can be reflected better.3)Optimal biaxial accelerometer placement for the transmission tower is studied.Optimal sensor placement is transferred to be a multi-objective issue.Modal Criterion Assurance,Maximum Singular Value Decomposition Ratio and Modal Kinetic Energy are established as sub-objective function.NSGA-II algorithm and multi-dimensional norm select strategy are adopted to analyze the most suitable optimal sensor placement.And the results show that multi-objective optimization method can balance several objective functions effectively,and it can place the sensors on the better locations as far as possible.4)Dynamic strain distribution feature of the transmission tower under the dynamic loads is studied.The characteristic of wind field of the transmission tower is studied in detail,wind time-history is simulated based on Kaimal spectrum which varies with the height.The wind load of the transmission tower is transferred and wind-induced vibration of the transmission tower is simulated based on transient analysis on the finite element analysis software.Lattice type structural strain modal analysis method is used to calculate the dynamic strain distribution of the tower induced by wind loads.And the dynamic strain distribution of the transmission tower can match the results of strain modal analysis well.From the analysis of force of local elements on the tower,change trends of each type strain loaded on the tower’s elements are not the same,and the tower elements may suffer from variable loads.And at the same time,transmission line system model is established,which is used to analyze the dynamic strain distribution characteristic under the ice shedding condition of whole span on one phase conductor and ground wire.5)Experiment of wind response of the transmission tower and modal parameter identification are studied.Combing with the sensor locations analyzed by multi-objective optimal sensor placement method,the wind-induced transmission tower vibration response is tested.Natural Excitation Technique based Eigensystem Realization Algorithm is adopted to identify the structure modal parameters together with the stability diagram.The natural frequencies and damping ratios of the transmission tower are extracted.6)Vibration displacement integration from acceleration under low frequency is studied.Vibration displacement gained by integration of acceleration under low sample frequencies is studied.Combing with the moving wind method,an acceleration integration methodology based on Lagrange polynomial is proposed.A simple calculation formula is deduced.In addition,Simpson integration based on Lagrange interpolation is derived to be a same calculation formula as the Lagrange polynomial method.Integration is done on the simulated signal and test acceleration of a model transmission tower respectively,and the results show that the proposed method is more accurate.7)Damage identification of transmission tower main columns is studied.The flexibility matrix can be constructed easily and higher accuracy can be gained through a few low order modal parameters.When the main column suffers from some damage,the structural flexibility will be changed,and according to this,damage detection of the transmission tower is done through the discrepancy of the flexibility.The “free end effect” of the maximum element of the columns in the minus of the flexibility matrices is analyzed and this may play bad impact on the effective of the damage detection when the damage element is near the top of the tower.A modified diagonal element of the discrepancy of flexibility matrices method is proposed which can eliminate the differences of the flexibility matrices on the free ends.And the method is used for the damage detection of a transmission tower in service,the result shows that the proposed method is better than the original one. |
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