Fragility Analysis Of Transmission Tower-line System Subjected To Near-fault Ground Motion

High voltage and ultra high voltage transmission lines are important carriers of power energy transmission,which can transmit and distribute power to users.They are an indispensable part of the whole power system.With the rapid development of national economy,the demand for power energy in all walks of life continues to grow,and the construction of transmission lines is very rapid.However,previous strong earthquake records show that the transmission tower-line system is prone to collapse under earthquake,especially near-field earthquake,and the damage of transmission lines usually causes huge economic losses directly or indirectly.Therefore,it is of great significance to study the collapse mechanism and vulnerability analysis of transmission tower-line system under near-field seismic excitation.At present,little research has been done on the collapse mechanism and vulnerability analysis of transmission tower-line system under near-field seismic excitation.Based on explicit analysis method,the collapse of transmission tower-line system under near-field earthquake is simulated and the seismic fragility analysis based on probabilistic seismic demand model is studied.The four aspects of research work done in this thesis are listed as follows:(1)A new material constitutive model is proposed,and a user subroutine is compiled based on the model,damage variables and fitting column curves.The validity and accuracy of the subroutine are verified by comparing the test results with the numerical results;(2)Based on the practical engineering data,a three-dimensional finite element model of transmission tower line-system is established.Based on the user subroutine,the collapse of transmission tower line-system under near-field ground motion is simulated and the collapse mechanism,element failure type and weak positions of transmission tower are studied.(3)An inter-segment damage index(SDI)is proposed to quantitatively evaluate the damage level of each segment of transmission towers and determine the ultimate bearing capacity and the weakest position.The effects of different ground motions and ground motion incident angle on SDI values are studied.Based on the top displacement and SDI value,the collapse fragility analysis of the transmission tower-line system under near-field vibration is investigated.(4)Based on the Probabilistic Seismic Demand Model(PSDM),the fragility analysis of transmission tower and transmission tower-line system under near-field earthquake is investigated.The seismic fragility of transmission tower-line system under far-field and near-field ground motion is compared.