Abstract:Overhead high-voltage electric-transmission lines play an important role in the operation of a reliable electrical power system.Damage to these lines can cause great economic loss and bring inconvenience to human life.A substantial number of transmission lines have been damaged by catastrophic earthquakes around the world.The transmission tower tilt or collapse,conductor breakage,foundation subsidence,and insulator destruction were the major types of failure.It is necessary to study not only the seismic response of transmission lines in the elastic and plastic phases but also their collapse process.Progressive collapse analysis is a well-understood physical occurrence in which the loss of local load-bearing capacity propagates through a system,precipitating complete collapse or a major portion of it.The vulnerable points,collapse mode,and capacity of the structure can be evaluated by it,and these data can be used for the design of new towers or for evaluating existing towers.Many scholars have studied the nonlinear responses of single transmission towers or tower-line coupled systems.Numerical simulation of progressive collapse is a challenging task,which includes material and geometric nonlinearity,contact and collision between elements,and losing the load-bearing capacity of elements.Nowadays,there are mainly four numerical analytical methods used for the collapse analysis:the discrete-element method (DEM),combined finite-discrete element method,applied-element method (AEM),and finite-element method (FEM).The FEM,based on continuum mechanics,is the most widely used method in structural engineering.For linear elastic problems,the method has proved to be advantageous.Furthermore,the method is very effective for solving nonlinear problems by using reasonable constitutive relationships.The method can be used in the solution of large-scale and complex industrial problems,while other methods are extremely difficult to use.During the collapse process under an earthquake,some elements lose load-bearing capacity,which is a problem for the FEM.Commonly,the method of removing these elements is used,which is called the birth-death element method.The conductors and ground wires can be simplified as concentrated masses for the seismic analysis of transmission tower-line coupled systems.In this paper,this method is used.With the simplified model,by using the finite-element program ABAQUS,the progressive collapse analysis of a transmission tower under an earthquake is conducted.The results show that the vulnerable points and progressive collapse process obtained are in good accord with the results obtained by using the tower-line coupled system with three towers and four span lines.Therefore,the simplified model can be used in the seismic analysis of transmission tower-line coupled systems.
