The Theoretical Analysis And Study Of Machanical Behaviour For Transmission Tower

A transmission tower is a form of highly indeterminate space structures used extensively. Most of transmission towers constructed of angles eccentrically bolted at nodes, so they are widely regarded as one form most difficult to be analyzed of all lattice structures. In this dissertation, on the basic of reviewing the study and design data available, the structural theory of transmission tower is discussed, and the mechanical behaviour of transmission tower is systematically studied.To meet the needs for finite element analysis, in an updated Langrangian framework, the geometric nonlinear tangent stiffness matrixes of the space bar element and space beam-column element, the revising matrix to allow for the eccentric connection, the plastic reducing matrix for the material nonlinearity, and the mass matrixes are all derived. The effects o fall internal forces and initial defaults are taken into account i n the geometric nonlinear tangent stiffness matrix of space beam-column element based on a general thin-walled beam-column member, so the matrix can be used in various nonlinear analyses of transmission towers or other structures composed of thin-walled members.After concluding the static and dynamic solution strategies employed in FEMs, a FEM program is developed, which is suitable for linear or nonlinear analyses of the static or dynamic behaviours or dynamic properties of transmission towers. In the program the Newton-Raphson's method is used to iterative computation; and the method of either the cylinder-arc-length or the minimum residual displacement is adopted to control the iterative process. A tower may be treated as a space truss or a space frame or a structure composed of bar elements and beam-column elements.Based on different constructions of tower nodes, the effects of nodal constructions, connection patterns of webs, joint rigidities and the slippage of bolts on the structural behaviour of transmission are systematically analyzed, which may be very useful in FEMmodeling of transmission tower.In a study case of a full-scale 500k V transmission tower, a space truss, a space frame and three structures constructed of bar and beam-column elements with deferent eccentric connections are modeled, and under many static loading conditions the tower is analyzed. The effects of FEM models, nodal rigidities, connection eccentricities and geometry nonlinearity on the static behaviour of the tower are discussed. The comparison between the test results and computation results is made, and some useful conclusions are drawn.The five FEM models are used for modal analyses of the transmission tower. The first 100 order intrinsic frequencies of each model have all drawn, based on the relative modes the effects of the models and connection eccentricities on the results from the modal analyses are studied. The characteristics and suitable conditions of each model are pointed out, which may be useful to direct the studies on the dynamic properties of transmission towers.Finally, the five FEM models are used to study the dynamic response of the transmission tower when the middle or side conductor broken. The effects of damp and geometric nonlinearity and connection eccentricity on the dynamic response of the tower are all studied. Some useful conclusions are obtained, and an improvement on the item of technical code in effect is suggested.