Dynamic Responses of Long-Span Transmission Tower-Line System Subjected to Broken Wires

A macroscopic finite element modeling approach was proposed to calculate the vibration of a tower-line system subjected to broken wires with software ANSYS/LS-DYNA. In the finite element model, not only the nonlinearity of wires and suspension insulators are considered, but also the support towers are included. The incremental and iterative approaches are combined by applying the unbalanced loads incrementally during each iteration cycle. The approach was illustrated with an example of a Hanjiang- River long-span transmission line system subjected to a shield wire and a conductor failure, respectively. The analysis results showed that the proposed dynamic simulation approach can demonstrate the kinetic process of the tower-line system subjected to wire ruptures： The frequencies of line components were lower and densely distributed, but the frequencies of tower components were higher and sparsely distributed. Anyhow, the dynamic effects of wire ruptures on tower-line system could not be ignored in analysis of tower-line system subjected wire failures.

Response of a transmission tower-line system at a canyon site to spatially varying ground motions

Collapses of transmission towers were often observed in previous large earthquakes such as the Chi-Chi earthquake in Taiwan and Wenchuan earthquake in Sichuan,China. These collapses were partially caused by the pulling forces from the transmission lines generated from out-of-phase responses of the adjacent towers owing to spatially varying earthquake ground motions. In this paper,a 3D finite element model of the transmission tower-line system is established considering the geometric nonlinearity of transmission lines. The nonlinear responses of the structural system at a canyon site are analyzed subjected to spatially varying ground motions. The spatial variations of ground motion associated with the wave passage,coherency loss,and local site effects are given. The spatially varying ground motions are simulated stochastically based on an empirical coherency loss function and a filtered Tajimi-Kanai power spectral density function. The site effect is considered by a transfer function derived from 1D wave propagation theory. Compared with structural responses calculated using the uniform ground motion and delayed excitations,numerical results indicate that seismic responses of transmission towers and power lines are amplified when considering spatially varying ground motions including site effects. Each factor of ground motion spatial variations has a significant effect on the seismic response of the structure,especially for the local site effect. Therefore,neglecting the earthquake ground motion spatial variations may lead to a substantial underestimation of the response of transmission tower-line system during strong earthquakes. Each effect of ground motion spatial variations should be incorporated in seismic analysis of the structural system.

An effective and practical method for solving an unnegligible problem inherent in the current calculation model for multi-support seismic analysis of structures

In the seismic analysis of extended structures subject to spatially varying motions, the displacement input model instead of acceleration model is usually adopted for accurate results. In this paper, a more detailed and comprehensive analysis of the displacement input model is carried out and the research shows that there exists an unnegligible problem in the current displacement model, which leads to the irrationality and unconvergence of some calculated results such as base shear etc. Based on the situation, an effective method named massless rigid element (MRE) method is presented to solve the problem. Moreover, the rationality and accuracy of the method are further assessed and the method is applied to a transmission tower-line system project using the commercially available structural analysis software SAP2000. The theoretical and numerical analyses indicate that the MRE approach is not only feasible with sufficient computational accuracy but also practical and can be easily implemented using the commercially available finite element software such as SAP2000.