Comparison of responses of guyed and freestanding transmission line towers under conductor breakage loading

Cascades have been a prominent feature of many transmission line (TL) accidents around the world. During these events, a localized member failure changes the boundary conditions of the structural system, magnifying member loads over a considerable extension of the line. This results in the progressive failure of successive support structures. Phase conductor breakage is regarded as the most severe cascade triggering event, generating a shock wave that propagates through the conductor and induces large unbalanced longitudinal loads on the transmission line components. Under such an extreme loading event, nonlinear time-history dynamic analysis has to be employed to predict the response of the TL system. In the present work, an explicit dynamic analysis scheme is developed to predict the response of a multi-span TL section. The analysis includes all the main structural components of a TL section. This procedure was used to investigate the response of two types of suspension steel latticed towers, guyed and freestanding, subjected to conductor breakage loading. Results indicate the occurrence of peak dynamic loads (PDLs), that signi¯cantly increase the internal forces in system components, exceeding their design capacities, particularly in tower's members. The results also show that the guyed tower accommodates such a loading event more adequately than the freestanding tower.