In the current practice and even in the regions of high seismicity, the transmission towers are usually not designed for seismic effects. No rigorous or comprehensive studies of seismic response of transmission line systems have commonly been performed to ascertain the significance of seismic loads. Recent studies showed that negligence of cable interaction in the analysis of long span systems may significantly underestimate the dynamic response. This research project examines the effects of cable dynamics on the tower response. The investigation includes the effect of insulators, coupling of vertical, lateral and longitudinal motions, foundation- tower interaction, different tower configurations and line layouts, spatial variations and rotational components of base ground motions and the mode localization effects in long transmission systems. A response spectrum approach is developed to establish the design load/response for this special lifetime system. This research is expected to provide useful tools to examine the transmission systems for seismic effects. The developed analytical approaches can also be used to ascertain better the reliability of a transmission network in the regions of high seismicity.
