A Study on the Nonlinear Seismic Response of Transmission Tower Systems Subjected to Successive Earthquake Ground Motions Considering SSI Effects

The present work focuses on the nonlinear seismic response of transmission tower systems when subjected to successive earthquake ground motions. To this end, nonlinear time-history analyses were carried out by applying multiple ground motion records in sequence, thereby replicating realistic scenarios in which structures endure repeated seismic loading during and following major earthquakes. The structural behavior was examined through two distinct modeling frameworks: a pinned configuration, where tower members are considered to resist axial forces only, and an SSI-based model, which captures the interaction between the structure and the supporting soil. Both frameworks were assessed in terms of several critical response quantities, namely peak displacements, permanent displacements following each seismic event, acceleration demands, and base shear forces developed at the foundation level. The comparative evaluation of the two models brought to light considerable discrepancies in the computed response, confirming that the dynamic characteristics of the soil and its coupling with the structure have a pronounced effect on the overall seismic performance of transmission towers. In addition, it was shown that the cumulative effect of successive seismic excitations drives a gradual buildup of deformations, yielding displacement demands that far exceed those obtained from conventional single-earthquake analyses. These outcomes point to the necessity of incorporating SSI and multi-sequence seismic loading into both the design and the seismic assessment of transmission infrastructure, as approaches relying solely on single-event excitation are likely to significantly underestimate the true seismic demand imposed on such structures.