Performance based assessment of transmission lines to seismic events

Abstract

Typical transmission line steel lattice towers are not designed for seismic excitations, based on the assumption that their ultimate limit state is governed by climatic actions (wind and ice). However, it is not unusual for line inspection reports to indicate the observation of moderate to severe structural damages after intense ground motions, which can ultimately reduce the capacity of tower elements. Performance-Based Earthquake Engineering (PBEE) assessment is a modern technique to earthquake resistant design frequently adopted for building frame structures, but not yet employed in the design of transmission line supports, to the best of the authors’ knowledge. The present article evaluates the seismic performance of two typical 230kV transmission towers in a PBEE framework, considering artificial and actual ground motions based on Chilean seismicity. Time-domain nonlinear dynamic analysis is employed to numerically obtain tower responses considering distinct earthquake loading scenarios according to two model configurations: stand-alone and tower-line section. Significant structural damage was detected even for moderate ground motions, which might reduce the tower capacity to future climatic events. The estimated failure probability for the ultimate limit state was found greater than the recommended values in the standard IEC 60826 (2017).