Failure mechanisms and seismic fragility analysis of overhead transmission lines incorporating pile-soil-structure interaction

Overhead transmission lines (OTLs) are responsible for long-distance electric power transmission from power plants to end-users, inevitably passing through seismically active regions. A thorough literature review regarding seismic design and assessment of various structures underscores the significance of incorporating soil-structure interaction (SSI) and depth-varying spatial effect (DVSE). However, previous studies typically assumed that OTLs are fixed directly to the ground, and depth-varying ground motions (DVGMs) are oversimplified as uniform excitations, which may yield questionable structural performance estimations. To address this concern, this paper focuses on investigating the SSI effect on the seismic response and failure mechanism of an OTL subjected to DVGMs. Prior to this investigation, two commonly used methods for modeling the SSI effect in software ABAQUS are compared, with a nonlinear spring-based modeling method deems comparable in accuracy yet superior in efficiency. Subsequently, a refined finite element model of an OTL-soil-pile system is developed utilizing this simplified modeling method, and a group of three-dimensional ground motions varying within layered soils is stochastically synthesized. The influences of SSI and DVSE are systematically explored in terms of the seismic responses, failure mechanisms, and fragility probabilities of the OTL. The results expose the potential of the SSI effect to weaken the seismic capacity of the OTL and increase the risk of failure, while disregarding the DVSE is likely to lead to overestimated outcomes. This research is expected to raise awareness of considering SSI and DVSE in the seismic design and analysis of OTLs.