Structural Performance of Lattice Steel Towers Subjected to Earthquake-Induced Support Displacement, in Probabilistic Risk Assessment of Electric Transmission Towers Subjected to Earthquake-Induced Landslides

Electric transmission infrastructure is subject to damage during earthquake events due to induced ground movement, which can cause differential displacement of the foundations of transmission towers, leading to localized member deformations or global instability. We propose a probabilistic framework to assess the risks of damage and collapse to lattice steel transmission towers due to differential support movement induced by coseismic landslides. The framework relies on empirical models for the landslide geometric properties, a probabilistic model for differential support movement patterns, and three-dimensional parametrized fragility functions which describe the variation of structural damage states with the ground displacement and slope angles. Our analysis highlights important trends of the structural response of lattice towers to landslide-induced differential support movement, and the associated deformation and failure patterns. We find the probability of tower damage and collapse to be sensitive to the tower size, number of moving supports, and slope angle. The annual rate of exceeding different structural damage states is also influenced by the probability of differential support movement, which is a function of the tower size, and size and aspect ratio of the landslide. Our proposed models are integrated with probabilistic seismic and landslide hazard analysis, and mapped soil and terrain properties, and implemented at the regional scale to estimate the annual rates of transmission towers exceeding multiple damage states in Northern California. This application highlights the utility of the proposed framework in identifying locations of the most vulnerable towers, which can be used to guide transmission line hardening and planning efforts.
The data produced in this project represents parameterized structural fragilities for lattice steel towers subjected to differential movement of the tower supports due to coseismic landslide displacements, in addition to annual failure rates of representative lattice tower models across the San Francisco Bay Area in Northern California.