Abstract
Transmission towers are a vital lifeline for modern living and are crucial structures that must remain operational even after a seismic event. However, the towers are largely designed to withstand the effects of wind alone and not earthquakes, and the seismic influences on tower design and construction have hitherto been ignored. The purpose of this study was to evaluate the seismic performance of a latticed steel transmission tower-line system that is subjected to a variety of seismic situations (Far-Field, Near-Field and Repeated Earthquakes) using probabilistic vulnerability functions and Collapse Margin Ratios in accordance with FEMA-P695. Nonlinear Time History Analyses were performed by incorporating an array of 36 strong ground motions to develop the Incremental Dynamic Analysis and to generate the fragility functions for three performance limit states as referenced in FEMA 356. The results showed that the single event seismic performance of the tower is better than its performance after multiple ground motions owing to aftershock impact, while near-field excitations led to greater susceptibility and fragility than far-field scenarios. Thus, near-field ground motion is more harmful to the tower and could result in its failure or collapse with only a small reduction in damage relative to the impact of the aftershock.
Highlights
Modern societies rely on tower-based transmission systems to provide electricity, the vital lifeline, to their citizens
This paper uses the probabilistic seismic demand model to investigate the seismic vulnerability of transmission towers in terms of the maximum Inter-Storey Drift Ratio (ISDR) and the intensity measure related to spectral acceleration
For the near-field case, it is tensile failure with fracture material, which becomes worse when subjected to repetitive aftershock excitation that results in a combination of tensile failure with material fracture and compression buckling at the base of the columns
Summary
Modern societies rely on tower-based transmission systems to provide electricity, the vital lifeline, to their citizens. Seismic loads are not taken into consideration in design codes and guidelines and many transmission towers have historically failed and even collapsed during earthquakes [1,2]. The 1995 Kobe earthquake in Japan destroyed half the transmission lines in the area and about 20 transmission towers were rendered tilted due to the movement of the earthquake’s epicentre [4]. The Wenchuan earthquake of 2008 in China caused the collapse of more than 20 transmission towers in the Mao County area, as well as the destruction of a 220 kV transmission line in the region [5,6,7].
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