Multihazard Vulnerability and Risk Assessment of a System of Lattice Steel Transmission Towers Prone to Wind and Ice

Multihazard wind and ice accretion pose risks to lattice steel transmission tower systems, which are the most common supporting structures for high-voltage overhead lines. This study investigated these risks within the framework of performance-based engineering. The analysis methodology - which is primarily intended for practitioners in the utility industry - relies on a generalization of the pushover curve-based analytical approach for fragility analysis of a single lattice steel transmission tower, and generates wind and ice fragility surfaces for individual towers of the system to account for all possible wind and ice load cases. The study then conducted probabilistic sampling of the fragility surfaces considering the degree of correlation between collapses of the towers of the system - to probabilistically capture the extent of any cascading failure - for constructing vulnerability maps of the system. The vulnerability maps were integrated with appropriately constructed hazard maps by utilizing an event-based algorithm for estimation of risks to the system of towers. The methodology was illustrated on a hypothetical line system that is assumed to be located in Long Island, NY. The risks to the line system were quantified in terms of the annual frequency of system failure along with probabilistic descriptions of the number of collapsed towers of the system due to any potential cascading effects, which could also be a relevant decision variable for a utility company that wishes to stock up in anticipation of extreme events. By comparing the quantified risks to the line system for various hazard scenarios and analysis assumptions, the importance of performing multihazard evaluation at the system level is highlighted.