Wind and Ice Fragility Analysis of a Lattice Steel Transmission Tower—A Limited Case Study

This paper presents a robust but simplified methodology for constructing damage and collapse fragility curves for lattice steel towers prone to wind and ice. The methodology, while robust enough to capture intricacies of a tower’s behavior amid the presence of redundancies and alternate load paths, allows for calculations of structural demand and capacity by utilizing structural models of towers similar to those commonly used by practitioners. By analyzing a 500 kV tower with a SAP2000 model, calibrated with full-scale test data, it is shown that the capacity and damage thresholds of a tower for different load cases—although these are significantly influenced by redundancies built into a tower design—can be estimated using a simplified modeling approach by implicitly categorizing members of a tower in terms of the significance of their damage on the overall performance of the tower and mapping the critical member damage and failure modes on appropriate pushover curves. The methodology is illustrated on the testbed tower for three load cases: a wind only, an ice-only, and a concurrent wind and ice case. For each case, critical members are identified; capacity and damage thresholds are quantified; and fragility curves are constructed by comparing simulated demand and estimated thresholds.