  Lifeline infrastructure systems such as a power transmission network in
coastal regions are vulnerable to strong winds generated during tropical
cyclones. Understanding the fragility of individual towers is helpful in
improving the resilience of such systems. Fragility curves have been developed
in the past for some regions, but without considering relevant epistemic
uncertainties. Further, risk and resilience studies are best performed using
the fragility curves specific to a region. Such studies become particularly
important if the region is exposed to cyclones rather frequently. This paper
presents the development of fragility curves for high-voltage power
transmission towers in the state of Odisha, India, based on macro-level damage
data from 2019 cyclone Fani, which was obtained through concerned government
offices. Two types of damages were identified, namely, collapse and partial
damage. Accordingly, fragility curves for collapse and functionality disruption
damage states were developed considering relevant aleatory and epistemic
uncertainties. The latter class of uncertainties included that associated with
wind speed estimation at a location and the finite sample uncertainty. The most
significant contribution in the epistemic uncertainty was due to the wind speed
estimation at a location. The median and logarithmic standard deviation for the
50th percentile fragility curve associated with collapse was close to that for
the functionality disruption damage state. These curves also compared
reasonably well with those reported for similar structures in other parts of
the world.
