Event-based collapse fragility development of electrical transmission towers for regional hurricane risk analysis

Abstract

In the United States, blackouts during hurricanes may be caused by collapse of electrical transmission towers. Fragility curves that document the likelihood of collapse of these towers are needed for fast damage assessment and emergency management of electrical transmission networks. This paper introduces a methodology for developing event-based fragility curves that relate the collapse probability of a transmission tower after a hurricane event to the hurricane intensity measure. The intensity measure of a hurricane is the storm-maximum gust wind speed at 10 m height. The fragility curve is the cumulative distribution function of the collapse capacity, which is a random variable defined as the intensity measure associated with the onset of collapse. Incremental dynamic analysis (IDA) is used along with a suite of selected hurricane wind records to model collapse and to propagate uncertainties from hurricane wind speeds, directions, and durations to the collapse capacity. To save computational resources, IDA can be run up to a certain moderate intensity level instead of collapse of a structure. This is called a truncated IDA, where some IDA curves may only provide a lower bound value of the collapse capacity. The collapse capacity is assumed to follow a lognormal distribution, whose parameters are estimated with the method of moments or the maximum likelihood method for the traditional IDA or truncated IDA, respectively. To facilitate regional damage assessment, the region of interest is discretized into a set of grids and a set of fragility curves are developed for each grid considering the variations in selected hurricane wind records and tower orientations. This procedure is demonstrated using Massachusetts as a testbed. Even though transmission towers are only considered in this paper, the event-based fragility methodology can be adopted to buildings or other structures subjected to hurricanes.