Fragility curves are essential tools to quantitatively assess the physical vulnerability of structures and infrastructures at risk for a given seismic hazard. They describe the probability of exceeding a given performance level under earthquake excitation, and are usually defined by a lognormal probability distribution function. Although debris from damaged buildings adjacent to road edges is the main cause of urban mobility disruption, studies on the fragility curves development for infrastructures subject to seismic actions focus on geotechnical effects, and do not analyze this type of road blockage. The article proposes an analytical procedure to construct fragility curves for urban road networks. It is based on the construction of debris graphs and the use of an appropriate fitting technique. For a given seismic intensity measure level, the developed fragility curves express the probability that the road is open or closed to the transit of emergency vehicles after debris fall. Therefore, the performance level is defined in terms of the width of the road pavement that remains free after the debris fall, or the width of the debris heap on the road pavement. Finally, the proposed framework is tested with real data of the main street in Amatrice, and the results are presented and discussed.
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