Fire Fragility Assessment of Steel-Concrete Composite Bridges in a Multi-hazard Framework

In last decades, the concept of urban resilience has been developed as the capability of the urban system to prepare, respond, and recover from multi-hazard threats with minimum damage to public safety, economy and security of a given urban area. This meaning links with the definition of multi-risk approach, to establish a ranking of different types of risk, considering possible conjoint and cascade effects. In particular, the seismic and fire risks were analysed in this paper, by also considering their interaction. Indeed, a probabilistic methodology based on Cloud Analysis by varying the key parameters in the fire action definition was proposed for evaluating the structural behavior of bridges already damaged by a previous earthquake. As case study, an existing steel-concrete composite bridge is considered. The bridge is simply supported with steel beams connected to the reinforced concrete slab. As one of the main results, lognormal fragility curves were obtained, measuring the capacity of a typological steel-concrete composite bridge, under different natural fires. Moreover, the efficiency of the different parameters of the fire curves on the structural performance is evaluated. The methodology also aims to design the optimal intervention, with efficient and effective damage mitigation strategies.