Estimation of the combined seismic-fire risk: a critical review and future research agenda

The estimation of the combined seismic-fire risk and the optimization of interventions for buildings and infrastructures in the context of metropolitan areas represent a very actual and critical theme. In fact, different forms of hazard can affect structures throughout their existence. The occurrence of a seismic event in areas exposed to various risks or already affected by other phenomena is highly probable, especially in countries characterized by high seismicity. Nevertheless, the seismic safety assessment of existing buildings/infrastructures is commonly carried out considering the seismic action only, generally applied to an analytical model, neglecting the stress-strain state induced by previous phenomena or without considering the cascading effect related to a different hazard, such as a fire induced by the earthquake. The devastating examples throughout history and the high dependency on uncertain factors of urban fires following earthquakes have motivated the proponent research units to study and develop models for estimating the probability of occurrence of this phenomenon, the possible consequences and damage mitigation strategies, starting from the strong expertise of each unit in the seismic and fire fields respectively. Therefore, the paper will focus on the few studies conducted in this field, trying to understand in there is the possibility of extending them to both buildings and infrastructures. In particular, the paper will set the overall methodology for estimating seismic and fire hazard and subsequentially the vulnerability/risk, starting from the definition of the main structural typologies belonging to urban metropolitan areas for both structures and infrastructures. Each class will include infrastructures and buildings sharing common essential features from the point of view of the earthquake and fire resistance. The methodologies will take into account the environment-induced existing damage. In the context of the safety assessment of existing buildings and infrastructures, a pivotal role is played by the possible degradation state of the existing structure, that will be considered in the work. The methodology will be very useful for the classification of building and bridge typology vulnerability against combined seismic and fire risk at metropolitan scale.