PSI - Issue 44

Lucia Minnucci et al. / Procedia Structural Integrity 44 (2023) 729–736 Lucia Minnucci/ Structural Integrity Procedia 00 (2022) 000–000

730

2

1. Introduction Vulnerability and risk analysis procedures for bridges are gaining more and more attention and the scientific literature on the topic is growing, with studies concerning various sources of hazard, such as seismic (Tubaldi et al. 2021, Kilanitis and Sextos 2019) or flood-induced actions (Tubaldi et al. 2017, Ragni et al. 2019). In the last decades, due to the occurrence of numerous bridge failures all over the world after earthquakes, the research community put efforts into the characterization not only of the bridges’ expected performance, but also in the quantification of consequences that seismic events may have on the functionality of road networks to which the bridges belong, especially when emergency actions are needed (Kaiser et al. 2012, Deodatis et al. 2014,). To date, the probabilistic tool widely accepted by the community to characterize the vulnerability of structural systems is represented by fragility curves, that in case of bridges may be built referring to the performance of the whole structure, after the selection of a synthetic parameter that mostly represents the behaviour of the bridge (Karim and Yamazaki 2003), or distinguishing the various contributes to the fragility from each structural element that composes the bridge (Nielson and Des Roches 2007). The problem of choosing one between the two approaches stems from the fact that a wide spectrum of different failure modes may develop (e.g., bridge failure may be attained due to maximum forces or stroke on bearings, forces on piers, abutments and decks) and the failure scenario may vary sensibly from case to case, in particular for existing bridges. A further issue in the selection of the optimal and most reliable strategy for the fragility evaluation lies in its suitability for the evaluation of risk at a more general point of view, that is at road network level, where results of the fragility analysis must be used to quantify the performance of the transport system. In this paper, a preliminary proposal for a probabilistic framework addressing the aforementioned issues is illustrated. In the framework, following the PEER’s scheme (Porter 2003), the evaluation of the road network performance starts with the seismic hazard analysis in the area of interest. The fragility analysis follows, considering meaningful performance levels associable to the quantification of consequences after the damage of the structural components (such as piers, abutments, bearings and so on) of the bridges being part of a road network. Consequences are defined into a decision-making process about the usability of each damaged bridge and reflect on the usability of the entire infrastructural system. Therefore, various indicators for the performance of the road network can be outlined, expressing the monetary losses linked to the worsening of the traffic conditions (indirect costs) such as the lengthening of the travel time and the increase of the pollutant emissions. An application of the proposed framework is made on the SS76 road, a principal thoroughfare in Central Italy connecting the central coast of the Marche region to the hinterland. Results of the fragility analysis are exploited in the decision-making process, where some assumptions about the impact of the fragility of each bridge on the functionality of the overall network are made. In this paper two main descriptors of the traffic conditions and the associated monetary losses are defined as a measure of the road network health condition. As a result, the influence that the fragility of each structural component has on the overall performance is explicitly tracked; moreover, the economic analysis of the post-disaster configuration of the road network may be used by the stakeholders to better evaluate the most effective strategies of intervention both before and after the occurrence of a seismic event. In the sequel, the following nomenclature will be used: Nomenclature IM intensity measure PGA Peak Ground Acceleration S a Spectral Acceleration SSI Soil Structure Interaction LPM Lumped Parameter Model MSA Multiple Stripe Analysis TTC Total Traffic Cost TPC Total Pollutant Cost