PSI - Issue 44

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

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2. The framework A schematic representation of the framework is offered in Fig. 1. Following the PEER’s scheme, the framework is composed by different steps that can be evaluated in sequence. In the following, each step composing the framework is briefly commented. 2.1. Hazard analysis The first step of the framework is the hazard analysis. The hazard curve that characterizes the seismic scenario in a certain area is built referring to a proper measure for the seismic intensity, that is the Intensity Measure ( IM ). The literature counts several studies in which the most suitable IM s are evaluated in case of bridges, such as the Peak Ground Acceleration (PGA) (Stefanidou and Kappos 2017) and the spectral acceleration S a at the period of 1.0 s (Ramanathan 2012). A set of ground motions (natural or artificially generated) is then required to perform structural analyses.

Fig. 1. Flow-chart of the probabilistic framework for the evaluation of road network performances after a seismic event.

2.2. SSI analysis At an intermediary point between hazard and fragility analyses, the modelling of Soil Structure Interaction (SSI) phenomena is introduced. Since it is well known that SSI may have detrimental effects in case of bridges and viaducts (Mylonakis and Gazetas 2000), the introduction of SSI ensures a more reliable description of the bridge seismic response. Results from the work by Morici et al. (2019) can be employed to easily take into account the influence of the interaction between deep foundations (typical for bridge structures) and the subsoil in the superstructural response through an analytical Lumped Parameter Model (LPM) characterizing the combined soil-foundation response. Moreover, an additional improvement of this intermediary step could be provided by the introduction of variability on soil and foundation parameters reflecting their intrinsic aleatoric nature. Basing on the study by Minnucci et al. (2022), probabilistic trends can be associated to the variability of the soil shear velocity V s , that reveals as the most influencing parameter of the behaviour of the soil-foundation combined system in terms of impedances and kinematic response factors. 2.3. Fragility analysis As a preliminary step to the evaluation of the fragility, the definition of performance levels useful to assess the bridge response is required. The choice can be made basing on the overall structural behaviour, so choosing a unique demand parameter, or evaluating the single components performance, to which different demand