PSI - Issue 62

Paolo Borlenghi et al. / Procedia Structural Integrity 62 (2024) 468–475 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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management; however, the limited resources that small Public Institutions (e.g. Provinces and Municipalities) can dedicate to inspections, maintenance and monitoring of road infrastructures is a well-known issue requiring specific management tools for the definition of priorities. As a consequence, a research agreement between Politecnico di Milano and Regione Lombardia was established in 2018, to provide guidelines (denoted to as RL Guidelines) on both the prioritization of maintenance interventions and the design of structural monitoring systems. According to the RL Guidelines, the bridge prioritization is based on the computation of two indicators: (1) Functional Priority Index (FPI) and (2) Technical Priority Index (TPI). The FPI represents the bridge exposure in terms of impact associated to the bridge closure and is computed aggregating the information on road network and Origin Destination matrices. Hence, the FPI of each bridge is computed once and updated in case of network modifications. The outcome is a ranking of bridges based on induced travel delay and four classes of FPI are defined. Full details on the FPI are reported by Arena et al. (2022). The TPI considers the vulnerability and hazard of single bridges due to structural and hydraulic aspects. Primary parameters are only related to vulnerability, particularly structural vulnerability (i.e. material, static scheme, year of construction, last inspection date, and damage level and type) and hydraulic vulnerability (i.e. elevation of deck intrados and levees/banks, foundations and riverbed elevations, number of piers in the riverbed, pier width, presence of bed/banks protections, and scour at foundations). The secondary parameters are related to both structural/hydraulic vulnerability and hazard. The attention class k is defined by the primary parameters, while the secondary parameters define the inter-class subdivisions α k . The combination of the two-level evaluation defines the TPI as k- α k . The peculiarity of the TPI is the possibility of computing it from a documentary-only level, without the need of (new) onsite inspections. A detailed description of the methodology is reported by Biondini et al. (2022). All the parameters related to the TPI are included in a bridge form developed by Politecnico di Milano and included in the bridge inventory of StradeNet (Bianchi et al. 2022b), i.e. the Road Information System of Regione Lombardia. The bridge form collects available information from different databases, archive documents and past inspection reports, without requiring onsite visits. Once the bridge inventory of StradeNet is completed, the computation of the TPI can be fully automated. Finally, the TPI and the FPI are combined to obtain a unique Risk Classification Index (from 1=high to 4=low) and a ranking indicating the bridges for which an action is required first. Subsequently, the assessment process is the one required by the Italian Guidelines: (1) inspections and compiling of defects forms; (2) definition of a Class of Attention; (3) possible further in-depth evaluations according to the assigned class of attention (i.e. permanent monitoring, special inspections, and simplified or detailed structural assessment). As previously stated, the research agreement between Politecnico di Milano and Regione Lombardia was also aimed at the development of guidelines for the design and implementation of monitoring systems on bridges (Limongelli et al. 2022), with 9 bridges being selected to exemplify the design and installation of structural monitoring techniques (see e.g. Bianchi et al. 2022a, Borlenghi et al. 2022b , D’Angelo et al. 2022 ). The present paper exemplifies the application of the overall procedure of risk classification and continuous monitoring on a historical masonry bridge: the Candia bridge (Fig. 1). The Candia bridge is a multi-span masonry arch bridge that crosses the Sesia River between the small municipalities of Candia Lomellina and Casale Monferrato. The structure is 325 m long and it is composed of 16 segmental arches, 15 piers and end abutments. The span of each arch is 17.5 m; the deck is 10 m wide and includes a roadway and a railway track, with the latter being inactive since 2010. All the piers were subjected to the strengthening of the foundation due to scouring.

Fig. 1. The Candia Bridge: (a) plan and elevation and (b) view from the downstream side.