PSI - Issue 44

Andrea Nettis et al. / Procedia Structural Integrity 44 (2023) 1996–2003 Andrea Nettis et al. / Structural Integrity Procedia 00 (2022) 000 – 000

1997

2

Nomenclature DDV

Differential deformation velocity Global deformation velocity

GDV LoS

Line-of-sight

MTInSAR

Multi-temporal SAR interferometry

POP

Population parameter Persistent Scatterer Synthetic Aperture Radar

PS

SAR

1. Introduction The structural performance of bridges is essential for the serviceability and safety of transportation networks. Bridge failures may be related to human-related factors (e.g. traffic loads) and natural hazards (e.g. seismic events, floods or landslides), and may involve significant losses in terms of direct (i.e. structural damages, casualties) and indirect losses (e.g. traffic disruptions). Bridge collapses (Bazzucchi et al., 2018) may strongly impact the economy of large populated areas. To ensure the structural safety of existing bridges, the conventional procedures by transport authorities’ operators consist in performing on-site periodic inspections and targeted refined structural assessment/monitoring aimed to address appropriate maintenance or retrofit interventions. Considering the huge number of existing bridges to be managed, these conventional management procedures result to be time-consuming and manpower-demanding and inefficient for managing large bridge portfolios. Additionally, periodic structure-specific on-site visual surveys are generally carried out by bridge inspectors with a limited inspection frequency (e.g. one per year in Italy for relevant bridges, on an annual/biennial basis in the United States) according to the availability of number of inspectors, financial budgets and support facilities (e.g. elevating platforms, testing tools, laser scanners). The low inspection frequency may limit the surveillance of fast-evolution anomalous degradation/deformation phenomena. Real-time remote monitoring via in-contact sensors (e.g. accelerometers, strain gauges) may be effective for timely identification of structural warnings for structural safety (Floris et al., 2021; Porco et al., 2013). However, the high financial budgets required by this last approach prevent an extensive application on large bridge portfolios. On the basis of these critical issues related to the conventional procedures, transportation authority’s managers strongly need efficient procedures supporting the surveillance of existing bridge portfolios involving a reasonable demand of resources. In this context, the new Italian “ Guidelines on the classification and management of risk, safety assessment and monitoring of existing bridges ” (Ministero delle Infrastrutture e dei Trasporti, 2020) are to introduce homogeneous procedures for supporting bridge managers in risk-based prioritisation in Italy. Additionally, several research studies propose methodologies suitable for risk-based prioritisation of bridges considering multiple hazard sources (Anisha et al., 2022; Gentile et al., 2020; Nettis et al., 2022). Recent research efforts are aimed at the application of remote-sensing technologies for the structural monitoring of bridges within transportation networks. These techniques may be adopted to collect significant data for structural assessment purposes if integrated into the conventional civil engineering methodologies. The remote-sensing approaches avoid direct contact with the investigated structure involving advantages for the safety of inspectors, limited use of traffic reductions and service interruptions. The category of remote-sensing approaches includes the use of unmanned aerial vehicles (commonly referred to as drones) equipped with sets of sensors which can be customized depending on the data to be collected (Duque et al., 2018; Nettis et al., 2020). Satellite imagery presents potential applications in regional-scale preliminary screening on single structures and infrastructure systems. Particularly, advances in terms of increasing number of satellite platforms acquiring data, increasing the spatial resolution of images and decreasing the revisiting time of the satellites motivate the research interest in developing procedures for monitoring structures from space. Particularly, the satellite-based multi-temporal synthetic aperture radar interferometry (MTInSAR) uses satellite-based synthetic aperture radar (SAR) imagery to detect the displacement of scatterers on the terrestrial surface with a sub-centimetric accuracy. Several recent applications are focused on the use of MTInSAR for structural monitoring applications by developing methodologies and tools for the analysis and elaboration of interferometric products to investigate anomalous structural behaviours and perform a preliminary