PSI - Issue 62

Stefano Grimaz et al. / Procedia Structural Integrity 62 (2024) 161–168 S. Grimaz et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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bridge inspection vehicles. Drone inspections also yield higher performance and improved output quality. Drones can reach and inspect even the most remote points of infrastructure, which are challenging to access with conventional methods. They collect high-quality images and easily accessible information. In practice, using drones in tandem with inspections instantly enhances an inspector's visual capabilities. Moreover, using AI algorithms, it will be possible in the future to have an automatic tool which helps inspectors to identify and localize the asset defects (Orsini & Piras, 2023). Drones are also used with advanced photography and LiDAR (Light Detection and Ranging) technologies (Feroz & Dabous, 2021). These technologies allow the use of drones equipped with LiDAR cameras and scanners to obtain highly detailed surveys. Investigations conducted using drones and LiDAR scanning generate a high volume of unstructured data, which must be processed and organized effectively using digital twins to enable remote inspections of facilities at a later time. The quality of the bridge 3D digital twin, constructed using photogrammetry and LiDAR scans, depends on the amount of data and processing power for resolution, accuracy and geometric precision and can be effectively navigated using modern multi-resolution 3D rendering techniques. Many drone applications on bridges are primarily focused on the maintenance or retrofitting objectives of managing entities, and not for surveillance purposes. In the framework of the VISIVIA project, the authors asked themselves: what is the most efficient way to utilize drones for surveillance activities using the VISIT methodology? To answer this question, the authors decided to explore the strengths and limitations of various drone usage modalities, organizing a comparative test in a real-scale scenario, with the goal of gathering information to enhance the effectiveness of VISIT inspections. 4. Design of comparative tests on drone use for VISIT inspections Within the framework of the VISIVIA project, the authors devised a comparative test to determine the most suitable approach for utilizing drones in inspections conducted with the VISIT methodology. The primary objective was to compare two distinct approaches, each characterized by varying levels of precision and time consumption. Two modalities of drone usage were tested: • TC (Comprehensive Technique). Comprehensive and accurate drone survey involving 3D reconstruction for subsequent analysis. • TG (Guided Technique). Targeted and real-time drone survey, guided by an inspector. The TC modality requires an all-encompassing survey to provide a 3D reconstruction through photogrammetry or LiDAR techniques. These are widely adopted survey techniques that are very useful in VISIT inspections. Photogrammetry involves capturing high-resolution images, creating accurate digital replicas of the real world. This method can be used to produce georeferenced 2D orthomosaics and detailed 3D models. The LiDAR drone also provides reconstruction using laser pulses to create detailed 3D maps. The 3D models are then used to virtually inspect details of the digital twin, enabling remote inspections. The TG modality is based on real-time targeted inspections using a high-resolution drone camera, allowing inspectors to remotely examine almost every part of a bridge even using zoom. The drone camera acts as the inspector's eyes, capturing images during flight - the images can also be used for later detailed review. This approach offers numerous advantages, including identifying small defects, rust, or missing parts without the need for operational

interruptions to vehicular traffic and eliminating risks for inspectors. 5. The inspection of existing bridges near the road SS13 "Pontebbana"

The tests on a real case study were collaboratively conducted by SPRINT-Lab researchers and ANSFISA experts. The prototype test area covered the section of SS 13 "Pontebbana" from kilometer 177+200 to kilometer 184+500, located in the municipalities of Resia and Chiusaforte, in the province of Udine (northeastern Italy). This specific section was selected because it allowed for the inspection of four bridges (Fig. 2). The tests involved only three