PSI - Issue 84

Davide Caliò et al. / Procedia Structural Integrity 84 (2026) 513–520

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the construction of the bridge likely goes back to the sixties of the last century. The bearing system at abutment 1 (Catania side) shows evident deterioration, potentially leading to loss of functionality. In addition, the longitudinal beams are almost in contact with the retaining wall, limiting the displacement capacity of the bearing system. Defects of lower severity are present along the left side of the deck, where loss of concrete cover and exposure of reinforcement were observed. 2.3. Hydraulic aspects and implications for viaduct safety In addition to the process analysed in this study, viaducts crossing watercourses are affected by further critical issue related to hydraulic dynamics, which play an important role in infrastructures safety. Phenomena such as overtopping during flood events, general riverbed erosion, local scour at pier foundations and bank instability are widely recognized as major risk factors and are explicitly considered in technical viaduct, these issues are particularly evident. One of the main piers is located directly within the incised channel of the stream, in a setting characterised by coarse alluvial deposits and a highly dynamic fluvial behaviour. Field observations and UAV imagery clearly show the presence of a pronounced scour at the base of the pier, together with concrete damage and exposed reinforcement bars. These features are consistent with the combined effects of local erosion processes and impacts caused by coarse sediment transport during flood events, confirming that the interaction between fluvial dynamics and structural elements represents a critical source of vulnerability for the infrastructure. 3. Materials and methods The integrated analysis of the Cantera viaduct was developed through a multisensor workflow based on the use of UAV systems and photogrammetric techniques in the visible (RGB) and thermal infrared (IRT) domains. The objective was to obtain a high-resolution three-dimensional characterization of selected critical elements of the viaduct and of the surrounding geological context, together with the identification of thermal anomalies attributable to structural degradation phenomena, fractures, and areas with different surface emissivity. The overall operational workflow includes the following phases: (i) flight planning; (ii) acquisition of RGB and IRT imagery; (iii) photogrammetric processing using Structure-from-Motion (SfM) techniques; (iv) generation of three-dimensional models; and (v) engineering and geo-structural integration and interpretation. In the first two methodological phases, the survey was carried out using a DJI Mavic 3 Thermal, a multisensory UAV. The platform integrates a 48 MP wide- angle RGB camera equipped with a 1/2″ CMOS sensor and a radiometric thermal sensor operating in the 8–1 4 μm range, with a spatial resolution of 640 × 512 px. This configuration allows the simultaneous acquisition of geometric and radiometric datasets suitable for structural and engineering-geological characterization, as well as for the detection of associated thermal anomalies. All flight operations were conducted entirely in manual mode, a necessary choice to precisely control flight trajectories and operational distances. Data acquisition focused on the pair of piers considered the most critical and on the south viaduct abutment. In the first case, the piers were analysed both from a geological technical perspective, as they are located directly within the riverbed and exposed to potential erosion and scour processes, and from a structural-engineering perspective, due to the presence of clear evidence of surface degradation. The abutment was investigated with specific reference to the near rock mass instability features that are represented by rock volume detachment and fall. The piers were surveyed through dual acquisition, RGB and IRT, following multi-oriented trajectories with closely spaced circular and vertical flight paths, ensuring complete coverage of the structures. RGB imagery was used to generate a high-resolution three-dimensional model through an SfM–MVS pipeline, aimed at mapping visible damage, while thermograms were acquired in the absence of solar radiation, according to previous accounts (Mineo et al., 2025; Pappalardo et al., 2016), in order to minimize irradiation effects and enhance the detectability of radiometric differences related to variations in the thermal conductivity of concrete surfaces. for the first time in the structural engineering field, an advanced workflow for thermal imagery processing was implemented, originally developed for landslide investigations and following the methodology proposed by Caliò et al., (2025) This approach includes a pre-processing and homogenization phase of the thermograms using the dedicated Infrared Thermal Point Cloud (IRT-PC) tool, aimed at correcting radiometric inconsistencies prior to three-