PSI - Issue 44

Dora Foti et al. / Procedia Structural Integrity 44 (2023) 1506–1513 D. Foti et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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3. Survey from UAV Italy is one of the European countries with the highest density of archaeological traces and ancient structures. Many of these are architectural artifacts built to solve functional problems such as aqueducts and bridges; their survival to the present day is derived precisely from their indispensable function to which they continue to rise, and which has been ensured by continuous maintenance over time. These interventions that have occurred in the past as well as in the present require a careful study of the state of preservation of the structures and the forces to which it is subjected, analyses that base their foundations on a precise and meticulous survey. There are several methodologies and tools useful for carrying out a survey, each of which has advantages and disadvantages, and their choice is influenced by the results to be achieved. The research on Santa Teresa bridge requires the realization of a survey that does not have as its only output a geometric datum of the forms on which to set up an FE model, but also the one that accurately investigates both the structural system and the degradation of the materials that compose it, useful for planning conservation and structural restoration interventions. Until a few years ago, compiling a dataset that met all the needs presented would have been a task involving the co-participation of several pieces of equipment, making the task costly in terms of both time and money. An answer to this problem was given with the advent of UAVs and their application to photogrammetry, small aircraft capable of reaching difficult-to-access places by taking advantage of a privileged vantage point such as the aerial viewpoint and acquiring georeferenced photographic data that, carefully processed, in collaboration with a measuring instrument (total station, laser scanner, GNSS Station) allow a materially interpretable and metrically correct survey to be drawn up. Given the orographic conditions of the blade and its relationship to the architectural artifact, a combined survey methodology was pursued using terrestrial and aerial photogrammetry integrated with total station celerimetry. The UAV aircraft used is a Mavic 2 Pro equipped with Hassemblad 4K camera with +/- 0.5m vertical and +/- 1.5m horizontal positioning accuracy. The drone flight allowed us to find data referring to the elevations, focusing more on the elevated parts that are difficult to access and the extrados of the bridge where the driveway is located. The ground camera used was a Nikon D3100. The celerimetry base was made with Leica TCR 805 power total station. The instrumental survey was responsible for recording the local coordinates of 3 G.C.P. (Ground Control Points), whose Cartesian coordinates were essential for metric calibration of the data. Due to the presence of additional aerial obstacles (poles and electric cables) we proceeded by means of a manual flight in V-LOS (Visual Line Of Sight) mode, allowing the pilot to have the maximum control of the UAV's movements. The drone conducted data acquisition at different elevations and different camera inclinations with take-off base positioned within the riverbed not interfering with vehicular traffic. In the first phase, photographic shots were conducted at elevations ranging from 4.5m to 9m with the axis of displacement parallel to the building elevations. In the second phase, the drone was conducted at altitudes between 14 m and 16 m performing flight trajectories similar to the first phase but acquiring photographs referring to the driveway and the ditching of the elevations. In the last aerial mission, photographs were taken at an elevation between 20 m and 30 m with nadiral camera orientation by retrieving data with reference to the orographic trend of the river slopes. Terrestrial photogrammetry focused exclusively on acquiring overlap data to ensure complete matching with aerophotogrammetry and integrating the vault intrados data by taking photographs following a trajectory placed in the center of the environments and taking photographs by circumferential arcs. The terrestrial data returned photographs with G.S.D. not exceeding 0.1 cm/pix. (Figure 4).