PSI - Issue 64

Andrea Armonico et al. / Procedia Structural Integrity 64 (2024) 604–611 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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the photogrammetry theory based on triangularization (Linder, 2009) to estimate the spatial position of every point. The success of this operation is linked to the overlapping factor between each photo (Chen et al., 2019, 2017). A point must be identified in at least three photos to be positioned appropriately. Several software equipped with photogrammetry algorithms can provide the presented computer-aided procedure. Agisoft Metashape by Photoscan (Agisoft, 2019) is a photogrammetry software based on the SFM algorithm employed for photo processing. The cloud points creation steps consist of the photo-alignment, which allows creating a sparse cloud (Figure 20), then the photo alignment is optimized using the GPS coordinates, and a dense cloud is created (Figure 2a). For this study, the dense cloud is sufficient; however, the software allows the creation of additional elements, such as the mesh produced by triangulating the dense cloud (Figure 2b) and the textured model produced by superimposing the input photos on the previously created 3D model (Figure 2c) . This procedure is carried out several times over time, creating a “snapshot” of the various historical moments of the structural element.

(a) Sparse cloud of the strengthened beam

(b) Dense cloud of the strengthened beam

(c) Solid model (mesh) of the strengthened beam Figure 2 : Textured 3D model

The dense clouds are saved and processed to evaluate the displacement along the element in CloudCompare software. The procedure consists of a cloud-cloud comparison. The software can align the two point clouds using the point cloud corresponding to the zero time as a reference, thanks to the GPS coordinates and calculate the point-point distance through a software algorithm that can detect and compare the near points. Distributed Measurement of Strain – Optical Fibre Sensors, Digital Image Corelation All the specimens are equipped with an optic sensor produced by SHM System; in particular, the EpsilonRebar distributed sensors are used for the experimental tests. The measuring device consists of an optical fibre embedded in a composite rod (glass fibre) with a diameter of 10 mm. The optical fibre sensors rod have been placed in a groove in the concrete before that FRP layers are bonded. The strain measurement resolution is equal to 1με, while the strain measurement range is 4%, and the elastic modulus is 50GPa (SHMSystem). The total length of the sensor is equal to 5 meters, and the chosen spatial resolution is equal to 5.2 mm. In addition, crack openings are measured using digital image correlation technology; the procedures for specimens’ preparation and software settings are reported by Armonico et al. (2024). The inspected area has a rectangular inspection zone measuring 900 mm x 275 mm. 2.2 Materials The elastic modulus (E f ) of carbon sheet was 245 GPa, whereas the composite single-layer thickness was 0.169 mm, as reported in the technical datasheets provided by the manufacturer (Fibre NET, Pavia di Udine (UD), Italy). The FRP was applied by wet lay-up method of CFRP fabrics bonded using a bicomponent epoxy resin. The beams were retrofitted using a carbon-fiber-reinforced polymer consisting of unidirectional carbon fabric Betontex FB-GV330U HT produced by Fiber Net s.p.a. The layers had a nominal thickn ess of 0.169 mm and Young’s modulus (Ef) of 245 GPa, as reported in the technical datasheets provided by the manufacturer. The fibers were glued using a bicomponent epoxy resin Betontex FB- RC02 with a declared Young’s modulus (E m ) of 3000 MPa and an ultimate strain equal to 2.9%. For concrete, four cylindrical specimens have been tested. Results shows a mean compression strength equal to 48 MPa with a consequent characteristic value equal to 40 MPa, and a mean elastic modulus of 36 MPa.