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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3.2 Crack Behaviour Cracking was monitored using DIC technology. The crack pattern is shown in Figure 4 for the tested beams, and the chosen crack is the maximum measured. The analyse was done one one-half of the beam without being able to access the area corresponding to the axis of symmetry. The crack patterns obtained show symmetrical behaviour in both beams, allowing the left side of the beam to be considered representative of its overall behaviour.

Figure 4 Crack pattern measured using DIC in the reference beam All the crack width results are shown in Figure 5. The reinforcement system's influence on the crack pattern's evolution is evident: in the reinforced beam, the maximum crack amplitude increases gradually and for greater load values than in the reference specimen (Yang et al., 2021). The evolution in crack amplitude faithfully follows the post-yielding steel strain trend shown in Figure 5. In fact, in the reference beam, an increase for almost constant loads can be perceived similarly to the elastoplastic trend in the steel. In parallel, in the CFRP-reinforced beam, a reduction in slope in the cracking curve corresponds to the hardening present in the reinforcing steel.

Figure 5 Maximum crack width comparison in referential and strengthened beams

Optical Fibre Distributed Monitoring After evaluating the effectiveness and consistency of the measurements, this tool can be used to study its potential and usefulness in the field of structural monitoring as well. The deformation profile was evaluated in a distributed manner for both tested specimens with a continuous acquisition. In order to reduce the size of the data file, it was decided to take one measurement per second by launching the acquisition with the test machine to find a correspondence with the measurement taken by the load cell. Figure 6 shows a comparison, at the same load (2F = 20kN), of the measurements taken by the optical fibre in the reference beam and the reinforced beam. The first noticeable result is the maximum deformation threshold measured at the steel level. The absolute peak of deformation measured in the reference beam is 1.8 times higher than that measured in the strengthened beam. This trend, is due to the CFRP reinforcement's beneficial influence, which contributes to the bending resistance by absorbing part of the stress otherwise assigned to the steel. Furthermore, looking again at the comparison of the deformation profiles, the trend shown in the curve referring to the reference beam is much more regular, presenting deformation peaks that subtend a greater area than what is measured in the strengthened beam. The optical fibre results allows to evaluated to identify the position of the cracks along its measurement profile to validate the cracks' pattern considerations (Antunes et al.,