PSI - Issue 64

Francesco Bencardino et al. / Procedia Structural Integrity 64 (2024) 932–943 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

939

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These results highlight the crucial importance of considering both peel and shear stresses at the ends of the C-FRP plate and the consequent slippage between the C-FRP plate and the concrete substrate, which can lead to premature failures. The results obtained were also evaluated in terms of deflection ductility µ D , defined as follows: µ D = D u /D y (1) Where D u corresponds to the mid-span deflection at ultimate; while D y is the mid-span deflection at yielding of the tension steel. As reported in Table 3, it is clear that beams reinforced solely with a C-FRP plate experience substantial losses in terms of deformation capacity. Indeed, the ductility of beam A1.1 is only 24% compared to that of the original control beam. On the other hand, the use of appropriate anchorage systems can limit this loss of ductility, allowing beam A1.2 to retain approximately 70% of the ductility, compared to specimen A1. In conclusion, the above mentioned results highlight the importance of careful considerations regarding the use of external anchorage systems to maintain the ductility characteristics of the original unreinforced beam when designing adequate strengthening interventions.

Table 3. Ductility properties of the tested beams.

Beam

µ Δ

Δ

A1

6.2 1.5 4.3

1

A1.1 A1.2

0.24 0.70

3.2. Flexural strengthening of the RC frames Based on the experimental study reported in section 3.1, it can be seen that the use of C-FRP plates, when combined with external anchorages (cf. beam A1.2), can increase the load-bearing capacity of the RC beams up to 81% when compared to the control beam, while maintaining a proper level of ductility. In this context, the rehabilitation project considered the application of a C-FRP plate (with dimensions of 1.2×100×9800 mm 3 ) to the tension face of the beams. After consulting with suppliers of FRP materials, it was decided to use a C-FRP system consisting of Sika Carbodur plates embedded in a two-component epoxy adhesive. The material properties of the proposed C-FRP system are listed in Table 4.

Table 4. Properties of the C-FRP plate.

Density [g/cm 3 ]

1.45

Fibre volume fraction [%] Longitudinal strength [MPa]

66

2200 155 1.40

Longitudinal Young’s Modulus [GPa]

Strain at failure [%]

The shear capacity of the beam was also evaluated. From the results obtained it can be seen that there is no need for designing any additional shear strengthening. As reported in Figure 6, U-shaped steel brackets made with a thickness of 2 mm, a height of 500 mm, and a length of 1000 mm were positioned in the two end sections of the C-FRP plate with the objective of counteract the detachment of the C-FRP plate when the stress level increase. Furthermore, the beams were also repaired next to section K-K (where localized cracks were observed) by (i) injecting resin and (ii) installing U-shaped steel brackets with a thickness of 2 mm, a height of 500 mm, and a length of 400 mm.