PSI - Issue 54

Jamal A. Abdalla et al. / Procedia Structural Integrity 54 (2024) 609–616 Abdalla et al./ Structural Integrity Procedia 00 (2019) 000 – 000

613

5

illustrated in Fig. 3. To monitor the strain in the CFRP laminates, strain gauges were placed at the center of the CFRP wraps on both sides, as indicated in Fig. 3. Additionally, a concrete strain gauge was mounted at the top center of the beam's midspan to record the strain in the concrete.

Fig. 2. Geometrical configuration of the tested beams (a) B; (b) BU; (c) A2 ; (d) A4

3. Results and Discussion 3.1. Failure modes

Fig. 3 demonstrates the failure modes of the tested specimens. The failure mode of the control beams (NC and RC) was the typical shear failure with diagonal shear cracks at an angle of 45º as depicted in Fig. 3-a. The failure of the second set of specimens, which were strengthened with U-wraps (NU-90 and RU-90), was controlled by debonding of the laminates. Diagonal shear cracks can also be seen in both specimens (Fig. 3-b). In the case of the side-bonded beams (Fig. 3-c), they failed in shear with a 45-degree crack, accompanied by debonding of the laminates. The brittle debonding observed at low displacement limited the strain development in the CFRP, leading to low strain levels and preventing the beams from reaching their maximum load-carrying capacity. Flexural cracking was observed in specimens NCU and BCU (Fig. 3-d). Notably, the continuous wrapping method proved to be the most effective, as the beam displayed a strength corresponding to the main shear strength of the beam, despite not reaching its maximum shear strength due to flexure failure. Beam RU-45 also failed by flexure without debonding of the FRP laminates, in contrast to specimen NU-45, which exhibited premature brittle failure, likely attributed to inadequate bond development length or anchorage.

(a) Control beams (NC and RC)

(b) NU-90 and RU-90