PSI - Issue 42

Haya H. Mhanna et al. / Procedia Structural Integrity 42 (2022) 1190–1197 Mhanna et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 4. Failure modes of specimens (a) CB; (b) C; (c) P; (d) CP; (e) PC

3.2. Load-deflection responses

The load-deflection graphs of the tested specimens are presented in Fig 5. In addition, Fig. 6 compares the strengthened specimens to the control specimen and highlight the percentage change of P y , P u , δ y , δ u , and δ f . The load deflection curves shown in Fig. 5 show that all specimens had similar pre-cracking stiffness until attaining a load of ~10 kN. After which, the strengthened specimens showed substantial improvement in the post cracking stiffness than the control beam. Specifically, the stiffness of the specimens strengthened with CFRP laminates (C, CP, and PC) was superior to that of specimen P due to the high elastic modulus of the CFRP material. The third stage of the load deflection curves indicate sudden drop in specimens C, CP, and PC after attaining the ultimate load. This drop was due to the brittle failure of the specimens by the premature debonding of the concrete cover. Specimen P, on the other hand, displayed a similar response to that of the control beam, where it maintained the load while the deflection increased until failure. This is due to the large rupture strain capacity of the PET-FRP laminates which resulted in higher deformation capacity of the PET-strengthened beam (P). It can be also observed from Fig. 5 that the load deflection responses of specimens CP and PC coincided, which shows that the stacking consequence is irrelevant and result in similar behavior of the strengthened specimen. However, this conclusion may not be true if the laminates were anchored. Therefore, it is recommended in future research studies to investigate the effect of stacking consequence when the laminates are anchored by means of U-wraps or FRP spike anchors. It is clearly indicated in Table 2 and Figs. 5 and 6 that the ultimate load-carrying capacity of the strengthened specimens outweighed that of the control beam (CB). Particularly, the enhancement in the yield and ultimate loads ranged from 16-48% and 24-48% compared to CB, respectively. Specimens C, CP, and PC provided similar strength improvement (46-48%), while specimen P displayed inferior capacity than the CFRP-strengthened beams. This is due to the significantly higher tensile capacity of CFRP compared to PET-FRP laminates, which resulted in better performance in terms of load-carrying capacity. However, the strength enhancement was at the expense of ductility, where the deflection at ultimate and failure of specimens C, CP, and PC was reduced by 21-42% and 49-62% compared to the control beam, respectively. Similarly, the ductility at ultimate and failure of these specimens was reduced by 23-48% and 50-66% compared to CB, respectively. An interesting behavior was observed in specimen P, where the deflection at yield, ultimate, and failure loads was enhanced by 3, 6, and 12% than the control beam, respectively. Consequently, the ductility at ultimate and failure of specimen P outweighed CB by 3 and 9%, respectively. This interesting performance is untypical for FRP-strengthened beams and is a result of the LRS capacity of the PET-FRP.

Fig. 5. Load-deflection response curves