PSI - Issue 42

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

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Fig.6. Percentage increase in P y , P u , δ y , δ u , and δ f .

Test results also showed that the stiffness of the specimens strengthened with the hybrid mix of CFRP and PET FRP laminates surpassed that of single sheets of CFRP and PET-FRP. However, the strength and deformation capacity of the hybrid mix was limited by the low strain capacity of the CFRP laminates. As a result, specimens CP and PC failed when the debonding strain in the CFRP was attained. The strength and ductility of the strengthened specimens could be improved by anchoring the laminates to exploit the tensile capacity of the CFRP laminates and the elongation capacity of PET-FRP laminates in the hybrid mix. 3.3. Strain in the FRP laminates The maximum strain values attained in the FRP laminates before failure ( ε f ) are presented in Table 2. It can be seen from Table 2 that the maximum strain recorded in the CFRP laminate is 0.0085 mm/mm corresponding to 65% strain utilization. On the other hand, the specimen strengthened with one layer of PET-FRP laminate attained a significantly higher maximum strain value of 0.0353 mm/mm than the CFRP-strengthened beam. This value corresponds to 45% FRP strain utilization. As for the hybrid CP and PC specimens, 54 and 41% of the rupture strain was utilized, respectively. The difference in the strain values between CP and PC is due to the type of the FRP at the outer layer at which the strain gauge was placed. Therefore, specimen CP which has PET-FRP as the outer layer recorded higher strain value due to the high elongation capacity of the PET-FRP. As a result, it can be concluded that PET-FRP is a promising type of FRP material that can be successfully used to strengthen RC beams in flexure, especially in the applications that require excellent ductility performance. Hybridizing PET-FRP with conventional CFRP could be a feasible solution; however, the system is limited by failure of the CFRP laminate. Therefore, anchoring the laminates to the concrete substrate is a necessity to prevent premature failure of the laminates and to utilize the high deformation capacity of the PET-FRP laminates. 4. Conclusions This paper presented an experimental study that investigated the flexural behavior of RC beams strengthened with CFRP, PET-FRP, and the hybrid mix of both materials. Based on the results, the following could be drawn: • The strengthened specimens failed by the debonding of the FRP laminates with a layer of concrete cover. • The ultimate load-carrying capacity of the strengthened specimens outweighed that of the control beam by 24 48%. • The load-carrying capacity of the beams that consisted of CFRP laminates was superior to that of the PET strengthened beam. However, the strength enhancement was at the expense of ductility which was reduced by 50 66% at failure load compared to the control beam. • The PET-strengthened beam displayed an outstanding ductile behavior, up to 9% enhancement over the control beam. • The stiffness of the specimens strengthened with the hybrid mix of CFRP and PET-FRP laminates surpassed that of single laminate of CFRP and PET-FRP. However, the strength and deformation capacity of the hybrid system was limited by the low strain capacity of the CFRP laminates. Therefore, it is recommended to anchor the laminates to exploit the benefits of both types of FRPs.