PSI - Issue 64

Annalisa Napoli et al. / Procedia Structural Integrity 64 (2024) 975–982 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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where: A s and A r are, respectively, the total area of steel rebars employed as beam’s internal reinforcement and the total area of steel plates used as external reinforcement (in a few cases, 2 or 3 plates were used); f s,y and f r,y are, respectively, the yielding strength of the steel used for the internal and internal reinforcement, while f c = 0.85 f’ c ·is the cylinder compressive strength of concrete f’ c multiplied by 0.85. The values of f s,y , f r,y and f’ c are those provided by the original authors and generally obtained by the common characterization tests. To this purpose, it is worth highlighting that 70% of beams is characterized by f’ c values lower than 40 MPa while for one member only the strength goes up to 80 MPa; the yielding strength of the external steel plates ranges between 214 and 324 MPa, while f s,y spans between 337 and 638 MPa. In some cases, high carbon steel was employed as internal reinforcement so that f s,y is indicated as “0.2% proof strength” in the related papers. By focusing on Figure 4a it can be noted that the value of  s is mostly lower than 0.25 and for many beams is about 0.10; the beams identified in the plot with the numbers 56 and 57 were characterized by  s =0; concerning the ratio  r /  s , about 70% of the beams shows values lower than 1, and for 4 beams this ratio goes up to 2.25 (  r /  s is not evaluated for the beam 56 and 57). In the case of beams strengthened with MF plate, the values of the parameters are more homogeneous; the mechanical percentages  s and  r show slight changes in the values so that for the first half of the beams the ratio  r /  s is constantly equal to 0.75 and for the second half of them is equal to 1.15 (Fig.4b).

RC beams strengthened with EB plate

RC beams strengthened with MF plate

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 1 5 9 131721252933374145495357 Beam number  r /  s  s

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 1 2 3 4 5 6 7 8 9 10111213141516 Beam number  s  r /  s

(a)

(b)

Fig. 4. Values of the mechanical percentage  s and of the ratio  r /  s for RC strengthened beams with EB plate (a) and MF plate (b).

Finally, it might be of interest to classify the strengthened beams based on the failure mode exhibited during the bending tests, as described by their authors. It is relevant to highlight that, such a classification was not an easy task, as this information is often not well-detailed in the scientific papers. Additionally, when plate debonding is experienced as a failure mode, it is often not well-specified whether it is “end debonding (EB)” or “intermediate debonding (ID)”, the latter being promoted by the occurrence of flexural cracks and a complex interaction between yielding occurring in the internal rebars. Of course, the lack of information about the debonding typology is also due to the more recent nature of insights into intermediate debonding, which have increased with the growing number of studies on the EB strengthening with FRP systems. The pie charts in Figure 5 show the distribution of RC beams per failure mode in the case of EB (Fig. 5a) or MF (Fig. 5b) strengthening, as indicated by the researchers in the scientific papers. In Figure 5a, the beams are classified in six categories which correspond to different typologies of failure mode; an exception is represented by the class “n/a” which identifies one member for which the failure mode is not mentioned in the paper (Ozbek et al. 2016). The failure types have the following meaning: ID = intermediate debonding of the steel plate; E-DB = end debonding of the steel plate; DB = generic plate debonding (not specified in the paper the debonding type); FL = flexural crisis characterized by crushing of concrete in compression and yielding of steel plate in tension; FL+ID = flexural crisis combined to intermediate debonding of the steel plate.