PSI - Issue 64

Sadeq Mo. Annooz et al. / Procedia Structural Integrity 64 (2024) 1565–1572 Annooz, Williams, and Myers / Structural Integrity Procedia 00 (2024) 000–000

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Figure 7. BFRP rebar diameter reduction. Data from this study were added to the BFRP test results collected by Myers (2024) that included multiple manufactures, different surface treatments and different bar properties as reported in the cited publication from that study. This was examined to benchmark and compare to other obtained results published in literature. They were grouped within the #4 and #6 rebar size categories as shown in Figure 8 and then compared to a lower and upper envelop based on the variation of the material geometry and properties from the database collected. The number of collected test results on the larger bars were limited as may be anticipated with the development of a newer bar type like BFRP. Based upon the data collected, the results from this study were within the ACI anticipated bond strength estimation. Most of the other collected data fell in general above Eq. 2 including the average for the data set. Overall, the BFRP data set appears less conservative relative to the 440.1R-15 provisions compared to the GFRP data set collected by Myers, (2024). This may suggest a calibration factor is required for BFRP compared to GFRP and CFRP.

0 10 20 30 40 50 60 70 80 90 Maximum Developable Bar Stress (ksi) [ACI 440 Eq 10.1c] 0.0

0 10 20 30 40 50 60 70 80 90 Maximum Developable Bar Stress (ksi) [ACI 440 Eq 10.1c] 0.0

Range of Limits: d b = 0.75 to 0.75 in 2 f' c = 4000 to 9000 psi f fu * = 113 to 113 ksi

20d b = 9.4" to 10"

Range of Limits: d b = 0.47 to 0.50 in 2 f' c = 4000 to 10000 psi f fu * = 115 to 250 ksi

20d b = 15.0"

2.0

4.0

6.0

8.0

10.0 12.0 14.0 16.0

5.0

10.0

15.0

20.0

Embedment Length (inches)

Embedment Length (inches)

0.47 ‐ 4000 ‐ 115 [in^2 ‐ psi ‐ ksi]

0.50 ‐ 10,000 ‐ 250 [in^2 ‐ psi ‐ ksi]

0.75 ‐ 4000 ‐ 113 [in^2 ‐ psi ‐ ksi]

0.75 ‐ 9000 ‐ 113 [in^2 ‐ psi ‐ ksi]

(Conversions: 1 ksi = 6.89 MPa, 1 inch = 25.4 mm, 1 in 2 = 645.16 mm 2 )

a) #4 BFRP bar pull-out test results b) #6 BFRP rebar pull-out test results Figure 8. BFRP peak bar stress in this study and developed from experimental data relative to ACI 440.1R Eq. 10.1c (Myers, 2024)

Conclusion

 Bond Strength: The bond strength of #4 BFRP and #6 BFRP rebars were found to be 34% and 25% lower, respectively, than that of mild steel rebars. This lower bond strength is attributed to the absence of bearing forces, which are present in steel rebars due to their ribbed surfaces.  Failure Modes: The mild steel rebar specimens exhibited a splitting failure mode, likely due to the higher than-designed compressive strength of the concrete and improved bond behavior due to the rebar lugs in bearing. In contrast, all BFRP rebar specimens experienced a pullout failure mode, highlighting the differences in failure mechanisms between the two bar types and configurations.

 Effect of larger diameter: Larger diameter exhibited less bond strength. The lower bond strength in larger