Title:
Exploring Strength of Straight and Bent GFRP Bars: Refinements to CSA S807:19 Annex E
Author(s):
Ahmed Khalil, Rami A. Hawileh, and Mousa Attom
Publication:
Symposium Paper
Volume:
360
Issue:
Appears on pages(s):
242-253
Keywords:
Durability, CSA, ACI, ASTM, Bent, FRP, Strength.
DOI:
10.14359/51740628
Date:
3/1/2024
Abstract:
This study explores technological advancements enabling the utilization of GFRP bars in concrete structures, particularly in coastal areas. However, GFRP bars often encounter reduced bend strength at specific bend locations, which may pose a challenge in their practical application. Various properties such as the strength of bent GFRP bars are crucial for quality assurance, yet existing testing methods stated in ASTM D7914M-21 and ACI 440.3R-15 have limitations when applied to different GFRP bent shapes. Furthermore, those methods require special precautions to ensure symmetry and avoid eccentricities in specimens. To address these challenges, CSA S807:19 introduced a simpler standardized testing procedure that involves embedding a single L-shaped GFRP stirrup in a concrete block. However, the specified large block size in CSA S807:19 Annex E may pose difficulties for both laboratory and on-site quality control tests. Therefore, CSA S807:19 Annex E (Clause 7.1.2b) permits the use of a customized block size, as long as it meets the bend strength of the FRP bars without causing concrete splitting. To date, very few prior research has explored the use of custom block sizes. Therefore, this study aims to thoroughly investigate the strength of bent FRP bars with custom block sizes and without block confinement. Such an investigation serves to highlight the user-friendliness and efficiency of the CSA S807:19 Annex E method. The study recommends two block sizes: 200x400x300 mm (7.87x15.75x11.81 in) for bars <16 mm (0.63 in) diameter and 200x200x300 mm (7.87x7.87x11.81 in) for bars <12 mm (0.39 in). Additionally, the study cautions against using confinement reinforcement, especially with smaller blocks, as it could interfere with the embedded bent FRP bar. Furthermore, the study suggests incorporating additional tail length to mitigate the debonding effects resulting from fixing the strain gauges to the bent portion of the embedded FRP bar. By exploring these modifications, the study seeks to enhance the effectiveness of the testing procedure and expand its practical application for both laboratory and on-site quality assurance. The findings hold implications for the reliable testing of GFRP bars' strength, advancing their use as reinforcement in concrete structures.
Related References:
1. Maruyama, T., Honma, M., and Okamura, H., 1993, “Experimental study on tensile strength of bent portion of FRP rods” Special publication, 138, 163–176.
2. Imjai, T., Guadagnini, M., and Pilakoutas, K., 2017, “Bend Strength of FRP Bars: Experimental Investigation and Bond Modeling” Journal of Materials in Civil Engineering, 29(7), 04017024. doi: 10.1061/(ASCE)MT.1943-5533.0001855
3. Imjai, T., Guadagnini, M. and Pilakoutas, K., 2009, “Curved FRP as concrete reinforcement” Proceedings of the Institution of Civil Engineers-Engineering and Computational Mechanics, 162(3), 171-178.
4. Vint, L. and Sheikh, S., 2015, “Investigation of bond properties of alternate anchorage schemes for glass fiber-reinforced polymer bars”, Structural Journal, 112(1), 59-68.
5. Ahmed, E., 2010, “Shear behaviour of concrete beams reinforced with fibre-reinforced polymer (FRP) stirrups= Étude du comportement à l'effort tranchant de poutres en béton armé avec des étriers en polymère renforcé de fibres (PRF)” Library and Archives Canada= Bibliothèque et Archives Canada, Ottawa.
6. Spadea, S., Orr, J. and Ivanova, K., 2017, “Bend-strength of novel filament wound shear reinforcement”, Composite Structures, 176, 244-253.
7. Ascione, L., Razaqpur, A.G. and Spadea, S., 2014, “Effectiveness of FRP stirrups in concrete beams subject to shear”, 7th International Conference on FRP Composites in Civil Engineering, CICE 2014. International Institute for FRP in Construction.
8. Ahmed, E.A., El-Sayed, A.K., El-Salakawy, E. and Benmokrane, B., 2010, “Bend strength of FRP stirrups: Comparison and evaluation of testing methods”, Journal of composites for construction, 14(1), 3-10.
9. Nakamura, H. and Higai, T., 1995, “Evaluation of shear strength of concrete beams reinforced with FRP”, Doboku Gakkai Ronbunshu, 1995(508), 89-100.
10. Morphy, R., Shehata, E. and Rizkalla, S., 1997, “Bent effect on strength of CFRP stirrups”, Proceedings of the Third International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures, 2, 19-26.
11. Nagasaka, T., Fukuyama, H. and Tanigaki, M., 1993, “Shear performance of concrete beams reinforced with FRP stirrups”, Special publication, 138, 789-812.
12. Lee, C., Ko, M. and Lee, Y., 2014, “Bend strength of complete closed-type carbon fiber-reinforced polymer stirrups with rectangular section”, Journal of Composites for Construction, 18(1), 04013022.
13. Shehata, E., Morphy, R. and Rizkalla, S., 2000, “Fibre reinforced polymer shear reinforcement for concrete members: behaviour and design guidelines”, Canadian Journal of Civil Engineering, 27(5), 859-872.
14. Ehsani, M.R., Saadatmanesh, H. and Tao, S., 1995, “Bond of hooked GFRP rebars to concrete”, Materials Journal, 92(4), 391-400.
15. Porter, M.L. and Harries, K., 2007, “Future directions for research in FRP composites in concrete construction”, Journal of Composites for Construction, 11(3), 252-257.
16. Elgabbas, F., Ahmed, E. and Benmokrane, B., 2013, “Basalt FRP reinforcing bars for concrete structures”, Proceedings of the 4th Asia-Pacific Conference on FRP in Structures, APFIS, 440, 11-13.
17. Wu, H.C. and Eamon, C.D., 2017, “Strengthening of concrete structures using fiber reinforced polymers (FRP): design, construction and practical applications”.
18. Van Den Einde, L., Zhao, L. and Seible, F., 2003, “Use of FRP composites in civil structural applications”, Construction and building materials, 17(6-7), 389-403.
19. Currier, J., Fogstad, C., Walrath, D. and Dolan, C., 1994, “Bond development of thermoplastic FRP shear reinforcement stirrups”, Infrastructure: New Materials and Methods of Repair, 592-597.
20. Imjai, T., Garcia, R., Guadagnini, M. and Pilakoutas, K., 2020, “Strength degradation in curved Fiber-reinforced Polymer (FRP) bars used as concrete reinforcement”, Polymers, 12(8), 1653.
21. Lee, C., Ko, M. and Lee, Y., 2014, “Bend strength of complete closed-type carbon fiber-reinforced polymer stirrups with rectangular section”, Journal of Composites for Construction, 18(1), 04013022.
22. Ahmed, E.A., El-Sayed, A.K., El-Salakawy, E. and Benmokrane, B., 2010, “Bend strength of FRP stirrups: Comparison and evaluation of testing methods”, Journal of composites for construction, 14(1), 3-10.
23. Jeremic, N. and Sheikh, S.A., 2021, “Performance of Glass Fiber-Reinforced Polymer Bent Bars. ACI Structural Journal, (2).”
24. Mohamed, K., Benmokrane, B., Nazair, C. and Loranger, M.A., 2021, “Development and validation of a testing procedure for determining tensile strength of bent GFRP reinforcing bars”, Journal of Composites for Construction, 25(2), 04020087.
25. Benmokrane, B., Mohamed, K. and Cousin, P., 2020, “Performance and durability of in-plant partially cured GFRP bent bars in steam-cured precast concrete elements”, Journal of Composites for Construction, 24(4), 04020020.
26. Al-Salloum, Y.A., El-Gamal, S., Almusallam, T.H., Alsayed, S.H. and Aqel, M., 2013, “Effect of harsh environmental conditions on the tensile properties of GFRP bars”, Composites Part B: Engineering, 45(1), 835-844.
27. Yan, F., Lin, Z. and Yang, M., 2016, “Bond mechanism and bond strength of GFRP bars to concrete: A review”, Composites Part B: Engineering, 98, 56-69.
28. Iqbal, M., Zhang, D., Jalal, F.E. and Javed, M.F., 2021, “Computational AI prediction models for residual tensile strength of GFRP bars aged in the alkaline concrete environment”, Ocean Engineering, 232, 109134.
29. Liu, S., Bai, C., Zhang, J., Zhao, K., Li, Q. and Jin, G., 2023, “Experimental study on bonding performance of GFRP bars-recycled aggregate concrete under sulfate attack environment”, Construction and Building Materials, 379, 131231.
30. CSA S807:19, 2019, “Specification for fibre-reinforced polymers”, Toronto, ON, CA.
31. ACI 440, 2012, “Guide Test Methods for Fiber-Reinforced Polymers (FRP) Composites for Reinforcing Or Strengthening Concrete and Masonry Structures”, American Concrete Institute.
32. ASTM D7914/D7914M, 2021, “Standard specification for strength of fiber reinforced polymer (FRP) bent bars in bend locations”, West Conshohocken, PA, US.
33. Miyata, S., 1989, “Experimental study on tensile strength of FRP bent bar”, Proceedings of JCI, 11(1), 789-794.
34. CSA S806-12, 2012, “Design and construction of building structures with fibre-reinforced polymers”, Toronto, ON, CA.
35. ASTM D7205/D7205M, 2016, “Standard Test Method for Tensile Properties of Fiber Reinforced Polymer Matrix Composite Bars”, West Conshohocken, PA, US