FRP U-Wrap Anchorage for Preventing Concrete Cover Separation: Experimental Study and Design Method
Publication: Journal of Composites for Construction
Volume 26, Issue 4
Abstract
Fiber-reinforced polymer (FRP) systems are commonly used in the flexural strengthening of reinforced concrete beams. However, concrete cover separation (CCS) is one of the main debonding failure modes that negatively impact the strengthening efficiency. This premature failure mode occurs at a lower fraction of tensile strain capacity of the longitudinal FRP reinforcement. Placing FRP U-wrap anchorage at the end regions of FRP longitudinal plates appears to be a promising technique that could mitigate or prevent CCS. This study characterized, experimentally, the effect of FRP U-wraps in enhancing the strengthening efficiency by mitigating CCS in FRP-strengthened RC beams. The study included full-scale RC beams strengthened in flexure using FRP sheets and anchored at their ends using FRP U-wraps. The beams were simply supported and tested under four-point bending. The test variables were the width and layout of the FRP U-wraps. The test results indicate the effectiveness of FRP U-wraps in preventing CCS once the required area of U-wrap is provided. The paper also presents a proposed design method for quantifying the minimum area of FRP U-wrap anchorage required to prevent CCS. The proposed design method was verified using the test results obtained from this study and also from a database of beams reported in the literature. Based on the findings of the study, recommendations are suggested for the design of a FRP U-wrap anchorage system that is capable of preventing CCS in FRP-strengthened RC beams.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The authors extend their appreciation to the Center of Excellence for Concrete Research and Testing (CoE-CRT), King Saud University, for funding this research study.
Notation
The following symbols are used in this paper:
- Af
- cross-sectional area of FRP longitudinal reinforcement;
- Afw
- cross-sectional area of FRP U-wrap;
- Afw,cal
- calculated cross-sectional area of FRP U-wrap;
- Afw,exp
- experimental cross-sectional area of FRP U-wrap;
- bf
- width of FRP longitudinal reinforcement;
- bfw
- width of FRP U-wrap;
- c
- depth of neutral axis;
- df
- depth of FRP longitudinal reinforcement;
- dfw
- effective bond length of FRP U-wrap;
- Ef
- tensile modulus of elasticity of FRP longitudinal reinforcement;
- Efw
- tensile modulus of elasticity of FRP U-wrap;
- specified compressive strength of concrete;
- fct
- tensile strength of concrete;
- ffu
- rupture stress of FRP longitudinal reinforcement;
- k1
- factor accounting for concrete strength;
- k2
- factor accounting for wrapping scheme;
- kv
- bond reduction coefficient;
- Le
- active bond length;
- nf
- number of longitudinal FRP plies;
- nfw
- number of FRP U-wrap plies;
- P
- total applied load;
- Pcr
- cracking load;
- Pu
- ultimate load;
- Pu,exp
- experimental ultimate load;
- Py
- yield load;
- Sfw
- spacing of FRP U-wrap;
- Tf
- maximum tensile force in FRP longitudinal reinforcement;
- Tsw
- tensile force in FRP U-wrap;
- tf
- thickness of one ply of FRP longitudinal reinforcement;
- tfw
- thickness of one ply of FRP U-wrap;
- ΔPu
- increase in experimental ultimate load of anchored beam with respect to control beam;
- δcr
- midspan deflection at cracking load;
- δu
- midspan deflection at ultimate load;
- δy
- midspan deflection at yield load;
- ɛbi
- strain in concrete substrate at time of longitudinal FRP installation;
- ɛc
- compressive strain of concrete;
- ɛcu
- crushing strain of concrete;
- ɛf
- tensile strain in FRP longitudinal reinforcement;
- ɛfd
- debonding strain of FRP reinforcement;
- ɛfu
- rupture strain of FRP longitudinal reinforcement;
- ɛfw,e
- design tensile strain in FRP U-wrap;
- ɛfw,u
- rupture strain of FRP U-wrap;
- ɛs
- tensile strain in steel reinforcement; and
- μ
- coefficient of friction.
References
ACI (American Concrete Institute). 2017. Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures. ACI 440.2R-17. Farmington Hills, MI: ACI.
ACI (American Concrete Institute). 2019. Building code requirements for structural concrete. ACI318-19. Farmington Hills, MI: ACI.
Al-Negheimish, A. I., A. K. El-Sayed, M. A. Al-Saawani, and A. M. Alhozaimy. 2021. “Effect of stirrups on plate end debonding in reinforced concrete beams strengthened with fiber reinforced polymers.” Polymers 13 (19): 3322. https://doi.org/10.3390/polym13193322.
Al-Negheimish, A. I., A. K. El-Sayed, R. A. Al-Zaid, A. B. Shuraim, and A. M. Alhozaimy. 2012. “Behavior of wide shallow RC beams strengthened with CFRP reinforcement.” J. Compos. Constr. 16 (4): 418–429. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000274.
Al-Saawani, M. A., A. K. El-Sayed, and A. I. Al-Negheimish. 2015. “Effect of basic design parameters on IC debonding of CFRP-strengthened shallow RC beams.” J. Reinf. Plast. Compos. 34 (18): 1526–1539. https://doi.org/10.1177/0731684415593816.
Al-Saawani, M. A., A. K. El-Sayed, and A. I. Al-Negheimish. 2017. “Crack width prediction for concrete beams strengthened with carbon FRP composites.” J. Compos. Constr. 21 (5): 04017023. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000805.
Al-Saawani, M. A., A. K. El-Sayed, and A. I. Al-Negheimish. 2020. “Effect of shear-span/depth ratio on debonding failures of FRP-strengthened RC beams.” J. Build. Eng. 32: 101771. https://doi.org/10.1016/j.jobe.2020.101771.
Al-Tamimi, A. K., R. J. Hawileh, J. Abdalla, and H. A. Rasheed. 2011. “Effects of ratio of CFRP plate length to shear span and end anchorage on flexural behavior of SCC RC beams.” J. Compos. Constr. 15 (6): 908–919. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000221.
Al-Zaid, R. A., A. K. El-Sayed, A. I. Al-Negheimish, A. B. Shuraim, and A. M. Alhozaimy. 2014. “Strengthening of structurally damaged wide shallow RC beams using externally bonded CFRP plates.” Latin Am. J. Solids Struct. 11 (6): 946–965. https://doi.org/10.1590/S1679-78252014000600003.
Al-Zaid, R. Z., A. I. Al-Negheimish, M. A. Al-Saawani, and A. K. El-Sayed. 2012. “Analytical study on RC beams strengthened for flexure with externally bonded FRP reinforcement.” Composites, Part B 43 (2): 129–141. https://doi.org/10.1016/j.compositesb.2011.11.015.
ASTM. 2018. Standard test method for compressive strength of cylindrical concrete specimens. ASTM C39/C39M-18. West Conshohocken, PA: ASTM.
ASTM. 2019. Standard test methods and definitions for mechanical testing of steel products. ASTM A370-19e1. West Conshohocken, PA: ASTM.
Brena, S. F., R. M. Bramblett, S. L. Wood, and M. E. Kreger. 2003. “Increasing flexural capacity of reinforced concrete beams using carbon fiber-reinforced polymer composites.” ACI Struct. J. 100 (1): 36–46.
Buyle-Bodin, F., and E. David. 2004. “Use of carbon fibre textile to control premature failure of reinforced concrete beams strengthened with bonded CFRP plates.” J. Ind. Test. 33 (3): 145–157. https://doi.org/10.1177/1528083704039251.
Buyukozturk, O., O. Gunes, and E. Karaca. 2004. “Progress on understanding debonding problems in reinforced concrete and steel members strengthened using FRP composites.” Constr. Build. Mater. 18 (1): 9–19. https://doi.org/10.1016/S0950-0618(03)00094-1.
Ceroni, F. 2010. “Experimental performances of RC beams strengthened with FRP materials.” Constr. Build. Mater. 24 (9): 1547–1559. https://doi.org/10.1016/j.conbuildmat.2010.03.008.
Ceroni, F., M. Pecce, S. Matthys, and L. Taerwe. 2008. “Debonding strength and anchorage devices for reinforced concrete elements strengthened with FRP sheets.” Composites, Part B 39 (3): 429–441. https://doi.org/10.1016/j.compositesb.2007.05.002.
China Planning Press. 2010. Technical code for infrastructure application of FRP composites. GB-50608. Beijing: China Planning Press.
CNR (Consiglio Nazionale delle Ricerche). 2013. Guide for the design and construction of externally bonded FRP systems for strengthening existing structures. CNR-DT200 R1. Rome: CNR.
Concrete Society Committee. 2012. Design guidance for strengthening concrete structures using fibre composite materials. Technical Rep. 55. Crowthorne: Concrete Society Committee.
Demakos, C., and D. Koutsoukos. 2003. “Effective strengthening of reinforced concrete beams with anchored FRPs.” In Recent advances in composite materials, edited by E. E. Gdoutos and Z. P. Marioli-Riga, 345–355. Dordrecht, Netherlands: Springer
fib (International Federation for Structural Concrete). 1993. CEB-FIP model code 1990. CEB-FIP MC90. London: Thomas Telford.
Fu, B., J. G. Teng, J. F. Chen, G. M. Chen, and Y. C. Guo. 2017. “Concrete cover separation in FRP-plated RC beams: Mitigation using FRP U-jackets.” J. Compos. Constr. 21 (2): 04016077. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000721.
Grelle, S. V., and L. H. Sneed. 2013. “Review of anchorage systems for externally bonded FRP laminates.” Int. J. Concr. Struct. Mater. 7 (1): 17–33. https://doi.org/10.1007/s40069-013-0029-0.
Hasnat, A., M. Islam, and A. Amin. 2016. “Enhancing the debonding strain limit for CFRP-strengthened RC beams using U-clamps: Identification of design parameters.” J. Compos. Constr. 20 (1): 04015039. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000599.
Jeevan, N., and J. Reddy. 2018. “Strengthening of RC beams using externally bonded laminate (EBL) technique with end anchorages under flexure.” Asian J. Civ. Eng. 19: 263–272. https://doi.org/10.1007/s42107-018-0022-7.
Kalfat, R., R. Al-Mahaidi, and S. T. Smith. 2013. “Anchorage devices used to improve the performance of reinforced concrete beams retrofitted with FRP composites: State-of-the-art review.” J. Compos. Constr. 17 (1): 14–33. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000276.
Khalifa, E. S., and S. H. Al-Tersawy. 2013. “Experimental and analytical investigation for enhancement of flexural beams using multilayer wraps.” Composites, Part B 45 (1): 1432–1440. https://doi.org/10.1016/j.compositesb.2012.08.021.
Khan, A. A. R., and T. Ayub. 2010. “Effectiveness of U-shaped CFRP wraps as end anchorages in predominant flexure and shear region.” In Proc., 5th Int. Conf. on FRP Composites in Civil Engineering, 533–536. Beijing: Tsinghue University Press.
Kotynia, R., H. A. Baky, K. W. Neale, and U. A. Ebead. 2008. “Flexural strengthening of RC beams with externally bonded CFRP systems: Test results and 3D nonlinear FE analysis.” J. Compos. Constr. 12 (2): 190–201. https://doi.org/10.1061/(ASCE)1090-0268(2008)12:2(190).
Lee, J., R. Chacko, and M. Lopez. 2010. “Use of mixed-mode fracture interfaces for the modeling of large-scale FRP-strengthened beams.” J. Compos. Constr. 14 (6): 845–855. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000143.
Lee, J., and M. Lopez. 2016. “Characterization of FRP U wrap anchors for externally bonded FRP-reinforced concrete elements: An experimental study.” J. Compos. Constr. 20 (4): 1–11. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000642.
Li, X., X. L. Gu, X. B. Song, Y. Ouyang, and Z. L. Feng. 2013. “Contribution of U-shaped strips to the flexural capacity of low-strength reinforced concrete beams strengthened with carbon fibre composite sheets.” Composites, Part B 45 (1): 117–126. https://doi.org/10.1016/j.compositesb.2012.09.036.
Orton, S. L., J. O. Jirsa, and O. Bayrak. 2008. “Design considerations of carbon fiber anchors.” J. Compos. Constr. 12 (6): 608–616. https://doi.org/10.1061/(ASCE)1090-0268(2008)12:6(608).
Pham, H. B., and R. Al-Mahaidi. 2006. “Prediction models for debonding failure loads of carbon fiber reinforced polymer retrofitted reinforced concrete beams.” J. Compos. Constr. 10 (1): 48–59. https://doi.org/10.1061/(ASCE)1090-0268(2006)10:1(48).
Pimanmas, A., and P. Pornpongsaroj. 2004. “Peeling behaviour of reinforced concrete beams strengthened with CFRP plates under various end restraint conditions.” Mag. Concr. Res. 56 (2): 73–81. https://doi.org/10.1680/macr.2004.56.2.73.
Rasheed, H. A., B. R. Decker, A. Esmaeily, R. J. Peterman, and H. G. Melhem. 2015. “The influence of CFRP anchorage on achieving sectional flexural capacity of strengthened concrete beams.” Fibers 3: 539–559. https://doi.org/10.3390/fib3040539.
Rosenboom, O., and S. Rizkalla. 2008. “Experimental study of intermediate crack debonding in fiber-reinforced polymer strengthened beams.” ACI Struct. J. 105 (1): 41–50.
Sadrmomtazi, A., H. Rasmi Atigh, and J. Sobhan. 2014. “Experimental and analytical investigation on bond performance of the interfacial debonding in flexural strengthened RC beams with CFRP sheets at tensile face.” Asian J. Civ. Eng. (BHRC) 15 (3): 391–410.
Smith, S. T., and J. G. Teng. 2003. “Shear-bending interaction in debonding failures of FRP-plated RC beams.” Adv. Struct. Eng. 6 (3): 183–199. https://doi.org/10.1260/136943303322419214.
Sobuz, H. R., E. Ahmed, N. M. Sutan, N. M. Hasan, M. D. Uddin, and M. J. Uddin. 2012. “Bending and time-dependent responses of RC beams strengthened with bonded carbon fiber composite laminates.” Constr. Build. Mater. 29: 597–611. https://doi.org/10.1016/j.conbuildmat.2011.11.006.
Spadea, G., F. Bencardino, and R. N. Swamy. 1998. “Structural behavior of composite RC beams with externally bonded CFRP.” J. Compos. Constr. 2 (3): 132–137. https://doi.org/10.1061/(ASCE)1090-0268(1998)2:3(132).
Teng, J. G., S. T. Smith, J. Yao, and J. F. Chen. 2003. “Intermediate crack-induced debonding in RC beams and slabs.” Constr. Build. Mater. 17 (6–7): 447–462. https://doi.org/10.1016/S0950-0618(03)00043-6.
Zhang, D., T. Ueda, and H. Furuuchi. 2012. “Concrete cover separation failure of overlay-strengthened reinforced concrete beams.” Constr. Build. Mater. 26: 735–745. https://doi.org/10.1016/j.conbuildmat.2011.06.082.
Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 26 • Issue 4 • August 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: May 5, 2021
Accepted: Feb 16, 2022
Published online: May 3, 2022
Published in print: Aug 1, 2022
Discussion open until: Oct 3, 2022
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.
Cited by
- Vui Van Cao, Effects of CFRP U-Wraps on the Behavior of NSM GFRP Retrofitted Reinforced Concrete Beams, Journal of Composites for Construction, 10.1061/JCCOF2.CCENG-4884, 29, 1, (2025).
- Hao Zhou, Yan Yang, Dilum Fernando, undefined Tianli-Huang, Ya Ou, Bond behaviour of CFRP-to-concrete bonded joints with a GFRP interlayer: An experimental study, Construction and Building Materials, 10.1016/j.conbuildmat.2024.137042, 438, (137042), (2024).
- Mohammed A. Zaki, Hayder A. Rasheed, Konstantinos Mitsios, Improvements in lightweight concrete T beams CFRP strengthened and anchored with U ‐wraps , Structural Concrete, 10.1002/suco.202300968, 25, 3, (2206-2221), (2024).
- Mohammed A. Al-Saawani, Ahmed K. El-Sayed, Abdulaziz I. Al-Negheimish, Abdulrahman M. Alhozaimy, FRP U-Wraps for Mitigating Plate-End Debonding in FRP-Strengthened Beams: Finite Element Modeling and Parametric Study, Arabian Journal for Science and Engineering, 10.1007/s13369-024-08853-6, 49, 10, (14001-14019), (2024).
- P. Firsov, Bachar Ali Kaafarani, THEORETICAL ASPECTS OF AVOIDING DELAMINATION OF COMPOSITE MATERIALS DURING STRENGTHENING OF REINFORCED CONCRETE STRUCTURES, Municipal economy of cities, 10.33042/2522-1809-2023-1-175-32-38, 1, 175, (32-38), (2023).
- Mohammed A. Al-Saawani, Ahmed K. El-Sayed, Abdulaziz I. Al-Negheimish, Inclined FRP U-Wrap Anchorage for Preventing Concrete Cover Separation in FRP Strengthened RC Beams, Arabian Journal for Science and Engineering, 10.1007/s13369-022-07186-6, 48, 4, (4879-4892), (2022).
- Shuai Tian, Xiaotao Zhang, Wenjing Hu, Fatigue Analysis of CFRP-Reinforced Concrete Ribbed Girder Bridge Deck Slabs, Polymers, 10.3390/polym14183814, 14, 18, (3814), (2022).