Flexural Performance of RC Continuous Beams Strengthening by CFRP with Grooves

Document Type : Regular Paper


Civil Engineering Department, College of Engineering, University of Thi-Qar, Iraq



Externally Bonded Reinforcement (EBR) is the most common technique used to strengthen the RC members with carbon fiber reinforced polymer (CFRP) sheets. Recently, a new proposed technique was named Externally Bonded Reinforcement on Grooves (EBROG) has been presented as an alternative method to avoid or eliminate the undesirable de-bonging failure mode that is accompanying to EBR method. This paper is devoted to investigating the effect of the strengthening techniques on the flexural behavior of RC continuous beams externally strengthened with CFRP sheets in both hogging and sagging zones, by testing twelve beam specimens. All beams have the same cross-section (200×130) mm and 2300 mm length. The parameters of this study include strengthening methods, length and layers number of CFRP sheet and number, length and direction of grooves, in addition to the effect of presence of steel fiber in the hogging zone. The results are introduced in terms of ultimate load, ultimate deflection, ductility index and mode of failure. The test results showed that the EBROG strengthening method has highly effective in improving the ultimate load of strengthened beams. The specimens strengthened by one and two layers of CFRP using EBROG with three longitudinal grooves have a rising in the ultimate load by about (24.4 and 52.6) % respectively, in comparison with the same beams but strengthened by EBR. Also, the mode of failure was changed from CFRP debonding in case of EBR beams to CFRP rupture, or to concrete cover separation in EBROG beams. Finally, the strengthened beams with CFRP sheets presented a more brittle behavior at failure than the unstrengthening specimen.


  • Strengthening the continuous RC beam strengthening with CFRP sheets, results in enhancing the ultimate load. The EBROG technique is more effective than EBR.
  • EBROG has the ability to eliminate the undesirable debonding failure mode that is accompanying to EBR method.
  • More brittle behavior was achieved in strengthened beams by CFRP using EBR, However, the ductility was increased when EBROG insteated of EBR.


Main Subjects

[1]     Toutanji H, Zhao L, Zhang Y. Flexural behavior of reinforced concrete beams externally strengthened with CFRP sheets bonded with an inorganic matrix. Eng Struct 2006. https://doi.org/10.1016/j.engstruct.2005.09.011.
[2]     Esfahani MR, Kianoush MR, Tajari AR. Flexural behaviour of reinforced concrete beams strengthened by CFRP sheets. Eng Struct 2007. https://doi.org/10.1016/j.engstruct.2006.12.008.
[3]     Siddiqui NA. Experimental investigation of RC beams strengthened with externally bonded FRP composites. Lat Am J Solids Struct 2009.
[4]     Heffernan PJ. Behavior of reinforced concrete beams strengthened with CFRP sheets 2013:1–7.
[5]     Hawileh RA, Rasheed HA, Abdalla JA, Al-Tamimi AK. Behavior of reinforced concrete beams strengthened with externally bonded hybrid fiber reinforced polymer systems. Mater Des 2014. https://doi.org/10.1016/j.matdes.2013.07.087.
[6]     Al-zu’bi H, Abdel-Jaber M, Katkhuda H. Flexural Strengthening of Reinforced Concrete Beams with Variable Compressive Strength Using Near-Surface Mounted Carbon-Fiber-Reinforced Polymer Strips [NSM-CFRP]. Fibers 2022. https://doi.org/10.3390/fib10100086.
[7]     Liu D, Qin F, Di J, Zhang Z. Flexural behavior of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) and ECC. Case Stud Constr Mater 2023;19:e02270. https://doi.org/10.1016/j.cscm.2023.e02270.
[8]     Hemida OAR, Abdalla HA, Fouad HEE. Flexural behaviour of recycled reinforced concrete beams strengthened/ repaired with CFRP laminates. J Eng Appl Sci 2023;70:1–19. https://doi.org/10.1186/s44147-023-00235-3.
[9]     Mostofinejad D, Mahmoudabadi E. Grooving as Alternative Method of Surface Preparation to Postpone Debonding of FRP Laminates in Concrete Beams. J Compos Constr 2010;14:804–11. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000117.
[10]   Mallikarjuna K, Ravindra PM, Archana DP, Daniyal M, Asiri ANM, Khan MA, et al. Employing Carbon Fiber Reinforced Polymer Composites toward the Flexural Strengthening of Reinforced Concrete T-Beams. ACS Omega 2023;8:18830–8. https://doi.org/10.1021/acsomega.3c00988.
[11]   Turki AY, Al-Farttoosi MH. Flexural Strength of Damaged RC Beams Repaired with Carbon Fiber-Reinforced Polymer (CFRP) Using Different Techniques. Fibers 2023;11. https://doi.org/10.3390/fib11070061.
[12]   Mostofinejad D, Shameli M. Performance of EBROG method under multilayer FRP sheets for flexural strengthening of concrete beams. Procedia Eng., 2011. https://doi.org/10.1016/j.proeng.2011.07.401.
[13]   Mostofinejad D, Hajrasouliha MJ. Experimental study on grooving detail for elimination of debonding of FRP sheets from concrete surface. Adv. FRP Compos. Civ. Eng. - Proc. 5th Int. Conf. FRP Compos. Civ. Eng. CICE 2010, 2011. https://doi.org/10.1007/978-3-642-17487-2_118.
[14]   Hosseini A, Mostofinejad D. Experimental evaluation of FRP-to-concrete bond strength in EBROG technique for strengthening concrete members 2013.
[15]   Mostofinejad D, Shameli SM, Hosseini A. EBROG and EBRIG methods for strengthening of RC beams by FRP sheets. Eur J Environ Civ Eng 2014. https://doi.org/10.1080/19648189.2014.900523.
[16]   Mashrei MA, Makki JS, Sultan AA. Flexural strengthening of reinforced concrete beams using carbon fiber reinforced polymer (CFRP) sheets with grooves. Lat Am J Solids Struct 2019;16. https://doi.org/10.1590/1679-78255514.
[17]   Saadoon AM, Mashrei MA, Al Oumari KA. Punching shear strength of recycled aggregate-steel fibrous concrete slabs with and without strengthening. Adv Struct Eng 2022;25:2175–90. https://doi.org/10.1177/13694332221090288.
[18]   Abed RJ, Mashrei MA, Sultan AA. Flexural behavior of reinforced concrete beams strengthened by carbon fiber reinforced polymer using different strengthening techniques. Adv Struct Eng 2022. https://doi.org/10.1177/13694332211049992.
[19]   Ouda MA, Mashrei MA. Shear strength of steel fibrous concrete beams strengthened by CFRP using various techniques. Structures 2022. https://doi.org/10.1016/j.istruc.2022.02.027.
[20]   Ashour AF, El-Refaie SA, Garrity SW. Flexural strengthening of RC continuous beams using CFRP laminates. Cem Concr Compos 2004. https://doi.org/10.1016/j.cemconcomp.2003.07.002.
[21]   El-Zohairy A, Salim H, Shaaban H, Mustafa S, El-Shihy A. Experimental and FE parametric study on continuous steel-concrete composite beams strengthened with CFRP laminates. Constr Build Mater 2017. https://doi.org/10.1016/j.conbuildmat.2017.09.148.
[22]   Al-sarraf SZ, Mohammed DH, Al-kashan MMR. Flexural Behavior of Self-Compacting RC Continuous Beams Strengthened by CFRP Sheets. J Univ Babylo 2018;26:181–91.
[23]   Ism MM, Rabie M. Flexural behavior of continuous RC beams strengthened with externally bonded CFRP sheets. Alexandria Eng J 2019. https://doi.org/10.1016/j.aej.2019.07.001.
[24]   Al-Khafaji A, Salim H. Flexural strengthening of RC continuous t-beams using CFRP. Fibers 2020. https://doi.org/10.3390/fib8060041.
[25]   Akbarzadeh H, Maghsoudi AA. Experimental and analytical investigation of reinforced high strength concrete continuous beams strengthened with fiber reinforced polymer. Mater Des 2010;31:1130–47. https://doi.org/10.1016/j.matdes.2009.09.041.
[26]   Abdzaid HM, Kamonna HH. Flexural Strengthening of Continuous Reinforced Concrete Beams with Near-Surface-Mounted Reinforcement. Pract Period Struct Des Constr 2019. https://doi.org/10.1061/(asce)sc.1943-5576.0000428.
[27]   Abdallah M, Al Mahmoud F, Khelil A, Mercier J. Efficiency of EB CFRP composites for flexural strengthening of continuous RC beams: A comparative study with NSM CFRP rods. Structures 2021. https://doi.org/10.1016/j.istruc.2021.08.073.
[28]   Ali H, Assih J, Li A. Flexural capacity of continuous reinforced concrete beams strengthened or repaired by CFRP/GFRP sheets. Int J Adhes Adhes 2021. https://doi.org/10.1016/j.ijadhadh.2020.102759.
[29]   The Concrete Society. Design Guidance for Strengthening Concrete Structures Using Fiber Composite Materials. 2012.
[30]   440.2R-17: Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures. 2017. https://doi.org/10.14359/51700867.
[31]   ACI Committee 318. Building Code Requirements for Structural Concrete (ACI 318-19) and Commentary on Building Code Requirements for Structural Concrete (ACI 318R-19). 2019.
[32]   Ali M.Saadoon MAM. Punching Shear Strength of Recycled Aggregate- Steel Fibrous Concrete Slabs with and without Strengthening 2022:141.