Debonding-Related Strain Limits for Externally Bonded FRP Sheets in Flexurally Strengthened Reinforced Concrete Beams

Guibing Li*, 1, Aihui Zhang2, Yugang Guo3
1 College of Management Science and Engineering, Shandong Institute of Business & Technology, Yantai 264005, China
2 College of Civil Engineering & Architecture, Zhejiang University, Hangzhou 310058, China
3 International Business College, Shandong Institute of Business and Technology, Yantai, 264005, China

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© 2013 Li et al;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to the authorat the College of Management Science and Engineering,Shandong Institute of Business & Technology, Yantai 264005, China; Tel: +86-535-6903575; E-mails:,


Debonding problems of externally bonded fiber reinforced polymer (FRP) sheets in flexurally FRP-strengthened reinforced concrete (RC) beams have been a concern and a research challenge since their application of this strengthening technique. Intermediate crack induced debonding is the most common failure mode which is that the debonding initiates at the critical flexural-shear or flexural cracks and propagates towards the direction of moment decrease. To mitigate debonding failure, most Codes and proposed models take the method by limiting the allowable tensile strain in FRP laminates. This paper presents experimental tests of concrete beams flexurally strengthened with externally bonded CFRP sheets to investigate debonding initiation and tensile strain of FRP laminates. The allowable tensile strain of FRP sheets in flexurally FRP-strengthened RC beams proposed by prevalent Code provisions and models was assessed based on the data obtained from experimental programs. It has beenshown that the allowable tensile strains provided by these provisions and models have a great difference with that of experimental results and exhibit a high level of dispersion. Furthermore, the FRP laminates of most tested RC beams were debonded before reaching the proposed allowable tensile strain. The Code provisions and models are inadequate to effectively prevent intermediate crack induced debonding failure in flexurally FRP-strengthened RC members. This is known to be a critical issue in engineering design and application of RC beams flexurally strengthened by FRP sheets.

Keywords: RC Beam, FRP sheet, strengthening, debonding failure, allowable tensile strain.