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Abstract
Despite the enhancement in the flexural capacity of reinforced concrete (RC) members externally strengthened with fiber reinforced polymer (FRP) composites, debonding of the FRP from the concrete substrate at its ends is a major concern. This premature failure mostly occurs at a low fraction of the FRP rupture strain, thus compromises the effectiveness of FRP-strengthening. This paper presents a review on plate-end (PE) debonding as a critical failure mode in FRP-strengthened beams. The available models for predicting this mode of failure are also presented and assessed against experimental database established from previous studies. The precautions recommended by the relevant design codes to prevent PE debonding are also discussed and assessed. Based on the assessment, several conclusions are emphasized, including the inaccuracy in predictions of PE debonding given by most available models when compared with the experimental database and the inconsistency among these models. The assessment also revealed that the precautions recommended by most of the design codes are not adequate to prevent PE debonding.
Highlights
Strengthening of reinforced concrete (RC) beams in flexure with fiber-reinforced polymer (FRP) plates/sheets externally bonded (EB) to the tension face of concrete is an excellent alternative to traditional strengthening methods
Debonding at the FRP plate end (PE debonding) or at locations within the beam induced by an intermediate crack (IC debonding) are the two common debonding failure modes in FRP-strengthened RC beams [Smith and Teng 2003; Teng and Yao 2007; Yao and Teng 2007]
In another study conducted by Gao et al (2004b), the test results have shown that increasing the CFRP strip thickness from 0.22 to 0.44 mm has resulted in a transition in the failure mechanism from PE interfacial debonding along the CFRP-concrete interface to Concrete cover separation (CCS)
Summary
IC debonding normally initiates at the high moment region due to flexural or flexural-shear cracks and propagates toward the plate end [Teng et al 2003; Al-Negheimish et al 2012; Yao et al 2002] Such failure is critical for beams with relatively long shear-spans or where the end-peeling has been effectively mitigated [ACI 440.2 2017]. PE debonding initiates by high interfacial stresses at the FRP plate end and propagates toward the mid-span of the beam [Yao and Teng 2007; Smith and Teng 2002a; Smith and Teng 2002b; Lu et al 2005] It occurs in a very brittle manner (mostly before the yielding of tension steel) which is not preferred in design as the governing failure mode. Mitigation of PE debonding of FRP reinforcement using available end anchorage systems is briefly discussed
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