Effect of Stirrups on Plate End Debonding in Reinforced Concrete Beams Strengthened with Fiber Reinforced Polymers

Abstract

Plate end (PE) debonding is one of the critical debonding failure modes that may occur in reinforced concrete (RC) beams strengthened with externally bonded fiber reinforced polymers (FRPs). This study investigated the effect of internal steel stirrups on the PE debonding failure load of FRP-strengthened RC beams. The dimensions of the beams were 3400 × 400 × 200 mm. The beams were strengthened with carbon FRP (CFRP) sheets bonded to the soffit of the beams. The beams were divided into two series based on the distance of the cutoff point of the CFRP sheets from the nearest support. This distance was 50 mm or 300 mm, and the amount of steel stirrups was varied in terms of varying the stirrup diameter and spacing. The beams were simply supported and tested under four-point bending. The test results indicate that the effect of stirrups on the load carrying capacity of the beams was more pronounced for the beams with CFRP sheets extended close to the supports. It was also indicated that beams with larger amounts of stirrups failed in PE debonding by concrete cover separation while beams with lower amounts of stirrups failed in PE by either PE interfacial debonding or critical diagonal crack-induced debonding. The beams were analyzed using several analytical models from design guidelines and the literature. The result of analysis indicates that most of the available models failed to reflect the effect of stirrups in predicting PE debonding failure load of the beams. On the other hand, the models of El-Sayed et al. and Teng and Yao were able to capture such an effect with the best predictions provided by El-Sayed et al. model.

Finite Element Modeling of Debonding Failures in FRP-Strengthened Concrete Beams Using Cohesive Zone Model

“…This, in turn, caused an increase in the interfacial shear and normal stresses at the plate end, which triggered the CCS failure at decreased load capacities of the strengthened beams. These numerical findings agree with the experimental results reported in the recent study conducted by Al-Negheimish et al [8] that reported reduced capacities of 11.6% and 15.9% in the tested beams that failed by CCS when the stirrup spacing increased from 100 mm to 150 mm and 250 mm, respectively. In the case of beams that are prone to fail by IC debonding, the decrease in the load capacity was marginal in the case of the beam S-5.0/S-200 with stirrups spaced at 200 mm compared to the beam S-5.0/S-100 with stirrups spaced at 100 mm.…”

“…Strengthening of reinforced concrete (RC) members using FRP externally bonded (EB) to the concrete substrate is an excellent method to increase the load capacity of such members. Many experimental and analytical investigations have been conducted and their results have indicated the effectiveness of FRP strengthening in increasing the load-carrying capacity of RC members [2][3][4][5][6][7][8]. However, these studies have reported that only a small percentage of FRP tensile strength is utilized before the premature failure by FRP debonding.…”

“…Polymers 2022, 14, x FOR PEER REVIEW 2 of 23 their results have indicated the effectiveness of FRP strengthening in increasing the loadcarrying capacity of RC members [2][3][4][5][6][7][8]. However, these studies have reported that only a small percentage of FRP tensile strength is utilized before the premature failure by FRP debonding.…”

Strength of Compressed Reinforced Concrete Elements Reinforced with CFRP at Different Load Application Eccentricity

“…External reinforcement of the beams due to the attachment of a polymer plate in the lower tension zone [ 33 ] leads to the delamination of the FRB plate and is one of the critical failure modes. The authors of [ 33 ] studied the effect of CFRP stirrups for reinforcing reinforcement and showed the effectiveness of this approach.…”