Bend Strength of FRP Bars: Experimental Investigation and Bond Modeling

The unique properties of internal fiber-reinforced polymer (FRP) reinforcement influence their bond interaction with the surrounding concrete. This is especially true in the case of bent FRP reinforcement, which bond behavior is not well understood. Equations included in existing design recommendations do not predict accurately the experimental data. This paper investigates experimentally and analytically the mechanical and bond performance of two main types of bent FRP reinforcement. To achieve this, a total of 73 specimens of thermosetting and thermoplastic composite bars with 32 different configurations embedded in concrete cubes were tested in direct pullout. The effects of bent geometry, surface treatment, front embedment length, and concrete strength on bent capacity of FRPs are examined. The test results show that the capacity of bent FRP bars embedded in concrete ranges from 25 to 84% of the theoretical strength of the composite. It is found that a bending radius to diameter ratio r/d>4 is required to guarantee a minimum bend capacity of 40% of the theoretical composite strength. The test results are further analysed numerically to gain additional insight into the examined parameters. The results confirm that high stresses are concentrated at the beginning of the bent portion, inducing failure at this location. Larger bending radius or sufficient bonded length along the bent portion reduces stress concentrations and leads to higher bend capacities.