Effect of Bond Condition on Cyclic Behavior of Post- Tensioned Concrete Beams with Carbon Fiber-Reinforced Polymer Tendons

Abstract

The lack of ductility is the main concern in the use of carbon fiber-reinforced polymer (CFRP) reinforcement as prestressing tendon in concrete members. To address this concern, a partially bonded concept has been proposed. In this approach, CFRP tendons are intentionally debonded from the concrete in the middle region of the prestressed concrete beam, while remaining bonded at each end. In this study, eight post-tensioned beams, including five beams with CFRP tendons and three beams with steel tendons, are tested under cyclic loading. Three bond conditions, including fully bonded, partially bonded, and fully unbonded, are considered. The results indicate that increasing the unbonded length of the tendon changed the failure mode from CFRP rupture to concrete crushing. There is a trend that the flexural capacity decreased with the increase of the unbonded length. The displacement ductility (μ) of partially bonded CFRP prestressed beams ranged from 5.38 to 5.70, which is significantly higher than that of the fully bonded beam (μ = 2.83) and slightly lower than that of the fully unbonded beam (μ = 6.10). Finally, by introducing a relative bond length coefficient into the ultimate tensile stress equation for internally unbonded tendons, a modified design approach for estimating flexural capacities of the partially bonded beams is proposed. The experimental flexural capacities are in close agreement with the values predicted using the modified design approach.