Bond Anchorage of Pretensioned FRP Tendon at Force Release

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Abstract
The anchorage of fiber‐reinforced plastic (FRP) tendons in pretensioned prestressed concrete (PC) members may cause the formation of cracks as a result of tendon wedge effect and mechanical interlocking during prestress force transfer. This paper presents experimental results obtained with a braided epoxy‐impregnated aramid FRP tendon having a 16‐mm nominal diameter and initial prestress force of 125.6 kN. Minimum concrete cover was 52 mm. End‐zone reinforcement and tendon partial blanketing were used to determine their effect on concrete stress field intensity and on cracking due to prestress force transfer. It was found that steel stirrups do not prevent cracking, but they limit its propagation. A carbon FRP coil of small pitch inhibits crack formation, but the concrete tensile strain remains high. Partial blanketing is the most effective solution, causing only a limited increase in transfer length (approximately 20%). An analytical solution to the experiment was obtained by using the finite element method, assuming a partly cracked elastic concrete ring model. This proved to be an effective tool for predicting the occurrence of cracks when using tendons of different size and/or initial prestress force.

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