International Concrete Abstracts Portal

The main objective of this study was to develop a new type of FRP rebar with focus on ductility and health-monitoring issues. One approach to provide ductility was the use of a hybrid FRP reinforcing bar consisting of different types of fibers, which fail at different strains during the load history of the rebar, thereby allowing a gradual failure of the rebar. The rebar was manufactured using pultrusion and filament winding techniques. These techniques have made it possible to embed fiber optic sensors within the reinforcement, for health monitoring, thus protecting the sensor from the harsh concrete environment. Pseudo-ductile behavior was validated through testing of coupon FRP rebar as well as RC beams. Testing of large-scale beams reinforced with the hybrid FRP rebar exhibited remarkable ductility behavior with ductility indices close to that of beams reinforced with steel rebar. Furthermore, the strain measured from the embedded fibers optics replicates the measurement of conventional LVDT and was reliable up to failure of the beams.

The bond between an aramid fibre reinforced plastic (AFRP) tendon and concrete has a significant effect on the flexural behaviour of a concrete beam pre-tensioned with AFRP. In particular, the performance of beams with prestressed AFRP tendons can be enhanced by the use of partially-bonded tendons. Two types of partial bond are possible; intermittent bond, where sections of the tendon are alternately bonded and debonded from the concrete, and adhesive bond, where the tendon is coated with a resin of known, low shear strength. However, the choice between these methods, and the determination of the values of the various parameters required, are not trivial problems. It is found that a major obstacle in the development of a generalised design procedure for the partially-bonded beams is the uncertainty regarding the rotation at which the concrete will fail. Nevertheless, insight into design aspects of the intermittently-bonded and adhesively-bonded beams is gained and a design methodology is proposed.

The use of FRP for reinforcing is not as popular as its use for prestressing because the modulus of elasticity to strength ratio of most FRP bars is relatively small compared to steel, and the unit price is significantly higher than steel. Therefore, to control deflection and crack width under service conditions, FRP reinforced sections often need to be greatly over-reinforced, which increases the overall cost of the structure. This paper offers an innovative solution to the latter problem by suggesting the use of tension elements as reinforcement. The CFRP tension elements developed in the present investigation are concentrically pretensioned prisms of small cross-section. Such elements would reduce the need for high reinforcement ratio while simultaneously endowing the member with greater flexural rigidity. This paper will briefly explain the concept of FRP prestressed tension elements used for reinforcement of concrete beams, followed by the description of an experimental investigation related to the development of CFRP tension elements and their use as flexural reinforcement in concrete beams. The effectiveness of the tension elements in controlling crack width and deflections under service loads is demonstrated.

The development of Arapree, about fifteen years ago in the Netherlands, can be considered as one of the initiatives, which started the use of FRP reinforcement for concrete structures. Today, although no longer produced in the Netherlands, Arapree is still commercially available. Hence, over the years a considerable amount of information on the use of this type of AFRP has become available, including test data and practical experience. Several approaches have been developed regarding the design philosophy. Based on the information available to the authors, and their own experience concerning the use of Arapree, a design philosophy for concrete elements prestressed with Arapree is given in this paper.

Investigation of the long-term characteristics of the Highly Expansive Material (HEM) anchorage for CFRP strands is very important. In the post-tensioning type of prestressed concrete structures, considerations should be made for the loss of prestressing force due to the pull-out displacement which is caused by the creep of the HEM. The long-term characteristics of the HEM anchorage were investigated by creep test on five specimens. From the creep test, some important characteristics of HEM anchorage were observed, for example, time-dependent change of pull-out displacement at the loaded end, unit shear “q” distributions and the tensile force distributions “Tp”. An analytical relationship on how the long-term behavior of prestressing force can be predicted by using the measured values for the time-dependent change of pull-out displacement at the loaded end is presented. Also from the simulated results of this relationship, it was found that the loss of prestressing force is negligible in practice when the CFRP strand is 10 meters long. Normally the expansive pressure of HEM at prestressing is 50MPa. However, when the expansive pressure is 100MPa, the pull-out displacement at the loaded end and the loss of prestressing force can be reduced to more than the half of one with 50MPa.