Strengthening of Concrete Structures Using Prestressed FRP – A Review

Abstract

AbstractFibre-reinforced polymers (FRP) reinforcement has been used for flexural strengthening either as an externally bonded (EB) system in the form of FRP laminate (sheets, plates or strips) applied to the tension side of reinforced concrete (RC) members or as a near-surface mounted (NSM) system. The NSM system is composed of an FRP strip or bar embedded inside a pre-cut groove filled with epoxy. The groove is made into the concrete cover at the tension side of the RC member.Although flexural strengthening using non-prestressed FRP reinforcement increases the ultimate strength of a member, it does not significantly improve the member performance under service loads (i.e. it does not increase the stiffness of the member under service loads). This is because non-prestressed FRP strengthening is a passive strengthening technique where the FRP remains inactive until additional loads are applied. To increase the stiffness of the member, the strengthening system must be active rather than passive. Active strengthening is achieved by prestressing the FRP reinforcement before being bonded to the concrete. The advantages of prestressed FRP strengthening are (i) more effective use of the material because a greater portion of its tensile capacity is employed, and (ii) the FRP material contributes to the load-bearing capacity under both service and ultimate conditions. Prestressing the EB and NSM FRP requires a special anchorage system that should be practical in implementation.In general, prestressing is used to enhance the flexural behaviour of reinforced concrete members under service loads, especially in bridges and beams with large spans. There is a limitation on the deflection and serviceability conditions. Because of their high tensile strength properties, FRP materials have significant advantages for use in prestressing and post-tensioning strengthening applications. The specialized application of prestressing the FRP reinforcement for flexural strengthening of structures combines the non-corrosive and lightweight benefits of the FRP reinforcement with the advantages associated with external prestressing. However, the challenging part of the active FRP strengthening system is applying prestressing force to the FRP material using a suitable practical anchorage and prestressing system.The paper presents a review of the state-of-art research related to (i) the anchorage systems developed to prestress EB and NSM FRP with the focus on the practicality of the prestressing systems where the FRP is prestressed against the member itself, and (ii) the performance of members strengthened using prestressed FRP reinforcement.KeywordsActiveAnchorageFlexuralPrestressingExternally bondedNear-surface mounted