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AbstractFiber-reinforced polymer (FRP) tendons and reinforcing bars (rebars) have been developed for use with concrete. FRP productsare non-corrosive and lightweight when compared to traditional steel members. The current test program involves the design,fabrication, and testing to failure of two full-scale high-strength concrete bridge beams with FRP products for prestressing and shearreinforcement. Ó 2000 Elsevier Science Ltd. All rights reserved.Keywords: Bridge beams; Prestressed; High-strength concrete; Carbon-®ber-reinforced-polymers; Composite; FRP; Tendons; Leadline; C-Bar;Rebar; Bending moment; Ultimate strength tests.35312
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1. IntroductionOf the 583 000 bridges in USA, 235 000 are non-pre-stressed steel-reinforced concrete and 108 000 are steel-prestressed concrete [1]. A major problem with this steel/concrete composite construction is corrosion of the steelmembers. In recent years, ®ber-reinforced polymer (FRP)tendons and reinforcing bars (rebars) have been devel-oped for use with concrete. FRPs oer improved corro-sion and fatigue resistance compared to steel. These FRPproducts oer the possibility of reinforced/prestressedconcrete bridges with greatly increased life in corrosiveenvironments compared to steel/concrete construction.In the current program, full-scale FRP-prestressedand reinforced high-strength concrete bridge beamswere designed, fabricated and tested. The current pro-gram provided a single-point assessment of the appli-cability of current design methods to FRP-prestressedand reinforced concrete bridge beams.2. Current state of design code development eortCurrent design guidelines for steel-reinforced concrete[2] are the result of decades of research and ®eld experi-ence. Because of their composite nature, FRP rein-forcements behave not only dierently from steel, butalso with more complicated modes of response.
There-fore FRP reinforcement technology and practices remainin a developmental state despite numerous researchinvestigations and some successful ®eld applications.A brief review of FRP prestressing work is provided.2.1. Design code development eortsIn 1996, the Federal Highway Administration(FHWA) of the US Department of Transportation ini-tiated a four-year research program entitled ``FRPPrestressing for Highway Bridges''. This program is in-tended to advance all areas related to product standardsand design codes. Under this program, a survey of codedevelopment eorts in other countries was conducted[3]. The American Concrete Institute (ACI) Subcom-mittee 440-I on FRP Prestressing is working to developa design code for FRP-prestressed concrete [4]. ACICommittee 440 on FRP Reinforcement has published areport summarizing the state of the art of all FRPreinforcement technology for concrete as of 1996 [5].A provisional design code for FRP-reinforced concretedeveloped in Japan has been translated into English [6].2.2. Fiber characteristicsWhile carbon [7±14], glass [8,15,16], and Kevlar [8,9]have all been investigated as ®bers for FRP prestressing, carbon-®ber-reinforced polymers (CFRPs) haveemerged as the leading FRP material for prestressing.Experiments have shown CFRP to have 0 creep lossover a period of 1 year [17] and to have 0 strength lossdue to salt water exposure in experiments ranging from6 months to 1 year [11,17]. Exposure of CFRP to analkaline environment was found in one study to have noeect on strength after 6 months [11]. In another study,CFRP was exposed to an alkaline environment for 1year, and was found to have ``... an equal or greaterresistance than that of regular steel tendon [17]''. ACFRP-prestressed scale-model bridge design was fatiguetested to 7 million cycles at 60% ultimate load, withnegligible eects on the stress levels and dynamic char-acteristics of the bridge [12].2.3. Tendon strength characterizationManufacturer-supplied strength data for two leadingCFRP prestressing products were included in Ref. [18].Using these data, ratios of guaranteed-strength to ulti-mate-strength were computed to be 0.67 for Leadline(by Mitsubishi Kasei, Japan) and 0.81 for CFCC (byTokyo Rope, Japan). This discrepancy suggests thatthere is not a consistent methodology in use by dierenttendon manufacturers to establish characteristicstrength values.2.4. Gripping and hold-down issuesBecause FRP tendon materials lack the ductility ofprestressing steel, it has found been necessary to developnew grip/anchor designs for FRP tendon tensioning.FRP tendon anchorage technology was reviewed in 1993[19]. Reusable wedge-type grips have been developed forsome speci®c FRP prestressing products [14,19]. Potted-end anchorage has been demonstrated using a variety oforganic resins and cementitious materials as grout[16,19,20].