Carbon Fiber-reinforced Polymer Strands Research Articles

Experimental study on the flexural performance of prestressed RC beams with post-tensioned CFRP strands

Carbon fiber reinforced polymer (CFRP) exhibits multiple advantages over conventional steel, such as high strength and corrosion resistance. By replacing prestressing steel with prestressing CFRP in new prestressed reinforced concrete (RC) structures, the corrosion issue of prestressing steel can be resolved. At present, there remains scarce research on the application of CFRP strands in the prestressed RC structures. An experimental study was conducted on prestressed RC beams with internal post-tensioned CFRP strands under flexure. The study aimed to analyze the effects of the prestress level, number of CFRP strands, layout shape of CFRP strands, bonding layer, and reinforcement ratio of steel bars on the flexural behavior. The test results indicated that all specimens experienced concrete crushing failure. After applying prestressing CFRP strands to ordinary RC beams, the cracking load increased by 50.0% to 102.2%, the yielding load increased by 20.2% to 38.6%, and the ultimate load increased by 20.3% to 41.4%. Reducing the reinforcement ratio of steel bars had a minor effect on the cracking load but resulted in a noticeable decrease in the yielding and ultimate loads of the prestressed CFRP strand-reinforced concrete beams. Moreover, the bonded specimen showed a slight increment in the cracking, yielding, and ultimate loads as well as stiffness compared to the unbonded specimen, while the deformation capacity of the unbonded specimen remained superior. The specimens with curved and straight prestressing CFRP strands exhibited very similar mechanical properties.

Effect of various factors related to the bond-type anchorage system on tensile performance of carbon fiber-reinforced polymer strand cables

Steel strands, which are most frequently used as internal/external tendons of prestressed concrete (PSC), are highly susceptible to corrosion, which degrades the structural stability of the PSC structures. Studies are underway to utilize carbon fiber-reinforced polymer (CFRP) strands in PSC structures as tendons to achieve structural performance comparable to that of existing steel strands, with the additional feature of corrosion resistance. However, such applications of CFRP strands require the accurate identification of the intrinsic properties of the material. This study conducted an analysis to establish a test method using bond-type anchorage that can evaluate the intrinsic properties of CFRP strands by setting several factors related to the bond-type anchorage system as variables. Tensile tests were conducted on the CFRP strands after fabricating the specimens according to the variables of the bond-type anchorage system (shape of the CFRP strand located inside the steel pipe and type of internal filler material). In addition, the compressive strength was measured to determine the mechanical properties of the cementitious filler materials. Based on the experimental results, the load-displacement curves, stress-strain curves, fracture shapes, and tensile strengths of various cases of CFRP strands were analyzed. The results of the study revealed that the split-strand CFRP fabricated with CP0.25 mixture as the bond-type anchorage system had the ability to fully obtained intrinsic tensile properties.

"Evaluating fatigue, relaxation, and creep rupture of carbon-fiber- reinforced polymer strands for highway bridge construction"

Fatigue strength, relaxation, and creep rupture strength of carbon-fiber-reinforced polymer (CFRP) strands were evaluated experimentally, and their impact on bridge beam design was investigated. The long-term relaxation of CFRP strands was evaluated by loading CFRP test specimens under different environmental conditions and monitoring prestress loss over time. Creep rupture strength of CFRP strands after 1 million hours of sustained stress exposure was predicted by loading and monitoring CFRP test specimens under a range of sustained stress levels for an extended time. The fatigue strength of CFRP strands was established by cyclically loading CFRP test specimens using different stress amplitudes. In addition, and as a benchmark for fatigue evaluation, low-relaxation steel and stainless steel strand test specimens were prepared and cyclically loaded within the fatigue test matrix. Test results showed that fatigue strength of CFRP strands is superior to that of low-relaxation steel and stainless steel prestressing strands. In addition, the one-million-hour relaxation loss of CFRP strands is approximately 2% for a wide range of initial stress levels. Furthermore, the one-million-hour creep rupture strength is at least 88% of the average tensile strength of the strands. Extended exposure to environmental conditions did not seem to affect the tensile capacity of CFRP strands.

GFRP composite bars for splicing prestressed precast concrete piles: Design and experimental investigation

Glass Fiber Reinforced Polymer (GFRP) composite bars were investigated in this study as a corrosion-resistant dowel for splicing prestressed precast concrete piles (PPCPs). In addition to their durability and good mechanical performance, GFRP bars show cost advantage when compared to other corrosion-resistant material. Using available design guides for FRP-reinforced concrete sections, a typical epoxy bonded dowel splice using GFRP bars was designed for an 18 × 18 in (457 × 457 mm) PPCP. In order to validate the adopted design procedure and to investigate the effectiveness of GFRP reinforcing bars as bonded dowels for pile splice design, 10 full-scale PPCP specimens of 18 × 18 in (457 × 457 mm) cross-section with a total length of 28 ft (8.5 m) were designed, fabricated, and tested at the Florida Department of Transportation (FDOT) Structures Research Center. In these specimens, three different materials for dowels; GFRP reinforcing bars, Carbon Fiber Reinforced Polymer (CFRP) strand, and traditional carbon-steel reinforcing bars were used in combination with CFRP and steel prestressing strands for PPCPs for both unforeseen and preplanned drivable splicing cases. The focus of this study was on the flexural performance at the splice. The experimental results show that the proposed epoxy GFRP dowel pile splice can match the required design flexural resistance for a preplanned PPCP carbon-steel pile splice. The laboratory tests performed in this research validates the new design procedure for the GFRP dowel splice. The design flexural resistance for the GFRP dowel splice calculated by the new procedure provides 68 % of 245 kip-ft (332.2 kNm), the flexural resistance required by the FDOT design specifications for mechanical preplanned splices. This research will help to improve the standard designs and construction specifications.

Charpy impact properties of uni-directional carbon fiber-reinforced polymer tendons with protective layers

The present study explored potential forms of impact protection for carbon fiber-reinforced polymer (CFRP) tendons. Charpy impact tests were performed on CFRP rods and strands under protections of polyvinyl chloride (PVC) and poly-ethylen (PE). In the experimental program, the impact damage pattern and absorbed energy of CFRP tendons with and without external protection were obtained. The results show that the energy absorption capacity of CFRP tendons was improved under the protection of surface layers; and PE layers exhibited the highest protection effectiveness among all protection forms in terms of the increased absorbed energy and caused additional structural weight. Besides, two empirical expressions were established to quantify the relationship between the thickness of PE layers and the energy absorption capacity of the protected CFRP tendons, which may provide a simple tool to estimate the thickness of the layer required for the protection of a specific CFRP tendon in practical applications.

Effect of Temperature Fluctuation and Severe Environments on Durability of CFRP Strands

Abstract This paper will present the results from an experimental study to examine the effect of severe environmental conditions on the performance of carbon fiber–reinforced polymer (CFRP) prestre...

Effect of Elevated Temperatures on the Mechanical Properties and Relaxation of CFRP Strands

Abstract Although prestressing carbon fiber–reinforced polymer (CFRP) strands outperform steel strands on different levels, such as strength and durability, their performance under elevated tempera...

Durability of CFRP strands used for prestressing of concrete structural members

This paper presents a comprehensive research conducted to study the synergistic effect of environmental conditions and sustained loading on the mechanical properties of Carbon Fiber Reinforced Polymer (CFRP) prestressing strands. The environmental conditions included exposure of CFRP strands to alkaline solution and sustained loading at an elevated temperature of 55 °C for 3000 and 7000 h. The sustained loading was equivalent to 65 percent of the guaranteed tensile strength of the strands. Mechanical testing performed on the strands included tensile, shear and bond strength as well as evaluation of the elastic modulus of the CFRP strands as affected by the environmental conditions and sustained loading. Durability of the constituent materials of the CFRP strands was also studied.

Design Analysis and Experimental Behavior of Precast Concrete Double-Tee Girders Prestressed with Carbonfiber-Reinforced Polymer Strands

Design Analysis and Experimental Behavior of Precast Concrete Double-Tee Girders Prestressed with Carbonfiber-Reinforced Polymer Strands

Prestressing bridge girders with carbon fiber–reinforced polymer: State of knowledge and research needs

Prestressing concrete bridge beams with composite materials has been investigated extensively within the last two decades. The outcomes of these research efforts, however, emerged only in a limited number of representative applications in the United States. This is partly due to a lack of comprehensive design guidelines for use by bridge engineers, especially in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design format. An extensive review of literature related to the prestressing of concrete bridge beams with carbon fiber–reinforced polymer strands was conducted. A database of the beams prestressed with carbon fiber–reinforced polymer was established, and the existing design methods along with the required parameters were reviewed. Based on the collected data, the flexural and shear capacity of beams was calculated and compared with the experimentally obtained capacity and that obtained from selected design guidelines. Variables related to the design of carbon fiber–reinforced polymer prestressing that need calibration with dedicated material properties were examined, and the effects of carbon fiber–reinforced polymer on long- and short-term losses were identified.

Mechanical Behaviors of High Performance Concrete Beams Prestressed with CFRP Strands

The merits of high performance concrete (HPC) and fiber reinforced polymer (FRP) could be combined for using in the concrete structures to improve the structural mechanical behavior. Six beams cast with HPC and prestressed with Carbon FRP (CFRP) strands were tested and discussed in this paper. Test variables included partial prestressing ratio (PPR) of CFRP strands and material of reinforcements (steel and Glass FRP). Test results indicated that all the beams failed in two modes, i.e., compression failure mode and tension failure mode. The ultimate deflection of all the beams reached 1/70-1/41 of the spans and the ductility coefficients of the steel reinforced beams were higher than 3.5 (except the one with the highest steel reinforcement ratio), indicating good deformability and ductility. An increase in partial prestressing ratio (PPR) had a positive effect on ductility. The ductility of Glass FRP reinforced beam was much lower than that of steel reinforced beams while the deformability was quite similar.

Bond mechanism of a new anchorage technique for FRP shear-strengthened T-beams using CFRP rope

Carbon fiber-reinforced polymer (CFRP) rope was recently developed to anchor fiber-reinforced polymers (FRP) shear-strengthened beams that conventionally uses U-wrap scheme. The rope is a bundle of flexible CFRP strands held together by a thin tissue net. In this technique, holes are drilled through the web at the web-flange intersection, and CFRP ropes are inserted through the holes and flared onto the two free ends of the U-wrap scheme. The technique offers substantial improvements in bond strength and ductility because it converts the U-wrap scheme similar to a full-wrap scheme. The objective of this paper was to investigate the bond behavior of CFRP L-strip plates anchored with CFRP ropes. The experimental program consisted of 16 tests on FRP-to-concrete joints, of which six were unanchored (control specimens) and 10 were anchored by CFRP ropes. The influence of concrete strength, rope length, and plate width on bond behavior was examined. Experimental results showed that the bond performance greatly improved with increasing FRP plate width and rope length, but concrete strength had a negligible effect, which is attributed to high thickness and narrow width of CFRP L-strips used. Theoretical formulations provided to account for the ultimate bond load were compared with the experimental results, and a modification factor to estimate the effect of the presence of CFRP rope was suggested.

New Anchorage Technique for FRP Shear-Strengthened RC T-Beams Using CFRP Rope

AbstractThis study investigates the effectiveness of a new anchorage technique for fiber-reinforced polymer (FRP) shear-strengthened reinforced concrete T-beams using carbon fiber-reinforced polymer (CFRP) ropes. The rope is a bundle of flexible CFRP strands held together using a thin tissue net. In this technique, holes are drilled through the web at the web-flange intersection, where the CFRP ropes are inserted and flared onto the two free ends of the U-wrap scheme. This converts the U-wrap scheme to a full-wrap scheme. The experimental program includes three series based on the number of steel stirrups. No steel stirrups are provided in the first series, whereas the spacing between steel stirrups is 260 and 175 mm in the second and the third series, respectively. Each series includes a control specimen, with no external CFRP for shear strengthening, a specimen strengthened with CFRP sheets, a specimen strengthened with CFRP L-strips, and a specimen strengthened with CFRP L-strips and anchored with CFRP...

Bond Properties of High-Strength Carbon Fiber-Reinforced Polymer Strands

Forty-eight pullout tests were conducted to examine the bond properties of high-strength carbon fiber-reinforced polymer (CFRP) strands in different bonding agents, including normal concrete, high-performance concrete, epoxy resin, and grout. The bond properties were examined through measurements of slippages and corresponding bond stresses for CFRP strands as well as steel strands for comparison purposes. Studies show that bond stresses reach a maximum when the slippages of high-strength CFRP strands range from 0.012 to 0.016 in. (0.3 to 0.4 mm), and for steel strands, the slippages are approximately 0.787 in. (20 mm). Bar diameters 0.492 to 0.598 in. (12.5 to 15.2 mm) of CFRP strands have a moderate influence on allowable bond strength. The higher concrete compressive strength develops higher bond strength. The allowable bond strength (determined at 0.03937 in. [1.0 mm] slippage) of CFRP strands is 1.3 to 1.4 times that of steel strands, whereas the maximum bond stresses of steel strands are 30 to 50% higher than that of CFRP strands. Although the maximum bond stresses in steel strands are higher than those in CFRP strands, they occur at large slips, which explains why the allowable bond stresses are lower. In addition, on the basis of experimental tests, bond stress versus slip models for high-strength CFRP strands and steel strands are proposed.

Carbon Fiber-Reinforced Polymer Strand Application on Cable-Stayed Bridge, Penobscot Narrows, Maine

Maine's first cable-stayed bridge opened to traffic on December 30, 2006. Designed as an emergency replacement for the Waldo–Hancock Bridge, the new bridge uses an innovative cradle system to carry the stays from the bridge deck through the pylon and back to the bridge deck. Each strand is anchored independently; thus, strands may be removed, inspected, and replaced while the bridge carries traffic. This advantage, coupled with Maine Department of Transportation concerns for the premature loss of the Waldo–Hancock Bridge due to corrosion, created interest in an opportunity to install and monitor representative carbon fiber-reinforced polymer (CFRP) strands in the cable stays of this bridge. CFRP strands were installed for the purposes of assessing their performance in a service condition and evaluating them for use on future bridges. Three representative stays in the bridge were designed to include two reference strands each, which may be removed and not replaced without change to the bridge's structural integrity. Six epoxy-coated steel strands were removed and successfully replaced with CFRP strands in June 2007. Data are being collected from the monitoring equipment installed on all of the strands (both traditional steel and CFRP strands) in the bridge to evaluate CFRP strand performance for future bridge cable stay and post-tensioning installations. The bridge location ensures that the test strands will be evaluated under a wide range of temperatures and variety of wind loads.