Journal of Composites for Construction

A technique for strengthening damaged concrete beams using prestressed carbon fiber reinforced polymer (CFRP) sheets was developed at Queen’s University and the Royal Military College of Canada. As part of this study, an anchorage system was developed to directly prestress the CFRP sheets by jacking and reacting against the strengthened concrete beam itself. The feasibility and effectiveness of using bonded prestressed CFRP sheets to strengthen precracked concrete beams at both room (+22°C,+72°F) and low (−28°C,−20°F) temperatures have been investigated experimentally. Materials and prestress changes due to temperature variations that would affect and cause changes in flexural behavior were studied. The strengthened beams showed significant increases in flexural stiffness and ultimate capacity as compared to the control-unstrengthened beams. The flexural behavior of the strengthened beams was not adversely affected by short-term exposure to reduced temperature (−28°C,−20°F). In addition to the experimental investigation, analytical models were developed to predict the overall flexural behavior of the strengthened beams during prestressing of the CFRP sheets and under external loading at both room and low temperatures. The model accurately predicted the flexural beam behavior. Improved serviceability behavior and higher strength were predicted for beams strengthened with the bonded prestressed CFRP sheets.

This paper presents the experimental results of the first phase of a study undertaken at the American University of Beirut to examine the effectiveness of fiber reinforced polymer (FRP) wraps to confine steel reinforcement in a tension lap splice region anchored in high-strength reinforced-concrete beams. Seven beam specimens were constructed. The specimens were reinforced on the tension side with three deformed bars spliced at midspan. The splice region was devoid of any transverse reinforcement to allow a full examination of the FRP wrap contribution. Glass fiber reinforced polymer (GFRP) sheets were used. The main test variables were the GFRP configuration in the splice region (one strip, two strips, or a continuous strip), and the number of layers of the GFRP wraps placed around the splice region (one layer or two layers). All GFRP wraps were U-shaped. Except for the epoxy adhesive, no other anchorage mechanism or bonding procedure was applied for the GFRP wraps on the concrete beam. Following the application of the GFRP wraps, the beams were tested in positive bending. The test results demonstrated that GFRP wraps were effective in enhancing the bond strength and ductility of failure mode of the tension lap splices, especially when continuous strips were applied over the splice region.

Externally bonded laminates of fiber reinforced polymers (FRPs) are becoming more and more common for rehabilitation and strengthening of RC structures, to solve problems either in serviceability or at ultimate conditions. This paper focuses on the behavior in the serviceability state: in particular, verifications in terms of cracks widths and crack spacing, used to warrant the functionality of FRP-RC structures, are considered. Test results on RC ties externally reinforced with FRP laminate are reported and the applicability of the Eurocode2 formulation used for RC elements is discussed. Provisions given by the International Federation for Structural Concrete are also analyzed.

Four different fiber-reinforced polymer (FRP) panel systems were installed in a 207 m, five-span, three-lane bridge in an effort to assess the constructability, performance, and applicability of bridges with fiber-reinforced polymer composite decks. This paper examines whether four common deck systems are able to realize many of the anticipated benefits of using FRP composites in lieu of conventional reinforced concrete bridge decks. Particular installation issues, connection details, and specific construction techniques for each deck system are described, along with a discussion of the shortcomings in terms of handling, performance, and serviceability. Other factors such as key design parameters (e.g., impact factor and thermal characteristics) and unexpected responses are used to further quantify the performance of four FRP representative deck systems under identical traffic and environmental constraints.

The seismic performance of rectangular hollow bridge columns is a significant issue of the high-speed rail project in Taiwan. The flexural ductility and shear capacity of such columns with the configuration of lateral reinforcement used in Taiwan have been studied recently. This paper reports that hollow rectangular bridge columns retrofitted with fiber-reinforced polymer (FRP) sheets were tested under a constant axial load and a cyclically reversed horizontal load to investigate their seismic behavior, including flexural ductility, dissipated energy, and shear capacity. An analytical model was also developed to predict the moment-curvature curve of sections and the load-displacement relationship of columns. Based on the test results, the seismic behavior of such columns will be presented. The test results were also compared to the proposed analytical model. It was found that the ductility factors of the tested piers are in the range from 3.4 to 6.3, and the proposed analytical model can predict the load-displacement relationship of such columns with acceptable accuracy. All in all, FRP sheets can effectively improve both the ductility factor and shear capacity of hollow rectangular bridge columns.

A set of 30 concrete beams reinforced with carbon/epoxy FRP (fiber-reinforced plastic) and four reinforced with comparable size steel rebars were subjected to static bending tests. Adequate bond between the FRP and the concrete was obtained, due to the use of carbon fiber overwrap on the smooth pultruded FRP rods. With adequate bond, the large strain to failure (>2%) of the FRP determines the ductility and failure mode of the FRP reinforced beams. An analytical evaluation of the fracture energy in these experiments shows that there is ductility due to the large fraction of the total strain energy that is absorbed in the concrete, because of the formation of distributed cracking. Variations in overwrap configuration, addition of steel stirrups, addition of polypropylene fibers, and comparison with four beams reinforced with equivalent steel reinforcement were also analyzed.

Seven concrete beams reinforced internally with varying amounts of steel and externally with precured carbon fiber-reinforced polymer (FRP) plates applied after the concrete had cracked under service loads were tested under four-point bending. Strains measured along the beam depth allowed computation of the beam curvature in the constant moment region. Results show that FRP is very effective for flexural strengthening. As the amount of steel increases, the additional strength provided by the carbon FRP plates decreases. Compared to a beam reinforced heavily with steel only, beams reinforced with both steel and carbon have adequate deformation capacity, in spite of their brittle mode of failure. Clamping or wrapping of the ends of the precured FRP plate enhances the capacity of adhesively bonded FRP anchorage. Design equations for anchorage, allowable stress, ductility, and amount of reinforcement are discussed.

The development and testing of a pseudoductile hybrid fiber-reinforced polymer rod consisting of glass and carbon fibers is described. Two different hybrid forms were considered for the development of the hybrid rods, including (1) random dispersion of the glass and carbon fibers; and (2) a core-shell design with a glass fiber core protected by the carbon fiber shells. The mechanical properties of the hybrids were evaluated through uniaxial tension tests. The hybrid rods developed by way of the core-shell approach exhibited pseudoductile properties that included a yield point of 1,153 MPa and an ultimate strength of 1,191 MPa, with a strain of 3.5% at ultimate. The experimental program also included damage assessment by way of a single-channel fiber optic acoustic emission (AE) sensor. The acoustic emission technique was employed for real-time determination of the progressive damage due to rupture of fibers. Moreover, the spectral energies of the frequency spectrum from the AE signals were employed for assessment of the state of damage in the rods. The spectral energies distinguish between the carbon and glass fiber ruptures. This differentiation of signals provides information about the condition and the state of health of the hybrid rod.

Thirty masonry walls strengthened using three different fiber-reinforced polymer (FRP) systems, with three anchorage methods, were fabricated and tested under a concentrated load over a 100 mm square area or a patch load over a 500 mm square area. The test results indicated a significant increase in the out-of-plane wall strength over the unstrengthened wall. While failure occurred in the unstrengthened wall by bending, four different modes of failure, that is, punching shear through the bricks, debonding of FRP reinforcement from the masonry substrate, crushing of brick in compression, and tensile rupture of the FRP reinforcement, were observed in the strengthened walls, depending on the types and configurations of FRP and anchorage systems. With appropriate surface preparation and anchorage systems, premature failure due to FRP debonding is prevented. Based on the principles of strain compatibility and force equilibrium, simple analytical models are presented to predict the ultimate load-carrying capacity of the strengthened walls. The test results compared well with the analytical predictions.

The U.S. Interstate 80 bridge over State Street in Salt Lake City is very near the Wasatch fault, which is active and capable of producing large earthquakes. The bridge was designed and built in 1965 according to the 1961 American Association of State Highway Officials specifications, which did not consider earthquake-induced forces or displacements. The bridge consists of reinforced concrete bents supporting steel plate welded girders. The bents are supported on cast-in-place concrete piles and pile caps. A seismic retrofit design was developed using carbon fiber reinforced polymer (CFRP) composites, which was implemented in the summer of 2000 and the summer of 2001, to improve the displacement ductility of the bridge. The seismic retrofit included column jacketing, as well as wrapping of the bent cap and bent cap-column joints for confinement, flexural, and shear strength increase. This paper describes the specifications developed for the CFRP composite column jackets and composite bent wrap. The specifications included provisions for materials, constructed thickness based on strength capacity, and an environmental durability reduction factor. Surface preparation, finish coat requirements, quality assurance provisions, which included sampling and testing, and constructability issues regarding the application of fiber composite materials in the retrofit of concrete bridges are also described.