Journal of Composites for Construction

Corrosion of reinforcement in bridge piers is encouraged by chloride contamination from exposure to marine environment and from deicing salts used in bridges during winter. Because corrosion products generally occupy greater volume than the original material, expansive forces are generated in concrete leading to spalling of the cover and further acceleration of the reinforcement disintegration. Jacketing of such structures by fiber-reinforced composite sheets is an effective remedy, not only as a means of slowing down the rate of the reaction, but also by confining the concrete core thereby imparting to it ductility and strength. This paper presents results of an experimental parametric study of this method as a repair alternative for corroded structures. Several small-size concrete columns with various reinforcement configurations were subjected to accelerated corrosion conditions in the laboratory. After a target level of steel loss was attained the columns were repaired using a variety of repair alternatives. Most of the repair schemes considered included jacketing the damaged specimens with glass-fiber wraps, in combination with grouting the voids between the jacket and the original lateral surface of the specimen with either conventional or expansive grouts. To protect the glass fiber material from exposure to alkali activity of the fresh grout, and to reduce the supply of oxygen and water to the mechanism of corrosion, different types of diffusion barriers were considered in the study. The efficacy of each repair system was evaluated by (1) assessing the postrepair corrosion resistance of the specimens under repeated exposure to accelerated conditions; and (2) the mechanical strength and ductility enhancement under concentric compression loading.

The performance of a series of 1.5 m-long reinforced concrete beams with CFRP plates bonded to the soffit is presented. Effects of the plate length, the reinforcing steel ratio, and the thickness of the concrete cover on behavior of the beams are discussed with particular emphasis on the brittle failure mode of the concrete ripping. It was found that before the brittle failure, the composite action of the beam could be divided into three distinct zones based on the distribution of the strains along the CFRP plate: (1) The “destressed” zone, (2) the “bond development” zone; and (3) the “fully composite” zone. Concrete ripping may be prevented by limiting the strain at the transition point of the composite zone of the plate. An analytical formulation to predict the failure load corresponding to the concrete ripping failure mode is proposed based on composite theory in combination with a strain limiting criterion. The strain limit can be determined based on simple bond tests with various bond lengths for a given CFRP and adhesive combination.

This paper evaluates the flexural performance of simply supported concrete beams subjected to four-point monotonic loading and reinforced with a 2D fiber-reinforced plastic (FRP) grid. The main parameter of the study is the amount of longitudinal FRP reinforcement. With respect to a balanced strain condition, three underreinforced and two overreinforced FRP designs were tested with three identical beams per design. Laboratory recorded load-deflection, failure mode, cracking behavior, and reinforcement strain data are compared with theoretical predictions calculated according to traditional steel-reinforced concrete procedures. The study concludes that, with respect to ACI 318-95, flexural capacity is accurately predicted, but shear strength is not. Deflection compatibility between test results and ACI predictions employing the Branson effective moment of inertia was dependent on the percentage of longitudinal reinforcement. In general, observed flexural stiffness was less than that predicted by Branson's equation. A moment-curvature deflection procedure employing a bilinear concrete model compared very well with measured deflections. Finally, the grid configuration provides an effective force transfer mechanism. Cracking occurred at transverse bar locations only, and FRP tensile rupture was achieved with no observed deterioration in force transfer mechanics.

Due to confinement effects, concrete-filled fiber-reinforced polymer (FRP) tubes have an enhanced performance comparable to conventionally reinforced concrete members. However, the strength and ductility enhancements may result in slender sections, which may be susceptible to instability or geometric and loading imperfections. Because stiffness of FRP is less than that of steel, designers cannot directly use current specifications to size compression members. Uniaxial compression tests on a total of seven hybrid columns, with slenderness ratios up to 36, showed that strength is reduced by as much as 71% of the equivalent short column, and the axial and hoop strains are reduced by as much as 85 and 87%, respectively. These significant reductions result in underutilization of confinement in slender columns. An analytical tool with an incremental approach was developed and compared favorably with test results. A parametric study was carried out, which showed the modulus of elasticity of the tube to have a pronounced effect on the slenderness limit of the column. A new equation was proposed for the slenderness limit of hybrid columns based on a maximum of 5% strength reduction.

This paper critically assesses the applicability and reliability of existing analytical techniques to predict and/or prevent brittle plate debonding failure that occurs in reinforced concrete (RC) beams strengthened with externally bonded steel or fiber-reinforced-polymer composite plates. The experimental results, available to date in literature, have been very carefully reviewed and analyzed for this purpose. A new approach, very different from existing methods, and based on the interface shear stress obtained form elastic analysis of RC beam cross section and the fundamentals of force transfer mechanism in a bonded joint, is presented to predict the premature plate debonding phenomenon. The paper identifies important structural, material, and force parameters that influence this critical interface shear stress value between the bonded plate and concrete. The relations between these parameters and interface shear stress value are also examined and found to be consistent and logical to predict plate debonding at the plate cutoff end. The validity of this new design-oriented approach and scope for further research are also discussed.

The structural behavior of reinforced concrete beams strengthened with adhesively bonded fiber-reinforced plastics (FRP) is presented. The experimental work included flexural testing of 2.3-m-long concrete beams with bonded external reinforcements. The test variables included the amount of conventional (internal) reinforcement and also the type and amount of external reinforcement. For comparison, some of the beams were strengthened with bonded steel plates. Theoretical analyses included 2D nonlinear finite-element modeling incorporating a “damage” material model for concrete. In general there were reasonably good correlations between the experimental results and nonlinear finite-element models. It is suggested that the detachment of bonded external plates from the concrete, at ultimate loads, is governed by a limiting principal stress value at the concrete/external plate interface.

The low impedance of some glass fiber-reinforced polymer (GFRP) composite piles may limit their usefulness as bearing piles for structures due to drivability limitations. The high strength of glass fibers used in their manufacture makes the necessary pile cross-sectional area similar to that of a comparable steel pipe pile, while the compression wave velocity and mass density are much closer to that of concrete. This results in a very low impedance and limits the ability of the GFRP piles to be driven to high bearing capacities. A comparison of the drivability of four composite piles to conventional steel and concrete piles shows that all of the piles reviewed can be reasonably expected to attain design bearing capacities of 400 kN (90 kips), but that the extremely low impedance of glass fiber-reinforced matrix composite piles limits the ultimate capacity that can be achieved through impact driving.