Journal of Composites for Construction

There are considerable problems associated with the use of traditional piling materials in corrosive soils and marine environments. The durability of concrete, corrosion of steel, and vulnerability of timber piles to marine borers are serious hindrances to construction in these environments. In the case of timber marine piling, the toxic chemicals used in their treatment, such as creosote, pose a threat to marine life. Creosote-treated timber is also a growing environmental disposal problem. Composite materials such as fiber-reinforced polymers (FRP) can offer performance advantages when compared to steel, concrete, or timber. Composites can be designed to perform according to the required specifications for piling in adverse environments. However, composites face obstacles because they do not have a long track record of use in civil engineering structures. A comprehensive review of the American experience in research, testing, design, and practice of composite piles is presented in this paper. The technical and economical viability of composite piles is discussed. Emphasis is given to material properties, durability, drivability, and soil-pile interaction.

Winding helical fiber around fiber reinforced plastic (FRP) rods, which serve as concrete reinforcement, is used to enhance the bond between the rod and the concrete. A theoretical analysis of the strain development in the helical fiber when the rod is subjected to tension shows that the fiber may shorten or lengthen, depending on the winding step size of the helical fiber and the Poisson coefficient of the rod. When the rod is subjected to cyclic loading, extensive damage is caused to the longitudinal fibers by lateral load imposed by the helical fiber, which may lead to a premature failure of the rod. An experimental study on the fatigue behavior of helically-wrapped glass fiber reinforced plastics (GFRP) rods showed that the longitudinal fibers in the region underneath the helical fiber fractured locally by local shear or bending, while the other fibers in the core broke under direct tension. A microscopic study of the fibers along the rod after cyclic loading showed extensive damage to the fibers located under the helical fiber.

This paper presents ultrasonic methodologies to measure the engineering constants of pultruded fiber-reinforced polymeric (FRP) composite structural members. These ultrasonic methods have several advantages over mechanical tests, particularly the ability to make a localized measurement of all of the engineering constants in a structural component. This research blends immersion and contact ultrasonic methodologies with surface acoustic wave measurements to completely characterize the elastic properties of FRP specimens. The elastic constants that are measured nondestructively are compared to values measured with mechanical tests (for exactly the same specimens), and the advantages of the ultrasonic methodologies are clearly shown.

The overall objective of this paper is to establish the structural behavior of reinforced concrete (RC) beams strengthened with externally bonded carbon-fiber-reinforced plastic (CFRP) sheets. Four beams, three with bonded CFRP plates on the tension face, and two of which were provided with carefully designed external anchorages at the ends of the plates and along the span, were tested under four-point bending over a span of 4.8 m. The tests were carried out under displacement control. The beams were extensively instrumented to monitor strains, deflection, and curvature over the entire spectrum of loading to total failure, and to determine the structural response to load of the composite beams. The results show that bonding a CFRP plate on the tension face of a RC beam, without consideration of the end-anchorage stresses and the bond slip between the plate and the concrete substrate, can lead to significant degradation in the structural response of the plated beam. Carefully designed external anchorages, on the other hand, can lead to preservation of composite action to almost the failure load, increases in load capacity of up to 70%, substantial regain of structural ductility, and the transformation of a brittle failure to a more ductile failure.

The addition of fiber-reinforced plastic (FRP) laminates bonded to the tension face of concrete girders is becoming an attractive solution to the rehabilitation and retrofit of damaged structural systems. Flexural strength is enhanced with this method but the failure behavior of the system can become more brittle, often involving delamination of the composite and shear failure of the girder. This study first reviews failure modes including delamination with the use of FRP to rehabilitate various concrete structures and discusses methodologies used to characterize the failure processes of the system. Then, failure modes observed in an experimental program involving FRP-laminated laboratory models are reported. Physical models of reinforced concrete beams with variations in shear strengths, bonded laminate lengths, and epoxy types are precracked, then retrofitted with glass and carbon fiber-reinforced plastics and tested in an experimental program. Strengths are shown to increase with the addition of FRPs, but the specimens are observed to fail through a variety of mechanisms. Parameters affecting these failure modes are discussed, and techniques used in the analysis of these modes are reviewed. Results of this review are used to make recommendations for future work in the understanding of FRP retrofitted concrete behavior.

The use of concrete reinforced with nonmetallic bars in composite materials, characterized by higher values of strength and by lower values of Young's modulus compared to steel, implies that the design of structures will be influenced almost exclusively by the serviceability limit state (SLS). This circumstance deserves some reflection on the values of the actions to be considered at the SLS and at the ultimate limit state (ULS). As the actual codes consider the same distribution of actions obtained by statistical methods, for the SLS and, amplified, for the ULS, it is necessary to reexamine from a probabilistic point of view the effective distributions of actions to be adopted for the two different limit states. This, which is obviously true for any kind of structure built with any material, becomes paramount for concrete structures with nonmetallic reinforcement. In this paper some possible statistical distributions of actions for the verification at the ULS and the statistical distribution of the sampled values, to be correctly used for the SLS verifications, are evaluated.