Lateral confinement of concrete members by means of spirally wrapping fiber-reinforced-plastic (FRP) composites onto the concrete surface may increase compressive strength and ultimate strain (pseudo-ductility). It may also provide a mechanism for shear resistance, and inhibit longitudinal steel reinforcement buckling. Lateral confinement of concrete members as a strengthening/repair technology is expected to have an impact in the rehabilitation/renovation of buildings and infrastructure. Structures that have been damaged, or need to comply with new code requirements, or are subjected to more severe usage are the primary targets. In this project, an experimental and analytical study of concrete strengthened with FRP lateral confinement I conducted using compression cylinders (300 and 600 mm in length) and l/4 scale column-type specimens. The latter specimens have a circular cross section and given longitudinal/transverse steel reinforcement characteristics. Column-type specimens are subjected to cyclic flexure with and without axial compression. When an aramid FRP tape is used as the lateral reinforcement, the variables are tape area and spiral pitch. In the case of filament winding with glass fiber, the thickness of the FRP shell is varied. The limited experimental results obtained at this stage of the research program indicate that lateral confinement significantly increases compressive strength and pseudoductility under uniaxial compression.

PC members reinforced with FRP as tendons show brittle failure regardless of the failure mode. The authors' objective was to improve the ductility of PC members reinforced with FRP as tendons. First, the compressive properties of concrete confined with FRP as transverse reinforcement was investigated. Major improvement can be made in the stress-strain relationship of concrete laterally reinforced with FRP, and the concrete members can be given ductility characteristics similar to those of steel-reinforced members by confining the concrete with FRP. Secondly, several PC members reinforced with FRP as tendons and transverse reinforcement were tested and investigated. It was found that marked improvements could be made in the ductility of PC members with FRP tendons by confining the part of concrete subjected to flexural compression with FRP and forcing the members to undergo flexural compression compression failure. 235-493

Bond tests with beam specimens were performed to research the bond characteristics of fiber reinforced plastic bars in concrete members that were made of such continuous fibers as carbon, aramid, glass, and vinylon, as well as epoxy resin matrix, especially when the ends of the bars were not reinforced. It was observed that bars whose surfaces were processed into a spiral shape or covered by cohesive grains of sand did not pull out if the bond length was more than 40d, where d was the diameter of the fiber reinforced plastic bar. Based on these tests, using carbon fiber reinforced plastic bars, tests of lap splice joints were performed by arranging an anchoring position in the center of a truss-type concrete specimen. It was found that the unit bond strength increased as the length of the lap splice joint increased, but that it decreased for lap splice lengths between 40d and 60d.

Fiber composites have become increasingly popular in the civil engineering community in recent years. The primary area of research and development of fiber composites in the concrete industry has been related to fiber reinforced plastic (FRP) reinforcing bars. Paper presents a different application of fiber composites in concrete structures, namely, confinement of concrete columns with fiber composite wraps for improved ductility and seismic performance. The confinement is accomplished by wrapping high-strength fiber composite belts around the columns. The belts are made very thin, resulting in flexibility sufficient to their being wrapped around circular as well as rectangular columns. The belts can be wrapped around the column in individual rings or in a continuous spiral. The ends of the belts can be mechanically coupled or they can be epoxy-bonded to the column. The confinement provided by the belts results in significant increase in the crushing strain of concrete well above that of unconfined concrete. This will improve the overall strength and ductility of the column. Paper presents the results of an analytical study and ongoing experimental study of concrete columns externally confined with fiber composite wraps.

Because fibers made of such materials as glass, carbon, aramid, and vinylon have very high resistance to corrosion, more attempts are being made to utilize continuous fiber reinforcing materials (CFRM) in reinforced and prestressed concrete structures instead of ordinary steel. However, CFRM are composite materials composed of millions of fibers and binding material, and have little plastic behavior. The mechanical behavior of reinforced concrete using CFRM is quite different from conventional reinforced concrete. As of the present, there is no general agreement relating to the methodology to be adopted in design or testing methods of such fibers. Realizing this problem, the Concrete Committee of the Japan Society of Civil Engineers (JSCE) organized a subcommittee on CFRM in 1989. The following results have been published as the committee report in 1992: design concept for concrete members using CFRM; test methods for durability of CFRM; concept for durability of CFRM; and a state-of-the-art report on CFRM for concrete structures. Paper describes the design concept for concrete members using CFRM.